Merge tag 'branch-0.13' into bugfix_gitdir

1 files changed, 3569 insertions, 1345 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 9e1c41ada7..73fbe53afb 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,33 +1,53 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2014 The Bitcoin developers
+// Copyright (c) 2009-2015 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "main.h"
 
 #include "addrman.h"
-#include "alert.h"
+#include "arith_uint256.h"
+#include "blockencodings.h"
 #include "chainparams.h"
 #include "checkpoints.h"
 #include "checkqueue.h"
+#include "consensus/consensus.h"
+#include "consensus/merkle.h"
+#include "consensus/validation.h"
+#include "hash.h"
 #include "init.h"
 #include "merkleblock.h"
 #include "net.h"
+#include "policy/fees.h"
+#include "policy/policy.h"
 #include "pow.h"
+#include "primitives/block.h"
+#include "primitives/transaction.h"
+#include "random.h"
+#include "script/script.h"
+#include "script/sigcache.h"
+#include "script/standard.h"
+#include "tinyformat.h"
 #include "txdb.h"
 #include "txmempool.h"
 #include "ui_interface.h"
+#include "undo.h"
 #include "util.h"
 #include "utilmoneystr.h"
+#include "utilstrencodings.h"
+#include "validationinterface.h"
+#include "versionbits.h"
 
+#include <atomic>
 #include <sstream>
 
 #include <boost/algorithm/string/replace.hpp>
+#include <boost/algorithm/string/join.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/filesystem/fstream.hpp>
+#include <boost/math/distributions/poisson.hpp>
 #include <boost/thread.hpp>
 
-using namespace boost;
 using namespace std;
 
 #if defined(NDEBUG)
@@ -50,22 +70,49 @@ int nScriptCheckThreads = 0;
 bool fImporting = false;
 bool fReindex = false;
 bool fTxIndex = false;
-bool fIsBareMultisigStd = true;
-unsigned int nCoinCacheSize = 5000;
-
-
-/** Fees smaller than this (in satoshi) are considered zero fee (for relaying and mining) */
-CFeeRate minRelayTxFee = CFeeRate(1000);
+bool fHavePruned = false;
+bool fPruneMode = false;
+bool fIsBareMultisigStd = DEFAULT_PERMIT_BAREMULTISIG;
+bool fRequireStandard = true;
+unsigned int nBytesPerSigOp = DEFAULT_BYTES_PER_SIGOP;
+bool fCheckBlockIndex = false;
+bool fCheckpointsEnabled = DEFAULT_CHECKPOINTS_ENABLED;
+size_t nCoinCacheUsage = 5000 * 300;
+uint64_t nPruneTarget = 0;
+int64_t nMaxTipAge = DEFAULT_MAX_TIP_AGE;
+bool fEnableReplacement = DEFAULT_ENABLE_REPLACEMENT;
+
+
+CFeeRate minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
+CAmount maxTxFee = DEFAULT_TRANSACTION_MAXFEE;
 
 CTxMemPool mempool(::minRelayTxFee);
+FeeFilterRounder filterRounder(::minRelayTxFee);
+
+struct IteratorComparator
+{
+    template<typename I>
+    bool operator()(const I& a, const I& b)
+    {
+        return &(*a) < &(*b);
+    }
+};
 
 struct COrphanTx {
     CTransaction tx;
     NodeId fromPeer;
+    int64_t nTimeExpire;
 };
-map<uint256, COrphanTx> mapOrphanTransactions;
-map<uint256, set<uint256> > mapOrphanTransactionsByPrev;
-void EraseOrphansFor(NodeId peer);
+map<uint256, COrphanTx> mapOrphanTransactions GUARDED_BY(cs_main);
+map<COutPoint, set<map<uint256, COrphanTx>::iterator, IteratorComparator>> mapOrphanTransactionsByPrev GUARDED_BY(cs_main);
+void EraseOrphansFor(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+
+/**
+ * Returns true if there are nRequired or more blocks of minVersion or above
+ * in the last Consensus::Params::nMajorityWindow blocks, starting at pstart and going backwards.
+ */
+static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned nRequired, const Consensus::Params& consensusParams);
+static void CheckBlockIndex(const Consensus::Params& consensusParams);
 
 /** Constant stuff for coinbase transactions we create: */
 CScript COINBASE_FLAGS;
@@ -77,7 +124,7 @@ namespace {
 
     struct CBlockIndexWorkComparator
     {
-        bool operator()(CBlockIndex *pa, CBlockIndex *pb) {
+        bool operator()(CBlockIndex *pa, CBlockIndex *pb) const {
             // First sort by most total work, ...
             if (pa->nChainWork > pb->nChainWork) return false;
             if (pa->nChainWork < pb->nChainWork) return true;
@@ -99,18 +146,26 @@ namespace {
     CBlockIndex *pindexBestInvalid;
 
     /**
-     * The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS or better that are at least
-     * as good as our current tip. Entries may be failed, though.
+     * The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS (for itself and all ancestors) and
+     * as good as our current tip or better. Entries may be failed, though, and pruning nodes may be
+     * missing the data for the block.
      */
     set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexCandidates;
     /** Number of nodes with fSyncStarted. */
     int nSyncStarted = 0;
-    /** All pairs A->B, where A (or one if its ancestors) misses transactions, but B has transactions. */
+    /** All pairs A->B, where A (or one of its ancestors) misses transactions, but B has transactions.
+     * Pruned nodes may have entries where B is missing data.
+     */
     multimap<CBlockIndex*, CBlockIndex*> mapBlocksUnlinked;
 
     CCriticalSection cs_LastBlockFile;
     std::vector<CBlockFileInfo> vinfoBlockFile;
     int nLastBlockFile = 0;
+    /** Global flag to indicate we should check to see if there are
+     *  block/undo files that should be deleted.  Set on startup
+     *  or if we allocate more file space when we're in prune mode
+     */
+    bool fCheckForPruning = false;
 
     /**
      * Every received block is assigned a unique and increasing identifier, so we
@@ -121,19 +176,47 @@ namespace {
     uint32_t nBlockSequenceId = 1;
 
     /**
-     * Sources of received blocks, to be able to send them reject messages or ban
-     * them, if processing happens afterwards. Protected by cs_main.
+     * Sources of received blocks, saved to be able to send them reject
+     * messages or ban them when processing happens afterwards. Protected by
+     * cs_main.
      */
     map<uint256, NodeId> mapBlockSource;
 
+    /**
+     * Filter for transactions that were recently rejected by
+     * AcceptToMemoryPool. These are not rerequested until the chain tip
+     * changes, at which point the entire filter is reset. Protected by
+     * cs_main.
+     *
+     * Without this filter we'd be re-requesting txs from each of our peers,
+     * increasing bandwidth consumption considerably. For instance, with 100
+     * peers, half of which relay a tx we don't accept, that might be a 50x
+     * bandwidth increase. A flooding attacker attempting to roll-over the
+     * filter using minimum-sized, 60byte, transactions might manage to send
+     * 1000/sec if we have fast peers, so we pick 120,000 to give our peers a
+     * two minute window to send invs to us.
+     *
+     * Decreasing the false positive rate is fairly cheap, so we pick one in a
+     * million to make it highly unlikely for users to have issues with this
+     * filter.
+     *
+     * Memory used: 1.3 MB
+     */
+    boost::scoped_ptr<CRollingBloomFilter> recentRejects;
+    uint256 hashRecentRejectsChainTip;
+
     /** Blocks that are in flight, and that are in the queue to be downloaded. Protected by cs_main. */
     struct QueuedBlock {
         uint256 hash;
-        CBlockIndex *pindex;  //! Optional.
-        int64_t nTime;  //! Time of "getdata" request in microseconds.
+        CBlockIndex* pindex;                                     //!< Optional.
+        bool fValidatedHeaders;                                  //!< Whether this block has validated headers at the time of request.
+        std::unique_ptr<PartiallyDownloadedBlock> partialBlock;  //!< Optional, used for CMPCTBLOCK downloads
     };
     map<uint256, pair<NodeId, list<QueuedBlock>::iterator> > mapBlocksInFlight;
 
+    /** Stack of nodes which we have set to announce using compact blocks */
+    list<NodeId> lNodesAnnouncingHeaderAndIDs;
+
     /** Number of preferable block download peers. */
     int nPreferredDownload = 0;
 
@@ -142,70 +225,17 @@ namespace {
 
     /** Dirty block file entries. */
     set<int> setDirtyFileInfo;
-} // anon namespace
-
-//////////////////////////////////////////////////////////////////////////////
-//
-// dispatching functions
-//
-
-// These functions dispatch to one or all registered wallets
-
-namespace {
 
-struct CMainSignals {
-    /** Notifies listeners of updated transaction data (transaction, and optionally the block it is found in. */
-    boost::signals2::signal<void (const CTransaction &, const CBlock *)> SyncTransaction;
-    /** Notifies listeners of an erased transaction (currently disabled, requires transaction replacement). */
-    boost::signals2::signal<void (const uint256 &)> EraseTransaction;
-    /** Notifies listeners of an updated transaction without new data (for now: a coinbase potentially becoming visible). */
-    boost::signals2::signal<void (const uint256 &)> UpdatedTransaction;
-    /** Notifies listeners of a new active block chain. */
-    boost::signals2::signal<void (const CBlockLocator &)> SetBestChain;
-    /** Notifies listeners about an inventory item being seen on the network. */
-    boost::signals2::signal<void (const uint256 &)> Inventory;
-    /** Tells listeners to broadcast their data. */
-    boost::signals2::signal<void ()> Broadcast;
-    /** Notifies listeners of a block validation result */
-    boost::signals2::signal<void (const CBlock&, const CValidationState&)> BlockChecked;
-} g_signals;
+    /** Number of peers from which we're downloading blocks. */
+    int nPeersWithValidatedDownloads = 0;
 
+    /** Relay map, protected by cs_main. */
+    typedef std::map<uint256, std::shared_ptr<const CTransaction>> MapRelay;
+    MapRelay mapRelay;
+    /** Expiration-time ordered list of (expire time, relay map entry) pairs, protected by cs_main). */
+    std::deque<std::pair<int64_t, MapRelay::iterator>> vRelayExpiration;
 } // anon namespace
 
-void RegisterValidationInterface(CValidationInterface* pwalletIn) {
-    g_signals.SyncTransaction.connect(boost::bind(&CValidationInterface::SyncTransaction, pwalletIn, _1, _2));
-    g_signals.EraseTransaction.connect(boost::bind(&CValidationInterface::EraseFromWallet, pwalletIn, _1));
-    g_signals.UpdatedTransaction.connect(boost::bind(&CValidationInterface::UpdatedTransaction, pwalletIn, _1));
-    g_signals.SetBestChain.connect(boost::bind(&CValidationInterface::SetBestChain, pwalletIn, _1));
-    g_signals.Inventory.connect(boost::bind(&CValidationInterface::Inventory, pwalletIn, _1));
-    g_signals.Broadcast.connect(boost::bind(&CValidationInterface::ResendWalletTransactions, pwalletIn));
-    g_signals.BlockChecked.connect(boost::bind(&CValidationInterface::BlockChecked, pwalletIn, _1, _2));
-}
-
-void UnregisterValidationInterface(CValidationInterface* pwalletIn) {
-    g_signals.BlockChecked.disconnect(boost::bind(&CValidationInterface::BlockChecked, pwalletIn, _1, _2));
-    g_signals.Broadcast.disconnect(boost::bind(&CValidationInterface::ResendWalletTransactions, pwalletIn));
-    g_signals.Inventory.disconnect(boost::bind(&CValidationInterface::Inventory, pwalletIn, _1));
-    g_signals.SetBestChain.disconnect(boost::bind(&CValidationInterface::SetBestChain, pwalletIn, _1));
-    g_signals.UpdatedTransaction.disconnect(boost::bind(&CValidationInterface::UpdatedTransaction, pwalletIn, _1));
-    g_signals.EraseTransaction.disconnect(boost::bind(&CValidationInterface::EraseFromWallet, pwalletIn, _1));
-    g_signals.SyncTransaction.disconnect(boost::bind(&CValidationInterface::SyncTransaction, pwalletIn, _1, _2));
-}
-
-void UnregisterAllValidationInterfaces() {
-    g_signals.BlockChecked.disconnect_all_slots();
-    g_signals.Broadcast.disconnect_all_slots();
-    g_signals.Inventory.disconnect_all_slots();
-    g_signals.SetBestChain.disconnect_all_slots();
-    g_signals.UpdatedTransaction.disconnect_all_slots();
-    g_signals.EraseTransaction.disconnect_all_slots();
-    g_signals.SyncTransaction.disconnect_all_slots();
-}
-
-void SyncWithWallets(const CTransaction &tx, const CBlock *pblock) {
-    g_signals.SyncTransaction(tx, pblock);
-}
-
 //////////////////////////////////////////////////////////////////////////////
 //
 // Registration of network node signals.
@@ -226,6 +256,10 @@ struct CBlockReject {
  * and we're no longer holding the node's locks.
  */
 struct CNodeState {
+    //! The peer's address
+    CService address;
+    //! Whether we have a fully established connection.
+    bool fCurrentlyConnected;
     //! Accumulated misbehaviour score for this peer.
     int nMisbehavior;
     //! Whether this peer should be disconnected and banned (unless whitelisted).
@@ -240,25 +274,49 @@ struct CNodeState {
     uint256 hashLastUnknownBlock;
     //! The last full block we both have.
     CBlockIndex *pindexLastCommonBlock;
+    //! The best header we have sent our peer.
+    CBlockIndex *pindexBestHeaderSent;
+    //! Length of current-streak of unconnecting headers announcements
+    int nUnconnectingHeaders;
     //! Whether we've started headers synchronization with this peer.
     bool fSyncStarted;
     //! Since when we're stalling block download progress (in microseconds), or 0.
     int64_t nStallingSince;
     list<QueuedBlock> vBlocksInFlight;
+    //! When the first entry in vBlocksInFlight started downloading. Don't care when vBlocksInFlight is empty.
+    int64_t nDownloadingSince;
     int nBlocksInFlight;
+    int nBlocksInFlightValidHeaders;
     //! Whether we consider this a preferred download peer.
     bool fPreferredDownload;
+    //! Whether this peer wants invs or headers (when possible) for block announcements.
+    bool fPreferHeaders;
+    //! Whether this peer wants invs or cmpctblocks (when possible) for block announcements.
+    bool fPreferHeaderAndIDs;
+    //! Whether this peer will send us cmpctblocks if we request them
+    bool fProvidesHeaderAndIDs;
+    //! Whether this peer can give us witnesses
+    bool fHaveWitness;
 
     CNodeState() {
+        fCurrentlyConnected = false;
         nMisbehavior = 0;
         fShouldBan = false;
         pindexBestKnownBlock = NULL;
-        hashLastUnknownBlock = uint256(0);
+        hashLastUnknownBlock.SetNull();
         pindexLastCommonBlock = NULL;
+        pindexBestHeaderSent = NULL;
+        nUnconnectingHeaders = 0;
         fSyncStarted = false;
         nStallingSince = 0;
+        nDownloadingSince = 0;
         nBlocksInFlight = 0;
+        nBlocksInFlightValidHeaders = 0;
         fPreferredDownload = false;
+        fPreferHeaders = false;
+        fPreferHeaderAndIDs = false;
+        fProvidesHeaderAndIDs = false;
+        fHaveWitness = false;
     }
 };
 
@@ -293,6 +351,7 @@ void InitializeNode(NodeId nodeid, const CNode *pnode) {
     LOCK(cs_main);
     CNodeState &state = mapNodeState.insert(std::make_pair(nodeid, CNodeState())).first->second;
     state.name = pnode->addrName;
+    state.address = pnode->addr;
 }
 
 void FinalizeNode(NodeId nodeid) {
@@ -302,51 +361,98 @@ void FinalizeNode(NodeId nodeid) {
     if (state->fSyncStarted)
         nSyncStarted--;
 
-    BOOST_FOREACH(const QueuedBlock& entry, state->vBlocksInFlight)
+    if (state->nMisbehavior == 0 && state->fCurrentlyConnected) {
+        AddressCurrentlyConnected(state->address);
+    }
+
+    BOOST_FOREACH(const QueuedBlock& entry, state->vBlocksInFlight) {
         mapBlocksInFlight.erase(entry.hash);
+    }
     EraseOrphansFor(nodeid);
     nPreferredDownload -= state->fPreferredDownload;
+    nPeersWithValidatedDownloads -= (state->nBlocksInFlightValidHeaders != 0);
+    assert(nPeersWithValidatedDownloads >= 0);
 
     mapNodeState.erase(nodeid);
+
+    if (mapNodeState.empty()) {
+        // Do a consistency check after the last peer is removed.
+        assert(mapBlocksInFlight.empty());
+        assert(nPreferredDownload == 0);
+        assert(nPeersWithValidatedDownloads == 0);
+    }
 }
 
 // Requires cs_main.
-void MarkBlockAsReceived(const uint256& hash) {
+// Returns a bool indicating whether we requested this block.
+// Also used if a block was /not/ received and timed out or started with another peer
+bool MarkBlockAsReceived(const uint256& hash) {
     map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
     if (itInFlight != mapBlocksInFlight.end()) {
         CNodeState *state = State(itInFlight->second.first);
+        state->nBlocksInFlightValidHeaders -= itInFlight->second.second->fValidatedHeaders;
+        if (state->nBlocksInFlightValidHeaders == 0 && itInFlight->second.second->fValidatedHeaders) {
+            // Last validated block on the queue was received.
+            nPeersWithValidatedDownloads--;
+        }
+        if (state->vBlocksInFlight.begin() == itInFlight->second.second) {
+            // First block on the queue was received, update the start download time for the next one
+            state->nDownloadingSince = std::max(state->nDownloadingSince, GetTimeMicros());
+        }
         state->vBlocksInFlight.erase(itInFlight->second.second);
         state->nBlocksInFlight--;
         state->nStallingSince = 0;
         mapBlocksInFlight.erase(itInFlight);
+        return true;
     }
+    return false;
 }
 
 // Requires cs_main.
-void MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, CBlockIndex *pindex = NULL) {
+// returns false, still setting pit, if the block was already in flight from the same peer
+// pit will only be valid as long as the same cs_main lock is being held
+bool MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, const Consensus::Params& consensusParams, CBlockIndex *pindex = NULL, list<QueuedBlock>::iterator **pit = NULL) {
     CNodeState *state = State(nodeid);
     assert(state != NULL);
 
+    // Short-circuit most stuff in case its from the same node
+    map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
+    if (itInFlight != mapBlocksInFlight.end() && itInFlight->second.first == nodeid) {
+        *pit = &itInFlight->second.second;
+        return false;
+    }
+
     // Make sure it's not listed somewhere already.
     MarkBlockAsReceived(hash);
 
-    QueuedBlock newentry = {hash, pindex, GetTimeMicros()};
-    list<QueuedBlock>::iterator it = state->vBlocksInFlight.insert(state->vBlocksInFlight.end(), newentry);
+    list<QueuedBlock>::iterator it = state->vBlocksInFlight.insert(state->vBlocksInFlight.end(),
+            {hash, pindex, pindex != NULL, std::unique_ptr<PartiallyDownloadedBlock>(pit ? new PartiallyDownloadedBlock(&mempool) : NULL)});
     state->nBlocksInFlight++;
-    mapBlocksInFlight[hash] = std::make_pair(nodeid, it);
+    state->nBlocksInFlightValidHeaders += it->fValidatedHeaders;
+    if (state->nBlocksInFlight == 1) {
+        // We're starting a block download (batch) from this peer.
+        state->nDownloadingSince = GetTimeMicros();
+    }
+    if (state->nBlocksInFlightValidHeaders == 1 && pindex != NULL) {
+        nPeersWithValidatedDownloads++;
+    }
+    itInFlight = mapBlocksInFlight.insert(std::make_pair(hash, std::make_pair(nodeid, it))).first;
+    if (pit)
+        *pit = &itInFlight->second.second;
+    return true;
 }
 
-/** Check whether the last unknown block a peer advertized is not yet known. */
+/** Check whether the last unknown block a peer advertised is not yet known. */
 void ProcessBlockAvailability(NodeId nodeid) {
     CNodeState *state = State(nodeid);
     assert(state != NULL);
 
-    if (state->hashLastUnknownBlock != 0) {
+    if (!state->hashLastUnknownBlock.IsNull()) {
         BlockMap::iterator itOld = mapBlockIndex.find(state->hashLastUnknownBlock);
         if (itOld != mapBlockIndex.end() && itOld->second->nChainWork > 0) {
             if (state->pindexBestKnownBlock == NULL || itOld->second->nChainWork >= state->pindexBestKnownBlock->nChainWork)
                 state->pindexBestKnownBlock = itOld->second;
-            state->hashLastUnknownBlock = uint256(0);
+            state->hashLastUnknownBlock.SetNull();
         }
     }
 }
@@ -369,6 +475,48 @@ void UpdateBlockAvailability(NodeId nodeid, const uint256 &hash) {
     }
 }
 
+void MaybeSetPeerAsAnnouncingHeaderAndIDs(const CNodeState* nodestate, CNode* pfrom) {
+    if (nLocalServices & NODE_WITNESS) {
+        // Don't ever request compact blocks when segwit is enabled.
+        return;
+    }
+    if (nodestate->fProvidesHeaderAndIDs) {
+        BOOST_FOREACH(const NodeId nodeid, lNodesAnnouncingHeaderAndIDs)
+            if (nodeid == pfrom->GetId())
+                return;
+        bool fAnnounceUsingCMPCTBLOCK = false;
+        uint64_t nCMPCTBLOCKVersion = 1;
+        if (lNodesAnnouncingHeaderAndIDs.size() >= 3) {
+            // As per BIP152, we only get 3 of our peers to announce
+            // blocks using compact encodings.
+            CNode* pnodeStop = FindNode(lNodesAnnouncingHeaderAndIDs.front());
+            if (pnodeStop) {
+                pnodeStop->PushMessage(NetMsgType::SENDCMPCT, fAnnounceUsingCMPCTBLOCK, nCMPCTBLOCKVersion);
+                lNodesAnnouncingHeaderAndIDs.pop_front();
+            }
+        }
+        fAnnounceUsingCMPCTBLOCK = true;
+        pfrom->PushMessage(NetMsgType::SENDCMPCT, fAnnounceUsingCMPCTBLOCK, nCMPCTBLOCKVersion);
+        lNodesAnnouncingHeaderAndIDs.push_back(pfrom->GetId());
+    }
+}
+
+// Requires cs_main
+bool CanDirectFetch(const Consensus::Params &consensusParams)
+{
+    return chainActive.Tip()->GetBlockTime() > GetAdjustedTime() - consensusParams.nPowTargetSpacing * 20;
+}
+
+// Requires cs_main
+bool PeerHasHeader(CNodeState *state, CBlockIndex *pindex)
+{
+    if (state->pindexBestKnownBlock && pindex == state->pindexBestKnownBlock->GetAncestor(pindex->nHeight))
+        return true;
+    if (state->pindexBestHeaderSent && pindex == state->pindexBestHeaderSent->GetAncestor(pindex->nHeight))
+        return true;
+    return false;
+}
+
 /** Find the last common ancestor two blocks have.
  *  Both pa and pb must be non-NULL. */
 CBlockIndex* LastCommonAncestor(CBlockIndex* pa, CBlockIndex* pb) {
@@ -413,7 +561,7 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBl
     }
 
     // If the peer reorganized, our previous pindexLastCommonBlock may not be an ancestor
-    // of their current tip anymore. Go back enough to fix that.
+    // of its current tip anymore. Go back enough to fix that.
     state->pindexLastCommonBlock = LastCommonAncestor(state->pindexLastCommonBlock, state->pindexBestKnownBlock);
     if (state->pindexLastCommonBlock == state->pindexBestKnownBlock)
         return;
@@ -440,9 +588,14 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBl
 
         // Iterate over those blocks in vToFetch (in forward direction), adding the ones that
         // are not yet downloaded and not in flight to vBlocks. In the mean time, update
-        // pindexLastCommonBlock as long as all ancestors are already downloaded.
+        // pindexLastCommonBlock as long as all ancestors are already downloaded, or if it's
+        // already part of our chain (and therefore don't need it even if pruned).
         BOOST_FOREACH(CBlockIndex* pindex, vToFetch) {
-            if (pindex->nStatus & BLOCK_HAVE_DATA) {
+            if (!pindex->IsValid(BLOCK_VALID_TREE)) {
+                // We consider the chain that this peer is on invalid.
+                return;
+            }
+            if (pindex->nStatus & BLOCK_HAVE_DATA || chainActive.Contains(pindex)) {
                 if (pindex->nChainTx)
                     state->pindexLastCommonBlock = pindex;
             } else if (mapBlocksInFlight.count(pindex->GetBlockHash()) == 0) {
@@ -512,6 +665,9 @@ CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& loc
             CBlockIndex* pindex = (*mi).second;
             if (chain.Contains(pindex))
                 return pindex;
+            if (pindex->GetAncestor(chain.Height()) == chain.Tip()) {
+                return chain.Tip();
+            }
         }
     }
     return chain.Genesis();
@@ -525,7 +681,7 @@ CBlockTreeDB *pblocktree = NULL;
 // mapOrphanTransactions
 //
 
-bool AddOrphanTx(const CTransaction& tx, NodeId peer)
+bool AddOrphanTx(const CTransaction& tx, NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     uint256 hash = tx.GetHash();
     if (mapOrphanTransactions.count(hash))
@@ -536,40 +692,42 @@ bool AddOrphanTx(const CTransaction& tx, NodeId peer)
     // large transaction with a missing parent then we assume
     // it will rebroadcast it later, after the parent transaction(s)
     // have been mined or received.
-    // 10,000 orphans, each of which is at most 5,000 bytes big is
-    // at most 500 megabytes of orphans:
-    unsigned int sz = tx.GetSerializeSize(SER_NETWORK, CTransaction::CURRENT_VERSION);
-    if (sz > 5000)
+    // 100 orphans, each of which is at most 99,999 bytes big is
+    // at most 10 megabytes of orphans and somewhat more byprev index (in the worst case):
+    unsigned int sz = GetTransactionCost(tx);
+    if (sz >= MAX_STANDARD_TX_COST)
     {
         LogPrint("mempool", "ignoring large orphan tx (size: %u, hash: %s)\n", sz, hash.ToString());
         return false;
     }
 
-    mapOrphanTransactions[hash].tx = tx;
-    mapOrphanTransactions[hash].fromPeer = peer;
-    BOOST_FOREACH(const CTxIn& txin, tx.vin)
-        mapOrphanTransactionsByPrev[txin.prevout.hash].insert(hash);
+    auto ret = mapOrphanTransactions.emplace(hash, COrphanTx{tx, peer, GetTime() + ORPHAN_TX_EXPIRE_TIME});
+    assert(ret.second);
+    BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+        mapOrphanTransactionsByPrev[txin.prevout].insert(ret.first);
+    }
 
-    LogPrint("mempool", "stored orphan tx %s (mapsz %u prevsz %u)\n", hash.ToString(),
+    LogPrint("mempool", "stored orphan tx %s (mapsz %u outsz %u)\n", hash.ToString(),
              mapOrphanTransactions.size(), mapOrphanTransactionsByPrev.size());
     return true;
 }
 
-void static EraseOrphanTx(uint256 hash)
+int static EraseOrphanTx(uint256 hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     map<uint256, COrphanTx>::iterator it = mapOrphanTransactions.find(hash);
     if (it == mapOrphanTransactions.end())
-        return;
+        return 0;
     BOOST_FOREACH(const CTxIn& txin, it->second.tx.vin)
     {
-        map<uint256, set<uint256> >::iterator itPrev = mapOrphanTransactionsByPrev.find(txin.prevout.hash);
+        auto itPrev = mapOrphanTransactionsByPrev.find(txin.prevout);
         if (itPrev == mapOrphanTransactionsByPrev.end())
             continue;
-        itPrev->second.erase(hash);
+        itPrev->second.erase(it);
         if (itPrev->second.empty())
             mapOrphanTransactionsByPrev.erase(itPrev);
     }
     mapOrphanTransactions.erase(it);
+    return 1;
 }
 
 void EraseOrphansFor(NodeId peer)
@@ -581,17 +739,36 @@ void EraseOrphansFor(NodeId peer)
         map<uint256, COrphanTx>::iterator maybeErase = iter++; // increment to avoid iterator becoming invalid
         if (maybeErase->second.fromPeer == peer)
         {
-            EraseOrphanTx(maybeErase->second.tx.GetHash());
-            ++nErased;
+            nErased += EraseOrphanTx(maybeErase->second.tx.GetHash());
         }
     }
     if (nErased > 0) LogPrint("mempool", "Erased %d orphan tx from peer %d\n", nErased, peer);
 }
 
 
-unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans)
+unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     unsigned int nEvicted = 0;
+    static int64_t nNextSweep;
+    int64_t nNow = GetTime();
+    if (nNextSweep <= nNow) {
+        // Sweep out expired orphan pool entries:
+        int nErased = 0;
+        int64_t nMinExpTime = nNow + ORPHAN_TX_EXPIRE_TIME - ORPHAN_TX_EXPIRE_INTERVAL;
+        map<uint256, COrphanTx>::iterator iter = mapOrphanTransactions.begin();
+        while (iter != mapOrphanTransactions.end())
+        {
+            map<uint256, COrphanTx>::iterator maybeErase = iter++;
+            if (maybeErase->second.nTimeExpire <= nNow) {
+                nErased += EraseOrphanTx(maybeErase->second.tx.GetHash());
+            } else {
+                nMinExpTime = std::min(maybeErase->second.nTimeExpire, nMinExpTime);
+            }
+        }
+        // Sweep again 5 minutes after the next entry that expires in order to batch the linear scan.
+        nNextSweep = nMinExpTime + ORPHAN_TX_EXPIRE_INTERVAL;
+        if (nErased > 0) LogPrint("mempool", "Erased %d orphan tx due to expiration\n", nErased);
+    }
     while (mapOrphanTransactions.size() > nMaxOrphans)
     {
         // Evict a random orphan:
@@ -605,185 +782,223 @@ unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans)
     return nEvicted;
 }
 
-
-
-
-
-
-
-bool IsStandardTx(const CTransaction& tx, string& reason)
+bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
 {
-    AssertLockHeld(cs_main);
-    if (tx.nVersion > CTransaction::CURRENT_VERSION || tx.nVersion < 1) {
-        reason = "version";
-        return false;
-    }
-
-    // Treat non-final transactions as non-standard to prevent a specific type
-    // of double-spend attack, as well as DoS attacks. (if the transaction
-    // can't be mined, the attacker isn't expending resources broadcasting it)
-    // Basically we don't want to propagate transactions that can't be included in
-    // the next block.
-    //
-    // However, IsFinalTx() is confusing... Without arguments, it uses
-    // chainActive.Height() to evaluate nLockTime; when a block is accepted, chainActive.Height()
-    // is set to the value of nHeight in the block. However, when IsFinalTx()
-    // is called within CBlock::AcceptBlock(), the height of the block *being*
-    // evaluated is what is used. Thus if we want to know if a transaction can
-    // be part of the *next* block, we need to call IsFinalTx() with one more
-    // than chainActive.Height().
-    //
-    // Timestamps on the other hand don't get any special treatment, because we
-    // can't know what timestamp the next block will have, and there aren't
-    // timestamp applications where it matters.
-    if (!IsFinalTx(tx, chainActive.Height() + 1)) {
-        reason = "non-final";
-        return false;
+    if (tx.nLockTime == 0)
+        return true;
+    if ((int64_t)tx.nLockTime < ((int64_t)tx.nLockTime < LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime))
+        return true;
+    BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+        if (!(txin.nSequence == CTxIn::SEQUENCE_FINAL))
+            return false;
     }
+    return true;
+}
 
-    // Extremely large transactions with lots of inputs can cost the network
-    // almost as much to process as they cost the sender in fees, because
-    // computing signature hashes is O(ninputs*txsize). Limiting transactions
-    // to MAX_STANDARD_TX_SIZE mitigates CPU exhaustion attacks.
-    unsigned int sz = tx.GetSerializeSize(SER_NETWORK, CTransaction::CURRENT_VERSION);
-    if (sz >= MAX_STANDARD_TX_SIZE) {
-        reason = "tx-size";
-        return false;
-    }
+bool CheckFinalTx(const CTransaction &tx, int flags)
+{
+    AssertLockHeld(cs_main);
 
-    BOOST_FOREACH(const CTxIn& txin, tx.vin)
-    {
-        // Biggest 'standard' txin is a 15-of-15 P2SH multisig with compressed
-        // keys. (remember the 520 byte limit on redeemScript size) That works
-        // out to a (15*(33+1))+3=513 byte redeemScript, 513+1+15*(73+1)+3=1627
-        // bytes of scriptSig, which we round off to 1650 bytes for some minor
-        // future-proofing. That's also enough to spend a 20-of-20
-        // CHECKMULTISIG scriptPubKey, though such a scriptPubKey is not
-        // considered standard)
-        if (txin.scriptSig.size() > 1650) {
-            reason = "scriptsig-size";
-            return false;
-        }
-        if (!txin.scriptSig.IsPushOnly()) {
-            reason = "scriptsig-not-pushonly";
-            return false;
-        }
-    }
+    // By convention a negative value for flags indicates that the
+    // current network-enforced consensus rules should be used. In
+    // a future soft-fork scenario that would mean checking which
+    // rules would be enforced for the next block and setting the
+    // appropriate flags. At the present time no soft-forks are
+    // scheduled, so no flags are set.
+    flags = std::max(flags, 0);
+
+    // CheckFinalTx() uses chainActive.Height()+1 to evaluate
+    // nLockTime because when IsFinalTx() is called within
+    // CBlock::AcceptBlock(), the height of the block *being*
+    // evaluated is what is used. Thus if we want to know if a
+    // transaction can be part of the *next* block, we need to call
+    // IsFinalTx() with one more than chainActive.Height().
+    const int nBlockHeight = chainActive.Height() + 1;
+
+    // BIP113 will require that time-locked transactions have nLockTime set to
+    // less than the median time of the previous block they're contained in.
+    // When the next block is created its previous block will be the current
+    // chain tip, so we use that to calculate the median time passed to
+    // IsFinalTx() if LOCKTIME_MEDIAN_TIME_PAST is set.
+    const int64_t nBlockTime = (flags & LOCKTIME_MEDIAN_TIME_PAST)
+                             ? chainActive.Tip()->GetMedianTimePast()
+                             : GetAdjustedTime();
+
+    return IsFinalTx(tx, nBlockHeight, nBlockTime);
+}
 
-    unsigned int nDataOut = 0;
-    txnouttype whichType;
-    BOOST_FOREACH(const CTxOut& txout, tx.vout) {
-        if (!::IsStandard(txout.scriptPubKey, whichType)) {
-            reason = "scriptpubkey";
-            return false;
+/**
+ * Calculates the block height and previous block's median time past at
+ * which the transaction will be considered final in the context of BIP 68.
+ * Also removes from the vector of input heights any entries which did not
+ * correspond to sequence locked inputs as they do not affect the calculation.
+ */
+static std::pair<int, int64_t> CalculateSequenceLocks(const CTransaction &tx, int flags, std::vector<int>* prevHeights, const CBlockIndex& block)
+{
+    assert(prevHeights->size() == tx.vin.size());
+
+    // Will be set to the equivalent height- and time-based nLockTime
+    // values that would be necessary to satisfy all relative lock-
+    // time constraints given our view of block chain history.
+    // The semantics of nLockTime are the last invalid height/time, so
+    // use -1 to have the effect of any height or time being valid.
+    int nMinHeight = -1;
+    int64_t nMinTime = -1;
+
+    // tx.nVersion is signed integer so requires cast to unsigned otherwise
+    // we would be doing a signed comparison and half the range of nVersion
+    // wouldn't support BIP 68.
+    bool fEnforceBIP68 = static_cast<uint32_t>(tx.nVersion) >= 2
+                      && flags & LOCKTIME_VERIFY_SEQUENCE;
+
+    // Do not enforce sequence numbers as a relative lock time
+    // unless we have been instructed to
+    if (!fEnforceBIP68) {
+        return std::make_pair(nMinHeight, nMinTime);
+    }
+
+    for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
+        const CTxIn& txin = tx.vin[txinIndex];
+
+        // Sequence numbers with the most significant bit set are not
+        // treated as relative lock-times, nor are they given any
+        // consensus-enforced meaning at this point.
+        if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_DISABLE_FLAG) {
+            // The height of this input is not relevant for sequence locks
+            (*prevHeights)[txinIndex] = 0;
+            continue;
         }
 
-        if (whichType == TX_NULL_DATA)
-            nDataOut++;
-        else if ((whichType == TX_MULTISIG) && (!fIsBareMultisigStd)) {
-            reason = "bare-multisig";
-            return false;
-        } else if (txout.IsDust(::minRelayTxFee)) {
-            reason = "dust";
-            return false;
+        int nCoinHeight = (*prevHeights)[txinIndex];
+
+        if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG) {
+            int64_t nCoinTime = block.GetAncestor(std::max(nCoinHeight-1, 0))->GetMedianTimePast();
+            // NOTE: Subtract 1 to maintain nLockTime semantics
+            // BIP 68 relative lock times have the semantics of calculating
+            // the first block or time at which the transaction would be
+            // valid. When calculating the effective block time or height
+            // for the entire transaction, we switch to using the
+            // semantics of nLockTime which is the last invalid block
+            // time or height.  Thus we subtract 1 from the calculated
+            // time or height.
+
+            // Time-based relative lock-times are measured from the
+            // smallest allowed timestamp of the block containing the
+            // txout being spent, which is the median time past of the
+            // block prior.
+            nMinTime = std::max(nMinTime, nCoinTime + (int64_t)((txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) << CTxIn::SEQUENCE_LOCKTIME_GRANULARITY) - 1);
+        } else {
+            nMinHeight = std::max(nMinHeight, nCoinHeight + (int)(txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) - 1);
         }
     }
 
-    // only one OP_RETURN txout is permitted
-    if (nDataOut > 1) {
-        reason = "multi-op-return";
+    return std::make_pair(nMinHeight, nMinTime);
+}
+
+static bool EvaluateSequenceLocks(const CBlockIndex& block, std::pair<int, int64_t> lockPair)
+{
+    assert(block.pprev);
+    int64_t nBlockTime = block.pprev->GetMedianTimePast();
+    if (lockPair.first >= block.nHeight || lockPair.second >= nBlockTime)
         return false;
-    }
 
     return true;
 }
 
-bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
+bool SequenceLocks(const CTransaction &tx, int flags, std::vector<int>* prevHeights, const CBlockIndex& block)
 {
-    AssertLockHeld(cs_main);
-    // Time based nLockTime implemented in 0.1.6
-    if (tx.nLockTime == 0)
-        return true;
-    if (nBlockHeight == 0)
-        nBlockHeight = chainActive.Height();
-    if (nBlockTime == 0)
-        nBlockTime = GetAdjustedTime();
-    if ((int64_t)tx.nLockTime < ((int64_t)tx.nLockTime < LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime))
-        return true;
-    BOOST_FOREACH(const CTxIn& txin, tx.vin)
-        if (!txin.IsFinal())
-            return false;
-    return true;
+    return EvaluateSequenceLocks(block, CalculateSequenceLocks(tx, flags, prevHeights, block));
 }
 
-/**
- * Check transaction inputs to mitigate two
- * potential denial-of-service attacks:
- * 
- * 1. scriptSigs with extra data stuffed into them,
- *    not consumed by scriptPubKey (or P2SH script)
- * 2. P2SH scripts with a crazy number of expensive
- *    CHECKSIG/CHECKMULTISIG operations
- */
-bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
+bool TestLockPointValidity(const LockPoints* lp)
 {
-    if (tx.IsCoinBase())
-        return true; // Coinbases don't use vin normally
-
-    for (unsigned int i = 0; i < tx.vin.size(); i++)
-    {
-        const CTxOut& prev = mapInputs.GetOutputFor(tx.vin[i]);
-
-        vector<vector<unsigned char> > vSolutions;
-        txnouttype whichType;
-        // get the scriptPubKey corresponding to this input:
-        const CScript& prevScript = prev.scriptPubKey;
-        if (!Solver(prevScript, whichType, vSolutions))
-            return false;
-        int nArgsExpected = ScriptSigArgsExpected(whichType, vSolutions);
-        if (nArgsExpected < 0)
+    AssertLockHeld(cs_main);
+    assert(lp);
+    // If there are relative lock times then the maxInputBlock will be set
+    // If there are no relative lock times, the LockPoints don't depend on the chain
+    if (lp->maxInputBlock) {
+        // Check whether chainActive is an extension of the block at which the LockPoints
+        // calculation was valid.  If not LockPoints are no longer valid
+        if (!chainActive.Contains(lp->maxInputBlock)) {
             return false;
+        }
+    }
 
-        // Transactions with extra stuff in their scriptSigs are
-        // non-standard. Note that this EvalScript() call will
-        // be quick, because if there are any operations
-        // beside "push data" in the scriptSig
-        // IsStandard() will have already returned false
-        // and this method isn't called.
-        vector<vector<unsigned char> > stack;
-        if (!EvalScript(stack, tx.vin[i].scriptSig, false, BaseSignatureChecker()))
-            return false;
+    // LockPoints still valid
+    return true;
+}
 
-        if (whichType == TX_SCRIPTHASH)
-        {
-            if (stack.empty())
-                return false;
-            CScript subscript(stack.back().begin(), stack.back().end());
-            vector<vector<unsigned char> > vSolutions2;
-            txnouttype whichType2;
-            if (Solver(subscript, whichType2, vSolutions2))
-            {
-                int tmpExpected = ScriptSigArgsExpected(whichType2, vSolutions2);
-                if (tmpExpected < 0)
-                    return false;
-                nArgsExpected += tmpExpected;
+bool CheckSequenceLocks(const CTransaction &tx, int flags, LockPoints* lp, bool useExistingLockPoints)
+{
+    AssertLockHeld(cs_main);
+    AssertLockHeld(mempool.cs);
+
+    CBlockIndex* tip = chainActive.Tip();
+    CBlockIndex index;
+    index.pprev = tip;
+    // CheckSequenceLocks() uses chainActive.Height()+1 to evaluate
+    // height based locks because when SequenceLocks() is called within
+    // ConnectBlock(), the height of the block *being*
+    // evaluated is what is used.
+    // Thus if we want to know if a transaction can be part of the
+    // *next* block, we need to use one more than chainActive.Height()
+    index.nHeight = tip->nHeight + 1;
+
+    std::pair<int, int64_t> lockPair;
+    if (useExistingLockPoints) {
+        assert(lp);
+        lockPair.first = lp->height;
+        lockPair.second = lp->time;
+    }
+    else {
+        // pcoinsTip contains the UTXO set for chainActive.Tip()
+        CCoinsViewMemPool viewMemPool(pcoinsTip, mempool);
+        std::vector<int> prevheights;
+        prevheights.resize(tx.vin.size());
+        for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
+            const CTxIn& txin = tx.vin[txinIndex];
+            CCoins coins;
+            if (!viewMemPool.GetCoins(txin.prevout.hash, coins)) {
+                return error("%s: Missing input", __func__);
             }
-            else
-            {
-                // Any other Script with less than 15 sigops OK:
-                unsigned int sigops = subscript.GetSigOpCount(true);
-                // ... extra data left on the stack after execution is OK, too:
-                return (sigops <= MAX_P2SH_SIGOPS);
+            if (coins.nHeight == MEMPOOL_HEIGHT) {
+                // Assume all mempool transaction confirm in the next block
+                prevheights[txinIndex] = tip->nHeight + 1;
+            } else {
+                prevheights[txinIndex] = coins.nHeight;
             }
         }
-
-        if (stack.size() != (unsigned int)nArgsExpected)
-            return false;
+        lockPair = CalculateSequenceLocks(tx, flags, &prevheights, index);
+        if (lp) {
+            lp->height = lockPair.first;
+            lp->time = lockPair.second;
+            // Also store the hash of the block with the highest height of
+            // all the blocks which have sequence locked prevouts.
+            // This hash needs to still be on the chain
+            // for these LockPoint calculations to be valid
+            // Note: It is impossible to correctly calculate a maxInputBlock
+            // if any of the sequence locked inputs depend on unconfirmed txs,
+            // except in the special case where the relative lock time/height
+            // is 0, which is equivalent to no sequence lock. Since we assume
+            // input height of tip+1 for mempool txs and test the resulting
+            // lockPair from CalculateSequenceLocks against tip+1.  We know
+            // EvaluateSequenceLocks will fail if there was a non-zero sequence
+            // lock on a mempool input, so we can use the return value of
+            // CheckSequenceLocks to indicate the LockPoints validity
+            int maxInputHeight = 0;
+            BOOST_FOREACH(int height, prevheights) {
+                // Can ignore mempool inputs since we'll fail if they had non-zero locks
+                if (height != tip->nHeight+1) {
+                    maxInputHeight = std::max(maxInputHeight, height);
+                }
+            }
+            lp->maxInputBlock = tip->GetAncestor(maxInputHeight);
+        }
     }
-
-    return true;
+    return EvaluateSequenceLocks(index, lockPair);
 }
 
+
 unsigned int GetLegacySigOpCount(const CTransaction& tx)
 {
     unsigned int nSigOps = 0;
@@ -813,8 +1028,24 @@ unsigned int GetP2SHSigOpCount(const CTransaction& tx, const CCoinsViewCache& in
     return nSigOps;
 }
 
+int64_t GetTransactionSigOpCost(const CTransaction& tx, const CCoinsViewCache& inputs, int flags)
+{
+    int64_t nSigOps = GetLegacySigOpCount(tx) * WITNESS_SCALE_FACTOR;
 
+    if (tx.IsCoinBase())
+        return nSigOps;
 
+    if (flags & SCRIPT_VERIFY_P2SH) {
+        nSigOps += GetP2SHSigOpCount(tx, inputs) * WITNESS_SCALE_FACTOR;
+    }
+
+    for (unsigned int i = 0; i < tx.vin.size(); i++)
+    {
+        const CTxOut &prevout = inputs.GetOutputFor(tx.vin[i]);
+        nSigOps += CountWitnessSigOps(tx.vin[i].scriptSig, prevout.scriptPubKey, i < tx.wit.vtxinwit.size() ? &tx.wit.vtxinwit[i].scriptWitness : NULL, flags);
+    }
+    return nSigOps;
+}
 
 
 
@@ -824,30 +1055,24 @@ bool CheckTransaction(const CTransaction& tx, CValidationState &state)
 {
     // Basic checks that don't depend on any context
     if (tx.vin.empty())
-        return state.DoS(10, error("CheckTransaction() : vin empty"),
-                         REJECT_INVALID, "bad-txns-vin-empty");
+        return state.DoS(10, false, REJECT_INVALID, "bad-txns-vin-empty");
     if (tx.vout.empty())
-        return state.DoS(10, error("CheckTransaction() : vout empty"),
-                         REJECT_INVALID, "bad-txns-vout-empty");
-    // Size limits
-    if (::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION) > MAX_BLOCK_SIZE)
-        return state.DoS(100, error("CheckTransaction() : size limits failed"),
-                         REJECT_INVALID, "bad-txns-oversize");
+        return state.DoS(10, false, REJECT_INVALID, "bad-txns-vout-empty");
+    // Size limits (this doesn't take the witness into account, as that hasn't been checked for malleability)
+    if (::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) > MAX_BLOCK_BASE_SIZE)
+        return state.DoS(100, false, REJECT_INVALID, "bad-txns-oversize");
 
     // Check for negative or overflow output values
     CAmount nValueOut = 0;
     BOOST_FOREACH(const CTxOut& txout, tx.vout)
     {
         if (txout.nValue < 0)
-            return state.DoS(100, error("CheckTransaction() : txout.nValue negative"),
-                             REJECT_INVALID, "bad-txns-vout-negative");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-vout-negative");
         if (txout.nValue > MAX_MONEY)
-            return state.DoS(100, error("CheckTransaction() : txout.nValue too high"),
-                             REJECT_INVALID, "bad-txns-vout-toolarge");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-vout-toolarge");
         nValueOut += txout.nValue;
         if (!MoneyRange(nValueOut))
-            return state.DoS(100, error("CheckTransaction() : txout total out of range"),
-                             REJECT_INVALID, "bad-txns-txouttotal-toolarge");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-txouttotal-toolarge");
     }
 
     // Check for duplicate inputs
@@ -855,95 +1080,130 @@ bool CheckTransaction(const CTransaction& tx, CValidationState &state)
     BOOST_FOREACH(const CTxIn& txin, tx.vin)
     {
         if (vInOutPoints.count(txin.prevout))
-            return state.DoS(100, error("CheckTransaction() : duplicate inputs"),
-                             REJECT_INVALID, "bad-txns-inputs-duplicate");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputs-duplicate");
         vInOutPoints.insert(txin.prevout);
     }
 
     if (tx.IsCoinBase())
     {
         if (tx.vin[0].scriptSig.size() < 2 || tx.vin[0].scriptSig.size() > 100)
-            return state.DoS(100, error("CheckTransaction() : coinbase script size"),
-                             REJECT_INVALID, "bad-cb-length");
+            return state.DoS(100, false, REJECT_INVALID, "bad-cb-length");
     }
     else
     {
         BOOST_FOREACH(const CTxIn& txin, tx.vin)
             if (txin.prevout.IsNull())
-                return state.DoS(10, error("CheckTransaction() : prevout is null"),
-                                 REJECT_INVALID, "bad-txns-prevout-null");
+                return state.DoS(10, false, REJECT_INVALID, "bad-txns-prevout-null");
     }
 
     return true;
 }
 
-CAmount GetMinRelayFee(const CTransaction& tx, unsigned int nBytes, bool fAllowFree)
-{
-    {
-        LOCK(mempool.cs);
-        uint256 hash = tx.GetHash();
-        double dPriorityDelta = 0;
-        CAmount nFeeDelta = 0;
-        mempool.ApplyDeltas(hash, dPriorityDelta, nFeeDelta);
-        if (dPriorityDelta > 0 || nFeeDelta > 0)
-            return 0;
-    }
-
-    CAmount nMinFee = ::minRelayTxFee.GetFee(nBytes);
-
-    if (fAllowFree)
-    {
-        // There is a free transaction area in blocks created by most miners,
-        // * If we are relaying we allow transactions up to DEFAULT_BLOCK_PRIORITY_SIZE - 1000
-        //   to be considered to fall into this category. We don't want to encourage sending
-        //   multiple transactions instead of one big transaction to avoid fees.
-        if (nBytes < (DEFAULT_BLOCK_PRIORITY_SIZE - 1000))
-            nMinFee = 0;
-    }
+void LimitMempoolSize(CTxMemPool& pool, size_t limit, unsigned long age) {
+    int expired = pool.Expire(GetTime() - age);
+    if (expired != 0)
+        LogPrint("mempool", "Expired %i transactions from the memory pool\n", expired);
 
-    if (!MoneyRange(nMinFee))
-        nMinFee = MAX_MONEY;
-    return nMinFee;
+    std::vector<uint256> vNoSpendsRemaining;
+    pool.TrimToSize(limit, &vNoSpendsRemaining);
+    BOOST_FOREACH(const uint256& removed, vNoSpendsRemaining)
+        pcoinsTip->Uncache(removed);
 }
 
+/** Convert CValidationState to a human-readable message for logging */
+std::string FormatStateMessage(const CValidationState &state)
+{
+    return strprintf("%s%s (code %i)",
+        state.GetRejectReason(),
+        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage(),
+        state.GetRejectCode());
+}
 
-bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
-                        bool* pfMissingInputs, bool fRejectInsaneFee)
+bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const CTransaction& tx, bool fLimitFree,
+                              bool* pfMissingInputs, bool fOverrideMempoolLimit, const CAmount& nAbsurdFee,
+                              std::vector<uint256>& vHashTxnToUncache)
 {
+    const uint256 hash = tx.GetHash();
     AssertLockHeld(cs_main);
     if (pfMissingInputs)
         *pfMissingInputs = false;
 
     if (!CheckTransaction(tx, state))
-        return error("AcceptToMemoryPool: : CheckTransaction failed");
+        return false; // state filled in by CheckTransaction
 
     // Coinbase is only valid in a block, not as a loose transaction
     if (tx.IsCoinBase())
-        return state.DoS(100, error("AcceptToMemoryPool: : coinbase as individual tx"),
-                         REJECT_INVALID, "coinbase");
+        return state.DoS(100, false, REJECT_INVALID, "coinbase");
+
+    // Don't relay version 2 transactions until CSV is active, and we can be
+    // sure that such transactions will be mined (unless we're on
+    // -testnet/-regtest).
+    const CChainParams& chainparams = Params();
+    if (fRequireStandard && tx.nVersion >= 2 && VersionBitsTipState(chainparams.GetConsensus(), Consensus::DEPLOYMENT_CSV) != THRESHOLD_ACTIVE) {
+        return state.DoS(0, false, REJECT_NONSTANDARD, "premature-version2-tx");
+    }
+
+    // Reject transactions with witness before segregated witness activates (override with -prematurewitness)
+    if (!GetBoolArg("-prematurewitness",false) && !tx.wit.IsNull() && !IsWitnessEnabled(chainActive.Tip(), Params().GetConsensus())) {
+        return state.DoS(0, false, REJECT_NONSTANDARD, "no-witness-yet", true);
+    }
 
     // Rather not work on nonstandard transactions (unless -testnet/-regtest)
     string reason;
-    if (Params().RequireStandard() && !IsStandardTx(tx, reason))
-        return state.DoS(0,
-                         error("AcceptToMemoryPool : nonstandard transaction: %s", reason),
-                         REJECT_NONSTANDARD, reason);
+    if (fRequireStandard && !IsStandardTx(tx, reason))
+        return state.DoS(0, false, REJECT_NONSTANDARD, reason);
+
+    // Only accept nLockTime-using transactions that can be mined in the next
+    // block; we don't want our mempool filled up with transactions that can't
+    // be mined yet.
+    if (!CheckFinalTx(tx, STANDARD_LOCKTIME_VERIFY_FLAGS))
+        return state.DoS(0, false, REJECT_NONSTANDARD, "non-final");
 
     // is it already in the memory pool?
-    uint256 hash = tx.GetHash();
     if (pool.exists(hash))
-        return false;
+        return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-in-mempool");
 
     // Check for conflicts with in-memory transactions
+    set<uint256> setConflicts;
     {
     LOCK(pool.cs); // protect pool.mapNextTx
-    for (unsigned int i = 0; i < tx.vin.size(); i++)
+    BOOST_FOREACH(const CTxIn &txin, tx.vin)
     {
-        COutPoint outpoint = tx.vin[i].prevout;
-        if (pool.mapNextTx.count(outpoint))
+        auto itConflicting = pool.mapNextTx.find(txin.prevout);
+        if (itConflicting != pool.mapNextTx.end())
         {
-            // Disable replacement feature for now
-            return false;
+            const CTransaction *ptxConflicting = itConflicting->second;
+            if (!setConflicts.count(ptxConflicting->GetHash()))
+            {
+                // Allow opt-out of transaction replacement by setting
+                // nSequence >= maxint-1 on all inputs.
+                //
+                // maxint-1 is picked to still allow use of nLockTime by
+                // non-replacable transactions. All inputs rather than just one
+                // is for the sake of multi-party protocols, where we don't
+                // want a single party to be able to disable replacement.
+                //
+                // The opt-out ignores descendants as anyone relying on
+                // first-seen mempool behavior should be checking all
+                // unconfirmed ancestors anyway; doing otherwise is hopelessly
+                // insecure.
+                bool fReplacementOptOut = true;
+                if (fEnableReplacement)
+                {
+                    BOOST_FOREACH(const CTxIn &txin, ptxConflicting->vin)
+                    {
+                        if (txin.nSequence < std::numeric_limits<unsigned int>::max()-1)
+                        {
+                            fReplacementOptOut = false;
+                            break;
+                        }
+                    }
+                }
+                if (fReplacementOptOut)
+                    return state.Invalid(false, REJECT_CONFLICT, "txn-mempool-conflict");
+
+                setConflicts.insert(ptxConflicting->GetHash());
+            }
         }
     }
     }
@@ -953,30 +1213,36 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         CCoinsViewCache view(&dummy);
 
         CAmount nValueIn = 0;
+        LockPoints lp;
         {
         LOCK(pool.cs);
         CCoinsViewMemPool viewMemPool(pcoinsTip, pool);
         view.SetBackend(viewMemPool);
 
         // do we already have it?
-        if (view.HaveCoins(hash))
-            return false;
+        bool fHadTxInCache = pcoinsTip->HaveCoinsInCache(hash);
+        if (view.HaveCoins(hash)) {
+            if (!fHadTxInCache)
+                vHashTxnToUncache.push_back(hash);
+            return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-known");
+        }
 
         // do all inputs exist?
         // Note that this does not check for the presence of actual outputs (see the next check for that),
-        // only helps filling in pfMissingInputs (to determine missing vs spent).
+        // and only helps with filling in pfMissingInputs (to determine missing vs spent).
         BOOST_FOREACH(const CTxIn txin, tx.vin) {
+            if (!pcoinsTip->HaveCoinsInCache(txin.prevout.hash))
+                vHashTxnToUncache.push_back(txin.prevout.hash);
             if (!view.HaveCoins(txin.prevout.hash)) {
                 if (pfMissingInputs)
                     *pfMissingInputs = true;
-                return false;
+                return false; // fMissingInputs and !state.IsInvalid() is used to detect this condition, don't set state.Invalid()
             }
         }
 
         // are the actual inputs available?
         if (!view.HaveInputs(tx))
-            return state.Invalid(error("AcceptToMemoryPool : inputs already spent"),
-                                 REJECT_DUPLICATE, "bad-txns-inputs-spent");
+            return state.Invalid(false, REJECT_DUPLICATE, "bad-txns-inputs-spent");
 
         // Bring the best block into scope
         view.GetBestBlock();
@@ -985,43 +1251,67 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 
         // we have all inputs cached now, so switch back to dummy, so we don't need to keep lock on mempool
         view.SetBackend(dummy);
+
+        // Only accept BIP68 sequence locked transactions that can be mined in the next
+        // block; we don't want our mempool filled up with transactions that can't
+        // be mined yet.
+        // Must keep pool.cs for this unless we change CheckSequenceLocks to take a
+        // CoinsViewCache instead of create its own
+        if (!CheckSequenceLocks(tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
+            return state.DoS(0, false, REJECT_NONSTANDARD, "non-BIP68-final");
         }
 
         // Check for non-standard pay-to-script-hash in inputs
-        if (Params().RequireStandard() && !AreInputsStandard(tx, view))
-            return error("AcceptToMemoryPool: : nonstandard transaction input");
+        if (fRequireStandard && !AreInputsStandard(tx, view))
+            return state.Invalid(false, REJECT_NONSTANDARD, "bad-txns-nonstandard-inputs");
 
-        // Check that the transaction doesn't have an excessive number of
-        // sigops, making it impossible to mine. Since the coinbase transaction
-        // itself can contain sigops MAX_TX_SIGOPS is less than
-        // MAX_BLOCK_SIGOPS; we still consider this an invalid rather than
-        // merely non-standard transaction.
-        unsigned int nSigOps = GetLegacySigOpCount(tx);
-        nSigOps += GetP2SHSigOpCount(tx, view);
-        if (nSigOps > MAX_TX_SIGOPS)
-            return state.DoS(0,
-                             error("AcceptToMemoryPool : too many sigops %s, %d > %d",
-                                   hash.ToString(), nSigOps, MAX_TX_SIGOPS),
-                             REJECT_NONSTANDARD, "bad-txns-too-many-sigops");
+        int64_t nSigOpsCost = GetTransactionSigOpCost(tx, view, STANDARD_SCRIPT_VERIFY_FLAGS);
 
         CAmount nValueOut = tx.GetValueOut();
         CAmount nFees = nValueIn-nValueOut;
-        double dPriority = view.GetPriority(tx, chainActive.Height());
+        // nModifiedFees includes any fee deltas from PrioritiseTransaction
+        CAmount nModifiedFees = nFees;
+        double nPriorityDummy = 0;
+        pool.ApplyDeltas(hash, nPriorityDummy, nModifiedFees);
+
+        CAmount inChainInputValue;
+        double dPriority = view.GetPriority(tx, chainActive.Height(), inChainInputValue);
+
+        // Keep track of transactions that spend a coinbase, which we re-scan
+        // during reorgs to ensure COINBASE_MATURITY is still met.
+        bool fSpendsCoinbase = false;
+        BOOST_FOREACH(const CTxIn &txin, tx.vin) {
+            const CCoins *coins = view.AccessCoins(txin.prevout.hash);
+            if (coins->IsCoinBase()) {
+                fSpendsCoinbase = true;
+                break;
+            }
+        }
 
-        CTxMemPoolEntry entry(tx, nFees, GetTime(), dPriority, chainActive.Height());
+        CTxMemPoolEntry entry(tx, nFees, GetTime(), dPriority, chainActive.Height(), pool.HasNoInputsOf(tx), inChainInputValue, fSpendsCoinbase, nSigOpsCost, lp);
         unsigned int nSize = entry.GetTxSize();
 
-        // Don't accept it if it can't get into a block
-        CAmount txMinFee = GetMinRelayFee(tx, nSize, true);
-        if (fLimitFree && nFees < txMinFee)
-            return state.DoS(0, error("AcceptToMemoryPool : not enough fees %s, %d < %d",
-                                      hash.ToString(), nFees, txMinFee),
-                             REJECT_INSUFFICIENTFEE, "insufficient fee");
+        // Check that the transaction doesn't have an excessive number of
+        // sigops, making it impossible to mine. Since the coinbase transaction
+        // itself can contain sigops MAX_STANDARD_TX_SIGOPS is less than
+        // MAX_BLOCK_SIGOPS; we still consider this an invalid rather than
+        // merely non-standard transaction.
+        if ((nSigOpsCost > MAX_STANDARD_TX_SIGOPS_COST) || (nBytesPerSigOp && nSigOpsCost > nSize * WITNESS_SCALE_FACTOR / nBytesPerSigOp))
+            return state.DoS(0, false, REJECT_NONSTANDARD, "bad-txns-too-many-sigops", false,
+                strprintf("%d", nSigOpsCost));
+
+        CAmount mempoolRejectFee = pool.GetMinFee(GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000).GetFee(nSize);
+        if (mempoolRejectFee > 0 && nModifiedFees < mempoolRejectFee) {
+            return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "mempool min fee not met", false, strprintf("%d < %d", nFees, mempoolRejectFee));
+        } else if (GetBoolArg("-relaypriority", DEFAULT_RELAYPRIORITY) && nModifiedFees < ::minRelayTxFee.GetFee(nSize) && !AllowFree(entry.GetPriority(chainActive.Height() + 1))) {
+            // Require that free transactions have sufficient priority to be mined in the next block.
+            return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "insufficient priority");
+        }
 
-        // Continuously rate-limit free (really, very-low-fee)transactions
+        // Continuously rate-limit free (really, very-low-fee) transactions
         // This mitigates 'penny-flooding' -- sending thousands of free transactions just to
         // be annoying or make others' transactions take longer to confirm.
-        if (fLimitFree && nFees < ::minRelayTxFee.GetFee(nSize))
+        if (fLimitFree && nModifiedFees < ::minRelayTxFee.GetFee(nSize))
         {
             static CCriticalSection csFreeLimiter;
             static double dFreeCount;
@@ -1035,81 +1325,294 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
             nLastTime = nNow;
             // -limitfreerelay unit is thousand-bytes-per-minute
             // At default rate it would take over a month to fill 1GB
-            if (dFreeCount >= GetArg("-limitfreerelay", 15)*10*1000)
-                return state.DoS(0, error("AcceptToMemoryPool : free transaction rejected by rate limiter"),
-                                 REJECT_INSUFFICIENTFEE, "insufficient priority");
+            if (dFreeCount + nSize >= GetArg("-limitfreerelay", DEFAULT_LIMITFREERELAY) * 10 * 1000)
+                return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "rate limited free transaction");
             LogPrint("mempool", "Rate limit dFreeCount: %g => %g\n", dFreeCount, dFreeCount+nSize);
             dFreeCount += nSize;
         }
 
-        if (fRejectInsaneFee && nFees > ::minRelayTxFee.GetFee(nSize) * 10000)
-            return error("AcceptToMemoryPool: : insane fees %s, %d > %d",
-                         hash.ToString(),
-                         nFees, ::minRelayTxFee.GetFee(nSize) * 10000);
+        if (nAbsurdFee && nFees > nAbsurdFee)
+            return state.Invalid(false,
+                REJECT_HIGHFEE, "absurdly-high-fee",
+                strprintf("%d > %d", nFees, nAbsurdFee));
+
+        // Calculate in-mempool ancestors, up to a limit.
+        CTxMemPool::setEntries setAncestors;
+        size_t nLimitAncestors = GetArg("-limitancestorcount", DEFAULT_ANCESTOR_LIMIT);
+        size_t nLimitAncestorSize = GetArg("-limitancestorsize", DEFAULT_ANCESTOR_SIZE_LIMIT)*1000;
+        size_t nLimitDescendants = GetArg("-limitdescendantcount", DEFAULT_DESCENDANT_LIMIT);
+        size_t nLimitDescendantSize = GetArg("-limitdescendantsize", DEFAULT_DESCENDANT_SIZE_LIMIT)*1000;
+        std::string errString;
+        if (!pool.CalculateMemPoolAncestors(entry, setAncestors, nLimitAncestors, nLimitAncestorSize, nLimitDescendants, nLimitDescendantSize, errString)) {
+            return state.DoS(0, false, REJECT_NONSTANDARD, "too-long-mempool-chain", false, errString);
+        }
+
+        // A transaction that spends outputs that would be replaced by it is invalid. Now
+        // that we have the set of all ancestors we can detect this
+        // pathological case by making sure setConflicts and setAncestors don't
+        // intersect.
+        BOOST_FOREACH(CTxMemPool::txiter ancestorIt, setAncestors)
+        {
+            const uint256 &hashAncestor = ancestorIt->GetTx().GetHash();
+            if (setConflicts.count(hashAncestor))
+            {
+                return state.DoS(10, false,
+                                 REJECT_INVALID, "bad-txns-spends-conflicting-tx", false,
+                                 strprintf("%s spends conflicting transaction %s",
+                                           hash.ToString(),
+                                           hashAncestor.ToString()));
+            }
+        }
+
+        // Check if it's economically rational to mine this transaction rather
+        // than the ones it replaces.
+        CAmount nConflictingFees = 0;
+        size_t nConflictingSize = 0;
+        uint64_t nConflictingCount = 0;
+        CTxMemPool::setEntries allConflicting;
+
+        // If we don't hold the lock allConflicting might be incomplete; the
+        // subsequent RemoveStaged() and addUnchecked() calls don't guarantee
+        // mempool consistency for us.
+        LOCK(pool.cs);
+        if (setConflicts.size())
+        {
+            CFeeRate newFeeRate(nModifiedFees, nSize);
+            set<uint256> setConflictsParents;
+            const int maxDescendantsToVisit = 100;
+            CTxMemPool::setEntries setIterConflicting;
+            BOOST_FOREACH(const uint256 &hashConflicting, setConflicts)
+            {
+                CTxMemPool::txiter mi = pool.mapTx.find(hashConflicting);
+                if (mi == pool.mapTx.end())
+                    continue;
+
+                // Save these to avoid repeated lookups
+                setIterConflicting.insert(mi);
+
+                // Don't allow the replacement to reduce the feerate of the
+                // mempool.
+                //
+                // We usually don't want to accept replacements with lower
+                // feerates than what they replaced as that would lower the
+                // feerate of the next block. Requiring that the feerate always
+                // be increased is also an easy-to-reason about way to prevent
+                // DoS attacks via replacements.
+                //
+                // The mining code doesn't (currently) take children into
+                // account (CPFP) so we only consider the feerates of
+                // transactions being directly replaced, not their indirect
+                // descendants. While that does mean high feerate children are
+                // ignored when deciding whether or not to replace, we do
+                // require the replacement to pay more overall fees too,
+                // mitigating most cases.
+                CFeeRate oldFeeRate(mi->GetModifiedFee(), mi->GetTxSize());
+                if (newFeeRate <= oldFeeRate)
+                {
+                    return state.DoS(0, false,
+                            REJECT_INSUFFICIENTFEE, "insufficient fee", false,
+                            strprintf("rejecting replacement %s; new feerate %s <= old feerate %s",
+                                  hash.ToString(),
+                                  newFeeRate.ToString(),
+                                  oldFeeRate.ToString()));
+                }
+
+                BOOST_FOREACH(const CTxIn &txin, mi->GetTx().vin)
+                {
+                    setConflictsParents.insert(txin.prevout.hash);
+                }
+
+                nConflictingCount += mi->GetCountWithDescendants();
+            }
+            // This potentially overestimates the number of actual descendants
+            // but we just want to be conservative to avoid doing too much
+            // work.
+            if (nConflictingCount <= maxDescendantsToVisit) {
+                // If not too many to replace, then calculate the set of
+                // transactions that would have to be evicted
+                BOOST_FOREACH(CTxMemPool::txiter it, setIterConflicting) {
+                    pool.CalculateDescendants(it, allConflicting);
+                }
+                BOOST_FOREACH(CTxMemPool::txiter it, allConflicting) {
+                    nConflictingFees += it->GetModifiedFee();
+                    nConflictingSize += it->GetTxSize();
+                }
+            } else {
+                return state.DoS(0, false,
+                        REJECT_NONSTANDARD, "too many potential replacements", false,
+                        strprintf("rejecting replacement %s; too many potential replacements (%d > %d)\n",
+                            hash.ToString(),
+                            nConflictingCount,
+                            maxDescendantsToVisit));
+            }
+
+            for (unsigned int j = 0; j < tx.vin.size(); j++)
+            {
+                // We don't want to accept replacements that require low
+                // feerate junk to be mined first. Ideally we'd keep track of
+                // the ancestor feerates and make the decision based on that,
+                // but for now requiring all new inputs to be confirmed works.
+                if (!setConflictsParents.count(tx.vin[j].prevout.hash))
+                {
+                    // Rather than check the UTXO set - potentially expensive -
+                    // it's cheaper to just check if the new input refers to a
+                    // tx that's in the mempool.
+                    if (pool.mapTx.find(tx.vin[j].prevout.hash) != pool.mapTx.end())
+                        return state.DoS(0, false,
+                                         REJECT_NONSTANDARD, "replacement-adds-unconfirmed", false,
+                                         strprintf("replacement %s adds unconfirmed input, idx %d",
+                                                  hash.ToString(), j));
+                }
+            }
+
+            // The replacement must pay greater fees than the transactions it
+            // replaces - if we did the bandwidth used by those conflicting
+            // transactions would not be paid for.
+            if (nModifiedFees < nConflictingFees)
+            {
+                return state.DoS(0, false,
+                                 REJECT_INSUFFICIENTFEE, "insufficient fee", false,
+                                 strprintf("rejecting replacement %s, less fees than conflicting txs; %s < %s",
+                                          hash.ToString(), FormatMoney(nModifiedFees), FormatMoney(nConflictingFees)));
+            }
+
+            // Finally in addition to paying more fees than the conflicts the
+            // new transaction must pay for its own bandwidth.
+            CAmount nDeltaFees = nModifiedFees - nConflictingFees;
+            if (nDeltaFees < ::minRelayTxFee.GetFee(nSize))
+            {
+                return state.DoS(0, false,
+                        REJECT_INSUFFICIENTFEE, "insufficient fee", false,
+                        strprintf("rejecting replacement %s, not enough additional fees to relay; %s < %s",
+                              hash.ToString(),
+                              FormatMoney(nDeltaFees),
+                              FormatMoney(::minRelayTxFee.GetFee(nSize))));
+            }
+        }
+
+        unsigned int scriptVerifyFlags = STANDARD_SCRIPT_VERIFY_FLAGS;
+        if (!Params().RequireStandard()) {
+            scriptVerifyFlags = GetArg("-promiscuousmempoolflags", scriptVerifyFlags);
+        }
 
         // Check against previous transactions
         // This is done last to help prevent CPU exhaustion denial-of-service attacks.
-        if (!CheckInputs(tx, state, view, true, STANDARD_SCRIPT_VERIFY_FLAGS, true))
+        if (!CheckInputs(tx, state, view, true, scriptVerifyFlags, true)) {
+            // SCRIPT_VERIFY_CLEANSTACK requires SCRIPT_VERIFY_WITNESS, so we
+            // need to turn both off, and compare against just turning off CLEANSTACK
+            // to see if the failure is specifically due to witness validation.
+            if (CheckInputs(tx, state, view, true, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true) &&
+                !CheckInputs(tx, state, view, true, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true)) {
+                // Only the witness is wrong, so the transaction itself may be fine.
+                state.SetCorruptionPossible();
+            }
+            return false;
+        }
+
+        // Check again against just the consensus-critical mandatory script
+        // verification flags, in case of bugs in the standard flags that cause
+        // transactions to pass as valid when they're actually invalid. For
+        // instance the STRICTENC flag was incorrectly allowing certain
+        // CHECKSIG NOT scripts to pass, even though they were invalid.
+        //
+        // There is a similar check in CreateNewBlock() to prevent creating
+        // invalid blocks, however allowing such transactions into the mempool
+        // can be exploited as a DoS attack.
+        if (!CheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true))
+        {
+            return error("%s: BUG! PLEASE REPORT THIS! ConnectInputs failed against MANDATORY but not STANDARD flags %s, %s",
+                __func__, hash.ToString(), FormatStateMessage(state));
+        }
+
+        // Remove conflicting transactions from the mempool
+        BOOST_FOREACH(const CTxMemPool::txiter it, allConflicting)
         {
-            return error("AcceptToMemoryPool: : ConnectInputs failed %s", hash.ToString());
+            LogPrint("mempool", "replacing tx %s with %s for %s BTC additional fees, %d delta bytes\n",
+                    it->GetTx().GetHash().ToString(),
+                    hash.ToString(),
+                    FormatMoney(nModifiedFees - nConflictingFees),
+                    (int)nSize - (int)nConflictingSize);
         }
+        pool.RemoveStaged(allConflicting, false);
+
         // Store transaction in memory
-        pool.addUnchecked(hash, entry);
+        pool.addUnchecked(hash, entry, setAncestors, !IsInitialBlockDownload());
+
+        // trim mempool and check if tx was trimmed
+        if (!fOverrideMempoolLimit) {
+            LimitMempoolSize(pool, GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY) * 60 * 60);
+            if (!pool.exists(hash))
+                return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "mempool full");
+        }
     }
 
-    SyncWithWallets(tx, NULL);
+    SyncWithWallets(tx, NULL, NULL);
 
     return true;
 }
 
+bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
+                        bool* pfMissingInputs, bool fOverrideMempoolLimit, const CAmount nAbsurdFee)
+{
+    std::vector<uint256> vHashTxToUncache;
+    bool res = AcceptToMemoryPoolWorker(pool, state, tx, fLimitFree, pfMissingInputs, fOverrideMempoolLimit, nAbsurdFee, vHashTxToUncache);
+    if (!res) {
+        BOOST_FOREACH(const uint256& hashTx, vHashTxToUncache)
+            pcoinsTip->Uncache(hashTx);
+    }
+    return res;
+}
+
 /** Return transaction in tx, and if it was found inside a block, its hash is placed in hashBlock */
-bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock, bool fAllowSlow)
+bool GetTransaction(const uint256 &hash, CTransaction &txOut, const Consensus::Params& consensusParams, uint256 &hashBlock, bool fAllowSlow)
 {
     CBlockIndex *pindexSlow = NULL;
+
+    LOCK(cs_main);
+
+    std::shared_ptr<const CTransaction> ptx = mempool.get(hash);
+    if (ptx)
     {
-        LOCK(cs_main);
-        {
-            if (mempool.lookup(hash, txOut))
-            {
-                return true;
-            }
-        }
+        txOut = *ptx;
+        return true;
+    }
 
-        if (fTxIndex) {
-            CDiskTxPos postx;
-            if (pblocktree->ReadTxIndex(hash, postx)) {
-                CAutoFile file(OpenBlockFile(postx, true), SER_DISK, CLIENT_VERSION);
-                CBlockHeader header;
-                try {
-                    file >> header;
-                    fseek(file.Get(), postx.nTxOffset, SEEK_CUR);
-                    file >> txOut;
-                } catch (std::exception &e) {
-                    return error("%s : Deserialize or I/O error - %s", __func__, e.what());
-                }
-                hashBlock = header.GetHash();
-                if (txOut.GetHash() != hash)
-                    return error("%s : txid mismatch", __func__);
-                return true;
+    if (fTxIndex) {
+        CDiskTxPos postx;
+        if (pblocktree->ReadTxIndex(hash, postx)) {
+            CAutoFile file(OpenBlockFile(postx, true), SER_DISK, CLIENT_VERSION);
+            if (file.IsNull())
+                return error("%s: OpenBlockFile failed", __func__);
+            CBlockHeader header;
+            try {
+                file >> header;
+                fseek(file.Get(), postx.nTxOffset, SEEK_CUR);
+                file >> txOut;
+            } catch (const std::exception& e) {
+                return error("%s: Deserialize or I/O error - %s", __func__, e.what());
             }
+            hashBlock = header.GetHash();
+            if (txOut.GetHash() != hash)
+                return error("%s: txid mismatch", __func__);
+            return true;
         }
+    }
 
-        if (fAllowSlow) { // use coin database to locate block that contains transaction, and scan it
-            int nHeight = -1;
-            {
-                CCoinsViewCache &view = *pcoinsTip;
-                const CCoins* coins = view.AccessCoins(hash);
-                if (coins)
-                    nHeight = coins->nHeight;
-            }
-            if (nHeight > 0)
-                pindexSlow = chainActive[nHeight];
+    if (fAllowSlow) { // use coin database to locate block that contains transaction, and scan it
+        int nHeight = -1;
+        {
+            const CCoinsViewCache& view = *pcoinsTip;
+            const CCoins* coins = view.AccessCoins(hash);
+            if (coins)
+                nHeight = coins->nHeight;
         }
+        if (nHeight > 0)
+            pindexSlow = chainActive[nHeight];
     }
 
     if (pindexSlow) {
         CBlock block;
-        if (ReadBlockFromDisk(block, pindexSlow)) {
+        if (ReadBlockFromDisk(block, pindexSlow, consensusParams)) {
             BOOST_FOREACH(const CTransaction &tx, block.vtx) {
                 if (tx.GetHash() == hash) {
                     txOut = tx;
@@ -1133,87 +1636,95 @@ bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock
 // CBlock and CBlockIndex
 //
 
-bool WriteBlockToDisk(CBlock& block, CDiskBlockPos& pos)
+bool WriteBlockToDisk(const CBlock& block, CDiskBlockPos& pos, const CMessageHeader::MessageStartChars& messageStart)
 {
     // Open history file to append
     CAutoFile fileout(OpenBlockFile(pos), SER_DISK, CLIENT_VERSION);
     if (fileout.IsNull())
-        return error("WriteBlockToDisk : OpenBlockFile failed");
+        return error("WriteBlockToDisk: OpenBlockFile failed");
 
     // Write index header
     unsigned int nSize = fileout.GetSerializeSize(block);
-    fileout << FLATDATA(Params().MessageStart()) << nSize;
+    fileout << FLATDATA(messageStart) << nSize;
 
     // Write block
     long fileOutPos = ftell(fileout.Get());
     if (fileOutPos < 0)
-        return error("WriteBlockToDisk : ftell failed");
+        return error("WriteBlockToDisk: ftell failed");
     pos.nPos = (unsigned int)fileOutPos;
     fileout << block;
 
     return true;
 }
 
-bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos)
+bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos, const Consensus::Params& consensusParams)
 {
     block.SetNull();
 
     // Open history file to read
     CAutoFile filein(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION);
     if (filein.IsNull())
-        return error("ReadBlockFromDisk : OpenBlockFile failed");
+        return error("ReadBlockFromDisk: OpenBlockFile failed for %s", pos.ToString());
 
     // Read block
     try {
         filein >> block;
     }
-    catch (std::exception &e) {
-        return error("%s : Deserialize or I/O error - %s", __func__, e.what());
+    catch (const std::exception& e) {
+        return error("%s: Deserialize or I/O error - %s at %s", __func__, e.what(), pos.ToString());
     }
 
     // Check the header
-    if (!CheckProofOfWork(block.GetHash(), block.nBits))
-        return error("ReadBlockFromDisk : Errors in block header");
+    if (!CheckProofOfWork(block.GetHash(), block.nBits, consensusParams))
+        return error("ReadBlockFromDisk: Errors in block header at %s", pos.ToString());
 
     return true;
 }
 
-bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex)
+bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
 {
-    if (!ReadBlockFromDisk(block, pindex->GetBlockPos()))
+    if (!ReadBlockFromDisk(block, pindex->GetBlockPos(), consensusParams))
         return false;
     if (block.GetHash() != pindex->GetBlockHash())
-        return error("ReadBlockFromDisk(CBlock&, CBlockIndex*) : GetHash() doesn't match index");
+        return error("ReadBlockFromDisk(CBlock&, CBlockIndex*): GetHash() doesn't match index for %s at %s",
+                pindex->ToString(), pindex->GetBlockPos().ToString());
     return true;
 }
 
-CAmount GetBlockValue(int nHeight, const CAmount& nFees)
+CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
 {
-    CAmount nSubsidy = 50 * COIN;
-    int halvings = nHeight / Params().SubsidyHalvingInterval();
-
+    int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
     // Force block reward to zero when right shift is undefined.
     if (halvings >= 64)
-        return nFees;
+        return 0;
 
+    CAmount nSubsidy = 50 * COIN;
     // Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
     nSubsidy >>= halvings;
-
-    return nSubsidy + nFees;
+    return nSubsidy;
 }
 
 bool IsInitialBlockDownload()
 {
+    const CChainParams& chainParams = Params();
+
+    // Once this function has returned false, it must remain false.
+    static std::atomic<bool> latchToFalse{false};
+    // Optimization: pre-test latch before taking the lock.
+    if (latchToFalse.load(std::memory_order_relaxed))
+        return false;
+
     LOCK(cs_main);
-    if (fImporting || fReindex || chainActive.Height() < Checkpoints::GetTotalBlocksEstimate())
-        return true;
-    static bool lockIBDState = false;
-    if (lockIBDState)
+    if (latchToFalse.load(std::memory_order_relaxed))
         return false;
+    if (fImporting || fReindex)
+        return true;
+    if (fCheckpointsEnabled && chainActive.Height() < Checkpoints::GetTotalBlocksEstimate(chainParams.Checkpoints()))
+        return true;
     bool state = (chainActive.Height() < pindexBestHeader->nHeight - 24 * 6 ||
-            pindexBestHeader->GetBlockTime() < GetTime() - 24 * 60 * 60);
+            std::max(chainActive.Tip()->GetBlockTime(), pindexBestHeader->GetBlockTime()) < GetTime() - nMaxTipAge);
     if (!state)
-        lockIBDState = true;
+        latchToFalse.store(true, std::memory_order_relaxed);
     return state;
 }
 
@@ -1221,6 +1732,23 @@ bool fLargeWorkForkFound = false;
 bool fLargeWorkInvalidChainFound = false;
 CBlockIndex *pindexBestForkTip = NULL, *pindexBestForkBase = NULL;
 
+static void AlertNotify(const std::string& strMessage)
+{
+    uiInterface.NotifyAlertChanged();
+    std::string strCmd = GetArg("-alertnotify", "");
+    if (strCmd.empty()) return;
+
+    // Alert text should be plain ascii coming from a trusted source, but to
+    // be safe we first strip anything not in safeChars, then add single quotes around
+    // the whole string before passing it to the shell:
+    std::string singleQuote("'");
+    std::string safeStatus = SanitizeString(strMessage);
+    safeStatus = singleQuote+safeStatus+singleQuote;
+    boost::replace_all(strCmd, "%s", safeStatus);
+
+    boost::thread t(runCommand, strCmd); // thread runs free
+}
+
 void CheckForkWarningConditions()
 {
     AssertLockHeld(cs_main);
@@ -1240,18 +1768,18 @@ void CheckForkWarningConditions()
         {
             std::string warning = std::string("'Warning: Large-work fork detected, forking after block ") +
                 pindexBestForkBase->phashBlock->ToString() + std::string("'");
-            CAlert::Notify(warning, true);
+            AlertNotify(warning);
         }
         if (pindexBestForkTip && pindexBestForkBase)
         {
-            LogPrintf("CheckForkWarningConditions: Warning: Large valid fork found\n  forking the chain at height %d (%s)\n  lasting to height %d (%s).\nChain state database corruption likely.\n",
+            LogPrintf("%s: Warning: Large valid fork found\n  forking the chain at height %d (%s)\n  lasting to height %d (%s).\nChain state database corruption likely.\n", __func__,
                    pindexBestForkBase->nHeight, pindexBestForkBase->phashBlock->ToString(),
                    pindexBestForkTip->nHeight, pindexBestForkTip->phashBlock->ToString());
             fLargeWorkForkFound = true;
         }
         else
         {
-            LogPrintf("CheckForkWarningConditions: Warning: Found invalid chain at least ~6 blocks longer than our best chain.\nChain state database corruption likely.\n");
+            LogPrintf("%s: Warning: Found invalid chain at least ~6 blocks longer than our best chain.\nChain state database corruption likely.\n", __func__);
             fLargeWorkInvalidChainFound = true;
         }
     }
@@ -1277,8 +1805,8 @@ void CheckForkWarningConditionsOnNewFork(CBlockIndex* pindexNewForkTip)
         pfork = pfork->pprev;
     }
 
-    // We define a condition which we should warn the user about as a fork of at least 7 blocks
-    // who's tip is within 72 blocks (+/- 12 hours if no one mines it) of ours
+    // We define a condition where we should warn the user about as a fork of at least 7 blocks
+    // with a tip within 72 blocks (+/- 12 hours if no one mines it) of ours
     // We use 7 blocks rather arbitrarily as it represents just under 10% of sustained network
     // hash rate operating on the fork.
     // or a chain that is entirely longer than ours and invalid (note that this should be detected by both)
@@ -1306,13 +1834,13 @@ void Misbehaving(NodeId pnode, int howmuch)
         return;
 
     state->nMisbehavior += howmuch;
-    int banscore = GetArg("-banscore", 100);
+    int banscore = GetArg("-banscore", DEFAULT_BANSCORE_THRESHOLD);
     if (state->nMisbehavior >= banscore && state->nMisbehavior - howmuch < banscore)
     {
-        LogPrintf("Misbehaving: %s (%d -> %d) BAN THRESHOLD EXCEEDED\n", state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
+        LogPrintf("%s: %s (%d -> %d) BAN THRESHOLD EXCEEDED\n", __func__, state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
         state->fShouldBan = true;
     } else
-        LogPrintf("Misbehaving: %s (%d -> %d)\n", state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
+        LogPrintf("%s: %s (%d -> %d)\n", __func__, state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
 }
 
 void static InvalidChainFound(CBlockIndex* pindexNew)
@@ -1320,13 +1848,15 @@ void static InvalidChainFound(CBlockIndex* pindexNew)
     if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
         pindexBestInvalid = pindexNew;
 
-    LogPrintf("InvalidChainFound: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n",
+    LogPrintf("%s: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n", __func__,
       pindexNew->GetBlockHash().ToString(), pindexNew->nHeight,
       log(pindexNew->nChainWork.getdouble())/log(2.0), DateTimeStrFormat("%Y-%m-%d %H:%M:%S",
       pindexNew->GetBlockTime()));
-    LogPrintf("InvalidChainFound:  current best=%s  height=%d  log2_work=%.8g  date=%s\n",
-      chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(), log(chainActive.Tip()->nChainWork.getdouble())/log(2.0),
-      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()));
+    CBlockIndex *tip = chainActive.Tip();
+    assert (tip);
+    LogPrintf("%s:  current best=%s  height=%d  log2_work=%.8g  date=%s\n", __func__,
+      tip->GetBlockHash().ToString(), chainActive.Height(), log(tip->nChainWork.getdouble())/log(2.0),
+      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", tip->GetBlockTime()));
     CheckForkWarningConditions();
 }
 
@@ -1335,7 +1865,8 @@ void static InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state
     if (state.IsInvalid(nDoS)) {
         std::map<uint256, NodeId>::iterator it = mapBlockSource.find(pindex->GetBlockHash());
         if (it != mapBlockSource.end() && State(it->second)) {
-            CBlockReject reject = {state.GetRejectCode(), state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), pindex->GetBlockHash()};
+            assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
+            CBlockReject reject = {(unsigned char)state.GetRejectCode(), state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), pindex->GetBlockHash()};
             State(it->second)->rejects.push_back(reject);
             if (nDoS > 0)
                 Misbehaving(it->second, nDoS);
@@ -1349,46 +1880,62 @@ void static InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state
     }
 }
 
-void UpdateCoins(const CTransaction& tx, CValidationState &state, CCoinsViewCache &inputs, CTxUndo &txundo, int nHeight)
+void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, CTxUndo &txundo, int nHeight)
 {
     // mark inputs spent
     if (!tx.IsCoinBase()) {
         txundo.vprevout.reserve(tx.vin.size());
         BOOST_FOREACH(const CTxIn &txin, tx.vin) {
-            txundo.vprevout.push_back(CTxInUndo());
-            bool ret = inputs.ModifyCoins(txin.prevout.hash)->Spend(txin.prevout, txundo.vprevout.back());
-            assert(ret);
+            CCoinsModifier coins = inputs.ModifyCoins(txin.prevout.hash);
+            unsigned nPos = txin.prevout.n;
+
+            if (nPos >= coins->vout.size() || coins->vout[nPos].IsNull())
+                assert(false);
+            // mark an outpoint spent, and construct undo information
+            txundo.vprevout.push_back(CTxInUndo(coins->vout[nPos]));
+            coins->Spend(nPos);
+            if (coins->vout.size() == 0) {
+                CTxInUndo& undo = txundo.vprevout.back();
+                undo.nHeight = coins->nHeight;
+                undo.fCoinBase = coins->fCoinBase;
+                undo.nVersion = coins->nVersion;
+            }
         }
     }
-
     // add outputs
-    inputs.ModifyCoins(tx.GetHash())->FromTx(tx, nHeight);
+    inputs.ModifyNewCoins(tx.GetHash(), tx.IsCoinBase())->FromTx(tx, nHeight);
+}
+
+void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight)
+{
+    CTxUndo txundo;
+    UpdateCoins(tx, inputs, txundo, nHeight);
 }
 
 bool CScriptCheck::operator()() {
     const CScript &scriptSig = ptxTo->vin[nIn].scriptSig;
-    if (!VerifyScript(scriptSig, scriptPubKey, nFlags, CachingSignatureChecker(*ptxTo, nIn, cacheStore), &error)) {
-        return ::error("CScriptCheck() : %s:%d VerifySignature failed: %s", ptxTo->GetHash().ToString(), nIn, ScriptErrorString(error));
+    const CScriptWitness *witness = (nIn < ptxTo->wit.vtxinwit.size()) ? &ptxTo->wit.vtxinwit[nIn].scriptWitness : NULL;
+    if (!VerifyScript(scriptSig, scriptPubKey, witness, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, amount, cacheStore), &error)) {
+        return false;
     }
     return true;
 }
 
-bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, std::vector<CScriptCheck> *pvChecks)
+int GetSpendHeight(const CCoinsViewCache& inputs)
 {
-    if (!tx.IsCoinBase())
-    {
-        if (pvChecks)
-            pvChecks->reserve(tx.vin.size());
+    LOCK(cs_main);
+    CBlockIndex* pindexPrev = mapBlockIndex.find(inputs.GetBestBlock())->second;
+    return pindexPrev->nHeight + 1;
+}
 
+namespace Consensus {
+bool CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoinsViewCache& inputs, int nSpendHeight)
+{
         // This doesn't trigger the DoS code on purpose; if it did, it would make it easier
         // for an attacker to attempt to split the network.
         if (!inputs.HaveInputs(tx))
-            return state.Invalid(error("CheckInputs() : %s inputs unavailable", tx.GetHash().ToString()));
+            return state.Invalid(false, 0, "", "Inputs unavailable");
 
-        // While checking, GetBestBlock() refers to the parent block.
-        // This is also true for mempool checks.
-        CBlockIndex *pindexPrev = mapBlockIndex.find(inputs.GetBestBlock())->second;
-        int nSpendHeight = pindexPrev->nHeight + 1;
         CAmount nValueIn = 0;
         CAmount nFees = 0;
         for (unsigned int i = 0; i < tx.vin.size(); i++)
@@ -1400,41 +1947,53 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
             // If prev is coinbase, check that it's matured
             if (coins->IsCoinBase()) {
                 if (nSpendHeight - coins->nHeight < COINBASE_MATURITY)
-                    return state.Invalid(
-                        error("CheckInputs() : tried to spend coinbase at depth %d", nSpendHeight - coins->nHeight),
-                        REJECT_INVALID, "bad-txns-premature-spend-of-coinbase");
+                    return state.Invalid(false,
+                        REJECT_INVALID, "bad-txns-premature-spend-of-coinbase",
+                        strprintf("tried to spend coinbase at depth %d", nSpendHeight - coins->nHeight));
             }
 
             // Check for negative or overflow input values
             nValueIn += coins->vout[prevout.n].nValue;
             if (!MoneyRange(coins->vout[prevout.n].nValue) || !MoneyRange(nValueIn))
-                return state.DoS(100, error("CheckInputs() : txin values out of range"),
-                                 REJECT_INVALID, "bad-txns-inputvalues-outofrange");
+                return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputvalues-outofrange");
 
         }
 
         if (nValueIn < tx.GetValueOut())
-            return state.DoS(100, error("CheckInputs() : %s value in (%s) < value out (%s)",
-                                        tx.GetHash().ToString(), FormatMoney(nValueIn), FormatMoney(tx.GetValueOut())),
-                             REJECT_INVALID, "bad-txns-in-belowout");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-in-belowout", false,
+                strprintf("value in (%s) < value out (%s)", FormatMoney(nValueIn), FormatMoney(tx.GetValueOut())));
 
         // Tally transaction fees
         CAmount nTxFee = nValueIn - tx.GetValueOut();
         if (nTxFee < 0)
-            return state.DoS(100, error("CheckInputs() : %s nTxFee < 0", tx.GetHash().ToString()),
-                             REJECT_INVALID, "bad-txns-fee-negative");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-fee-negative");
         nFees += nTxFee;
         if (!MoneyRange(nFees))
-            return state.DoS(100, error("CheckInputs() : nFees out of range"),
-                             REJECT_INVALID, "bad-txns-fee-outofrange");
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-fee-outofrange");
+    return true;
+}
+}// namespace Consensus
+
+bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, std::vector<CScriptCheck> *pvChecks)
+{
+    if (!tx.IsCoinBase())
+    {
+        if (!Consensus::CheckTxInputs(tx, state, inputs, GetSpendHeight(inputs)))
+            return false;
+
+        if (pvChecks)
+            pvChecks->reserve(tx.vin.size());
 
         // The first loop above does all the inexpensive checks.
         // Only if ALL inputs pass do we perform expensive ECDSA signature checks.
         // Helps prevent CPU exhaustion attacks.
 
-        // Skip ECDSA signature verification when connecting blocks
-        // before the last block chain checkpoint. This is safe because block merkle hashes are
-        // still computed and checked, and any change will be caught at the next checkpoint.
+        // Skip ECDSA signature verification when connecting blocks before the
+        // last block chain checkpoint. Assuming the checkpoints are valid this
+        // is safe because block merkle hashes are still computed and checked,
+        // and any change will be caught at the next checkpoint. Of course, if
+        // the checkpoint is for a chain that's invalid due to false scriptSigs
+        // this optimisation would allow an invalid chain to be accepted.
         if (fScriptChecks) {
             for (unsigned int i = 0; i < tx.vin.size(); i++) {
                 const COutPoint &prevout = tx.vin[i].prevout;
@@ -1454,9 +2013,9 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
                         // arguments; if so, don't trigger DoS protection to
                         // avoid splitting the network between upgraded and
                         // non-upgraded nodes.
-                        CScriptCheck check(*coins, tx, i,
+                        CScriptCheck check2(*coins, tx, i,
                                 flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheStore);
-                        if (check())
+                        if (check2())
                             return state.Invalid(false, REJECT_NONSTANDARD, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(check.GetScriptError())));
                     }
                     // Failures of other flags indicate a transaction that is
@@ -1464,8 +2023,8 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
                     // such nodes as they are not following the protocol. That
                     // said during an upgrade careful thought should be taken
                     // as to the correct behavior - we may want to continue
-                    // peering with non-upgraded nodes even after a soft-fork
-                    // super-majority vote has passed.
+                    // peering with non-upgraded nodes even after soft-fork
+                    // super-majority signaling has occurred.
                     return state.DoS(100,false, REJECT_INVALID, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(check.GetScriptError())));
                 }
             }
@@ -1475,9 +2034,116 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
     return true;
 }
 
+namespace {
 
+bool UndoWriteToDisk(const CBlockUndo& blockundo, CDiskBlockPos& pos, const uint256& hashBlock, const CMessageHeader::MessageStartChars& messageStart)
+{
+    // Open history file to append
+    CAutoFile fileout(OpenUndoFile(pos), SER_DISK, CLIENT_VERSION);
+    if (fileout.IsNull())
+        return error("%s: OpenUndoFile failed", __func__);
+
+    // Write index header
+    unsigned int nSize = fileout.GetSerializeSize(blockundo);
+    fileout << FLATDATA(messageStart) << nSize;
+
+    // Write undo data
+    long fileOutPos = ftell(fileout.Get());
+    if (fileOutPos < 0)
+        return error("%s: ftell failed", __func__);
+    pos.nPos = (unsigned int)fileOutPos;
+    fileout << blockundo;
+
+    // calculate & write checksum
+    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
+    hasher << hashBlock;
+    hasher << blockundo;
+    fileout << hasher.GetHash();
+
+    return true;
+}
+
+bool UndoReadFromDisk(CBlockUndo& blockundo, const CDiskBlockPos& pos, const uint256& hashBlock)
+{
+    // Open history file to read
+    CAutoFile filein(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
+    if (filein.IsNull())
+        return error("%s: OpenBlockFile failed", __func__);
+
+    // Read block
+    uint256 hashChecksum;
+    try {
+        filein >> blockundo;
+        filein >> hashChecksum;
+    }
+    catch (const std::exception& e) {
+        return error("%s: Deserialize or I/O error - %s", __func__, e.what());
+    }
+
+    // Verify checksum
+    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
+    hasher << hashBlock;
+    hasher << blockundo;
+    if (hashChecksum != hasher.GetHash())
+        return error("%s: Checksum mismatch", __func__);
+
+    return true;
+}
 
-bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex, CCoinsViewCache& view, bool* pfClean)
+/** Abort with a message */
+bool AbortNode(const std::string& strMessage, const std::string& userMessage="")
+{
+    strMiscWarning = strMessage;
+    LogPrintf("*** %s\n", strMessage);
+    uiInterface.ThreadSafeMessageBox(
+        userMessage.empty() ? _("Error: A fatal internal error occurred, see debug.log for details") : userMessage,
+        "", CClientUIInterface::MSG_ERROR);
+    StartShutdown();
+    return false;
+}
+
+bool AbortNode(CValidationState& state, const std::string& strMessage, const std::string& userMessage="")
+{
+    AbortNode(strMessage, userMessage);
+    return state.Error(strMessage);
+}
+
+} // anon namespace
+
+/**
+ * Apply the undo operation of a CTxInUndo to the given chain state.
+ * @param undo The undo object.
+ * @param view The coins view to which to apply the changes.
+ * @param out The out point that corresponds to the tx input.
+ * @return True on success.
+ */
+static bool ApplyTxInUndo(const CTxInUndo& undo, CCoinsViewCache& view, const COutPoint& out)
+{
+    bool fClean = true;
+
+    CCoinsModifier coins = view.ModifyCoins(out.hash);
+    if (undo.nHeight != 0) {
+        // undo data contains height: this is the last output of the prevout tx being spent
+        if (!coins->IsPruned())
+            fClean = fClean && error("%s: undo data overwriting existing transaction", __func__);
+        coins->Clear();
+        coins->fCoinBase = undo.fCoinBase;
+        coins->nHeight = undo.nHeight;
+        coins->nVersion = undo.nVersion;
+    } else {
+        if (coins->IsPruned())
+            fClean = fClean && error("%s: undo data adding output to missing transaction", __func__);
+    }
+    if (coins->IsAvailable(out.n))
+        fClean = fClean && error("%s: undo data overwriting existing output", __func__);
+    if (coins->vout.size() < out.n+1)
+        coins->vout.resize(out.n+1);
+    coins->vout[out.n] = undo.txout;
+
+    return fClean;
+}
+
+bool DisconnectBlock(const CBlock& block, CValidationState& state, const CBlockIndex* pindex, CCoinsViewCache& view, bool* pfClean)
 {
     assert(pindex->GetBlockHash() == view.GetBestBlock());
 
@@ -1489,12 +2155,12 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
     CBlockUndo blockUndo;
     CDiskBlockPos pos = pindex->GetUndoPos();
     if (pos.IsNull())
-        return error("DisconnectBlock() : no undo data available");
-    if (!blockUndo.ReadFromDisk(pos, pindex->pprev->GetBlockHash()))
-        return error("DisconnectBlock() : failure reading undo data");
+        return error("DisconnectBlock(): no undo data available");
+    if (!UndoReadFromDisk(blockUndo, pos, pindex->pprev->GetBlockHash()))
+        return error("DisconnectBlock(): failure reading undo data");
 
     if (blockUndo.vtxundo.size() + 1 != block.vtx.size())
-        return error("DisconnectBlock() : block and undo data inconsistent");
+        return error("DisconnectBlock(): block and undo data inconsistent");
 
     // undo transactions in reverse order
     for (int i = block.vtx.size() - 1; i >= 0; i--) {
@@ -1502,11 +2168,8 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
         uint256 hash = tx.GetHash();
 
         // Check that all outputs are available and match the outputs in the block itself
-        // exactly. Note that transactions with only provably unspendable outputs won't
-        // have outputs available even in the block itself, so we handle that case
-        // specially with outsEmpty.
+        // exactly.
         {
-        CCoins outsEmpty;
         CCoinsModifier outs = view.ModifyCoins(hash);
         outs->ClearUnspendable();
 
@@ -1517,7 +2180,7 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
         if (outsBlock.nVersion < 0)
             outs->nVersion = outsBlock.nVersion;
         if (*outs != outsBlock)
-            fClean = fClean && error("DisconnectBlock() : added transaction mismatch? database corrupted");
+            fClean = fClean && error("DisconnectBlock(): added transaction mismatch? database corrupted");
 
         // remove outputs
         outs->Clear();
@@ -1527,28 +2190,12 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
         if (i > 0) { // not coinbases
             const CTxUndo &txundo = blockUndo.vtxundo[i-1];
             if (txundo.vprevout.size() != tx.vin.size())
-                return error("DisconnectBlock() : transaction and undo data inconsistent");
+                return error("DisconnectBlock(): transaction and undo data inconsistent");
             for (unsigned int j = tx.vin.size(); j-- > 0;) {
                 const COutPoint &out = tx.vin[j].prevout;
                 const CTxInUndo &undo = txundo.vprevout[j];
-                CCoinsModifier coins = view.ModifyCoins(out.hash);
-                if (undo.nHeight != 0) {
-                    // undo data contains height: this is the last output of the prevout tx being spent
-                    if (!coins->IsPruned())
-                        fClean = fClean && error("DisconnectBlock() : undo data overwriting existing transaction");
-                    coins->Clear();
-                    coins->fCoinBase = undo.fCoinBase;
-                    coins->nHeight = undo.nHeight;
-                    coins->nVersion = undo.nVersion;
-                } else {
-                    if (coins->IsPruned())
-                        fClean = fClean && error("DisconnectBlock() : undo data adding output to missing transaction");
-                }
-                if (coins->IsAvailable(out.n))
-                    fClean = fClean && error("DisconnectBlock() : undo data overwriting existing output");
-                if (coins->vout.size() < out.n+1)
-                    coins->vout.resize(out.n+1);
-                coins->vout[out.n] = undo.txout;
+                if (!ApplyTxInUndo(undo, view, out))
+                    fClean = false;
             }
         }
     }
@@ -1559,9 +2206,9 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
     if (pfClean) {
         *pfClean = fClean;
         return true;
-    } else {
-        return fClean;
     }
+
+    return fClean;
 }
 
 void static FlushBlockFile(bool fFinalize = false)
@@ -1596,31 +2243,93 @@ void ThreadScriptCheck() {
     scriptcheckqueue.Thread();
 }
 
+// Protected by cs_main
+VersionBitsCache versionbitscache;
+
+int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params)
+{
+    LOCK(cs_main);
+    int32_t nVersion = VERSIONBITS_TOP_BITS;
+
+    for (int i = 0; i < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; i++) {
+        ThresholdState state = VersionBitsState(pindexPrev, params, (Consensus::DeploymentPos)i, versionbitscache);
+        if (state == THRESHOLD_LOCKED_IN || state == THRESHOLD_STARTED) {
+            nVersion |= VersionBitsMask(params, (Consensus::DeploymentPos)i);
+        }
+    }
+
+    return nVersion;
+}
+
+/**
+ * Threshold condition checker that triggers when unknown versionbits are seen on the network.
+ */
+class WarningBitsConditionChecker : public AbstractThresholdConditionChecker
+{
+private:
+    int bit;
+
+public:
+    WarningBitsConditionChecker(int bitIn) : bit(bitIn) {}
+
+    int64_t BeginTime(const Consensus::Params& params) const { return 0; }
+    int64_t EndTime(const Consensus::Params& params) const { return std::numeric_limits<int64_t>::max(); }
+    int Period(const Consensus::Params& params) const { return params.nMinerConfirmationWindow; }
+    int Threshold(const Consensus::Params& params) const { return params.nRuleChangeActivationThreshold; }
+
+    bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const
+    {
+        return ((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) &&
+               ((pindex->nVersion >> bit) & 1) != 0 &&
+               ((ComputeBlockVersion(pindex->pprev, params) >> bit) & 1) == 0;
+    }
+};
+
+// Protected by cs_main
+static ThresholdConditionCache warningcache[VERSIONBITS_NUM_BITS];
+
+static int64_t nTimeCheck = 0;
+static int64_t nTimeForks = 0;
 static int64_t nTimeVerify = 0;
 static int64_t nTimeConnect = 0;
 static int64_t nTimeIndex = 0;
 static int64_t nTimeCallbacks = 0;
 static int64_t nTimeTotal = 0;
 
-bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex, CCoinsViewCache& view, bool fJustCheck)
+bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex,
+                  CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck)
 {
     AssertLockHeld(cs_main);
+
+    int64_t nTimeStart = GetTimeMicros();
+
     // Check it again in case a previous version let a bad block in
-    if (!CheckBlock(block, state, !fJustCheck, !fJustCheck))
-        return false;
+    if (!CheckBlock(block, state, chainparams.GetConsensus(), !fJustCheck, !fJustCheck))
+        return error("%s: Consensus::CheckBlock: %s", __func__, FormatStateMessage(state));
 
     // verify that the view's current state corresponds to the previous block
-    uint256 hashPrevBlock = pindex->pprev == NULL ? uint256(0) : pindex->pprev->GetBlockHash();
+    uint256 hashPrevBlock = pindex->pprev == NULL ? uint256() : pindex->pprev->GetBlockHash();
     assert(hashPrevBlock == view.GetBestBlock());
 
     // Special case for the genesis block, skipping connection of its transactions
     // (its coinbase is unspendable)
-    if (block.GetHash() == Params().HashGenesisBlock()) {
-        view.SetBestBlock(pindex->GetBlockHash());
+    if (block.GetHash() == chainparams.GetConsensus().hashGenesisBlock) {
+        if (!fJustCheck)
+            view.SetBestBlock(pindex->GetBlockHash());
         return true;
     }
 
-    bool fScriptChecks = pindex->nHeight >= Checkpoints::GetTotalBlocksEstimate();
+    bool fScriptChecks = true;
+    if (fCheckpointsEnabled) {
+        CBlockIndex *pindexLastCheckpoint = Checkpoints::GetLastCheckpoint(chainparams.Checkpoints());
+        if (pindexLastCheckpoint && pindexLastCheckpoint->GetAncestor(pindex->nHeight) == pindex) {
+            // This block is an ancestor of a checkpoint: disable script checks
+            fScriptChecks = false;
+        }
+    }
+
+    int64_t nTime1 = GetTimeMicros(); nTimeCheck += nTime1 - nTimeStart;
+    LogPrint("bench", "    - Sanity checks: %.2fms [%.2fs]\n", 0.001 * (nTime1 - nTimeStart), nTimeCheck * 0.000001);
 
     // Do not allow blocks that contain transactions which 'overwrite' older transactions,
     // unless those are already completely spent.
@@ -1630,18 +2339,29 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
     // See BIP30 and http://r6.ca/blog/20120206T005236Z.html for more information.
     // This logic is not necessary for memory pool transactions, as AcceptToMemoryPool
     // already refuses previously-known transaction ids entirely.
-    // This rule was originally applied all blocks whose timestamp was after March 15, 2012, 0:00 UTC.
+    // This rule was originally applied to all blocks with a timestamp after March 15, 2012, 0:00 UTC.
     // Now that the whole chain is irreversibly beyond that time it is applied to all blocks except the
-    // two in the chain that violate it. This prevents exploiting the issue against nodes in their
+    // two in the chain that violate it. This prevents exploiting the issue against nodes during their
     // initial block download.
     bool fEnforceBIP30 = (!pindex->phashBlock) || // Enforce on CreateNewBlock invocations which don't have a hash.
-                          !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
-                           (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
+                          !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256S("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
+                           (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256S("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
+
+    // Once BIP34 activated it was not possible to create new duplicate coinbases and thus other than starting
+    // with the 2 existing duplicate coinbase pairs, not possible to create overwriting txs.  But by the
+    // time BIP34 activated, in each of the existing pairs the duplicate coinbase had overwritten the first
+    // before the first had been spent.  Since those coinbases are sufficiently buried its no longer possible to create further
+    // duplicate transactions descending from the known pairs either.
+    // If we're on the known chain at height greater than where BIP34 activated, we can save the db accesses needed for the BIP30 check.
+    CBlockIndex *pindexBIP34height = pindex->pprev->GetAncestor(chainparams.GetConsensus().BIP34Height);
+    //Only continue to enforce if we're below BIP34 activation height or the block hash at that height doesn't correspond.
+    fEnforceBIP30 = fEnforceBIP30 && (!pindexBIP34height || !(pindexBIP34height->GetBlockHash() == chainparams.GetConsensus().BIP34Hash));
+
     if (fEnforceBIP30) {
         BOOST_FOREACH(const CTransaction& tx, block.vtx) {
             const CCoins* coins = view.AccessCoins(tx.GetHash());
             if (coins && !coins->IsPruned())
-                return state.DoS(100, error("ConnectBlock() : tried to overwrite transaction"),
+                return state.DoS(100, error("ConnectBlock(): tried to overwrite transaction"),
                                  REJECT_INVALID, "bad-txns-BIP30");
         }
     }
@@ -1652,14 +2372,42 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
 
     unsigned int flags = fStrictPayToScriptHash ? SCRIPT_VERIFY_P2SH : SCRIPT_VERIFY_NONE;
 
+    // Start enforcing the DERSIG (BIP66) rules, for block.nVersion=3 blocks,
+    // when 75% of the network has upgraded:
+    if (block.nVersion >= 3 && IsSuperMajority(3, pindex->pprev, chainparams.GetConsensus().nMajorityEnforceBlockUpgrade, chainparams.GetConsensus())) {
+        flags |= SCRIPT_VERIFY_DERSIG;
+    }
+
+    // Start enforcing CHECKLOCKTIMEVERIFY, (BIP65) for block.nVersion=4
+    // blocks, when 75% of the network has upgraded:
+    if (block.nVersion >= 4 && IsSuperMajority(4, pindex->pprev, chainparams.GetConsensus().nMajorityEnforceBlockUpgrade, chainparams.GetConsensus())) {
+        flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
+    }
+
+    // Start enforcing BIP68 (sequence locks) and BIP112 (CHECKSEQUENCEVERIFY) using versionbits logic.
+    int nLockTimeFlags = 0;
+    if (VersionBitsState(pindex->pprev, chainparams.GetConsensus(), Consensus::DEPLOYMENT_CSV, versionbitscache) == THRESHOLD_ACTIVE) {
+        flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
+        nLockTimeFlags |= LOCKTIME_VERIFY_SEQUENCE;
+    }
+
+    // Start enforcing WITNESS rules using versionbits logic.
+    if (IsWitnessEnabled(pindex->pprev, chainparams.GetConsensus())) {
+        flags |= SCRIPT_VERIFY_WITNESS;
+    }
+
+    int64_t nTime2 = GetTimeMicros(); nTimeForks += nTime2 - nTime1;
+    LogPrint("bench", "    - Fork checks: %.2fms [%.2fs]\n", 0.001 * (nTime2 - nTime1), nTimeForks * 0.000001);
+
     CBlockUndo blockundo;
 
     CCheckQueueControl<CScriptCheck> control(fScriptChecks && nScriptCheckThreads ? &scriptcheckqueue : NULL);
 
-    int64_t nTimeStart = GetTimeMicros();
+    std::vector<uint256> vOrphanErase;
+    std::vector<int> prevheights;
     CAmount nFees = 0;
     int nInputs = 0;
-    unsigned int nSigOps = 0;
+    int64_t nSigOpsCost = 0;
     CDiskTxPos pos(pindex->GetBlockPos(), GetSizeOfCompactSize(block.vtx.size()));
     std::vector<std::pair<uint256, CDiskTxPos> > vPos;
     vPos.reserve(block.vtx.size());
@@ -1669,33 +2417,56 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
         const CTransaction &tx = block.vtx[i];
 
         nInputs += tx.vin.size();
-        nSigOps += GetLegacySigOpCount(tx);
-        if (nSigOps > MAX_BLOCK_SIGOPS)
-            return state.DoS(100, error("ConnectBlock() : too many sigops"),
-                             REJECT_INVALID, "bad-blk-sigops");
 
         if (!tx.IsCoinBase())
         {
             if (!view.HaveInputs(tx))
-                return state.DoS(100, error("ConnectBlock() : inputs missing/spent"),
+                return state.DoS(100, error("ConnectBlock(): inputs missing/spent"),
                                  REJECT_INVALID, "bad-txns-inputs-missingorspent");
 
-            if (fStrictPayToScriptHash)
-            {
-                // Add in sigops done by pay-to-script-hash inputs;
-                // this is to prevent a "rogue miner" from creating
-                // an incredibly-expensive-to-validate block.
-                nSigOps += GetP2SHSigOpCount(tx, view);
-                if (nSigOps > MAX_BLOCK_SIGOPS)
-                    return state.DoS(100, error("ConnectBlock() : too many sigops"),
-                                     REJECT_INVALID, "bad-blk-sigops");
+            // Check that transaction is BIP68 final
+            // BIP68 lock checks (as opposed to nLockTime checks) must
+            // be in ConnectBlock because they require the UTXO set
+            prevheights.resize(tx.vin.size());
+            for (size_t j = 0; j < tx.vin.size(); j++) {
+                prevheights[j] = view.AccessCoins(tx.vin[j].prevout.hash)->nHeight;
+            }
+
+            // Which orphan pool entries must we evict?
+            for (size_t j = 0; j < tx.vin.size(); j++) {
+                auto itByPrev = mapOrphanTransactionsByPrev.find(tx.vin[j].prevout);
+                if (itByPrev == mapOrphanTransactionsByPrev.end()) continue;
+                for (auto mi = itByPrev->second.begin(); mi != itByPrev->second.end(); ++mi) {
+                    const CTransaction& orphanTx = (*mi)->second.tx;
+                    const uint256& orphanHash = orphanTx.GetHash();
+                    vOrphanErase.push_back(orphanHash);
+                }
             }
 
+            if (!SequenceLocks(tx, nLockTimeFlags, &prevheights, *pindex)) {
+                return state.DoS(100, error("%s: contains a non-BIP68-final transaction", __func__),
+                                 REJECT_INVALID, "bad-txns-nonfinal");
+            }
+        }
+
+        // GetTransactionSigOpCost counts 3 types of sigops:
+        // * legacy (always)
+        // * p2sh (when P2SH enabled in flags and excludes coinbase)
+        // * witness (when witness enabled in flags and excludes coinbase)
+        nSigOpsCost += GetTransactionSigOpCost(tx, view, flags);
+        if (nSigOpsCost > MAX_BLOCK_SIGOPS_COST)
+            return state.DoS(100, error("ConnectBlock(): too many sigops"),
+                             REJECT_INVALID, "bad-blk-sigops");
+
+        if (!tx.IsCoinBase())
+        {
             nFees += view.GetValueIn(tx)-tx.GetValueOut();
 
             std::vector<CScriptCheck> vChecks;
-            if (!CheckInputs(tx, state, view, fScriptChecks, flags, false, nScriptCheckThreads ? &vChecks : NULL))
-                return false;
+            bool fCacheResults = fJustCheck; /* Don't cache results if we're actually connecting blocks (still consult the cache, though) */
+            if (!CheckInputs(tx, state, view, fScriptChecks, flags, fCacheResults, nScriptCheckThreads ? &vChecks : NULL))
+                return error("ConnectBlock(): CheckInputs on %s failed with %s",
+                    tx.GetHash().ToString(), FormatStateMessage(state));
             control.Add(vChecks);
         }
 
@@ -1703,24 +2474,25 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
         if (i > 0) {
             blockundo.vtxundo.push_back(CTxUndo());
         }
-        UpdateCoins(tx, state, view, i == 0 ? undoDummy : blockundo.vtxundo.back(), pindex->nHeight);
+        UpdateCoins(tx, view, i == 0 ? undoDummy : blockundo.vtxundo.back(), pindex->nHeight);
 
         vPos.push_back(std::make_pair(tx.GetHash(), pos));
         pos.nTxOffset += ::GetSerializeSize(tx, SER_DISK, CLIENT_VERSION);
     }
-    int64_t nTime1 = GetTimeMicros(); nTimeConnect += nTime1 - nTimeStart;
-    LogPrint("bench", "      - Connect %u transactions: %.2fms (%.3fms/tx, %.3fms/txin) [%.2fs]\n", (unsigned)block.vtx.size(), 0.001 * (nTime1 - nTimeStart), 0.001 * (nTime1 - nTimeStart) / block.vtx.size(), nInputs <= 1 ? 0 : 0.001 * (nTime1 - nTimeStart) / (nInputs-1), nTimeConnect * 0.000001);
+    int64_t nTime3 = GetTimeMicros(); nTimeConnect += nTime3 - nTime2;
+    LogPrint("bench", "      - Connect %u transactions: %.2fms (%.3fms/tx, %.3fms/txin) [%.2fs]\n", (unsigned)block.vtx.size(), 0.001 * (nTime3 - nTime2), 0.001 * (nTime3 - nTime2) / block.vtx.size(), nInputs <= 1 ? 0 : 0.001 * (nTime3 - nTime2) / (nInputs-1), nTimeConnect * 0.000001);
 
-    if (block.vtx[0].GetValueOut() > GetBlockValue(pindex->nHeight, nFees))
+    CAmount blockReward = nFees + GetBlockSubsidy(pindex->nHeight, chainparams.GetConsensus());
+    if (block.vtx[0].GetValueOut() > blockReward)
         return state.DoS(100,
-                         error("ConnectBlock() : coinbase pays too much (actual=%d vs limit=%d)",
-                               block.vtx[0].GetValueOut(), GetBlockValue(pindex->nHeight, nFees)),
+                         error("ConnectBlock(): coinbase pays too much (actual=%d vs limit=%d)",
+                               block.vtx[0].GetValueOut(), blockReward),
                                REJECT_INVALID, "bad-cb-amount");
 
     if (!control.Wait())
         return state.DoS(100, false);
-    int64_t nTime2 = GetTimeMicros(); nTimeVerify += nTime2 - nTimeStart;
-    LogPrint("bench", "    - Verify %u txins: %.2fms (%.3fms/txin) [%.2fs]\n", nInputs - 1, 0.001 * (nTime2 - nTimeStart), nInputs <= 1 ? 0 : 0.001 * (nTime2 - nTimeStart) / (nInputs-1), nTimeVerify * 0.000001);
+    int64_t nTime4 = GetTimeMicros(); nTimeVerify += nTime4 - nTime2;
+    LogPrint("bench", "    - Verify %u txins: %.2fms (%.3fms/txin) [%.2fs]\n", nInputs - 1, 0.001 * (nTime4 - nTime2), nInputs <= 1 ? 0 : 0.001 * (nTime4 - nTime2) / (nInputs-1), nTimeVerify * 0.000001);
 
     if (fJustCheck)
         return true;
@@ -1731,9 +2503,9 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
         if (pindex->GetUndoPos().IsNull()) {
             CDiskBlockPos pos;
             if (!FindUndoPos(state, pindex->nFile, pos, ::GetSerializeSize(blockundo, SER_DISK, CLIENT_VERSION) + 40))
-                return error("ConnectBlock() : FindUndoPos failed");
-            if (!blockundo.WriteToDisk(pos, pindex->pprev->GetBlockHash()))
-                return state.Abort("Failed to write undo data");
+                return error("ConnectBlock(): FindUndoPos failed");
+            if (!UndoWriteToDisk(blockundo, pos, pindex->pprev->GetBlockHash(), chainparams.MessageStart()))
+                return AbortNode(state, "Failed to write undo data");
 
             // update nUndoPos in block index
             pindex->nUndoPos = pos.nPos;
@@ -1746,26 +2518,36 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
 
     if (fTxIndex)
         if (!pblocktree->WriteTxIndex(vPos))
-            return state.Abort("Failed to write transaction index");
+            return AbortNode(state, "Failed to write transaction index");
 
     // add this block to the view's block chain
     view.SetBestBlock(pindex->GetBlockHash());
 
-    int64_t nTime3 = GetTimeMicros(); nTimeIndex += nTime3 - nTime2;
-    LogPrint("bench", "    - Index writing: %.2fms [%.2fs]\n", 0.001 * (nTime3 - nTime2), nTimeIndex * 0.000001);
+    int64_t nTime5 = GetTimeMicros(); nTimeIndex += nTime5 - nTime4;
+    LogPrint("bench", "    - Index writing: %.2fms [%.2fs]\n", 0.001 * (nTime5 - nTime4), nTimeIndex * 0.000001);
 
     // Watch for changes to the previous coinbase transaction.
     static uint256 hashPrevBestCoinBase;
-    g_signals.UpdatedTransaction(hashPrevBestCoinBase);
+    GetMainSignals().UpdatedTransaction(hashPrevBestCoinBase);
     hashPrevBestCoinBase = block.vtx[0].GetHash();
 
-    int64_t nTime4 = GetTimeMicros(); nTimeCallbacks += nTime4 - nTime3;
-    LogPrint("bench", "    - Callbacks: %.2fms [%.2fs]\n", 0.001 * (nTime4 - nTime3), nTimeCallbacks * 0.000001);
+    // Erase orphan transactions include or precluded by this block
+    if (vOrphanErase.size()) {
+        int nErased = 0;
+        BOOST_FOREACH(uint256 &orphanHash, vOrphanErase) {
+            nErased += EraseOrphanTx(orphanHash);
+        }
+        LogPrint("mempool", "Erased %d orphan tx included or conflicted by block\n", nErased);
+    }
+
+    int64_t nTime6 = GetTimeMicros(); nTimeCallbacks += nTime6 - nTime5;
+    LogPrint("bench", "    - Callbacks: %.2fms [%.2fs]\n", 0.001 * (nTime6 - nTime5), nTimeCallbacks * 0.000001);
 
     return true;
 }
 
 enum FlushStateMode {
+    FLUSH_STATE_NONE,
     FLUSH_STATE_IF_NEEDED,
     FLUSH_STATE_PERIODIC,
     FLUSH_STATE_ALWAYS
@@ -1773,51 +2555,103 @@ enum FlushStateMode {
 
 /**
  * Update the on-disk chain state.
- * The caches and indexes are flushed if either they're too large, forceWrite is set, or
- * fast is not set and it's been a while since the last write.
+ * The caches and indexes are flushed depending on the mode we're called with
+ * if they're too large, if it's been a while since the last write,
+ * or always and in all cases if we're in prune mode and are deleting files.
  */
 bool static FlushStateToDisk(CValidationState &state, FlushStateMode mode) {
-    LOCK(cs_main);
+    const CChainParams& chainparams = Params();
+    LOCK2(cs_main, cs_LastBlockFile);
     static int64_t nLastWrite = 0;
-    if ((mode == FLUSH_STATE_ALWAYS) ||
-        ((mode == FLUSH_STATE_PERIODIC || mode == FLUSH_STATE_IF_NEEDED) && pcoinsTip->GetCacheSize() > nCoinCacheSize) ||
-        (mode == FLUSH_STATE_PERIODIC && GetTimeMicros() > nLastWrite + DATABASE_WRITE_INTERVAL * 1000000)) {
-        // Typical CCoins structures on disk are around 100 bytes in size.
-        // Pushing a new one to the database can cause it to be written
-        // twice (once in the log, and once in the tables). This is already
-        // an overestimation, as most will delete an existing entry or
-        // overwrite one. Still, use a conservative safety factor of 2.
-        if (!CheckDiskSpace(100 * 2 * 2 * pcoinsTip->GetCacheSize()))
+    static int64_t nLastFlush = 0;
+    static int64_t nLastSetChain = 0;
+    std::set<int> setFilesToPrune;
+    bool fFlushForPrune = false;
+    try {
+    if (fPruneMode && fCheckForPruning && !fReindex) {
+        FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight());
+        fCheckForPruning = false;
+        if (!setFilesToPrune.empty()) {
+            fFlushForPrune = true;
+            if (!fHavePruned) {
+                pblocktree->WriteFlag("prunedblockfiles", true);
+                fHavePruned = true;
+            }
+        }
+    }
+    int64_t nNow = GetTimeMicros();
+    // Avoid writing/flushing immediately after startup.
+    if (nLastWrite == 0) {
+        nLastWrite = nNow;
+    }
+    if (nLastFlush == 0) {
+        nLastFlush = nNow;
+    }
+    if (nLastSetChain == 0) {
+        nLastSetChain = nNow;
+    }
+    size_t cacheSize = pcoinsTip->DynamicMemoryUsage();
+    // The cache is large and close to the limit, but we have time now (not in the middle of a block processing).
+    bool fCacheLarge = mode == FLUSH_STATE_PERIODIC && cacheSize * (10.0/9) > nCoinCacheUsage;
+    // The cache is over the limit, we have to write now.
+    bool fCacheCritical = mode == FLUSH_STATE_IF_NEEDED && cacheSize > nCoinCacheUsage;
+    // It's been a while since we wrote the block index to disk. Do this frequently, so we don't need to redownload after a crash.
+    bool fPeriodicWrite = mode == FLUSH_STATE_PERIODIC && nNow > nLastWrite + (int64_t)DATABASE_WRITE_INTERVAL * 1000000;
+    // It's been very long since we flushed the cache. Do this infrequently, to optimize cache usage.
+    bool fPeriodicFlush = mode == FLUSH_STATE_PERIODIC && nNow > nLastFlush + (int64_t)DATABASE_FLUSH_INTERVAL * 1000000;
+    // Combine all conditions that result in a full cache flush.
+    bool fDoFullFlush = (mode == FLUSH_STATE_ALWAYS) || fCacheLarge || fCacheCritical || fPeriodicFlush || fFlushForPrune;
+    // Write blocks and block index to disk.
+    if (fDoFullFlush || fPeriodicWrite) {
+        // Depend on nMinDiskSpace to ensure we can write block index
+        if (!CheckDiskSpace(0))
             return state.Error("out of disk space");
         // First make sure all block and undo data is flushed to disk.
         FlushBlockFile();
         // Then update all block file information (which may refer to block and undo files).
-        bool fileschanged = false;
-        for (set<int>::iterator it = setDirtyFileInfo.begin(); it != setDirtyFileInfo.end(); ) {
-            if (!pblocktree->WriteBlockFileInfo(*it, vinfoBlockFile[*it])) {
-                return state.Abort("Failed to write to block index");
+        {
+            std::vector<std::pair<int, const CBlockFileInfo*> > vFiles;
+            vFiles.reserve(setDirtyFileInfo.size());
+            for (set<int>::iterator it = setDirtyFileInfo.begin(); it != setDirtyFileInfo.end(); ) {
+                vFiles.push_back(make_pair(*it, &vinfoBlockFile[*it]));
+                setDirtyFileInfo.erase(it++);
+            }
+            std::vector<const CBlockIndex*> vBlocks;
+            vBlocks.reserve(setDirtyBlockIndex.size());
+            for (set<CBlockIndex*>::iterator it = setDirtyBlockIndex.begin(); it != setDirtyBlockIndex.end(); ) {
+                vBlocks.push_back(*it);
+                setDirtyBlockIndex.erase(it++);
+            }
+            if (!pblocktree->WriteBatchSync(vFiles, nLastBlockFile, vBlocks)) {
+                return AbortNode(state, "Files to write to block index database");
             }
-            fileschanged = true;
-            setDirtyFileInfo.erase(it++);
-        }
-        if (fileschanged && !pblocktree->WriteLastBlockFile(nLastBlockFile)) {
-            return state.Abort("Failed to write to block index");
-        }
-        for (set<CBlockIndex*>::iterator it = setDirtyBlockIndex.begin(); it != setDirtyBlockIndex.end(); ) {
-             if (!pblocktree->WriteBlockIndex(CDiskBlockIndex(*it))) {
-                 return state.Abort("Failed to write to block index");
-             }
-             setDirtyBlockIndex.erase(it++);
         }
-        pblocktree->Sync();
-        // Finally flush the chainstate (which may refer to block index entries).
+        // Finally remove any pruned files
+        if (fFlushForPrune)
+            UnlinkPrunedFiles(setFilesToPrune);
+        nLastWrite = nNow;
+    }
+    // Flush best chain related state. This can only be done if the blocks / block index write was also done.
+    if (fDoFullFlush) {
+        // Typical CCoins structures on disk are around 128 bytes in size.
+        // Pushing a new one to the database can cause it to be written
+        // twice (once in the log, and once in the tables). This is already
+        // an overestimation, as most will delete an existing entry or
+        // overwrite one. Still, use a conservative safety factor of 2.
+        if (!CheckDiskSpace(128 * 2 * 2 * pcoinsTip->GetCacheSize()))
+            return state.Error("out of disk space");
+        // Flush the chainstate (which may refer to block index entries).
         if (!pcoinsTip->Flush())
-            return state.Abort("Failed to write to coin database");
+            return AbortNode(state, "Failed to write to coin database");
+        nLastFlush = nNow;
+    }
+    if (fDoFullFlush || ((mode == FLUSH_STATE_ALWAYS || mode == FLUSH_STATE_PERIODIC) && nNow > nLastSetChain + (int64_t)DATABASE_WRITE_INTERVAL * 1000000)) {
         // Update best block in wallet (so we can detect restored wallets).
-        if (mode != FLUSH_STATE_IF_NEEDED) {
-            g_signals.SetBestChain(chainActive.GetLocator());
-        }
-        nLastWrite = GetTimeMicros();
+        GetMainSignals().SetBestChain(chainActive.GetLocator());
+        nLastSetChain = nNow;
+    }
+    } catch (const std::runtime_error& e) {
+        return AbortNode(state, std::string("System error while flushing: ") + e.what());
     }
     return true;
 }
@@ -1827,82 +2661,123 @@ void FlushStateToDisk() {
     FlushStateToDisk(state, FLUSH_STATE_ALWAYS);
 }
 
+void PruneAndFlush() {
+    CValidationState state;
+    fCheckForPruning = true;
+    FlushStateToDisk(state, FLUSH_STATE_NONE);
+}
+
 /** Update chainActive and related internal data structures. */
-void static UpdateTip(CBlockIndex *pindexNew) {
+void static UpdateTip(CBlockIndex *pindexNew, const CChainParams& chainParams) {
     chainActive.SetTip(pindexNew);
 
     // New best block
     nTimeBestReceived = GetTime();
     mempool.AddTransactionsUpdated(1);
 
-    LogPrintf("UpdateTip: new best=%s  height=%d  log2_work=%.8g  tx=%lu  date=%s progress=%f  cache=%u\n",
-      chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(), log(chainActive.Tip()->nChainWork.getdouble())/log(2.0), (unsigned long)chainActive.Tip()->nChainTx,
-      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()),
-      Checkpoints::GuessVerificationProgress(chainActive.Tip()), (unsigned int)pcoinsTip->GetCacheSize());
-
     cvBlockChange.notify_all();
 
-    // Check the version of the last 100 blocks to see if we need to upgrade:
     static bool fWarned = false;
-    if (!IsInitialBlockDownload() && !fWarned)
+    std::vector<std::string> warningMessages;
+    if (!IsInitialBlockDownload())
     {
         int nUpgraded = 0;
         const CBlockIndex* pindex = chainActive.Tip();
+        for (int bit = 0; bit < VERSIONBITS_NUM_BITS; bit++) {
+            WarningBitsConditionChecker checker(bit);
+            ThresholdState state = checker.GetStateFor(pindex, chainParams.GetConsensus(), warningcache[bit]);
+            if (state == THRESHOLD_ACTIVE || state == THRESHOLD_LOCKED_IN) {
+                if (state == THRESHOLD_ACTIVE) {
+                    strMiscWarning = strprintf(_("Warning: unknown new rules activated (versionbit %i)"), bit);
+                    if (!fWarned) {
+                        AlertNotify(strMiscWarning);
+                        fWarned = true;
+                    }
+                } else {
+                    warningMessages.push_back(strprintf("unknown new rules are about to activate (versionbit %i)", bit));
+                }
+            }
+        }
+        // Check the version of the last 100 blocks to see if we need to upgrade:
         for (int i = 0; i < 100 && pindex != NULL; i++)
         {
-            if (pindex->nVersion > CBlock::CURRENT_VERSION)
+            int32_t nExpectedVersion = ComputeBlockVersion(pindex->pprev, chainParams.GetConsensus());
+            if (pindex->nVersion > VERSIONBITS_LAST_OLD_BLOCK_VERSION && (pindex->nVersion & ~nExpectedVersion) != 0)
                 ++nUpgraded;
             pindex = pindex->pprev;
         }
         if (nUpgraded > 0)
-            LogPrintf("SetBestChain: %d of last 100 blocks above version %d\n", nUpgraded, (int)CBlock::CURRENT_VERSION);
+            warningMessages.push_back(strprintf("%d of last 100 blocks have unexpected version", nUpgraded));
         if (nUpgraded > 100/2)
         {
             // strMiscWarning is read by GetWarnings(), called by Qt and the JSON-RPC code to warn the user:
-            strMiscWarning = _("Warning: This version is obsolete, upgrade required!");
-            CAlert::Notify(strMiscWarning, true);
-            fWarned = true;
+            strMiscWarning = _("Warning: Unknown block versions being mined! It's possible unknown rules are in effect");
+            if (!fWarned) {
+                AlertNotify(strMiscWarning);
+                fWarned = true;
+            }
         }
     }
+    LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%.8g tx=%lu date='%s' progress=%f cache=%.1fMiB(%utx)", __func__,
+      chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(), chainActive.Tip()->nVersion,
+      log(chainActive.Tip()->nChainWork.getdouble())/log(2.0), (unsigned long)chainActive.Tip()->nChainTx,
+      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()),
+      Checkpoints::GuessVerificationProgress(chainParams.Checkpoints(), chainActive.Tip()), pcoinsTip->DynamicMemoryUsage() * (1.0 / (1<<20)), pcoinsTip->GetCacheSize());
+    if (!warningMessages.empty())
+        LogPrintf(" warning='%s'", boost::algorithm::join(warningMessages, ", "));
+    LogPrintf("\n");
+
 }
 
-/** Disconnect chainActive's tip. */
-bool static DisconnectTip(CValidationState &state) {
+/** Disconnect chainActive's tip. You probably want to call mempool.removeForReorg and manually re-limit mempool size after this, with cs_main held. */
+bool static DisconnectTip(CValidationState& state, const CChainParams& chainparams, bool fBare = false)
+{
     CBlockIndex *pindexDelete = chainActive.Tip();
     assert(pindexDelete);
-    mempool.check(pcoinsTip);
     // Read block from disk.
     CBlock block;
-    if (!ReadBlockFromDisk(block, pindexDelete))
-        return state.Abort("Failed to read block");
+    if (!ReadBlockFromDisk(block, pindexDelete, chainparams.GetConsensus()))
+        return AbortNode(state, "Failed to read block");
     // Apply the block atomically to the chain state.
     int64_t nStart = GetTimeMicros();
     {
         CCoinsViewCache view(pcoinsTip);
         if (!DisconnectBlock(block, state, pindexDelete, view))
-            return error("DisconnectTip() : DisconnectBlock %s failed", pindexDelete->GetBlockHash().ToString());
+            return error("DisconnectTip(): DisconnectBlock %s failed", pindexDelete->GetBlockHash().ToString());
         assert(view.Flush());
     }
     LogPrint("bench", "- Disconnect block: %.2fms\n", (GetTimeMicros() - nStart) * 0.001);
     // Write the chain state to disk, if necessary.
     if (!FlushStateToDisk(state, FLUSH_STATE_IF_NEEDED))
         return false;
-    // Resurrect mempool transactions from the disconnected block.
-    BOOST_FOREACH(const CTransaction &tx, block.vtx) {
-        // ignore validation errors in resurrected transactions
-        list<CTransaction> removed;
-        CValidationState stateDummy;
-        if (tx.IsCoinBase() || !AcceptToMemoryPool(mempool, stateDummy, tx, false, NULL))
-            mempool.remove(tx, removed, true);
+
+    if (!fBare) {
+        // Resurrect mempool transactions from the disconnected block.
+        std::vector<uint256> vHashUpdate;
+        BOOST_FOREACH(const CTransaction &tx, block.vtx) {
+            // ignore validation errors in resurrected transactions
+            list<CTransaction> removed;
+            CValidationState stateDummy;
+            if (tx.IsCoinBase() || !AcceptToMemoryPool(mempool, stateDummy, tx, false, NULL, true)) {
+                mempool.removeRecursive(tx, removed);
+            } else if (mempool.exists(tx.GetHash())) {
+                vHashUpdate.push_back(tx.GetHash());
+            }
+        }
+        // AcceptToMemoryPool/addUnchecked all assume that new mempool entries have
+        // no in-mempool children, which is generally not true when adding
+        // previously-confirmed transactions back to the mempool.
+        // UpdateTransactionsFromBlock finds descendants of any transactions in this
+        // block that were added back and cleans up the mempool state.
+        mempool.UpdateTransactionsFromBlock(vHashUpdate);
     }
-    mempool.removeCoinbaseSpends(pcoinsTip, pindexDelete->nHeight);
-    mempool.check(pcoinsTip);
+
     // Update chainActive and related variables.
-    UpdateTip(pindexDelete->pprev);
+    UpdateTip(pindexDelete->pprev, chainparams);
     // Let wallets know transactions went from 1-confirmed to
     // 0-confirmed or conflicted:
     BOOST_FOREACH(const CTransaction &tx, block.vtx) {
-        SyncWithWallets(tx, NULL);
+        SyncWithWallets(tx, pindexDelete->pprev, NULL);
     }
     return true;
 }
@@ -1913,19 +2788,19 @@ static int64_t nTimeFlush = 0;
 static int64_t nTimeChainState = 0;
 static int64_t nTimePostConnect = 0;
 
-/** 
+/**
  * Connect a new block to chainActive. pblock is either NULL or a pointer to a CBlock
  * corresponding to pindexNew, to bypass loading it again from disk.
  */
-bool static ConnectTip(CValidationState &state, CBlockIndex *pindexNew, CBlock *pblock) {
+bool static ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const CBlock* pblock)
+{
     assert(pindexNew->pprev == chainActive.Tip());
-    mempool.check(pcoinsTip);
     // Read block from disk.
     int64_t nTime1 = GetTimeMicros();
     CBlock block;
     if (!pblock) {
-        if (!ReadBlockFromDisk(block, pindexNew))
-            return state.Abort("Failed to read block");
+        if (!ReadBlockFromDisk(block, pindexNew, chainparams.GetConsensus()))
+            return AbortNode(state, "Failed to read block");
         pblock = &block;
     }
     // Apply the block atomically to the chain state.
@@ -1934,15 +2809,14 @@ bool static ConnectTip(CValidationState &state, CBlockIndex *pindexNew, CBlock *
     LogPrint("bench", "  - Load block from disk: %.2fms [%.2fs]\n", (nTime2 - nTime1) * 0.001, nTimeReadFromDisk * 0.000001);
     {
         CCoinsViewCache view(pcoinsTip);
-        CInv inv(MSG_BLOCK, pindexNew->GetBlockHash());
-        bool rv = ConnectBlock(*pblock, state, pindexNew, view);
-        g_signals.BlockChecked(*pblock, state);
+        bool rv = ConnectBlock(*pblock, state, pindexNew, view, chainparams);
+        GetMainSignals().BlockChecked(*pblock, state);
         if (!rv) {
             if (state.IsInvalid())
                 InvalidBlockFound(pindexNew, state);
-            return error("ConnectTip() : ConnectBlock %s failed", pindexNew->GetBlockHash().ToString());
+            return error("ConnectTip(): ConnectBlock %s failed", pindexNew->GetBlockHash().ToString());
         }
-        mapBlockSource.erase(inv.hash);
+        mapBlockSource.erase(pindexNew->GetBlockHash());
         nTime3 = GetTimeMicros(); nTimeConnectTotal += nTime3 - nTime2;
         LogPrint("bench", "  - Connect total: %.2fms [%.2fs]\n", (nTime3 - nTime2) * 0.001, nTimeConnectTotal * 0.000001);
         assert(view.Flush());
@@ -1956,18 +2830,17 @@ bool static ConnectTip(CValidationState &state, CBlockIndex *pindexNew, CBlock *
     LogPrint("bench", "  - Writing chainstate: %.2fms [%.2fs]\n", (nTime5 - nTime4) * 0.001, nTimeChainState * 0.000001);
     // Remove conflicting transactions from the mempool.
     list<CTransaction> txConflicted;
-    mempool.removeForBlock(pblock->vtx, pindexNew->nHeight, txConflicted);
-    mempool.check(pcoinsTip);
+    mempool.removeForBlock(pblock->vtx, pindexNew->nHeight, txConflicted, !IsInitialBlockDownload());
     // Update chainActive & related variables.
-    UpdateTip(pindexNew);
+    UpdateTip(pindexNew, chainparams);
     // Tell wallet about transactions that went from mempool
     // to conflicted:
     BOOST_FOREACH(const CTransaction &tx, txConflicted) {
-        SyncWithWallets(tx, NULL);
+        SyncWithWallets(tx, pindexNew, NULL);
     }
     // ... and about transactions that got confirmed:
     BOOST_FOREACH(const CTransaction &tx, pblock->vtx) {
-        SyncWithWallets(tx, pblock);
+        SyncWithWallets(tx, pindexNew, pblock);
     }
 
     int64_t nTime6 = GetTimeMicros(); nTimePostConnect += nTime6 - nTime5; nTimeTotal += nTime6 - nTime1;
@@ -1997,15 +2870,29 @@ static CBlockIndex* FindMostWorkChain() {
         CBlockIndex *pindexTest = pindexNew;
         bool fInvalidAncestor = false;
         while (pindexTest && !chainActive.Contains(pindexTest)) {
-            assert(pindexTest->nStatus & BLOCK_HAVE_DATA);
             assert(pindexTest->nChainTx || pindexTest->nHeight == 0);
-            if (pindexTest->nStatus & BLOCK_FAILED_MASK) {
-                // Candidate has an invalid ancestor, remove entire chain from the set.
-                if (pindexBestInvalid == NULL || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
+
+            // Pruned nodes may have entries in setBlockIndexCandidates for
+            // which block files have been deleted.  Remove those as candidates
+            // for the most work chain if we come across them; we can't switch
+            // to a chain unless we have all the non-active-chain parent blocks.
+            bool fFailedChain = pindexTest->nStatus & BLOCK_FAILED_MASK;
+            bool fMissingData = !(pindexTest->nStatus & BLOCK_HAVE_DATA);
+            if (fFailedChain || fMissingData) {
+                // Candidate chain is not usable (either invalid or missing data)
+                if (fFailedChain && (pindexBestInvalid == NULL || pindexNew->nChainWork > pindexBestInvalid->nChainWork))
                     pindexBestInvalid = pindexNew;
                 CBlockIndex *pindexFailed = pindexNew;
+                // Remove the entire chain from the set.
                 while (pindexTest != pindexFailed) {
-                    pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
+                    if (fFailedChain) {
+                        pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
+                    } else if (fMissingData) {
+                        // If we're missing data, then add back to mapBlocksUnlinked,
+                        // so that if the block arrives in the future we can try adding
+                        // to setBlockIndexCandidates again.
+                        mapBlocksUnlinked.insert(std::make_pair(pindexFailed->pprev, pindexFailed));
+                    }
                     setBlockIndexCandidates.erase(pindexFailed);
                     pindexFailed = pindexFailed->pprev;
                 }
@@ -2036,16 +2923,18 @@ static void PruneBlockIndexCandidates() {
  * Try to make some progress towards making pindexMostWork the active block.
  * pblock is either NULL or a pointer to a CBlock corresponding to pindexMostWork.
  */
-static bool ActivateBestChainStep(CValidationState &state, CBlockIndex *pindexMostWork, CBlock *pblock) {
+static bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const CBlock* pblock, bool& fInvalidFound)
+{
     AssertLockHeld(cs_main);
-    bool fInvalidFound = false;
     const CBlockIndex *pindexOldTip = chainActive.Tip();
     const CBlockIndex *pindexFork = chainActive.FindFork(pindexMostWork);
 
     // Disconnect active blocks which are no longer in the best chain.
+    bool fBlocksDisconnected = false;
     while (chainActive.Tip() && chainActive.Tip() != pindexFork) {
-        if (!DisconnectTip(state))
+        if (!DisconnectTip(state, chainparams))
             return false;
+        fBlocksDisconnected = true;
     }
 
     // Build list of new blocks to connect.
@@ -2053,43 +2942,49 @@ static bool ActivateBestChainStep(CValidationState &state, CBlockIndex *pindexMo
     bool fContinue = true;
     int nHeight = pindexFork ? pindexFork->nHeight : -1;
     while (fContinue && nHeight != pindexMostWork->nHeight) {
-    // Don't iterate the entire list of potential improvements toward the best tip, as we likely only need
-    // a few blocks along the way.
-    int nTargetHeight = std::min(nHeight + 32, pindexMostWork->nHeight);
-    vpindexToConnect.clear();
-    vpindexToConnect.reserve(nTargetHeight - nHeight);
-    CBlockIndex *pindexIter = pindexMostWork->GetAncestor(nTargetHeight);
-    while (pindexIter && pindexIter->nHeight != nHeight) {
-        vpindexToConnect.push_back(pindexIter);
-        pindexIter = pindexIter->pprev;
-    }
-    nHeight = nTargetHeight;
-
-    // Connect new blocks.
-    BOOST_REVERSE_FOREACH(CBlockIndex *pindexConnect, vpindexToConnect) {
-        if (!ConnectTip(state, pindexConnect, pindexConnect == pindexMostWork ? pblock : NULL)) {
-            if (state.IsInvalid()) {
-                // The block violates a consensus rule.
-                if (!state.CorruptionPossible())
-                    InvalidChainFound(vpindexToConnect.back());
-                state = CValidationState();
-                fInvalidFound = true;
-                fContinue = false;
-                break;
+        // Don't iterate the entire list of potential improvements toward the best tip, as we likely only need
+        // a few blocks along the way.
+        int nTargetHeight = std::min(nHeight + 32, pindexMostWork->nHeight);
+        vpindexToConnect.clear();
+        vpindexToConnect.reserve(nTargetHeight - nHeight);
+        CBlockIndex *pindexIter = pindexMostWork->GetAncestor(nTargetHeight);
+        while (pindexIter && pindexIter->nHeight != nHeight) {
+            vpindexToConnect.push_back(pindexIter);
+            pindexIter = pindexIter->pprev;
+        }
+        nHeight = nTargetHeight;
+
+        // Connect new blocks.
+        BOOST_REVERSE_FOREACH(CBlockIndex *pindexConnect, vpindexToConnect) {
+            if (!ConnectTip(state, chainparams, pindexConnect, pindexConnect == pindexMostWork ? pblock : NULL)) {
+                if (state.IsInvalid()) {
+                    // The block violates a consensus rule.
+                    if (!state.CorruptionPossible())
+                        InvalidChainFound(vpindexToConnect.back());
+                    state = CValidationState();
+                    fInvalidFound = true;
+                    fContinue = false;
+                    break;
+                } else {
+                    // A system error occurred (disk space, database error, ...).
+                    return false;
+                }
             } else {
-                // A system error occurred (disk space, database error, ...).
-                return false;
-            }
-        } else {
-            PruneBlockIndexCandidates();
-            if (!pindexOldTip || chainActive.Tip()->nChainWork > pindexOldTip->nChainWork) {
-                // We're in a better position than we were. Return temporarily to release the lock.
-                fContinue = false;
-                break;
+                PruneBlockIndexCandidates();
+                if (!pindexOldTip || chainActive.Tip()->nChainWork > pindexOldTip->nChainWork) {
+                    // We're in a better position than we were. Return temporarily to release the lock.
+                    fContinue = false;
+                    break;
+                }
             }
         }
     }
+
+    if (fBlocksDisconnected) {
+        mempool.removeForReorg(pcoinsTip, chainActive.Tip()->nHeight + 1, STANDARD_LOCKTIME_VERIFY_FLAGS);
+        LimitMempoolSize(mempool, GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY) * 60 * 60);
     }
+    mempool.check(pcoinsTip);
 
     // Callbacks/notifications for a new best chain.
     if (fInvalidFound)
@@ -2100,49 +2995,110 @@ static bool ActivateBestChainStep(CValidationState &state, CBlockIndex *pindexMo
     return true;
 }
 
+static void NotifyHeaderTip() {
+    bool fNotify = false;
+    bool fInitialBlockDownload = false;
+    static CBlockIndex* pindexHeaderOld = NULL;
+    CBlockIndex* pindexHeader = NULL;
+    {
+        LOCK(cs_main);
+        if (!setBlockIndexCandidates.empty()) {
+            pindexHeader = *setBlockIndexCandidates.rbegin();
+        }
+        if (pindexHeader != pindexHeaderOld) {
+            fNotify = true;
+            fInitialBlockDownload = IsInitialBlockDownload();
+            pindexHeaderOld = pindexHeader;
+        }
+    }
+    // Send block tip changed notifications without cs_main
+    if (fNotify) {
+        uiInterface.NotifyHeaderTip(fInitialBlockDownload, pindexHeader);
+    }
+}
+
 /**
  * Make the best chain active, in multiple steps. The result is either failure
  * or an activated best chain. pblock is either NULL or a pointer to a block
  * that is already loaded (to avoid loading it again from disk).
  */
-bool ActivateBestChain(CValidationState &state, CBlock *pblock) {
-    CBlockIndex *pindexNewTip = NULL;
+bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams, const CBlock *pblock) {
     CBlockIndex *pindexMostWork = NULL;
+    CBlockIndex *pindexNewTip = NULL;
     do {
         boost::this_thread::interruption_point();
+        if (ShutdownRequested())
+            break;
 
+        const CBlockIndex *pindexFork;
         bool fInitialDownload;
+        int nNewHeight;
         {
             LOCK(cs_main);
-            pindexMostWork = FindMostWorkChain();
+            CBlockIndex *pindexOldTip = chainActive.Tip();
+            if (pindexMostWork == NULL) {
+                pindexMostWork = FindMostWorkChain();
+            }
 
             // Whether we have anything to do at all.
             if (pindexMostWork == NULL || pindexMostWork == chainActive.Tip())
                 return true;
 
-            if (!ActivateBestChainStep(state, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : NULL))
+            bool fInvalidFound = false;
+            if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : NULL, fInvalidFound))
                 return false;
 
+            if (fInvalidFound) {
+                // Wipe cache, we may need another branch now.
+                pindexMostWork = NULL;
+            }
             pindexNewTip = chainActive.Tip();
+            pindexFork = chainActive.FindFork(pindexOldTip);
             fInitialDownload = IsInitialBlockDownload();
+            nNewHeight = chainActive.Height();
         }
         // When we reach this point, we switched to a new tip (stored in pindexNewTip).
 
         // Notifications/callbacks that can run without cs_main
-        if (!fInitialDownload) {
-            uint256 hashNewTip = pindexNewTip->GetBlockHash();
-            // Relay inventory, but don't relay old inventory during initial block download.
-            int nBlockEstimate = Checkpoints::GetTotalBlocksEstimate();
-            {
-                LOCK(cs_vNodes);
-                BOOST_FOREACH(CNode* pnode, vNodes)
-                    if (chainActive.Height() > (pnode->nStartingHeight != -1 ? pnode->nStartingHeight - 2000 : nBlockEstimate))
-                        pnode->PushInventory(CInv(MSG_BLOCK, hashNewTip));
+        // Always notify the UI if a new block tip was connected
+        if (pindexFork != pindexNewTip) {
+            uiInterface.NotifyBlockTip(fInitialDownload, pindexNewTip);
+
+            if (!fInitialDownload) {
+                // Find the hashes of all blocks that weren't previously in the best chain.
+                std::vector<uint256> vHashes;
+                CBlockIndex *pindexToAnnounce = pindexNewTip;
+                while (pindexToAnnounce != pindexFork) {
+                    vHashes.push_back(pindexToAnnounce->GetBlockHash());
+                    pindexToAnnounce = pindexToAnnounce->pprev;
+                    if (vHashes.size() == MAX_BLOCKS_TO_ANNOUNCE) {
+                        // Limit announcements in case of a huge reorganization.
+                        // Rely on the peer's synchronization mechanism in that case.
+                        break;
+                    }
+                }
+                // Relay inventory, but don't relay old inventory during initial block download.
+                int nBlockEstimate = 0;
+                if (fCheckpointsEnabled)
+                    nBlockEstimate = Checkpoints::GetTotalBlocksEstimate(chainparams.Checkpoints());
+                {
+                    LOCK(cs_vNodes);
+                    BOOST_FOREACH(CNode* pnode, vNodes) {
+                        if (nNewHeight > (pnode->nStartingHeight != -1 ? pnode->nStartingHeight - 2000 : nBlockEstimate)) {
+                            BOOST_REVERSE_FOREACH(const uint256& hash, vHashes) {
+                                pnode->PushBlockHash(hash);
+                            }
+                        }
+                    }
+                }
+                // Notify external listeners about the new tip.
+                if (!vHashes.empty()) {
+                    GetMainSignals().UpdatedBlockTip(pindexNewTip);
+                }
             }
-            // Notify external listeners about the new tip.
-            uiInterface.NotifyBlockTip(hashNewTip);
         }
-    } while(pindexMostWork != chainActive.Tip());
+    } while (pindexNewTip != pindexMostWork);
+    CheckBlockIndex(chainparams.GetConsensus());
 
     // Write changes periodically to disk, after relay.
     if (!FlushStateToDisk(state, FLUSH_STATE_PERIODIC)) {
@@ -2152,7 +3108,8 @@ bool ActivateBestChain(CValidationState &state, CBlock *pblock) {
     return true;
 }
 
-bool InvalidateBlock(CValidationState& state, CBlockIndex *pindex) {
+bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex)
+{
     AssertLockHeld(cs_main);
 
     // Mark the block itself as invalid.
@@ -2167,26 +3124,30 @@ bool InvalidateBlock(CValidationState& state, CBlockIndex *pindex) {
         setBlockIndexCandidates.erase(pindexWalk);
         // ActivateBestChain considers blocks already in chainActive
         // unconditionally valid already, so force disconnect away from it.
-        if (!DisconnectTip(state)) {
+        if (!DisconnectTip(state, chainparams)) {
+            mempool.removeForReorg(pcoinsTip, chainActive.Tip()->nHeight + 1, STANDARD_LOCKTIME_VERIFY_FLAGS);
             return false;
         }
     }
 
+    LimitMempoolSize(mempool, GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY) * 60 * 60);
+
     // The resulting new best tip may not be in setBlockIndexCandidates anymore, so
-    // add them again.
+    // add it again.
     BlockMap::iterator it = mapBlockIndex.begin();
     while (it != mapBlockIndex.end()) {
-        if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->nChainTx && setBlockIndexCandidates.value_comp()(chainActive.Tip(), it->second)) {
-            setBlockIndexCandidates.insert(pindex);
+        if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->nChainTx && !setBlockIndexCandidates.value_comp()(it->second, chainActive.Tip())) {
+            setBlockIndexCandidates.insert(it->second);
         }
         it++;
     }
 
     InvalidChainFound(pindex);
+    mempool.removeForReorg(pcoinsTip, chainActive.Tip()->nHeight + 1, STANDARD_LOCKTIME_VERIFY_FLAGS);
     return true;
 }
 
-bool ReconsiderBlock(CValidationState& state, CBlockIndex *pindex) {
+bool ResetBlockFailureFlags(CBlockIndex *pindex) {
     AssertLockHeld(cs_main);
 
     int nHeight = pindex->nHeight;
@@ -2262,11 +3223,10 @@ bool ReceivedBlockTransactions(const CBlock &block, CValidationState& state, CBl
     pindexNew->nDataPos = pos.nPos;
     pindexNew->nUndoPos = 0;
     pindexNew->nStatus |= BLOCK_HAVE_DATA;
-    pindexNew->RaiseValidity(BLOCK_VALID_TRANSACTIONS);
-    {
-         LOCK(cs_nBlockSequenceId);
-         pindexNew->nSequenceId = nBlockSequenceId++;
+    if (IsWitnessEnabled(pindexNew->pprev, Params().GetConsensus())) {
+        pindexNew->nStatus |= BLOCK_OPT_WITNESS;
     }
+    pindexNew->RaiseValidity(BLOCK_VALID_TRANSACTIONS);
     setDirtyBlockIndex.insert(pindexNew);
 
     if (pindexNew->pprev == NULL || pindexNew->pprev->nChainTx) {
@@ -2279,7 +3239,13 @@ bool ReceivedBlockTransactions(const CBlock &block, CValidationState& state, CBl
             CBlockIndex *pindex = queue.front();
             queue.pop_front();
             pindex->nChainTx = (pindex->pprev ? pindex->pprev->nChainTx : 0) + pindex->nTx;
-            setBlockIndexCandidates.insert(pindex);
+            {
+                LOCK(cs_nBlockSequenceId);
+                pindex->nSequenceId = nBlockSequenceId++;
+            }
+            if (chainActive.Tip() == NULL || !setBlockIndexCandidates.value_comp()(pindex, chainActive.Tip())) {
+                setBlockIndexCandidates.insert(pindex);
+            }
             std::pair<std::multimap<CBlockIndex*, CBlockIndex*>::iterator, std::multimap<CBlockIndex*, CBlockIndex*>::iterator> range = mapBlocksUnlinked.equal_range(pindex);
             while (range.first != range.second) {
                 std::multimap<CBlockIndex*, CBlockIndex*>::iterator it = range.first;
@@ -2308,8 +3274,6 @@ bool FindBlockPos(CValidationState &state, CDiskBlockPos &pos, unsigned int nAdd
 
     if (!fKnown) {
         while (vinfoBlockFile[nFile].nSize + nAddSize >= MAX_BLOCKFILE_SIZE) {
-            LogPrintf("Leaving block file %i: %s\n", nFile, vinfoBlockFile[nFile].ToString());
-            FlushBlockFile(true);
             nFile++;
             if (vinfoBlockFile.size() <= nFile) {
                 vinfoBlockFile.resize(nFile + 1);
@@ -2319,14 +3283,26 @@ bool FindBlockPos(CValidationState &state, CDiskBlockPos &pos, unsigned int nAdd
         pos.nPos = vinfoBlockFile[nFile].nSize;
     }
 
-    nLastBlockFile = nFile;
-    vinfoBlockFile[nFile].nSize += nAddSize;
+    if ((int)nFile != nLastBlockFile) {
+        if (!fKnown) {
+            LogPrintf("Leaving block file %i: %s\n", nLastBlockFile, vinfoBlockFile[nLastBlockFile].ToString());
+        }
+        FlushBlockFile(!fKnown);
+        nLastBlockFile = nFile;
+    }
+
     vinfoBlockFile[nFile].AddBlock(nHeight, nTime);
+    if (fKnown)
+        vinfoBlockFile[nFile].nSize = std::max(pos.nPos + nAddSize, vinfoBlockFile[nFile].nSize);
+    else
+        vinfoBlockFile[nFile].nSize += nAddSize;
 
     if (!fKnown) {
         unsigned int nOldChunks = (pos.nPos + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;
         unsigned int nNewChunks = (vinfoBlockFile[nFile].nSize + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;
         if (nNewChunks > nOldChunks) {
+            if (fPruneMode)
+                fCheckForPruning = true;
             if (CheckDiskSpace(nNewChunks * BLOCKFILE_CHUNK_SIZE - pos.nPos)) {
                 FILE *file = OpenBlockFile(pos);
                 if (file) {
@@ -2358,6 +3334,8 @@ bool FindUndoPos(CValidationState &state, int nFile, CDiskBlockPos &pos, unsigne
     unsigned int nOldChunks = (pos.nPos + UNDOFILE_CHUNK_SIZE - 1) / UNDOFILE_CHUNK_SIZE;
     unsigned int nNewChunks = (nNewSize + UNDOFILE_CHUNK_SIZE - 1) / UNDOFILE_CHUNK_SIZE;
     if (nNewChunks > nOldChunks) {
+        if (fPruneMode)
+            fCheckForPruning = true;
         if (CheckDiskSpace(nNewChunks * UNDOFILE_CHUNK_SIZE - pos.nPos)) {
             FILE *file = OpenUndoFile(pos);
             if (file) {
@@ -2373,119 +3351,176 @@ bool FindUndoPos(CValidationState &state, int nFile, CDiskBlockPos &pos, unsigne
     return true;
 }
 
-bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, bool fCheckPOW)
+bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW)
 {
     // Check proof of work matches claimed amount
-    if (fCheckPOW && !CheckProofOfWork(block.GetHash(), block.nBits))
-        return state.DoS(50, error("CheckBlockHeader() : proof of work failed"),
-                         REJECT_INVALID, "high-hash");
-
-    // Check timestamp
-    if (block.GetBlockTime() > GetAdjustedTime() + 2 * 60 * 60)
-        return state.Invalid(error("CheckBlockHeader() : block timestamp too far in the future"),
-                             REJECT_INVALID, "time-too-new");
+    if (fCheckPOW && !CheckProofOfWork(block.GetHash(), block.nBits, consensusParams))
+        return state.DoS(50, false, REJECT_INVALID, "high-hash", false, "proof of work failed");
 
     return true;
 }
 
-bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW, bool fCheckMerkleRoot)
+bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW, bool fCheckMerkleRoot)
 {
     // These are checks that are independent of context.
 
+    if (block.fChecked)
+        return true;
+
     // Check that the header is valid (particularly PoW).  This is mostly
     // redundant with the call in AcceptBlockHeader.
-    if (!CheckBlockHeader(block, state, fCheckPOW))
+    if (!CheckBlockHeader(block, state, consensusParams, fCheckPOW))
         return false;
 
     // Check the merkle root.
     if (fCheckMerkleRoot) {
         bool mutated;
-        uint256 hashMerkleRoot2 = block.BuildMerkleTree(&mutated);
+        uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated);
         if (block.hashMerkleRoot != hashMerkleRoot2)
-            return state.DoS(100, error("CheckBlock() : hashMerkleRoot mismatch"),
-                             REJECT_INVALID, "bad-txnmrklroot", true);
+            return state.DoS(100, false, REJECT_INVALID, "bad-txnmrklroot", true, "hashMerkleRoot mismatch");
 
         // Check for merkle tree malleability (CVE-2012-2459): repeating sequences
         // of transactions in a block without affecting the merkle root of a block,
         // while still invalidating it.
         if (mutated)
-            return state.DoS(100, error("CheckBlock() : duplicate transaction"),
-                             REJECT_INVALID, "bad-txns-duplicate", true);
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-duplicate", true, "duplicate transaction");
     }
 
     // All potential-corruption validation must be done before we do any
     // transaction validation, as otherwise we may mark the header as invalid
     // because we receive the wrong transactions for it.
+    // Note that witness malleability is checked in ContextualCheckBlock, so no
+    // checks that use witness data may be performed here.
 
     // Size limits
-    if (block.vtx.empty() || block.vtx.size() > MAX_BLOCK_SIZE || ::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION) > MAX_BLOCK_SIZE)
-        return state.DoS(100, error("CheckBlock() : size limits failed"),
-                         REJECT_INVALID, "bad-blk-length");
+    if (block.vtx.empty() || block.vtx.size() > MAX_BLOCK_BASE_SIZE || ::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) > MAX_BLOCK_BASE_SIZE)
+        return state.DoS(100, false, REJECT_INVALID, "bad-blk-length", false, "size limits failed");
 
     // First transaction must be coinbase, the rest must not be
     if (block.vtx.empty() || !block.vtx[0].IsCoinBase())
-        return state.DoS(100, error("CheckBlock() : first tx is not coinbase"),
-                         REJECT_INVALID, "bad-cb-missing");
+        return state.DoS(100, false, REJECT_INVALID, "bad-cb-missing", false, "first tx is not coinbase");
     for (unsigned int i = 1; i < block.vtx.size(); i++)
         if (block.vtx[i].IsCoinBase())
-            return state.DoS(100, error("CheckBlock() : more than one coinbase"),
-                             REJECT_INVALID, "bad-cb-multiple");
+            return state.DoS(100, false, REJECT_INVALID, "bad-cb-multiple", false, "more than one coinbase");
 
     // Check transactions
     BOOST_FOREACH(const CTransaction& tx, block.vtx)
         if (!CheckTransaction(tx, state))
-            return error("CheckBlock() : CheckTransaction failed");
+            return state.Invalid(false, state.GetRejectCode(), state.GetRejectReason(),
+                                 strprintf("Transaction check failed (tx hash %s) %s", tx.GetHash().ToString(), state.GetDebugMessage()));
 
     unsigned int nSigOps = 0;
     BOOST_FOREACH(const CTransaction& tx, block.vtx)
     {
         nSigOps += GetLegacySigOpCount(tx);
     }
-    if (nSigOps > MAX_BLOCK_SIGOPS)
-        return state.DoS(100, error("CheckBlock() : out-of-bounds SigOpCount"),
-                         REJECT_INVALID, "bad-blk-sigops", true);
+    if (nSigOps * WITNESS_SCALE_FACTOR > MAX_BLOCK_SIGOPS_COST)
+        return state.DoS(100, false, REJECT_INVALID, "bad-blk-sigops", false, "out-of-bounds SigOpCount");
+
+    if (fCheckPOW && fCheckMerkleRoot)
+        block.fChecked = true;
 
     return true;
 }
 
-bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, CBlockIndex * const pindexPrev)
+static bool CheckIndexAgainstCheckpoint(const CBlockIndex* pindexPrev, CValidationState& state, const CChainParams& chainparams, const uint256& hash)
 {
-    uint256 hash = block.GetHash();
-    if (hash == Params().HashGenesisBlock())
+    if (*pindexPrev->phashBlock == chainparams.GetConsensus().hashGenesisBlock)
         return true;
 
-    assert(pindexPrev);
-
     int nHeight = pindexPrev->nHeight+1;
+    // Don't accept any forks from the main chain prior to last checkpoint
+    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(chainparams.Checkpoints());
+    if (pcheckpoint && nHeight < pcheckpoint->nHeight)
+        return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight));
 
+    return true;
+}
+
+bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)
+{
+    LOCK(cs_main);
+    return (VersionBitsState(pindexPrev, params, Consensus::DEPLOYMENT_SEGWIT, versionbitscache) == THRESHOLD_ACTIVE);
+}
+
+// Compute at which vout of the block's coinbase transaction the witness
+// commitment occurs, or -1 if not found.
+static int GetWitnessCommitmentIndex(const CBlock& block)
+{
+    int commitpos = -1;
+    for (size_t o = 0; o < block.vtx[0].vout.size(); o++) {
+        if (block.vtx[0].vout[o].scriptPubKey.size() >= 38 && block.vtx[0].vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0].vout[o].scriptPubKey[1] == 0x24 && block.vtx[0].vout[o].scriptPubKey[2] == 0xaa && block.vtx[0].vout[o].scriptPubKey[3] == 0x21 && block.vtx[0].vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0].vout[o].scriptPubKey[5] == 0xed) {
+            commitpos = o;
+        }
+    }
+    return commitpos;
+}
+
+void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams)
+{
+    int commitpos = GetWitnessCommitmentIndex(block);
+    static const std::vector<unsigned char> nonce(32, 0x00);
+    if (commitpos != -1 && IsWitnessEnabled(pindexPrev, consensusParams) && block.vtx[0].wit.IsEmpty()) {
+        block.vtx[0].wit.vtxinwit.resize(1);
+        block.vtx[0].wit.vtxinwit[0].scriptWitness.stack.resize(1);
+        block.vtx[0].wit.vtxinwit[0].scriptWitness.stack[0] = nonce;
+    }
+}
+
+std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams)
+{
+    std::vector<unsigned char> commitment;
+    int commitpos = GetWitnessCommitmentIndex(block);
+    bool fHaveWitness = false;
+    for (size_t t = 1; t < block.vtx.size(); t++) {
+        if (!block.vtx[t].wit.IsNull()) {
+            fHaveWitness = true;
+            break;
+        }
+    }
+    std::vector<unsigned char> ret(32, 0x00);
+    if (fHaveWitness && IsWitnessEnabled(pindexPrev, consensusParams)) {
+        if (commitpos == -1) {
+            uint256 witnessroot = BlockWitnessMerkleRoot(block, NULL);
+            CHash256().Write(witnessroot.begin(), 32).Write(&ret[0], 32).Finalize(witnessroot.begin());
+            CTxOut out;
+            out.nValue = 0;
+            out.scriptPubKey.resize(38);
+            out.scriptPubKey[0] = OP_RETURN;
+            out.scriptPubKey[1] = 0x24;
+            out.scriptPubKey[2] = 0xaa;
+            out.scriptPubKey[3] = 0x21;
+            out.scriptPubKey[4] = 0xa9;
+            out.scriptPubKey[5] = 0xed;
+            memcpy(&out.scriptPubKey[6], witnessroot.begin(), 32);
+            commitment = std::vector<unsigned char>(out.scriptPubKey.begin(), out.scriptPubKey.end());
+            const_cast<std::vector<CTxOut>*>(&block.vtx[0].vout)->push_back(out);
+            block.vtx[0].UpdateHash();
+        }
+    }
+    UpdateUncommittedBlockStructures(block, pindexPrev, consensusParams);
+    return commitment;
+}
+
+bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, CBlockIndex * const pindexPrev, int64_t nAdjustedTime)
+{
     // Check proof of work
-    if ((!Params().SkipProofOfWorkCheck()) &&
-       (block.nBits != GetNextWorkRequired(pindexPrev, &block)))
-        return state.DoS(100, error("%s : incorrect proof of work", __func__),
-                         REJECT_INVALID, "bad-diffbits");
+    if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
+        return state.DoS(100, false, REJECT_INVALID, "bad-diffbits", false, "incorrect proof of work");
 
     // Check timestamp against prev
     if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
-        return state.Invalid(error("%s : block's timestamp is too early", __func__),
-                             REJECT_INVALID, "time-too-old");
-
-    // Check that the block chain matches the known block chain up to a checkpoint
-    if (!Checkpoints::CheckBlock(nHeight, hash))
-        return state.DoS(100, error("%s : rejected by checkpoint lock-in at %d", __func__, nHeight),
-                         REJECT_CHECKPOINT, "checkpoint mismatch");
+        return state.Invalid(false, REJECT_INVALID, "time-too-old", "block's timestamp is too early");
 
-    // Don't accept any forks from the main chain prior to last checkpoint
-    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint();
-    if (pcheckpoint && nHeight < pcheckpoint->nHeight)
-        return state.DoS(100, error("%s : forked chain older than last checkpoint (height %d)", __func__, nHeight));
+    // Check timestamp
+    if (block.GetBlockTime() > nAdjustedTime + 2 * 60 * 60)
+        return state.Invalid(false, REJECT_INVALID, "time-too-new", "block timestamp too far in the future");
 
-    // Reject block.nVersion=1 blocks when 95% (75% on testnet) of the network has upgraded:
-    if (block.nVersion < 2 && 
-        CBlockIndex::IsSuperMajority(2, pindexPrev, Params().RejectBlockOutdatedMajority()))
-    {
-        return state.Invalid(error("%s : rejected nVersion=1 block", __func__),
-                             REJECT_OBSOLETE, "bad-version");
-    }
+    // Reject outdated version blocks when 95% (75% on testnet) of the network has upgraded:
+    for (int32_t version = 2; version < 5; ++version) // check for version 2, 3 and 4 upgrades
+        if (block.nVersion < version && IsSuperMajority(version, pindexPrev, consensusParams.nMajorityRejectBlockOutdated, consensusParams))
+            return state.Invalid(false, REJECT_OBSOLETE, strprintf("bad-version(0x%08x)", version - 1),
+                                 strprintf("rejected nVersion=0x%08x block", version - 1));
 
     return true;
 }
@@ -2493,60 +3528,124 @@ bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& sta
 bool ContextualCheckBlock(const CBlock& block, CValidationState& state, CBlockIndex * const pindexPrev)
 {
     const int nHeight = pindexPrev == NULL ? 0 : pindexPrev->nHeight + 1;
+    const Consensus::Params& consensusParams = Params().GetConsensus();
+
+    // Start enforcing BIP113 (Median Time Past) using versionbits logic.
+    int nLockTimeFlags = 0;
+    if (VersionBitsState(pindexPrev, consensusParams, Consensus::DEPLOYMENT_CSV, versionbitscache) == THRESHOLD_ACTIVE) {
+        nLockTimeFlags |= LOCKTIME_MEDIAN_TIME_PAST;
+    }
+
+    int64_t nLockTimeCutoff = (nLockTimeFlags & LOCKTIME_MEDIAN_TIME_PAST)
+                              ? pindexPrev->GetMedianTimePast()
+                              : block.GetBlockTime();
 
     // Check that all transactions are finalized
-    BOOST_FOREACH(const CTransaction& tx, block.vtx)
-        if (!IsFinalTx(tx, nHeight, block.GetBlockTime())) {
-            return state.DoS(10, error("%s : contains a non-final transaction", __func__), REJECT_INVALID, "bad-txns-nonfinal");
+    BOOST_FOREACH(const CTransaction& tx, block.vtx) {
+        if (!IsFinalTx(tx, nHeight, nLockTimeCutoff)) {
+            return state.DoS(10, false, REJECT_INVALID, "bad-txns-nonfinal", false, "non-final transaction");
         }
+    }
 
     // Enforce block.nVersion=2 rule that the coinbase starts with serialized block height
     // if 750 of the last 1,000 blocks are version 2 or greater (51/100 if testnet):
-    if (block.nVersion >= 2 && 
-        CBlockIndex::IsSuperMajority(2, pindexPrev, Params().EnforceBlockUpgradeMajority()))
+    if (block.nVersion >= 2 && IsSuperMajority(2, pindexPrev, consensusParams.nMajorityEnforceBlockUpgrade, consensusParams))
     {
         CScript expect = CScript() << nHeight;
         if (block.vtx[0].vin[0].scriptSig.size() < expect.size() ||
             !std::equal(expect.begin(), expect.end(), block.vtx[0].vin[0].scriptSig.begin())) {
-            return state.DoS(100, error("%s : block height mismatch in coinbase", __func__), REJECT_INVALID, "bad-cb-height");
+            return state.DoS(100, false, REJECT_INVALID, "bad-cb-height", false, "block height mismatch in coinbase");
         }
     }
 
+    // Validation for witness commitments.
+    // * We compute the witness hash (which is the hash including witnesses) of all the block's transactions, except the
+    //   coinbase (where 0x0000....0000 is used instead).
+    // * The coinbase scriptWitness is a stack of a single 32-byte vector, containing a witness nonce (unconstrained).
+    // * We build a merkle tree with all those witness hashes as leaves (similar to the hashMerkleRoot in the block header).
+    // * There must be at least one output whose scriptPubKey is a single 36-byte push, the first 4 bytes of which are
+    //   {0xaa, 0x21, 0xa9, 0xed}, and the following 32 bytes are SHA256^2(witness root, witness nonce). In case there are
+    //   multiple, the last one is used.
+    bool fHaveWitness = false;
+    if (IsWitnessEnabled(pindexPrev, consensusParams)) {
+        int commitpos = GetWitnessCommitmentIndex(block);
+        if (commitpos != -1) {
+            bool malleated = false;
+            uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated);
+            // The malleation check is ignored; as the transaction tree itself
+            // already does not permit it, it is impossible to trigger in the
+            // witness tree.
+            if (block.vtx[0].wit.vtxinwit.size() != 1 || block.vtx[0].wit.vtxinwit[0].scriptWitness.stack.size() != 1 || block.vtx[0].wit.vtxinwit[0].scriptWitness.stack[0].size() != 32) {
+                return state.DoS(100, error("%s : invalid witness nonce size", __func__), REJECT_INVALID, "bad-witness-nonce-size", true);
+            }
+            CHash256().Write(hashWitness.begin(), 32).Write(&block.vtx[0].wit.vtxinwit[0].scriptWitness.stack[0][0], 32).Finalize(hashWitness.begin());
+            if (memcmp(hashWitness.begin(), &block.vtx[0].vout[commitpos].scriptPubKey[6], 32)) {
+                return state.DoS(100, error("%s : witness merkle commitment mismatch", __func__), REJECT_INVALID, "bad-witness-merkle-match", true);
+            }
+            fHaveWitness = true;
+        }
+    }
+
+    // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam
+    if (!fHaveWitness) {
+        for (size_t i = 0; i < block.vtx.size(); i++) {
+            if (!block.vtx[i].wit.IsNull()) {
+                return state.DoS(100, error("%s : unexpected witness data found", __func__), REJECT_INVALID, "unexpected-witness", true);
+            }
+        }
+    }
+
+    // After the coinbase witness nonce and commitment are verified,
+    // we can check if the block cost passes (before we've checked the
+    // coinbase witness, it would be possible for the cost to be too
+    // large by filling up the coinbase witness, which doesn't change
+    // the block hash, so we couldn't mark the block as permanently
+    // failed).
+    if (GetBlockCost(block) > MAX_BLOCK_COST) {
+        return state.DoS(100, error("ContextualCheckBlock(): cost limit failed"), REJECT_INVALID, "bad-blk-cost");
+    }
+
     return true;
 }
 
-bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBlockIndex** ppindex)
+static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex=NULL)
 {
     AssertLockHeld(cs_main);
     // Check for duplicate
     uint256 hash = block.GetHash();
     BlockMap::iterator miSelf = mapBlockIndex.find(hash);
     CBlockIndex *pindex = NULL;
-    if (miSelf != mapBlockIndex.end()) {
-        // Block header is already known.
-        pindex = miSelf->second;
-        if (ppindex)
-            *ppindex = pindex;
-        if (pindex->nStatus & BLOCK_FAILED_MASK)
-            return state.Invalid(error("%s : block is marked invalid", __func__), 0, "duplicate");
-        return true;
-    }
+    if (hash != chainparams.GetConsensus().hashGenesisBlock) {
+
+        if (miSelf != mapBlockIndex.end()) {
+            // Block header is already known.
+            pindex = miSelf->second;
+            if (ppindex)
+                *ppindex = pindex;
+            if (pindex->nStatus & BLOCK_FAILED_MASK)
+                return state.Invalid(error("%s: block %s is marked invalid", __func__, hash.ToString()), 0, "duplicate");
+            return true;
+        }
 
-    if (!CheckBlockHeader(block, state))
-        return false;
+        if (!CheckBlockHeader(block, state, chainparams.GetConsensus()))
+            return error("%s: Consensus::CheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
 
-    // Get prev block index
-    CBlockIndex* pindexPrev = NULL;
-    if (hash != Params().HashGenesisBlock()) {
+        // Get prev block index
+        CBlockIndex* pindexPrev = NULL;
         BlockMap::iterator mi = mapBlockIndex.find(block.hashPrevBlock);
         if (mi == mapBlockIndex.end())
-            return state.DoS(10, error("%s : prev block not found", __func__), 0, "bad-prevblk");
+            return state.DoS(10, error("%s: prev block not found", __func__), 0, "bad-prevblk");
         pindexPrev = (*mi).second;
-    }
+        if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
+            return state.DoS(100, error("%s: prev block invalid", __func__), REJECT_INVALID, "bad-prevblk");
 
-    if (!ContextualCheckBlockHeader(block, state, pindexPrev))
-        return false;
+        assert(pindexPrev);
+        if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, hash))
+            return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
 
+        if (!ContextualCheckBlockHeader(block, state, chainparams.GetConsensus(), pindexPrev, GetAdjustedTime()))
+            return error("%s: Consensus::ContextualCheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
+    }
     if (pindex == NULL)
         pindex = AddToBlockIndex(block);
 
@@ -2556,27 +3655,46 @@ bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBloc
     return true;
 }
 
-bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex, CDiskBlockPos* dbp)
+/** Store block on disk. If dbp is non-NULL, the file is known to already reside on disk */
+static bool AcceptBlock(const CBlock& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const CDiskBlockPos* dbp, bool* fNewBlock)
 {
+    if (fNewBlock) *fNewBlock = false;
     AssertLockHeld(cs_main);
 
-    CBlockIndex *&pindex = *ppindex;
+    CBlockIndex *pindexDummy = NULL;
+    CBlockIndex *&pindex = ppindex ? *ppindex : pindexDummy;
 
-    if (!AcceptBlockHeader(block, state, &pindex))
+    if (!AcceptBlockHeader(block, state, chainparams, &pindex))
         return false;
 
-    if (pindex->nStatus & BLOCK_HAVE_DATA) {
-        // TODO: deal better with duplicate blocks.
-        // return state.DoS(20, error("AcceptBlock() : already have block %d %s", pindex->nHeight, pindex->GetBlockHash().ToString()), REJECT_DUPLICATE, "duplicate");
-        return true;
-    }
-
-    if ((!CheckBlock(block, state)) || !ContextualCheckBlock(block, state, pindex->pprev)) {
+    // Try to process all requested blocks that we don't have, but only
+    // process an unrequested block if it's new and has enough work to
+    // advance our tip, and isn't too many blocks ahead.
+    bool fAlreadyHave = pindex->nStatus & BLOCK_HAVE_DATA;
+    bool fHasMoreWork = (chainActive.Tip() ? pindex->nChainWork > chainActive.Tip()->nChainWork : true);
+    // Blocks that are too out-of-order needlessly limit the effectiveness of
+    // pruning, because pruning will not delete block files that contain any
+    // blocks which are too close in height to the tip.  Apply this test
+    // regardless of whether pruning is enabled; it should generally be safe to
+    // not process unrequested blocks.
+    bool fTooFarAhead = (pindex->nHeight > int(chainActive.Height() + MIN_BLOCKS_TO_KEEP));
+
+    // TODO: deal better with return value and error conditions for duplicate
+    // and unrequested blocks.
+    if (fAlreadyHave) return true;
+    if (!fRequested) {  // If we didn't ask for it:
+        if (pindex->nTx != 0) return true;  // This is a previously-processed block that was pruned
+        if (!fHasMoreWork) return true;     // Don't process less-work chains
+        if (fTooFarAhead) return true;      // Block height is too high
+    }
+    if (fNewBlock) *fNewBlock = true;
+
+    if ((!CheckBlock(block, state, chainparams.GetConsensus(), GetAdjustedTime())) || !ContextualCheckBlock(block, state, pindex->pprev)) {
         if (state.IsInvalid() && !state.CorruptionPossible()) {
             pindex->nStatus |= BLOCK_FAILED_VALID;
             setDirtyBlockIndex.insert(pindex);
         }
-        return false;
+        return error("%s: %s", __func__, FormatStateMessage(state));
     }
 
     int nHeight = pindex->nHeight;
@@ -2588,24 +3706,26 @@ bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex,
         if (dbp != NULL)
             blockPos = *dbp;
         if (!FindBlockPos(state, blockPos, nBlockSize+8, nHeight, block.GetBlockTime(), dbp != NULL))
-            return error("AcceptBlock() : FindBlockPos failed");
+            return error("AcceptBlock(): FindBlockPos failed");
         if (dbp == NULL)
-            if (!WriteBlockToDisk(block, blockPos))
-                return state.Abort("Failed to write block");
+            if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart()))
+                AbortNode(state, "Failed to write block");
         if (!ReceivedBlockTransactions(block, state, pindex, blockPos))
-            return error("AcceptBlock() : ReceivedBlockTransactions failed");
-    } catch(std::runtime_error &e) {
-        return state.Abort(std::string("System error: ") + e.what());
+            return error("AcceptBlock(): ReceivedBlockTransactions failed");
+    } catch (const std::runtime_error& e) {
+        return AbortNode(state, std::string("System error: ") + e.what());
     }
 
+    if (fCheckForPruning)
+        FlushStateToDisk(state, FLUSH_STATE_NONE); // we just allocated more disk space for block files
+
     return true;
 }
 
-bool CBlockIndex::IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned int nRequired)
+static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned nRequired, const Consensus::Params& consensusParams)
 {
-    unsigned int nToCheck = Params().ToCheckBlockUpgradeMajority();
     unsigned int nFound = 0;
-    for (unsigned int i = 0; i < nToCheck && nFound < nRequired && pstart != NULL; i++)
+    for (int i = 0; i < consensusParams.nMajorityWindow && nFound < nRequired && pstart != NULL; i++)
     {
         if (pstart->nVersion >= minVersion)
             ++nFound;
@@ -2614,87 +3734,41 @@ bool CBlockIndex::IsSuperMajority(int minVersion, const CBlockIndex* pstart, uns
     return (nFound >= nRequired);
 }
 
-/** Turn the lowest '1' bit in the binary representation of a number into a '0'. */
-int static inline InvertLowestOne(int n) { return n & (n - 1); }
-
-/** Compute what height to jump back to with the CBlockIndex::pskip pointer. */
-int static inline GetSkipHeight(int height) {
-    if (height < 2)
-        return 0;
 
-    // Determine which height to jump back to. Any number strictly lower than height is acceptable,
-    // but the following expression seems to perform well in simulations (max 110 steps to go back
-    // up to 2**18 blocks).
-    return (height & 1) ? InvertLowestOne(InvertLowestOne(height - 1)) + 1 : InvertLowestOne(height);
-}
-
-CBlockIndex* CBlockIndex::GetAncestor(int height)
+bool ProcessNewBlock(CValidationState& state, const CChainParams& chainparams, CNode* pfrom, const CBlock* pblock, bool fForceProcessing, const CDiskBlockPos* dbp)
 {
-    if (height > nHeight || height < 0)
-        return NULL;
-
-    CBlockIndex* pindexWalk = this;
-    int heightWalk = nHeight;
-    while (heightWalk > height) {
-        int heightSkip = GetSkipHeight(heightWalk);
-        int heightSkipPrev = GetSkipHeight(heightWalk - 1);
-        if (heightSkip == height ||
-            (heightSkip > height && !(heightSkipPrev < heightSkip - 2 &&
-                                      heightSkipPrev >= height))) {
-            // Only follow pskip if pprev->pskip isn't better than pskip->pprev.
-            pindexWalk = pindexWalk->pskip;
-            heightWalk = heightSkip;
-        } else {
-            pindexWalk = pindexWalk->pprev;
-            heightWalk--;
-        }
-    }
-    return pindexWalk;
-}
-
-const CBlockIndex* CBlockIndex::GetAncestor(int height) const
-{
-    return const_cast<CBlockIndex*>(this)->GetAncestor(height);
-}
-
-void CBlockIndex::BuildSkip()
-{
-    if (pprev)
-        pskip = pprev->GetAncestor(GetSkipHeight(nHeight));
-}
-
-bool ProcessNewBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBlockPos *dbp)
-{
-    // Preliminary checks
-    bool checked = CheckBlock(*pblock, state);
-
     {
         LOCK(cs_main);
-        MarkBlockAsReceived(pblock->GetHash());
-        if (!checked) {
-            return error("%s : CheckBlock FAILED", __func__);
-        }
+        bool fRequested = MarkBlockAsReceived(pblock->GetHash());
+        fRequested |= fForceProcessing;
 
         // Store to disk
         CBlockIndex *pindex = NULL;
-        bool ret = AcceptBlock(*pblock, state, &pindex, dbp);
+        bool fNewBlock = false;
+        bool ret = AcceptBlock(*pblock, state, chainparams, &pindex, fRequested, dbp, &fNewBlock);
         if (pindex && pfrom) {
             mapBlockSource[pindex->GetBlockHash()] = pfrom->GetId();
+            if (fNewBlock) pfrom->nLastBlockTime = GetTime();
         }
+        CheckBlockIndex(chainparams.GetConsensus());
         if (!ret)
-            return error("%s : AcceptBlock FAILED", __func__);
+            return error("%s: AcceptBlock FAILED", __func__);
     }
 
-    if (!ActivateBestChain(state, pblock))
-        return error("%s : ActivateBestChain failed", __func__);
+    NotifyHeaderTip();
+
+    if (!ActivateBestChain(state, chainparams, pblock))
+        return error("%s: ActivateBestChain failed", __func__);
 
     return true;
 }
 
-bool TestBlockValidity(CValidationState &state, const CBlock& block, CBlockIndex * const pindexPrev, bool fCheckPOW, bool fCheckMerkleRoot)
+bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW, bool fCheckMerkleRoot)
 {
     AssertLockHeld(cs_main);
-    assert(pindexPrev == chainActive.Tip());
+    assert(pindexPrev && pindexPrev == chainActive.Tip());
+    if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, block.GetHash()))
+        return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
 
     CCoinsViewCache viewNew(pcoinsTip);
     CBlockIndex indexDummy(block);
@@ -2702,39 +3776,127 @@ bool TestBlockValidity(CValidationState &state, const CBlock& block, CBlockIndex
     indexDummy.nHeight = pindexPrev->nHeight + 1;
 
     // NOTE: CheckBlockHeader is called by CheckBlock
-    if (!ContextualCheckBlockHeader(block, state, pindexPrev))
-        return false;
-    if (!CheckBlock(block, state, fCheckPOW, fCheckMerkleRoot))
-        return false;
+    if (!ContextualCheckBlockHeader(block, state, chainparams.GetConsensus(), pindexPrev, GetAdjustedTime()))
+        return error("%s: Consensus::ContextualCheckBlockHeader: %s", __func__, FormatStateMessage(state));
+    if (!CheckBlock(block, state, chainparams.GetConsensus(), fCheckPOW, fCheckMerkleRoot))
+        return error("%s: Consensus::CheckBlock: %s", __func__, FormatStateMessage(state));
     if (!ContextualCheckBlock(block, state, pindexPrev))
-        return false;
-    if (!ConnectBlock(block, state, &indexDummy, viewNew, true))
+        return error("%s: Consensus::ContextualCheckBlock: %s", __func__, FormatStateMessage(state));
+    if (!ConnectBlock(block, state, &indexDummy, viewNew, chainparams, true))
         return false;
     assert(state.IsValid());
 
     return true;
 }
 
+/**
+ * BLOCK PRUNING CODE
+ */
 
+/* Calculate the amount of disk space the block & undo files currently use */
+uint64_t CalculateCurrentUsage()
+{
+    uint64_t retval = 0;
+    BOOST_FOREACH(const CBlockFileInfo &file, vinfoBlockFile) {
+        retval += file.nSize + file.nUndoSize;
+    }
+    return retval;
+}
 
+/* Prune a block file (modify associated database entries)*/
+void PruneOneBlockFile(const int fileNumber)
+{
+    for (BlockMap::iterator it = mapBlockIndex.begin(); it != mapBlockIndex.end(); ++it) {
+        CBlockIndex* pindex = it->second;
+        if (pindex->nFile == fileNumber) {
+            pindex->nStatus &= ~BLOCK_HAVE_DATA;
+            pindex->nStatus &= ~BLOCK_HAVE_UNDO;
+            pindex->nFile = 0;
+            pindex->nDataPos = 0;
+            pindex->nUndoPos = 0;
+            setDirtyBlockIndex.insert(pindex);
 
+            // Prune from mapBlocksUnlinked -- any block we prune would have
+            // to be downloaded again in order to consider its chain, at which
+            // point it would be considered as a candidate for
+            // mapBlocksUnlinked or setBlockIndexCandidates.
+            std::pair<std::multimap<CBlockIndex*, CBlockIndex*>::iterator, std::multimap<CBlockIndex*, CBlockIndex*>::iterator> range = mapBlocksUnlinked.equal_range(pindex->pprev);
+            while (range.first != range.second) {
+                std::multimap<CBlockIndex *, CBlockIndex *>::iterator it = range.first;
+                range.first++;
+                if (it->second == pindex) {
+                    mapBlocksUnlinked.erase(it);
+                }
+            }
+        }
+    }
 
+    vinfoBlockFile[fileNumber].SetNull();
+    setDirtyFileInfo.insert(fileNumber);
+}
 
 
+void UnlinkPrunedFiles(std::set<int>& setFilesToPrune)
+{
+    for (set<int>::iterator it = setFilesToPrune.begin(); it != setFilesToPrune.end(); ++it) {
+        CDiskBlockPos pos(*it, 0);
+        boost::filesystem::remove(GetBlockPosFilename(pos, "blk"));
+        boost::filesystem::remove(GetBlockPosFilename(pos, "rev"));
+        LogPrintf("Prune: %s deleted blk/rev (%05u)\n", __func__, *it);
+    }
+}
 
-bool AbortNode(const std::string &strMessage, const std::string &userMessage) {
-    strMiscWarning = strMessage;
-    LogPrintf("*** %s\n", strMessage);
-    uiInterface.ThreadSafeMessageBox(
-        userMessage.empty() ? _("Error: A fatal internal error occured, see debug.log for details") : userMessage,
-        "", CClientUIInterface::MSG_ERROR);
-    StartShutdown();
-    return false;
+/* Calculate the block/rev files that should be deleted to remain under target*/
+void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight)
+{
+    LOCK2(cs_main, cs_LastBlockFile);
+    if (chainActive.Tip() == NULL || nPruneTarget == 0) {
+        return;
+    }
+    if ((uint64_t)chainActive.Tip()->nHeight <= nPruneAfterHeight) {
+        return;
+    }
+
+    unsigned int nLastBlockWeCanPrune = chainActive.Tip()->nHeight - MIN_BLOCKS_TO_KEEP;
+    uint64_t nCurrentUsage = CalculateCurrentUsage();
+    // We don't check to prune until after we've allocated new space for files
+    // So we should leave a buffer under our target to account for another allocation
+    // before the next pruning.
+    uint64_t nBuffer = BLOCKFILE_CHUNK_SIZE + UNDOFILE_CHUNK_SIZE;
+    uint64_t nBytesToPrune;
+    int count=0;
+
+    if (nCurrentUsage + nBuffer >= nPruneTarget) {
+        for (int fileNumber = 0; fileNumber < nLastBlockFile; fileNumber++) {
+            nBytesToPrune = vinfoBlockFile[fileNumber].nSize + vinfoBlockFile[fileNumber].nUndoSize;
+
+            if (vinfoBlockFile[fileNumber].nSize == 0)
+                continue;
+
+            if (nCurrentUsage + nBuffer < nPruneTarget)  // are we below our target?
+                break;
+
+            // don't prune files that could have a block within MIN_BLOCKS_TO_KEEP of the main chain's tip but keep scanning
+            if (vinfoBlockFile[fileNumber].nHeightLast > nLastBlockWeCanPrune)
+                continue;
+
+            PruneOneBlockFile(fileNumber);
+            // Queue up the files for removal
+            setFilesToPrune.insert(fileNumber);
+            nCurrentUsage -= nBytesToPrune;
+            count++;
+        }
+    }
+
+    LogPrint("prune", "Prune: target=%dMiB actual=%dMiB diff=%dMiB max_prune_height=%d removed %d blk/rev pairs\n",
+           nPruneTarget/1024/1024, nCurrentUsage/1024/1024,
+           ((int64_t)nPruneTarget - (int64_t)nCurrentUsage)/1024/1024,
+           nLastBlockWeCanPrune, count);
 }
 
 bool CheckDiskSpace(uint64_t nAdditionalBytes)
 {
-    uint64_t nFreeBytesAvailable = filesystem::space(GetDataDir()).available;
+    uint64_t nFreeBytesAvailable = boost::filesystem::space(GetDataDir()).available;
 
     // Check for nMinDiskSpace bytes (currently 50MB)
     if (nFreeBytesAvailable < nMinDiskSpace + nAdditionalBytes)
@@ -2781,7 +3943,7 @@ boost::filesystem::path GetBlockPosFilename(const CDiskBlockPos &pos, const char
 
 CBlockIndex * InsertBlockIndex(uint256 hash)
 {
-    if (hash == 0)
+    if (hash.IsNull())
         return NULL;
 
     // Return existing
@@ -2792,7 +3954,7 @@ CBlockIndex * InsertBlockIndex(uint256 hash)
     // Create new
     CBlockIndex* pindexNew = new CBlockIndex();
     if (!pindexNew)
-        throw runtime_error("LoadBlockIndex() : new CBlockIndex failed");
+        throw runtime_error("LoadBlockIndex(): new CBlockIndex failed");
     mi = mapBlockIndex.insert(make_pair(hash, pindexNew)).first;
     pindexNew->phashBlock = &((*mi).first);
 
@@ -2801,7 +3963,8 @@ CBlockIndex * InsertBlockIndex(uint256 hash)
 
 bool static LoadBlockIndexDB()
 {
-    if (!pblocktree->LoadBlockIndexGuts())
+    const CChainParams& chainparams = Params();
+    if (!pblocktree->LoadBlockIndexGuts(InsertBlockIndex))
         return false;
 
     boost::this_thread::interruption_point();
@@ -2819,7 +3982,9 @@ bool static LoadBlockIndexDB()
     {
         CBlockIndex* pindex = item.second;
         pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + GetBlockProof(*pindex);
-        if (pindex->nStatus & BLOCK_HAVE_DATA) {
+        // We can link the chain of blocks for which we've received transactions at some point.
+        // Pruned nodes may have deleted the block.
+        if (pindex->nTx > 0) {
             if (pindex->pprev) {
                 if (pindex->pprev->nChainTx) {
                     pindex->nChainTx = pindex->pprev->nChainTx + pindex->nTx;
@@ -2876,6 +4041,11 @@ bool static LoadBlockIndexDB()
         }
     }
 
+    // Check whether we have ever pruned block & undo files
+    pblocktree->ReadFlag("prunedblockfiles", fHavePruned);
+    if (fHavePruned)
+        LogPrintf("LoadBlockIndexDB(): Block files have previously been pruned\n");
+
     // Check whether we need to continue reindexing
     bool fReindexing = false;
     pblocktree->ReadReindexing(fReindexing);
@@ -2883,7 +4053,7 @@ bool static LoadBlockIndexDB()
 
     // Check whether we have a transaction index
     pblocktree->ReadFlag("txindex", fTxIndex);
-    LogPrintf("LoadBlockIndexDB(): transaction index %s\n", fTxIndex ? "enabled" : "disabled");
+    LogPrintf("%s: transaction index %s\n", __func__, fTxIndex ? "enabled" : "disabled");
 
     // Load pointer to end of best chain
     BlockMap::iterator it = mapBlockIndex.find(pcoinsTip->GetBestBlock());
@@ -2893,10 +4063,10 @@ bool static LoadBlockIndexDB()
 
     PruneBlockIndexCandidates();
 
-    LogPrintf("LoadBlockIndexDB(): hashBestChain=%s height=%d date=%s progress=%f\n",
+    LogPrintf("%s: hashBestChain=%s height=%d date=%s progress=%f\n", __func__,
         chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(),
         DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()),
-        Checkpoints::GuessVerificationProgress(chainActive.Tip()));
+        Checkpoints::GuessVerificationProgress(chainparams.Checkpoints(), chainActive.Tip()));
 
     return true;
 }
@@ -2911,7 +4081,7 @@ CVerifyDB::~CVerifyDB()
     uiInterface.ShowProgress("", 100);
 }
 
-bool CVerifyDB::VerifyDB(CCoinsView *coinsview, int nCheckLevel, int nCheckDepth)
+bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview, int nCheckLevel, int nCheckDepth)
 {
     LOCK(cs_main);
     if (chainActive.Tip() == NULL || chainActive.Tip()->pprev == NULL)
@@ -2929,33 +4099,47 @@ bool CVerifyDB::VerifyDB(CCoinsView *coinsview, int nCheckLevel, int nCheckDepth
     CBlockIndex* pindexFailure = NULL;
     int nGoodTransactions = 0;
     CValidationState state;
+    int reportDone = 0;
+    LogPrintf("[0%]...");
     for (CBlockIndex* pindex = chainActive.Tip(); pindex && pindex->pprev; pindex = pindex->pprev)
     {
         boost::this_thread::interruption_point();
-        uiInterface.ShowProgress(_("Verifying blocks..."), std::max(1, std::min(99, (int)(((double)(chainActive.Height() - pindex->nHeight)) / (double)nCheckDepth * (nCheckLevel >= 4 ? 50 : 100)))));
+        int percentageDone = std::max(1, std::min(99, (int)(((double)(chainActive.Height() - pindex->nHeight)) / (double)nCheckDepth * (nCheckLevel >= 4 ? 50 : 100))));
+        if (reportDone < percentageDone/10) {
+            // report every 10% step
+            LogPrintf("[%d%%]...", percentageDone);
+            reportDone = percentageDone/10;
+        }
+        uiInterface.ShowProgress(_("Verifying blocks..."), percentageDone);
         if (pindex->nHeight < chainActive.Height()-nCheckDepth)
             break;
+        if (fPruneMode && !(pindex->nStatus & BLOCK_HAVE_DATA)) {
+            // If pruning, only go back as far as we have data.
+            LogPrintf("VerifyDB(): block verification stopping at height %d (pruning, no data)\n", pindex->nHeight);
+            break;
+        }
         CBlock block;
         // check level 0: read from disk
-        if (!ReadBlockFromDisk(block, pindex))
-            return error("VerifyDB() : *** ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
+        if (!ReadBlockFromDisk(block, pindex, chainparams.GetConsensus()))
+            return error("VerifyDB(): *** ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
         // check level 1: verify block validity
-        if (nCheckLevel >= 1 && !CheckBlock(block, state))
-            return error("VerifyDB() : *** found bad block at %d, hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
+        if (nCheckLevel >= 1 && !CheckBlock(block, state, chainparams.GetConsensus()))
+            return error("%s: *** found bad block at %d, hash=%s (%s)\n", __func__, 
+                         pindex->nHeight, pindex->GetBlockHash().ToString(), FormatStateMessage(state));
         // check level 2: verify undo validity
         if (nCheckLevel >= 2 && pindex) {
             CBlockUndo undo;
             CDiskBlockPos pos = pindex->GetUndoPos();
             if (!pos.IsNull()) {
-                if (!undo.ReadFromDisk(pos, pindex->pprev->GetBlockHash()))
-                    return error("VerifyDB() : *** found bad undo data at %d, hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
+                if (!UndoReadFromDisk(undo, pos, pindex->pprev->GetBlockHash()))
+                    return error("VerifyDB(): *** found bad undo data at %d, hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
             }
         }
         // check level 3: check for inconsistencies during memory-only disconnect of tip blocks
-        if (nCheckLevel >= 3 && pindex == pindexState && (coins.GetCacheSize() + pcoinsTip->GetCacheSize()) <= nCoinCacheSize) {
+        if (nCheckLevel >= 3 && pindex == pindexState && (coins.DynamicMemoryUsage() + pcoinsTip->DynamicMemoryUsage()) <= nCoinCacheUsage) {
             bool fClean = true;
             if (!DisconnectBlock(block, state, pindex, coins, &fClean))
-                return error("VerifyDB() : *** irrecoverable inconsistency in block data at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
+                return error("VerifyDB(): *** irrecoverable inconsistency in block data at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
             pindexState = pindex->pprev;
             if (!fClean) {
                 nGoodTransactions = 0;
@@ -2963,9 +4147,11 @@ bool CVerifyDB::VerifyDB(CCoinsView *coinsview, int nCheckLevel, int nCheckDepth
             } else
                 nGoodTransactions += block.vtx.size();
         }
+        if (ShutdownRequested())
+            return true;
     }
     if (pindexFailure)
-        return error("VerifyDB() : *** coin database inconsistencies found (last %i blocks, %i good transactions before that)\n", chainActive.Height() - pindexFailure->nHeight + 1, nGoodTransactions);
+        return error("VerifyDB(): *** coin database inconsistencies found (last %i blocks, %i good transactions before that)\n", chainActive.Height() - pindexFailure->nHeight + 1, nGoodTransactions);
 
     // check level 4: try reconnecting blocks
     if (nCheckLevel >= 4) {
@@ -2975,24 +4161,135 @@ bool CVerifyDB::VerifyDB(CCoinsView *coinsview, int nCheckLevel, int nCheckDepth
             uiInterface.ShowProgress(_("Verifying blocks..."), std::max(1, std::min(99, 100 - (int)(((double)(chainActive.Height() - pindex->nHeight)) / (double)nCheckDepth * 50))));
             pindex = chainActive.Next(pindex);
             CBlock block;
-            if (!ReadBlockFromDisk(block, pindex))
-                return error("VerifyDB() : *** ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
-            if (!ConnectBlock(block, state, pindex, coins))
-                return error("VerifyDB() : *** found unconnectable block at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
+            if (!ReadBlockFromDisk(block, pindex, chainparams.GetConsensus()))
+                return error("VerifyDB(): *** ReadBlockFromDisk failed at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
+            if (!ConnectBlock(block, state, pindex, coins, chainparams))
+                return error("VerifyDB(): *** found unconnectable block at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
         }
     }
 
+    LogPrintf("[DONE].\n");
     LogPrintf("No coin database inconsistencies in last %i blocks (%i transactions)\n", chainActive.Height() - pindexState->nHeight, nGoodTransactions);
 
     return true;
 }
 
+bool RewindBlockIndex(const CChainParams& params)
+{
+    LOCK(cs_main);
+
+    int nHeight = 1;
+    while (nHeight <= chainActive.Height()) {
+        if (IsWitnessEnabled(chainActive[nHeight - 1], params.GetConsensus()) && !(chainActive[nHeight]->nStatus & BLOCK_OPT_WITNESS)) {
+            break;
+        }
+        nHeight++;
+    }
+
+    // nHeight is now the height of the first insufficiently-validated block, or tipheight + 1
+    CValidationState state;
+    CBlockIndex* pindex = chainActive.Tip();
+    while (chainActive.Height() >= nHeight) {
+        if (fPruneMode && !(chainActive.Tip()->nStatus & BLOCK_HAVE_DATA)) {
+            // If pruning, don't try rewinding past the HAVE_DATA point;
+            // since older blocks can't be served anyway, there's
+            // no need to walk further, and trying to DisconnectTip()
+            // will fail (and require a needless reindex/redownload
+            // of the blockchain).
+            break;
+        }
+        if (!DisconnectTip(state, params, true)) {
+            return error("RewindBlockIndex: unable to disconnect block at height %i", pindex->nHeight);
+        }
+        // Occasionally flush state to disk.
+        if (!FlushStateToDisk(state, FLUSH_STATE_PERIODIC))
+            return false;
+    }
+
+    // Reduce validity flag and have-data flags.
+    // We do this after actual disconnecting, otherwise we'll end up writing the lack of data
+    // to disk before writing the chainstate, resulting in a failure to continue if interrupted.
+    for (BlockMap::iterator it = mapBlockIndex.begin(); it != mapBlockIndex.end(); it++) {
+        CBlockIndex* pindexIter = it->second;
+
+        // Note: If we encounter an insufficiently validated block that
+        // is on chainActive, it must be because we are a pruning node, and
+        // this block or some successor doesn't HAVE_DATA, so we were unable to
+        // rewind all the way.  Blocks remaining on chainActive at this point
+        // must not have their validity reduced.
+        if (IsWitnessEnabled(pindexIter->pprev, params.GetConsensus()) && !(pindexIter->nStatus & BLOCK_OPT_WITNESS) && !chainActive.Contains(pindexIter)) {
+            // Reduce validity
+            pindexIter->nStatus = std::min<unsigned int>(pindexIter->nStatus & BLOCK_VALID_MASK, BLOCK_VALID_TREE) | (pindexIter->nStatus & ~BLOCK_VALID_MASK);
+            // Remove have-data flags.
+            pindexIter->nStatus &= ~(BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO);
+            // Remove storage location.
+            pindexIter->nFile = 0;
+            pindexIter->nDataPos = 0;
+            pindexIter->nUndoPos = 0;
+            // Remove various other things
+            pindexIter->nTx = 0;
+            pindexIter->nChainTx = 0;
+            pindexIter->nSequenceId = 0;
+            // Make sure it gets written.
+            setDirtyBlockIndex.insert(pindexIter);
+            // Update indexes
+            setBlockIndexCandidates.erase(pindexIter);
+            std::pair<std::multimap<CBlockIndex*, CBlockIndex*>::iterator, std::multimap<CBlockIndex*, CBlockIndex*>::iterator> ret = mapBlocksUnlinked.equal_range(pindexIter->pprev);
+            while (ret.first != ret.second) {
+                if (ret.first->second == pindexIter) {
+                    mapBlocksUnlinked.erase(ret.first++);
+                } else {
+                    ++ret.first;
+                }
+            }
+        } else if (pindexIter->IsValid(BLOCK_VALID_TRANSACTIONS) && pindexIter->nChainTx) {
+            setBlockIndexCandidates.insert(pindexIter);
+        }
+    }
+
+    PruneBlockIndexCandidates();
+
+    CheckBlockIndex(params.GetConsensus());
+
+    if (!FlushStateToDisk(state, FLUSH_STATE_ALWAYS)) {
+        return false;
+    }
+
+    return true;
+}
+
 void UnloadBlockIndex()
 {
-    mapBlockIndex.clear();
+    LOCK(cs_main);
     setBlockIndexCandidates.clear();
     chainActive.SetTip(NULL);
     pindexBestInvalid = NULL;
+    pindexBestHeader = NULL;
+    mempool.clear();
+    mapOrphanTransactions.clear();
+    mapOrphanTransactionsByPrev.clear();
+    nSyncStarted = 0;
+    mapBlocksUnlinked.clear();
+    vinfoBlockFile.clear();
+    nLastBlockFile = 0;
+    nBlockSequenceId = 1;
+    mapBlockSource.clear();
+    mapBlocksInFlight.clear();
+    nPreferredDownload = 0;
+    setDirtyBlockIndex.clear();
+    setDirtyFileInfo.clear();
+    mapNodeState.clear();
+    recentRejects.reset(NULL);
+    versionbitscache.Clear();
+    for (int b = 0; b < VERSIONBITS_NUM_BITS; b++) {
+        warningcache[b].clear();
+    }
+
+    BOOST_FOREACH(BlockMap::value_type& entry, mapBlockIndex) {
+        delete entry.second;
+    }
+    mapBlockIndex.clear();
+    fHavePruned = false;
 }
 
 bool LoadBlockIndex()
@@ -3003,48 +4300,50 @@ bool LoadBlockIndex()
     return true;
 }
 
-
-bool InitBlockIndex() {
+bool InitBlockIndex(const CChainParams& chainparams) 
+{
     LOCK(cs_main);
+
+    // Initialize global variables that cannot be constructed at startup.
+    recentRejects.reset(new CRollingBloomFilter(120000, 0.000001));
+
     // Check whether we're already initialized
     if (chainActive.Genesis() != NULL)
         return true;
 
     // Use the provided setting for -txindex in the new database
-    fTxIndex = GetBoolArg("-txindex", false);
+    fTxIndex = GetBoolArg("-txindex", DEFAULT_TXINDEX);
     pblocktree->WriteFlag("txindex", fTxIndex);
     LogPrintf("Initializing databases...\n");
 
     // Only add the genesis block if not reindexing (in which case we reuse the one already on disk)
     if (!fReindex) {
         try {
-            CBlock &block = const_cast<CBlock&>(Params().GenesisBlock());
+            CBlock &block = const_cast<CBlock&>(chainparams.GenesisBlock());
             // Start new block file
             unsigned int nBlockSize = ::GetSerializeSize(block, SER_DISK, CLIENT_VERSION);
             CDiskBlockPos blockPos;
             CValidationState state;
             if (!FindBlockPos(state, blockPos, nBlockSize+8, 0, block.GetBlockTime()))
-                return error("LoadBlockIndex() : FindBlockPos failed");
-            if (!WriteBlockToDisk(block, blockPos))
-                return error("LoadBlockIndex() : writing genesis block to disk failed");
+                return error("LoadBlockIndex(): FindBlockPos failed");
+            if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart()))
+                return error("LoadBlockIndex(): writing genesis block to disk failed");
             CBlockIndex *pindex = AddToBlockIndex(block);
             if (!ReceivedBlockTransactions(block, state, pindex, blockPos))
-                return error("LoadBlockIndex() : genesis block not accepted");
-            if (!ActivateBestChain(state, &block))
-                return error("LoadBlockIndex() : genesis block cannot be activated");
-            // Force a chainstate write so that when we VerifyDB in a moment, it doesnt check stale data
+                return error("LoadBlockIndex(): genesis block not accepted");
+            if (!ActivateBestChain(state, chainparams, &block))
+                return error("LoadBlockIndex(): genesis block cannot be activated");
+            // Force a chainstate write so that when we VerifyDB in a moment, it doesn't check stale data
             return FlushStateToDisk(state, FLUSH_STATE_ALWAYS);
-        } catch(std::runtime_error &e) {
-            return error("LoadBlockIndex() : failed to initialize block database: %s", e.what());
+        } catch (const std::runtime_error& e) {
+            return error("LoadBlockIndex(): failed to initialize block database: %s", e.what());
         }
     }
 
     return true;
 }
 
-
-
-bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
+bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, CDiskBlockPos *dbp)
 {
     // Map of disk positions for blocks with unknown parent (only used for reindex)
     static std::multimap<uint256, CDiskBlockPos> mapBlocksUnknownParent;
@@ -3053,7 +4352,7 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
     int nLoaded = 0;
     try {
         // This takes over fileIn and calls fclose() on it in the CBufferedFile destructor
-        CBufferedFile blkdat(fileIn, 2*MAX_BLOCK_SIZE, MAX_BLOCK_SIZE+8, SER_DISK, CLIENT_VERSION);
+        CBufferedFile blkdat(fileIn, 2*MAX_BLOCK_SERIALIZED_SIZE, MAX_BLOCK_SERIALIZED_SIZE+8, SER_DISK, CLIENT_VERSION);
         uint64_t nRewind = blkdat.GetPos();
         while (!blkdat.eof()) {
             boost::this_thread::interruption_point();
@@ -3065,16 +4364,16 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
             try {
                 // locate a header
                 unsigned char buf[MESSAGE_START_SIZE];
-                blkdat.FindByte(Params().MessageStart()[0]);
+                blkdat.FindByte(chainparams.MessageStart()[0]);
                 nRewind = blkdat.GetPos()+1;
                 blkdat >> FLATDATA(buf);
-                if (memcmp(buf, Params().MessageStart(), MESSAGE_START_SIZE))
+                if (memcmp(buf, chainparams.MessageStart(), MESSAGE_START_SIZE))
                     continue;
                 // read size
                 blkdat >> nSize;
-                if (nSize < 80 || nSize > MAX_BLOCK_SIZE)
+                if (nSize < 80 || nSize > MAX_BLOCK_SERIALIZED_SIZE)
                     continue;
-            } catch (const std::exception &) {
+            } catch (const std::exception&) {
                 // no valid block header found; don't complain
                 break;
             }
@@ -3091,7 +4390,7 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
 
                 // detect out of order blocks, and store them for later
                 uint256 hash = block.GetHash();
-                if (hash != Params().HashGenesisBlock() && mapBlockIndex.find(block.hashPrevBlock) == mapBlockIndex.end()) {
+                if (hash != chainparams.GetConsensus().hashGenesisBlock && mapBlockIndex.find(block.hashPrevBlock) == mapBlockIndex.end()) {
                     LogPrint("reindex", "%s: Out of order block %s, parent %s not known\n", __func__, hash.ToString(),
                             block.hashPrevBlock.ToString());
                     if (dbp)
@@ -3101,15 +4400,26 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
 
                 // process in case the block isn't known yet
                 if (mapBlockIndex.count(hash) == 0 || (mapBlockIndex[hash]->nStatus & BLOCK_HAVE_DATA) == 0) {
+                    LOCK(cs_main);
                     CValidationState state;
-                    if (ProcessNewBlock(state, NULL, &block, dbp))
+                    if (AcceptBlock(block, state, chainparams, NULL, true, dbp, NULL))
                         nLoaded++;
                     if (state.IsError())
                         break;
-                } else if (hash != Params().HashGenesisBlock() && mapBlockIndex[hash]->nHeight % 1000 == 0) {
-                    LogPrintf("Block Import: already had block %s at height %d\n", hash.ToString(), mapBlockIndex[hash]->nHeight);
+                } else if (hash != chainparams.GetConsensus().hashGenesisBlock && mapBlockIndex[hash]->nHeight % 1000 == 0) {
+                    LogPrint("reindex", "Block Import: already had block %s at height %d\n", hash.ToString(), mapBlockIndex[hash]->nHeight);
                 }
 
+                // Activate the genesis block so normal node progress can continue
+                if (hash == chainparams.GetConsensus().hashGenesisBlock) {
+                    CValidationState state;
+                    if (!ActivateBestChain(state, chainparams)) {
+                        break;
+                    }
+                }
+
+                NotifyHeaderTip();
+
                 // Recursively process earlier encountered successors of this block
                 deque<uint256> queue;
                 queue.push_back(hash);
@@ -3119,12 +4429,13 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
                     std::pair<std::multimap<uint256, CDiskBlockPos>::iterator, std::multimap<uint256, CDiskBlockPos>::iterator> range = mapBlocksUnknownParent.equal_range(head);
                     while (range.first != range.second) {
                         std::multimap<uint256, CDiskBlockPos>::iterator it = range.first;
-                        if (ReadBlockFromDisk(block, it->second))
+                        if (ReadBlockFromDisk(block, it->second, chainparams.GetConsensus()))
                         {
-                            LogPrintf("%s: Processing out of order child %s of %s\n", __func__, block.GetHash().ToString(),
+                            LogPrint("reindex", "%s: Processing out of order child %s of %s\n", __func__, block.GetHash().ToString(),
                                     head.ToString());
+                            LOCK(cs_main);
                             CValidationState dummy;
-                            if (ProcessNewBlock(dummy, NULL, &block, &it->second))
+                            if (AcceptBlock(block, dummy, chainparams, NULL, true, &it->second, NULL))
                             {
                                 nLoaded++;
                                 queue.push_back(block.GetHash());
@@ -3132,13 +4443,14 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
                         }
                         range.first++;
                         mapBlocksUnknownParent.erase(it);
+                        NotifyHeaderTip();
                     }
                 }
-            } catch (std::exception &e) {
-                LogPrintf("%s : Deserialize or I/O error - %s", __func__, e.what());
+            } catch (const std::exception& e) {
+                LogPrintf("%s: Deserialize or I/O error - %s\n", __func__, e.what());
             }
         }
-    } catch(std::runtime_error &e) {
+    } catch (const std::runtime_error& e) {
         AbortNode(std::string("System error: ") + e.what());
     }
     if (nLoaded > 0)
@@ -3146,60 +4458,228 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
     return nLoaded > 0;
 }
 
-//////////////////////////////////////////////////////////////////////////////
-//
-// CAlert
-//
+void static CheckBlockIndex(const Consensus::Params& consensusParams)
+{
+    if (!fCheckBlockIndex) {
+        return;
+    }
+
+    LOCK(cs_main);
+
+    // During a reindex, we read the genesis block and call CheckBlockIndex before ActivateBestChain,
+    // so we have the genesis block in mapBlockIndex but no active chain.  (A few of the tests when
+    // iterating the block tree require that chainActive has been initialized.)
+    if (chainActive.Height() < 0) {
+        assert(mapBlockIndex.size() <= 1);
+        return;
+    }
+
+    // Build forward-pointing map of the entire block tree.
+    std::multimap<CBlockIndex*,CBlockIndex*> forward;
+    for (BlockMap::iterator it = mapBlockIndex.begin(); it != mapBlockIndex.end(); it++) {
+        forward.insert(std::make_pair(it->second->pprev, it->second));
+    }
+
+    assert(forward.size() == mapBlockIndex.size());
+
+    std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> rangeGenesis = forward.equal_range(NULL);
+    CBlockIndex *pindex = rangeGenesis.first->second;
+    rangeGenesis.first++;
+    assert(rangeGenesis.first == rangeGenesis.second); // There is only one index entry with parent NULL.
+
+    // Iterate over the entire block tree, using depth-first search.
+    // Along the way, remember whether there are blocks on the path from genesis
+    // block being explored which are the first to have certain properties.
+    size_t nNodes = 0;
+    int nHeight = 0;
+    CBlockIndex* pindexFirstInvalid = NULL; // Oldest ancestor of pindex which is invalid.
+    CBlockIndex* pindexFirstMissing = NULL; // Oldest ancestor of pindex which does not have BLOCK_HAVE_DATA.
+    CBlockIndex* pindexFirstNeverProcessed = NULL; // Oldest ancestor of pindex for which nTx == 0.
+    CBlockIndex* pindexFirstNotTreeValid = NULL; // Oldest ancestor of pindex which does not have BLOCK_VALID_TREE (regardless of being valid or not).
+    CBlockIndex* pindexFirstNotTransactionsValid = NULL; // Oldest ancestor of pindex which does not have BLOCK_VALID_TRANSACTIONS (regardless of being valid or not).
+    CBlockIndex* pindexFirstNotChainValid = NULL; // Oldest ancestor of pindex which does not have BLOCK_VALID_CHAIN (regardless of being valid or not).
+    CBlockIndex* pindexFirstNotScriptsValid = NULL; // Oldest ancestor of pindex which does not have BLOCK_VALID_SCRIPTS (regardless of being valid or not).
+    while (pindex != NULL) {
+        nNodes++;
+        if (pindexFirstInvalid == NULL && pindex->nStatus & BLOCK_FAILED_VALID) pindexFirstInvalid = pindex;
+        if (pindexFirstMissing == NULL && !(pindex->nStatus & BLOCK_HAVE_DATA)) pindexFirstMissing = pindex;
+        if (pindexFirstNeverProcessed == NULL && pindex->nTx == 0) pindexFirstNeverProcessed = pindex;
+        if (pindex->pprev != NULL && pindexFirstNotTreeValid == NULL && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_TREE) pindexFirstNotTreeValid = pindex;
+        if (pindex->pprev != NULL && pindexFirstNotTransactionsValid == NULL && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_TRANSACTIONS) pindexFirstNotTransactionsValid = pindex;
+        if (pindex->pprev != NULL && pindexFirstNotChainValid == NULL && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_CHAIN) pindexFirstNotChainValid = pindex;
+        if (pindex->pprev != NULL && pindexFirstNotScriptsValid == NULL && (pindex->nStatus & BLOCK_VALID_MASK) < BLOCK_VALID_SCRIPTS) pindexFirstNotScriptsValid = pindex;
+
+        // Begin: actual consistency checks.
+        if (pindex->pprev == NULL) {
+            // Genesis block checks.
+            assert(pindex->GetBlockHash() == consensusParams.hashGenesisBlock); // Genesis block's hash must match.
+            assert(pindex == chainActive.Genesis()); // The current active chain's genesis block must be this block.
+        }
+        if (pindex->nChainTx == 0) assert(pindex->nSequenceId == 0);  // nSequenceId can't be set for blocks that aren't linked
+        // VALID_TRANSACTIONS is equivalent to nTx > 0 for all nodes (whether or not pruning has occurred).
+        // HAVE_DATA is only equivalent to nTx > 0 (or VALID_TRANSACTIONS) if no pruning has occurred.
+        if (!fHavePruned) {
+            // If we've never pruned, then HAVE_DATA should be equivalent to nTx > 0
+            assert(!(pindex->nStatus & BLOCK_HAVE_DATA) == (pindex->nTx == 0));
+            assert(pindexFirstMissing == pindexFirstNeverProcessed);
+        } else {
+            // If we have pruned, then we can only say that HAVE_DATA implies nTx > 0
+            if (pindex->nStatus & BLOCK_HAVE_DATA) assert(pindex->nTx > 0);
+        }
+        if (pindex->nStatus & BLOCK_HAVE_UNDO) assert(pindex->nStatus & BLOCK_HAVE_DATA);
+        assert(((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TRANSACTIONS) == (pindex->nTx > 0)); // This is pruning-independent.
+        // All parents having had data (at some point) is equivalent to all parents being VALID_TRANSACTIONS, which is equivalent to nChainTx being set.
+        assert((pindexFirstNeverProcessed != NULL) == (pindex->nChainTx == 0)); // nChainTx != 0 is used to signal that all parent blocks have been processed (but may have been pruned).
+        assert((pindexFirstNotTransactionsValid != NULL) == (pindex->nChainTx == 0));
+        assert(pindex->nHeight == nHeight); // nHeight must be consistent.
+        assert(pindex->pprev == NULL || pindex->nChainWork >= pindex->pprev->nChainWork); // For every block except the genesis block, the chainwork must be larger than the parent's.
+        assert(nHeight < 2 || (pindex->pskip && (pindex->pskip->nHeight < nHeight))); // The pskip pointer must point back for all but the first 2 blocks.
+        assert(pindexFirstNotTreeValid == NULL); // All mapBlockIndex entries must at least be TREE valid
+        if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TREE) assert(pindexFirstNotTreeValid == NULL); // TREE valid implies all parents are TREE valid
+        if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_CHAIN) assert(pindexFirstNotChainValid == NULL); // CHAIN valid implies all parents are CHAIN valid
+        if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_SCRIPTS) assert(pindexFirstNotScriptsValid == NULL); // SCRIPTS valid implies all parents are SCRIPTS valid
+        if (pindexFirstInvalid == NULL) {
+            // Checks for not-invalid blocks.
+            assert((pindex->nStatus & BLOCK_FAILED_MASK) == 0); // The failed mask cannot be set for blocks without invalid parents.
+        }
+        if (!CBlockIndexWorkComparator()(pindex, chainActive.Tip()) && pindexFirstNeverProcessed == NULL) {
+            if (pindexFirstInvalid == NULL) {
+                // If this block sorts at least as good as the current tip and
+                // is valid and we have all data for its parents, it must be in
+                // setBlockIndexCandidates.  chainActive.Tip() must also be there
+                // even if some data has been pruned.
+                if (pindexFirstMissing == NULL || pindex == chainActive.Tip()) {
+                    assert(setBlockIndexCandidates.count(pindex));
+                }
+                // If some parent is missing, then it could be that this block was in
+                // setBlockIndexCandidates but had to be removed because of the missing data.
+                // In this case it must be in mapBlocksUnlinked -- see test below.
+            }
+        } else { // If this block sorts worse than the current tip or some ancestor's block has never been seen, it cannot be in setBlockIndexCandidates.
+            assert(setBlockIndexCandidates.count(pindex) == 0);
+        }
+        // Check whether this block is in mapBlocksUnlinked.
+        std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> rangeUnlinked = mapBlocksUnlinked.equal_range(pindex->pprev);
+        bool foundInUnlinked = false;
+        while (rangeUnlinked.first != rangeUnlinked.second) {
+            assert(rangeUnlinked.first->first == pindex->pprev);
+            if (rangeUnlinked.first->second == pindex) {
+                foundInUnlinked = true;
+                break;
+            }
+            rangeUnlinked.first++;
+        }
+        if (pindex->pprev && (pindex->nStatus & BLOCK_HAVE_DATA) && pindexFirstNeverProcessed != NULL && pindexFirstInvalid == NULL) {
+            // If this block has block data available, some parent was never received, and has no invalid parents, it must be in mapBlocksUnlinked.
+            assert(foundInUnlinked);
+        }
+        if (!(pindex->nStatus & BLOCK_HAVE_DATA)) assert(!foundInUnlinked); // Can't be in mapBlocksUnlinked if we don't HAVE_DATA
+        if (pindexFirstMissing == NULL) assert(!foundInUnlinked); // We aren't missing data for any parent -- cannot be in mapBlocksUnlinked.
+        if (pindex->pprev && (pindex->nStatus & BLOCK_HAVE_DATA) && pindexFirstNeverProcessed == NULL && pindexFirstMissing != NULL) {
+            // We HAVE_DATA for this block, have received data for all parents at some point, but we're currently missing data for some parent.
+            assert(fHavePruned); // We must have pruned.
+            // This block may have entered mapBlocksUnlinked if:
+            //  - it has a descendant that at some point had more work than the
+            //    tip, and
+            //  - we tried switching to that descendant but were missing
+            //    data for some intermediate block between chainActive and the
+            //    tip.
+            // So if this block is itself better than chainActive.Tip() and it wasn't in
+            // setBlockIndexCandidates, then it must be in mapBlocksUnlinked.
+            if (!CBlockIndexWorkComparator()(pindex, chainActive.Tip()) && setBlockIndexCandidates.count(pindex) == 0) {
+                if (pindexFirstInvalid == NULL) {
+                    assert(foundInUnlinked);
+                }
+            }
+        }
+        // assert(pindex->GetBlockHash() == pindex->GetBlockHeader().GetHash()); // Perhaps too slow
+        // End: actual consistency checks.
+
+        // Try descending into the first subnode.
+        std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> range = forward.equal_range(pindex);
+        if (range.first != range.second) {
+            // A subnode was found.
+            pindex = range.first->second;
+            nHeight++;
+            continue;
+        }
+        // This is a leaf node.
+        // Move upwards until we reach a node of which we have not yet visited the last child.
+        while (pindex) {
+            // We are going to either move to a parent or a sibling of pindex.
+            // If pindex was the first with a certain property, unset the corresponding variable.
+            if (pindex == pindexFirstInvalid) pindexFirstInvalid = NULL;
+            if (pindex == pindexFirstMissing) pindexFirstMissing = NULL;
+            if (pindex == pindexFirstNeverProcessed) pindexFirstNeverProcessed = NULL;
+            if (pindex == pindexFirstNotTreeValid) pindexFirstNotTreeValid = NULL;
+            if (pindex == pindexFirstNotTransactionsValid) pindexFirstNotTransactionsValid = NULL;
+            if (pindex == pindexFirstNotChainValid) pindexFirstNotChainValid = NULL;
+            if (pindex == pindexFirstNotScriptsValid) pindexFirstNotScriptsValid = NULL;
+            // Find our parent.
+            CBlockIndex* pindexPar = pindex->pprev;
+            // Find which child we just visited.
+            std::pair<std::multimap<CBlockIndex*,CBlockIndex*>::iterator,std::multimap<CBlockIndex*,CBlockIndex*>::iterator> rangePar = forward.equal_range(pindexPar);
+            while (rangePar.first->second != pindex) {
+                assert(rangePar.first != rangePar.second); // Our parent must have at least the node we're coming from as child.
+                rangePar.first++;
+            }
+            // Proceed to the next one.
+            rangePar.first++;
+            if (rangePar.first != rangePar.second) {
+                // Move to the sibling.
+                pindex = rangePar.first->second;
+                break;
+            } else {
+                // Move up further.
+                pindex = pindexPar;
+                nHeight--;
+                continue;
+            }
+        }
+    }
+
+    // Check that we actually traversed the entire map.
+    assert(nNodes == forward.size());
+}
 
-string GetWarnings(string strFor)
+std::string GetWarnings(const std::string& strFor)
 {
-    int nPriority = 0;
     string strStatusBar;
     string strRPC;
+    string strGUI;
 
-    if (!CLIENT_VERSION_IS_RELEASE)
-        strStatusBar = _("This is a pre-release test build - use at your own risk - do not use for mining or merchant applications");
+    if (!CLIENT_VERSION_IS_RELEASE) {
+        strStatusBar = "This is a pre-release test build - use at your own risk - do not use for mining or merchant applications";
+        strGUI = _("This is a pre-release test build - use at your own risk - do not use for mining or merchant applications");
+    }
 
-    if (GetBoolArg("-testsafemode", false))
-        strStatusBar = strRPC = "testsafemode enabled";
+    if (GetBoolArg("-testsafemode", DEFAULT_TESTSAFEMODE))
+        strStatusBar = strRPC = strGUI = "testsafemode enabled";
 
     // Misc warnings like out of disk space and clock is wrong
     if (strMiscWarning != "")
     {
-        nPriority = 1000;
-        strStatusBar = strMiscWarning;
+        strStatusBar = strGUI = strMiscWarning;
     }
 
     if (fLargeWorkForkFound)
     {
-        nPriority = 2000;
-        strStatusBar = strRPC = _("Warning: The network does not appear to fully agree! Some miners appear to be experiencing issues.");
+        strStatusBar = strRPC = "Warning: The network does not appear to fully agree! Some miners appear to be experiencing issues.";
+        strGUI = _("Warning: The network does not appear to fully agree! Some miners appear to be experiencing issues.");
     }
     else if (fLargeWorkInvalidChainFound)
     {
-        nPriority = 2000;
-        strStatusBar = strRPC = _("Warning: We do not appear to fully agree with our peers! You may need to upgrade, or other nodes may need to upgrade.");
-    }
-
-    // Alerts
-    {
-        LOCK(cs_mapAlerts);
-        BOOST_FOREACH(PAIRTYPE(const uint256, CAlert)& item, mapAlerts)
-        {
-            const CAlert& alert = item.second;
-            if (alert.AppliesToMe() && alert.nPriority > nPriority)
-            {
-                nPriority = alert.nPriority;
-                strStatusBar = alert.strStatusBar;
-            }
-        }
+        strStatusBar = strRPC = "Warning: We do not appear to fully agree with our peers! You may need to upgrade, or other nodes may need to upgrade.";
+        strGUI = _("Warning: We do not appear to fully agree with our peers! You may need to upgrade, or other nodes may need to upgrade.");
     }
 
-    if (strFor == "statusbar")
+    if (strFor == "gui")
+        return strGUI;
+    else if (strFor == "statusbar")
         return strStatusBar;
     else if (strFor == "rpc")
         return strRPC;
-    assert(!"GetWarnings() : invalid parameter");
+    assert(!"GetWarnings(): invalid parameter");
     return "error";
 }
 
@@ -3216,26 +4696,40 @@ string GetWarnings(string strFor)
 //
 
 
-bool static AlreadyHave(const CInv& inv)
+bool static AlreadyHave(const CInv& inv) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     switch (inv.type)
     {
     case MSG_TX:
+    case MSG_WITNESS_TX:
         {
-            bool txInMap = false;
-            txInMap = mempool.exists(inv.hash);
-            return txInMap || mapOrphanTransactions.count(inv.hash) ||
-                pcoinsTip->HaveCoins(inv.hash);
+            assert(recentRejects);
+            if (chainActive.Tip()->GetBlockHash() != hashRecentRejectsChainTip)
+            {
+                // If the chain tip has changed previously rejected transactions
+                // might be now valid, e.g. due to a nLockTime'd tx becoming valid,
+                // or a double-spend. Reset the rejects filter and give those
+                // txs a second chance.
+                hashRecentRejectsChainTip = chainActive.Tip()->GetBlockHash();
+                recentRejects->reset();
+            }
+
+            // Use pcoinsTip->HaveCoinsInCache as a quick approximation to exclude
+            // requesting or processing some txs which have already been included in a block
+            return recentRejects->contains(inv.hash) ||
+                   mempool.exists(inv.hash) ||
+                   mapOrphanTransactions.count(inv.hash) ||
+                   pcoinsTip->HaveCoinsInCache(inv.hash);
         }
     case MSG_BLOCK:
+    case MSG_WITNESS_BLOCK:
         return mapBlockIndex.count(inv.hash);
     }
     // Don't know what it is, just say we already got one
     return true;
 }
 
-
-void static ProcessGetData(CNode* pfrom)
+void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParams)
 {
     std::deque<CInv>::iterator it = pfrom->vRecvGetData.begin();
 
@@ -3253,58 +4747,84 @@ void static ProcessGetData(CNode* pfrom)
             boost::this_thread::interruption_point();
             it++;
 
-            if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK)
+            if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK || inv.type == MSG_CMPCT_BLOCK || inv.type == MSG_WITNESS_BLOCK)
             {
                 bool send = false;
                 BlockMap::iterator mi = mapBlockIndex.find(inv.hash);
                 if (mi != mapBlockIndex.end())
                 {
-                    // If the requested block is at a height below our last
-                    // checkpoint, only serve it if it's in the checkpointed chain
-                    int nHeight = mi->second->nHeight;
-                    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint();
-                    if (pcheckpoint && nHeight < pcheckpoint->nHeight) {
-                        if (!chainActive.Contains(mi->second))
-                        {
-                            LogPrintf("ProcessGetData(): ignoring request for old block that isn't in the main chain\n");
-                        } else {
-                            send = true;
-                        }
-                    } else {
+                    if (chainActive.Contains(mi->second)) {
                         send = true;
+                    } else {
+                        static const int nOneMonth = 30 * 24 * 60 * 60;
+                        // To prevent fingerprinting attacks, only send blocks outside of the active
+                        // chain if they are valid, and no more than a month older (both in time, and in
+                        // best equivalent proof of work) than the best header chain we know about.
+                        send = mi->second->IsValid(BLOCK_VALID_SCRIPTS) && (pindexBestHeader != NULL) &&
+                            (pindexBestHeader->GetBlockTime() - mi->second->GetBlockTime() < nOneMonth) &&
+                            (GetBlockProofEquivalentTime(*pindexBestHeader, *mi->second, *pindexBestHeader, consensusParams) < nOneMonth);
+                        if (!send) {
+                            LogPrintf("%s: ignoring request from peer=%i for old block that isn't in the main chain\n", __func__, pfrom->GetId());
+                        }
                     }
                 }
-                if (send)
+                // disconnect node in case we have reached the outbound limit for serving historical blocks
+                // never disconnect whitelisted nodes
+                static const int nOneWeek = 7 * 24 * 60 * 60; // assume > 1 week = historical
+                if (send && CNode::OutboundTargetReached(true) && ( ((pindexBestHeader != NULL) && (pindexBestHeader->GetBlockTime() - mi->second->GetBlockTime() > nOneWeek)) || inv.type == MSG_FILTERED_BLOCK) && !pfrom->fWhitelisted)
+                {
+                    LogPrint("net", "historical block serving limit reached, disconnect peer=%d\n", pfrom->GetId());
+
+                    //disconnect node
+                    pfrom->fDisconnect = true;
+                    send = false;
+                }
+                // Pruned nodes may have deleted the block, so check whether
+                // it's available before trying to send.
+                if (send && (mi->second->nStatus & BLOCK_HAVE_DATA))
                 {
                     // Send block from disk
                     CBlock block;
-                    if (!ReadBlockFromDisk(block, (*mi).second))
+                    if (!ReadBlockFromDisk(block, (*mi).second, consensusParams))
                         assert(!"cannot load block from disk");
                     if (inv.type == MSG_BLOCK)
-                        pfrom->PushMessage("block", block);
-                    else // MSG_FILTERED_BLOCK)
+                        pfrom->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCK, block);
+                    else if (inv.type == MSG_WITNESS_BLOCK)
+                        pfrom->PushMessage(NetMsgType::BLOCK, block);
+                    else if (inv.type == MSG_FILTERED_BLOCK)
                     {
                         LOCK(pfrom->cs_filter);
                         if (pfrom->pfilter)
                         {
                             CMerkleBlock merkleBlock(block, *pfrom->pfilter);
-                            pfrom->PushMessage("merkleblock", merkleBlock);
+                            pfrom->PushMessage(NetMsgType::MERKLEBLOCK, merkleBlock);
                             // CMerkleBlock just contains hashes, so also push any transactions in the block the client did not see
                             // This avoids hurting performance by pointlessly requiring a round-trip
-                            // Note that there is currently no way for a node to request any single transactions we didnt send here -
+                            // Note that there is currently no way for a node to request any single transactions we didn't send here -
                             // they must either disconnect and retry or request the full block.
                             // Thus, the protocol spec specified allows for us to provide duplicate txn here,
                             // however we MUST always provide at least what the remote peer needs
                             typedef std::pair<unsigned int, uint256> PairType;
                             BOOST_FOREACH(PairType& pair, merkleBlock.vMatchedTxn)
-                                if (!pfrom->setInventoryKnown.count(CInv(MSG_TX, pair.second)))
-                                    pfrom->PushMessage("tx", block.vtx[pair.first]);
+                                pfrom->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::TX, block.vtx[pair.first]);
                         }
                         // else
                             // no response
                     }
+                    else if (inv.type == MSG_CMPCT_BLOCK)
+                    {
+                        // If a peer is asking for old blocks, we're almost guaranteed
+                        // they wont have a useful mempool to match against a compact block,
+                        // and we dont feel like constructing the object for them, so
+                        // instead we respond with the full, non-compact block.
+                        if (mi->second->nHeight >= chainActive.Height() - 10) {
+                            CBlockHeaderAndShortTxIDs cmpctblock(block);
+                            pfrom->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::CMPCTBLOCK, cmpctblock);
+                        } else
+                            pfrom->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCK, block);
+                    }
 
-                    // Trigger them to send a getblocks request for the next batch of inventory
+                    // Trigger the peer node to send a getblocks request for the next batch of inventory
                     if (inv.hash == pfrom->hashContinue)
                     {
                         // Bypass PushInventory, this must send even if redundant,
@@ -3312,42 +4832,37 @@ void static ProcessGetData(CNode* pfrom)
                         // wait for other stuff first.
                         vector<CInv> vInv;
                         vInv.push_back(CInv(MSG_BLOCK, chainActive.Tip()->GetBlockHash()));
-                        pfrom->PushMessage("inv", vInv);
-                        pfrom->hashContinue = 0;
+                        pfrom->PushMessage(NetMsgType::INV, vInv);
+                        pfrom->hashContinue.SetNull();
                     }
                 }
             }
-            else if (inv.IsKnownType())
+            else if (inv.type == MSG_TX || inv.type == MSG_WITNESS_TX)
             {
                 // Send stream from relay memory
-                bool pushed = false;
-                {
-                    LOCK(cs_mapRelay);
-                    map<CInv, CDataStream>::iterator mi = mapRelay.find(inv);
-                    if (mi != mapRelay.end()) {
-                        pfrom->PushMessage(inv.GetCommand(), (*mi).second);
-                        pushed = true;
+                bool push = false;
+                auto mi = mapRelay.find(inv.hash);
+                if (mi != mapRelay.end()) {
+                    pfrom->PushMessageWithFlag(inv.type == MSG_TX ? SERIALIZE_TRANSACTION_NO_WITNESS : 0, NetMsgType::TX, *mi->second);
+                    push = true;
+                } else if (pfrom->timeLastMempoolReq) {
+                    auto txinfo = mempool.info(inv.hash);
+                    // To protect privacy, do not answer getdata using the mempool when
+                    // that TX couldn't have been INVed in reply to a MEMPOOL request.
+                    if (txinfo.tx && txinfo.nTime <= pfrom->timeLastMempoolReq) {
+                        pfrom->PushMessageWithFlag(inv.type == MSG_TX ? SERIALIZE_TRANSACTION_NO_WITNESS : 0, NetMsgType::TX, *txinfo.tx);
+                        push = true;
                     }
                 }
-                if (!pushed && inv.type == MSG_TX) {
-                    CTransaction tx;
-                    if (mempool.lookup(inv.hash, tx)) {
-                        CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
-                        ss.reserve(1000);
-                        ss << tx;
-                        pfrom->PushMessage("tx", ss);
-                        pushed = true;
-                    }
-                }
-                if (!pushed) {
+                if (!push) {
                     vNotFound.push_back(inv);
                 }
             }
 
             // Track requests for our stuff.
-            g_signals.Inventory(inv.hash);
+            GetMainSignals().Inventory(inv.hash);
 
-            if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK)
+            if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK || inv.type == MSG_CMPCT_BLOCK || inv.type == MSG_WITNESS_BLOCK)
                 break;
         }
     }
@@ -3362,14 +4877,21 @@ void static ProcessGetData(CNode* pfrom)
         // do that because they want to know about (and store and rebroadcast and
         // risk analyze) the dependencies of transactions relevant to them, without
         // having to download the entire memory pool.
-        pfrom->PushMessage("notfound", vNotFound);
+        pfrom->PushMessage(NetMsgType::NOTFOUND, vNotFound);
+    }
+}
+
+uint32_t GetFetchFlags(CNode* pfrom, CBlockIndex* pprev, const Consensus::Params& chainparams) {
+    uint32_t nFetchFlags = 0;
+    if (IsWitnessEnabled(pprev, chainparams) && State(pfrom->GetId())->fHaveWitness) {
+        nFetchFlags |= MSG_WITNESS_FLAG;
     }
+    return nFetchFlags;
 }
 
-bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv, int64_t nTimeReceived)
+bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv, int64_t nTimeReceived, const CChainParams& chainparams)
 {
-    RandAddSeedPerfmon();
-    LogPrint("net", "received: %s (%u bytes) peer=%d\n", strCommand, vRecv.size(), pfrom->id);
+    LogPrint("net", "received: %s (%u bytes) peer=%d\n", SanitizeString(strCommand), vRecv.size(), pfrom->id);
     if (mapArgs.count("-dropmessagestest") && GetRand(atoi(mapArgs["-dropmessagestest"])) == 0)
     {
         LogPrintf("dropmessagestest DROPPING RECV MESSAGE\n");
@@ -3377,14 +4899,29 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
+    if (!(nLocalServices & NODE_BLOOM) &&
+              (strCommand == NetMsgType::FILTERLOAD ||
+               strCommand == NetMsgType::FILTERADD ||
+               strCommand == NetMsgType::FILTERCLEAR))
+    {
+        if (pfrom->nVersion >= NO_BLOOM_VERSION) {
+            LOCK(cs_main);
+            Misbehaving(pfrom->GetId(), 100);
+            return false;
+        } else {
+            pfrom->fDisconnect = true;
+            return false;
+        }
+    }
 
 
-    if (strCommand == "version")
+    if (strCommand == NetMsgType::VERSION)
     {
         // Each connection can only send one version message
         if (pfrom->nVersion != 0)
         {
-            pfrom->PushMessage("reject", strCommand, REJECT_DUPLICATE, string("Duplicate version message"));
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_DUPLICATE, string("Duplicate version message"));
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 1);
             return false;
         }
@@ -3393,12 +4930,27 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         CAddress addrMe;
         CAddress addrFrom;
         uint64_t nNonce = 1;
-        vRecv >> pfrom->nVersion >> pfrom->nServices >> nTime >> addrMe;
+        uint64_t nServiceInt;
+        vRecv >> pfrom->nVersion >> nServiceInt >> nTime >> addrMe;
+        pfrom->nServices = ServiceFlags(nServiceInt);
+        if (!pfrom->fInbound)
+        {
+            addrman.SetServices(pfrom->addr, pfrom->nServices);
+        }
+        if (pfrom->nServicesExpected & ~pfrom->nServices)
+        {
+            LogPrint("net", "peer=%d does not offer the expected services (%08x offered, %08x expected); disconnecting\n", pfrom->id, pfrom->nServices, pfrom->nServicesExpected);
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_NONSTANDARD,
+                               strprintf("Expected to offer services %08x", pfrom->nServicesExpected));
+            pfrom->fDisconnect = true;
+            return false;
+        }
+
         if (pfrom->nVersion < MIN_PEER_PROTO_VERSION)
         {
             // disconnect from peers older than this proto version
             LogPrintf("peer=%d using obsolete version %i; disconnecting\n", pfrom->id, pfrom->nVersion);
-            pfrom->PushMessage("reject", strCommand, REJECT_OBSOLETE,
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_OBSOLETE,
                                strprintf("Version must be %d or greater", MIN_PEER_PROTO_VERSION));
             pfrom->fDisconnect = true;
             return false;
@@ -3409,15 +4961,19 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         if (!vRecv.empty())
             vRecv >> addrFrom >> nNonce;
         if (!vRecv.empty()) {
-            vRecv >> LIMITED_STRING(pfrom->strSubVer, 256);
+            vRecv >> LIMITED_STRING(pfrom->strSubVer, MAX_SUBVERSION_LENGTH);
             pfrom->cleanSubVer = SanitizeString(pfrom->strSubVer);
         }
-        if (!vRecv.empty())
+        if (!vRecv.empty()) {
             vRecv >> pfrom->nStartingHeight;
-        if (!vRecv.empty())
-            vRecv >> pfrom->fRelayTxes; // set to true after we get the first filter* message
-        else
-            pfrom->fRelayTxes = true;
+        }
+        {
+            LOCK(pfrom->cs_filter);
+            if (!vRecv.empty())
+                vRecv >> pfrom->fRelayTxes; // set to true after we get the first filter* message
+            else
+                pfrom->fRelayTxes = true;
+        }
 
         // Disconnect if we connected to ourself
         if (nNonce == nLocalHostNonce && nNonce > 1)
@@ -3439,11 +4995,20 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
         pfrom->fClient = !(pfrom->nServices & NODE_NETWORK);
 
+        if((pfrom->nServices & NODE_WITNESS))
+        {
+            LOCK(cs_main);
+            State(pfrom->GetId())->fHaveWitness = true;
+        }
+
         // Potentially mark this peer as a preferred download peer.
+        {
+        LOCK(cs_main);
         UpdatePreferredDownload(pfrom, State(pfrom->GetId()));
+        }
 
         // Change version
-        pfrom->PushMessage("verack");
+        pfrom->PushMessage(NetMsgType::VERACK);
         pfrom->ssSend.SetVersion(min(pfrom->nVersion, PROTOCOL_VERSION));
 
         if (!pfrom->fInbound)
@@ -3454,9 +5019,11 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 CAddress addr = GetLocalAddress(&pfrom->addr);
                 if (addr.IsRoutable())
                 {
+                    LogPrintf("ProcessMessages: advertising address %s\n", addr.ToString());
                     pfrom->PushAddress(addr);
                 } else if (IsPeerAddrLocalGood(pfrom)) {
                     addr.SetIP(pfrom->addrLocal);
+                    LogPrintf("ProcessMessages: advertising address %s\n", addr.ToString());
                     pfrom->PushAddress(addr);
                 }
             }
@@ -3464,7 +5031,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // Get recent addresses
             if (pfrom->fOneShot || pfrom->nVersion >= CADDR_TIME_VERSION || addrman.size() < 1000)
             {
-                pfrom->PushMessage("getaddr");
+                pfrom->PushMessage(NetMsgType::GETADDR);
                 pfrom->fGetAddr = true;
             }
             addrman.Good(pfrom->addr);
@@ -3476,13 +5043,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             }
         }
 
-        // Relay alerts
-        {
-            LOCK(cs_mapAlerts);
-            BOOST_FOREACH(PAIRTYPE(const uint256, CAlert)& item, mapAlerts)
-                item.second.RelayTo(pfrom);
-        }
-
         pfrom->fSuccessfullyConnected = true;
 
         string remoteAddr;
@@ -3494,25 +5054,52 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                   pfrom->nStartingHeight, addrMe.ToString(), pfrom->id,
                   remoteAddr);
 
-        AddTimeData(pfrom->addr, nTime);
+        int64_t nTimeOffset = nTime - GetTime();
+        pfrom->nTimeOffset = nTimeOffset;
+        AddTimeData(pfrom->addr, nTimeOffset);
     }
 
 
     else if (pfrom->nVersion == 0)
     {
         // Must have a version message before anything else
+        LOCK(cs_main);
         Misbehaving(pfrom->GetId(), 1);
         return false;
     }
 
 
-    else if (strCommand == "verack")
+    else if (strCommand == NetMsgType::VERACK)
     {
         pfrom->SetRecvVersion(min(pfrom->nVersion, PROTOCOL_VERSION));
+
+        // Mark this node as currently connected, so we update its timestamp later.
+        if (pfrom->fNetworkNode) {
+            LOCK(cs_main);
+            State(pfrom->GetId())->fCurrentlyConnected = true;
+        }
+
+        if (pfrom->nVersion >= SENDHEADERS_VERSION) {
+            // Tell our peer we prefer to receive headers rather than inv's
+            // We send this to non-NODE NETWORK peers as well, because even
+            // non-NODE NETWORK peers can announce blocks (such as pruning
+            // nodes)
+            pfrom->PushMessage(NetMsgType::SENDHEADERS);
+        }
+        if (pfrom->nVersion >= SHORT_IDS_BLOCKS_VERSION) {
+            // Tell our peer we are willing to provide version-1 cmpctblocks
+            // However, we do not request new block announcements using
+            // cmpctblock messages.
+            // We send this to non-NODE NETWORK peers as well, because
+            // they may wish to request compact blocks from us
+            bool fAnnounceUsingCMPCTBLOCK = false;
+            uint64_t nCMPCTBLOCKVersion = 1;
+            pfrom->PushMessage(NetMsgType::SENDCMPCT, fAnnounceUsingCMPCTBLOCK, nCMPCTBLOCKVersion);
+        }
     }
 
 
-    else if (strCommand == "addr")
+    else if (strCommand == NetMsgType::ADDR)
     {
         vector<CAddress> vAddr;
         vRecv >> vAddr;
@@ -3522,6 +5109,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         if (vAddr.size() > 1000)
         {
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 20);
             return error("message addr size() = %u", vAddr.size());
         }
@@ -3534,6 +5122,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         {
             boost::this_thread::interruption_point();
 
+            if ((addr.nServices & REQUIRED_SERVICES) != REQUIRED_SERVICES)
+                continue;
+
             if (addr.nTime <= 100000000 || addr.nTime > nNow + 10 * 60)
                 addr.nTime = nNow - 5 * 24 * 60 * 60;
             pfrom->AddAddressKnown(addr);
@@ -3544,26 +5135,21 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 {
                     LOCK(cs_vNodes);
                     // Use deterministic randomness to send to the same nodes for 24 hours
-                    // at a time so the setAddrKnowns of the chosen nodes prevent repeats
-                    static uint256 hashSalt;
-                    if (hashSalt == 0)
-                        hashSalt = GetRandHash();
+                    // at a time so the addrKnowns of the chosen nodes prevent repeats
+                    static const uint64_t salt0 = GetRand(std::numeric_limits<uint64_t>::max());
+                    static const uint64_t salt1 = GetRand(std::numeric_limits<uint64_t>::max());
                     uint64_t hashAddr = addr.GetHash();
-                    uint256 hashRand = hashSalt ^ (hashAddr<<32) ^ ((GetTime()+hashAddr)/(24*60*60));
-                    hashRand = Hash(BEGIN(hashRand), END(hashRand));
-                    multimap<uint256, CNode*> mapMix;
+                    multimap<uint64_t, CNode*> mapMix;
+                    const CSipHasher hasher = CSipHasher(salt0, salt1).Write(hashAddr << 32).Write((GetTime() + hashAddr) / (24*60*60));
                     BOOST_FOREACH(CNode* pnode, vNodes)
                     {
                         if (pnode->nVersion < CADDR_TIME_VERSION)
                             continue;
-                        unsigned int nPointer;
-                        memcpy(&nPointer, &pnode, sizeof(nPointer));
-                        uint256 hashKey = hashRand ^ nPointer;
-                        hashKey = Hash(BEGIN(hashKey), END(hashKey));
+                        uint64_t hashKey = CSipHasher(hasher).Write(pnode->id).Finalize();
                         mapMix.insert(make_pair(hashKey, pnode));
                     }
                     int nRelayNodes = fReachable ? 2 : 1; // limited relaying of addresses outside our network(s)
-                    for (multimap<uint256, CNode*>::iterator mi = mapMix.begin(); mi != mapMix.end() && nRelayNodes-- > 0; ++mi)
+                    for (multimap<uint64_t, CNode*>::iterator mi = mapMix.begin(); mi != mapMix.end() && nRelayNodes-- > 0; ++mi)
                         ((*mi).second)->PushAddress(addr);
                 }
             }
@@ -3578,38 +5164,65 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             pfrom->fDisconnect = true;
     }
 
+    else if (strCommand == NetMsgType::SENDHEADERS)
+    {
+        LOCK(cs_main);
+        State(pfrom->GetId())->fPreferHeaders = true;
+    }
+
+    else if (strCommand == NetMsgType::SENDCMPCT)
+    {
+        bool fAnnounceUsingCMPCTBLOCK = false;
+        uint64_t nCMPCTBLOCKVersion = 1;
+        vRecv >> fAnnounceUsingCMPCTBLOCK >> nCMPCTBLOCKVersion;
+        if (nCMPCTBLOCKVersion == 1) {
+            LOCK(cs_main);
+            State(pfrom->GetId())->fProvidesHeaderAndIDs = true;
+            State(pfrom->GetId())->fPreferHeaderAndIDs = fAnnounceUsingCMPCTBLOCK;
+        }
+    }
+
 
-    else if (strCommand == "inv")
+    else if (strCommand == NetMsgType::INV)
     {
         vector<CInv> vInv;
         vRecv >> vInv;
         if (vInv.size() > MAX_INV_SZ)
         {
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 20);
             return error("message inv size() = %u", vInv.size());
         }
 
+        bool fBlocksOnly = !fRelayTxes;
+
+        // Allow whitelisted peers to send data other than blocks in blocks only mode if whitelistrelay is true
+        if (pfrom->fWhitelisted && GetBoolArg("-whitelistrelay", DEFAULT_WHITELISTRELAY))
+            fBlocksOnly = false;
+
         LOCK(cs_main);
 
+        uint32_t nFetchFlags = GetFetchFlags(pfrom, chainActive.Tip(), chainparams.GetConsensus());
+
         std::vector<CInv> vToFetch;
 
         for (unsigned int nInv = 0; nInv < vInv.size(); nInv++)
         {
-            const CInv &inv = vInv[nInv];
+            CInv &inv = vInv[nInv];
 
             boost::this_thread::interruption_point();
-            pfrom->AddInventoryKnown(inv);
 
             bool fAlreadyHave = AlreadyHave(inv);
             LogPrint("net", "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom->id);
 
-            if (!fAlreadyHave && !fImporting && !fReindex && inv.type != MSG_BLOCK)
-                pfrom->AskFor(inv);
+            if (inv.type == MSG_TX) {
+                inv.type |= nFetchFlags;
+            }
 
             if (inv.type == MSG_BLOCK) {
                 UpdateBlockAvailability(pfrom->GetId(), inv.hash);
                 if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
-                    // First request the headers preceeding the announced block. In the normal fully-synced
+                    // First request the headers preceding the announced block. In the normal fully-synced
                     // case where a new block is announced that succeeds the current tip (no reorganization),
                     // there are no such headers.
                     // Secondly, and only when we are close to being synced, we request the announced block directly,
@@ -3617,19 +5230,34 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     // time the block arrives, the header chain leading up to it is already validated. Not
                     // doing this will result in the received block being rejected as an orphan in case it is
                     // not a direct successor.
-                    pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexBestHeader), inv.hash);
-                    if (chainActive.Tip()->GetBlockTime() > GetAdjustedTime() - Params().TargetSpacing() * 20) {
-                        vToFetch.push_back(inv);
+                    pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), inv.hash);
+                    CNodeState *nodestate = State(pfrom->GetId());
+                    if (CanDirectFetch(chainparams.GetConsensus()) &&
+                        nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER &&
+                        (!IsWitnessEnabled(chainActive.Tip(), chainparams.GetConsensus()) || State(pfrom->GetId())->fHaveWitness)) {
+                        inv.type |= nFetchFlags;
+                        if (nodestate->fProvidesHeaderAndIDs && !(nLocalServices & NODE_WITNESS))
+                            vToFetch.push_back(CInv(MSG_CMPCT_BLOCK, inv.hash));
+                        else
+                            vToFetch.push_back(inv);
                         // Mark block as in flight already, even though the actual "getdata" message only goes out
                         // later (within the same cs_main lock, though).
-                        MarkBlockAsInFlight(pfrom->GetId(), inv.hash);
+                        MarkBlockAsInFlight(pfrom->GetId(), inv.hash, chainparams.GetConsensus());
                     }
                     LogPrint("net", "getheaders (%d) %s to peer=%d\n", pindexBestHeader->nHeight, inv.hash.ToString(), pfrom->id);
                 }
             }
+            else
+            {
+                pfrom->AddInventoryKnown(inv);
+                if (fBlocksOnly)
+                    LogPrint("net", "transaction (%s) inv sent in violation of protocol peer=%d\n", inv.hash.ToString(), pfrom->id);
+                else if (!fAlreadyHave && !fImporting && !fReindex && !IsInitialBlockDownload())
+                    pfrom->AskFor(inv);
+            }
 
             // Track requests for our stuff
-            g_signals.Inventory(inv.hash);
+            GetMainSignals().Inventory(inv.hash);
 
             if (pfrom->nSendSize > (SendBufferSize() * 2)) {
                 Misbehaving(pfrom->GetId(), 50);
@@ -3638,16 +5266,17 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
 
         if (!vToFetch.empty())
-            pfrom->PushMessage("getdata", vToFetch);
+            pfrom->PushMessage(NetMsgType::GETDATA, vToFetch);
     }
 
 
-    else if (strCommand == "getdata")
+    else if (strCommand == NetMsgType::GETDATA)
     {
         vector<CInv> vInv;
         vRecv >> vInv;
         if (vInv.size() > MAX_INV_SZ)
         {
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 20);
             return error("message getdata size() = %u", vInv.size());
         }
@@ -3659,11 +5288,11 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             LogPrint("net", "received getdata for: %s peer=%d\n", vInv[0].ToString(), pfrom->id);
 
         pfrom->vRecvGetData.insert(pfrom->vRecvGetData.end(), vInv.begin(), vInv.end());
-        ProcessGetData(pfrom);
+        ProcessGetData(pfrom, chainparams.GetConsensus());
     }
 
 
-    else if (strCommand == "getblocks")
+    else if (strCommand == NetMsgType::GETBLOCKS)
     {
         CBlockLocator locator;
         uint256 hashStop;
@@ -3678,7 +5307,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         if (pindex)
             pindex = chainActive.Next(pindex);
         int nLimit = 500;
-        LogPrint("net", "getblocks %d to %s limit %d from peer=%d\n", (pindex ? pindex->nHeight : -1), hashStop==uint256(0) ? "end" : hashStop.ToString(), nLimit, pfrom->id);
+        LogPrint("net", "getblocks %d to %s limit %d from peer=%d\n", (pindex ? pindex->nHeight : -1), hashStop.IsNull() ? "end" : hashStop.ToString(), nLimit, pfrom->id);
         for (; pindex; pindex = chainActive.Next(pindex))
         {
             if (pindex->GetBlockHash() == hashStop)
@@ -3686,11 +5315,19 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 LogPrint("net", "  getblocks stopping at %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
                 break;
             }
+            // If pruning, don't inv blocks unless we have on disk and are likely to still have
+            // for some reasonable time window (1 hour) that block relay might require.
+            const int nPrunedBlocksLikelyToHave = MIN_BLOCKS_TO_KEEP - 3600 / chainparams.GetConsensus().nPowTargetSpacing;
+            if (fPruneMode && (!(pindex->nStatus & BLOCK_HAVE_DATA) || pindex->nHeight <= chainActive.Tip()->nHeight - nPrunedBlocksLikelyToHave))
+            {
+                LogPrint("net", " getblocks stopping, pruned or too old block at %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
+                break;
+            }
             pfrom->PushInventory(CInv(MSG_BLOCK, pindex->GetBlockHash()));
             if (--nLimit <= 0)
             {
-                // When this block is requested, we'll send an inv that'll make them
-                // getblocks the next batch of inventory.
+                // When this block is requested, we'll send an inv that'll
+                // trigger the peer to getblocks the next batch of inventory.
                 LogPrint("net", "  getblocks stopping at limit %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
                 pfrom->hashContinue = pindex->GetBlockHash();
                 break;
@@ -3699,14 +5336,52 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "getheaders")
+    else if (strCommand == NetMsgType::GETBLOCKTXN)
+    {
+        BlockTransactionsRequest req;
+        vRecv >> req;
+
+        BlockMap::iterator it = mapBlockIndex.find(req.blockhash);
+        if (it == mapBlockIndex.end() || !(it->second->nStatus & BLOCK_HAVE_DATA)) {
+            Misbehaving(pfrom->GetId(), 100);
+            LogPrintf("Peer %d sent us a getblocktxn for a block we don't have", pfrom->id);
+            return true;
+        }
+
+        if (it->second->nHeight < chainActive.Height() - 15) {
+            LogPrint("net", "Peer %d sent us a getblocktxn for a block > 15 deep", pfrom->id);
+            return true;
+        }
+
+        CBlock block;
+        assert(ReadBlockFromDisk(block, it->second, chainparams.GetConsensus()));
+
+        BlockTransactions resp(req);
+        for (size_t i = 0; i < req.indexes.size(); i++) {
+            if (req.indexes[i] >= block.vtx.size()) {
+                Misbehaving(pfrom->GetId(), 100);
+                LogPrintf("Peer %d sent us a getblocktxn with out-of-bounds tx indices", pfrom->id);
+                return true;
+            }
+            resp.txn[i] = block.vtx[req.indexes[i]];
+        }
+        pfrom->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCKTXN, resp);
+    }
+
+
+    else if (strCommand == NetMsgType::GETHEADERS)
     {
         CBlockLocator locator;
         uint256 hashStop;
         vRecv >> locator >> hashStop;
 
         LOCK(cs_main);
+        if (IsInitialBlockDownload() && !pfrom->fWhitelisted) {
+            LogPrint("net", "Ignoring getheaders from peer=%d because node is in initial block download\n", pfrom->id);
+            return true;
+        }
 
+        CNodeState *nodestate = State(pfrom->GetId());
         CBlockIndex* pindex = NULL;
         if (locator.IsNull())
         {
@@ -3734,13 +5409,26 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             if (--nLimit <= 0 || pindex->GetBlockHash() == hashStop)
                 break;
         }
-        pfrom->PushMessage("headers", vHeaders);
+        // pindex can be NULL either if we sent chainActive.Tip() OR
+        // if our peer has chainActive.Tip() (and thus we are sending an empty
+        // headers message). In both cases it's safe to update
+        // pindexBestHeaderSent to be our tip.
+        nodestate->pindexBestHeaderSent = pindex ? pindex : chainActive.Tip();
+        pfrom->PushMessage(NetMsgType::HEADERS, vHeaders);
     }
 
 
-    else if (strCommand == "tx")
+    else if (strCommand == NetMsgType::TX)
     {
-        vector<uint256> vWorkQueue;
+        // Stop processing the transaction early if
+        // We are in blocks only mode and peer is either not whitelisted or whitelistrelay is off
+        if (!fRelayTxes && (!pfrom->fWhitelisted || !GetBoolArg("-whitelistrelay", DEFAULT_WHITELISTRELAY)))
+        {
+            LogPrint("net", "transaction sent in violation of protocol peer=%d\n", pfrom->id);
+            return true;
+        }
+
+        deque<COutPoint> vWorkQueue;
         vector<uint256> vEraseQueue;
         CTransaction tx;
         vRecv >> tx;
@@ -3753,62 +5441,72 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         bool fMissingInputs = false;
         CValidationState state;
 
-        mapAlreadyAskedFor.erase(inv);
+        pfrom->setAskFor.erase(inv.hash);
+        mapAlreadyAskedFor.erase(inv.hash);
 
-        if (AcceptToMemoryPool(mempool, state, tx, true, &fMissingInputs))
-        {
+        if (!AlreadyHave(inv) && AcceptToMemoryPool(mempool, state, tx, true, &fMissingInputs)) {
             mempool.check(pcoinsTip);
             RelayTransaction(tx);
-            vWorkQueue.push_back(inv.hash);
-            vEraseQueue.push_back(inv.hash);
+            for (unsigned int i = 0; i < tx.vout.size(); i++) {
+                vWorkQueue.emplace_back(inv.hash, i);
+            }
+
+            pfrom->nLastTXTime = GetTime();
 
-            LogPrint("mempool", "AcceptToMemoryPool: peer=%d %s : accepted %s (poolsz %u)\n",
-                pfrom->id, pfrom->cleanSubVer,
+            LogPrint("mempool", "AcceptToMemoryPool: peer=%d: accepted %s (poolsz %u txn, %u kB)\n",
+                pfrom->id,
                 tx.GetHash().ToString(),
-                mempool.mapTx.size());
+                mempool.size(), mempool.DynamicMemoryUsage() / 1000);
 
             // Recursively process any orphan transactions that depended on this one
             set<NodeId> setMisbehaving;
-            for (unsigned int i = 0; i < vWorkQueue.size(); i++)
-            {
-                map<uint256, set<uint256> >::iterator itByPrev = mapOrphanTransactionsByPrev.find(vWorkQueue[i]);
+            while (!vWorkQueue.empty()) {
+                auto itByPrev = mapOrphanTransactionsByPrev.find(vWorkQueue.front());
+                vWorkQueue.pop_front();
                 if (itByPrev == mapOrphanTransactionsByPrev.end())
                     continue;
-                for (set<uint256>::iterator mi = itByPrev->second.begin();
+                for (auto mi = itByPrev->second.begin();
                      mi != itByPrev->second.end();
                      ++mi)
                 {
-                    const uint256& orphanHash = *mi;
-                    const CTransaction& orphanTx = mapOrphanTransactions[orphanHash].tx;
-                    NodeId fromPeer = mapOrphanTransactions[orphanHash].fromPeer;
+                    const CTransaction& orphanTx = (*mi)->second.tx;
+                    const uint256& orphanHash = orphanTx.GetHash();
+                    NodeId fromPeer = (*mi)->second.fromPeer;
                     bool fMissingInputs2 = false;
                     // Use a dummy CValidationState so someone can't setup nodes to counter-DoS based on orphan
                     // resolution (that is, feeding people an invalid transaction based on LegitTxX in order to get
                     // anyone relaying LegitTxX banned)
                     CValidationState stateDummy;
 
-                    vEraseQueue.push_back(orphanHash);
 
                     if (setMisbehaving.count(fromPeer))
                         continue;
-                    if (AcceptToMemoryPool(mempool, stateDummy, orphanTx, true, &fMissingInputs2))
-                    {
+                    if (AcceptToMemoryPool(mempool, stateDummy, orphanTx, true, &fMissingInputs2)) {
                         LogPrint("mempool", "   accepted orphan tx %s\n", orphanHash.ToString());
                         RelayTransaction(orphanTx);
-                        vWorkQueue.push_back(orphanHash);
+                        for (unsigned int i = 0; i < orphanTx.vout.size(); i++) {
+                            vWorkQueue.emplace_back(orphanHash, i);
+                        }
+                        vEraseQueue.push_back(orphanHash);
                     }
                     else if (!fMissingInputs2)
                     {
                         int nDos = 0;
-                        if (stateDummy.IsInvalid(nDos) && nDos > 0)
+                        if (stateDummy.IsInvalid(nDos) && nDos > 0 && (!state.CorruptionPossible() || State(fromPeer)->fHaveWitness))
                         {
                             // Punish peer that gave us an invalid orphan tx
                             Misbehaving(fromPeer, nDos);
                             setMisbehaving.insert(fromPeer);
                             LogPrint("mempool", "   invalid orphan tx %s\n", orphanHash.ToString());
                         }
-                        // too-little-fee orphan
+                        // Has inputs but not accepted to mempool
+                        // Probably non-standard or insufficient fee/priority
                         LogPrint("mempool", "   removed orphan tx %s\n", orphanHash.ToString());
+                        vEraseQueue.push_back(orphanHash);
+                        if (!stateDummy.CorruptionPossible()) {
+                            assert(recentRejects);
+                            recentRejects->insert(orphanHash);
+                        }
                     }
                     mempool.check(pcoinsTip);
                 }
@@ -3819,40 +5517,248 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
         else if (fMissingInputs)
         {
-            AddOrphanTx(tx, pfrom->GetId());
-
-            // DoS prevention: do not allow mapOrphanTransactions to grow unbounded
-            unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
-            unsigned int nEvicted = LimitOrphanTxSize(nMaxOrphanTx);
-            if (nEvicted > 0)
-                LogPrint("mempool", "mapOrphan overflow, removed %u tx\n", nEvicted);
-        } else if (pfrom->fWhitelisted) {
-            // Always relay transactions received from whitelisted peers, even
-            // if they are already in the mempool (allowing the node to function
-            // as a gateway for nodes hidden behind it).
-            RelayTransaction(tx);
+            bool fRejectedParents = false; // It may be the case that the orphans parents have all been rejected
+            BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+                if (recentRejects->contains(txin.prevout.hash)) {
+                    fRejectedParents = true;
+                    break;
+                }
+            }
+            if (!fRejectedParents) {
+                BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+                    CInv inv(MSG_TX, txin.prevout.hash);
+                    pfrom->AddInventoryKnown(inv);
+                    if (!AlreadyHave(inv)) pfrom->AskFor(inv);
+                }
+                AddOrphanTx(tx, pfrom->GetId());
+
+                // DoS prevention: do not allow mapOrphanTransactions to grow unbounded
+                unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
+                unsigned int nEvicted = LimitOrphanTxSize(nMaxOrphanTx);
+                if (nEvicted > 0)
+                    LogPrint("mempool", "mapOrphan overflow, removed %u tx\n", nEvicted);
+            } else {
+                LogPrint("mempool", "not keeping orphan with rejected parents %s\n",tx.GetHash().ToString());
+            }
+        } else {
+            if (!state.CorruptionPossible()) {
+                assert(recentRejects);
+                recentRejects->insert(tx.GetHash());
+            }
+
+            if (pfrom->fWhitelisted && GetBoolArg("-whitelistforcerelay", DEFAULT_WHITELISTFORCERELAY)) {
+                // Always relay transactions received from whitelisted peers, even
+                // if they were already in the mempool or rejected from it due
+                // to policy, allowing the node to function as a gateway for
+                // nodes hidden behind it.
+                //
+                // Never relay transactions that we would assign a non-zero DoS
+                // score for, as we expect peers to do the same with us in that
+                // case.
+                int nDoS = 0;
+                if (!state.IsInvalid(nDoS) || nDoS == 0) {
+                    LogPrintf("Force relaying tx %s from whitelisted peer=%d\n", tx.GetHash().ToString(), pfrom->id);
+                    RelayTransaction(tx);
+                } else {
+                    LogPrintf("Not relaying invalid transaction %s from whitelisted peer=%d (%s)\n", tx.GetHash().ToString(), pfrom->id, FormatStateMessage(state));
+                }
+            }
         }
         int nDoS = 0;
         if (state.IsInvalid(nDoS))
         {
-            LogPrint("mempool", "%s from peer=%d %s was not accepted into the memory pool: %s\n", tx.GetHash().ToString(),
-                pfrom->id, pfrom->cleanSubVer,
-                state.GetRejectReason());
-            pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),
-                               state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
-            if (nDoS > 0)
+            LogPrint("mempoolrej", "%s from peer=%d was not accepted: %s\n", tx.GetHash().ToString(),
+                pfrom->id,
+                FormatStateMessage(state));
+            if (state.GetRejectCode() < REJECT_INTERNAL) // Never send AcceptToMemoryPool's internal codes over P2P
+                pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
+                                   state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
+            if (nDoS > 0 && (!state.CorruptionPossible() || State(pfrom->id)->fHaveWitness)) {
+                // When a non-witness-supporting peer gives us a transaction that would
+                // be accepted if witness validation was off, we can't blame them for it.
                 Misbehaving(pfrom->GetId(), nDoS);
+            }
         }
+        FlushStateToDisk(state, FLUSH_STATE_PERIODIC);
     }
 
 
-    else if (strCommand == "headers" && !fImporting && !fReindex) // Ignore headers received while importing
+    else if (strCommand == NetMsgType::CMPCTBLOCK && !fImporting && !fReindex) // Ignore blocks received while importing
+    {
+        CBlockHeaderAndShortTxIDs cmpctblock;
+        vRecv >> cmpctblock;
+
+        LOCK(cs_main);
+
+        if (mapBlockIndex.find(cmpctblock.header.hashPrevBlock) == mapBlockIndex.end()) {
+            // Doesn't connect (or is genesis), instead of DoSing in AcceptBlockHeader, request deeper headers
+            if (!IsInitialBlockDownload())
+                pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), uint256());
+            return true;
+        }
+
+        CBlockIndex *pindex = NULL;
+        CValidationState state;
+        if (!AcceptBlockHeader(cmpctblock.header, state, chainparams, &pindex)) {
+            int nDoS;
+            if (state.IsInvalid(nDoS)) {
+                if (nDoS > 0)
+                    Misbehaving(pfrom->GetId(), nDoS);
+                LogPrintf("Peer %d sent us invalid header via cmpctblock\n", pfrom->id);
+                return true;
+            }
+        }
+
+        // If AcceptBlockHeader returned true, it set pindex
+        assert(pindex);
+        UpdateBlockAvailability(pfrom->GetId(), pindex->GetBlockHash());
+
+        std::map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator blockInFlightIt = mapBlocksInFlight.find(pindex->GetBlockHash());
+        bool fAlreadyInFlight = blockInFlightIt != mapBlocksInFlight.end();
+
+        if (pindex->nStatus & BLOCK_HAVE_DATA) // Nothing to do here
+            return true;
+
+        if (pindex->nChainWork <= chainActive.Tip()->nChainWork || // We know something better
+                pindex->nTx != 0) { // We had this block at some point, but pruned it
+            if (fAlreadyInFlight) {
+                // We requested this block for some reason, but our mempool will probably be useless
+                // so we just grab the block via normal getdata
+                std::vector<CInv> vInv(1);
+                vInv[0] = CInv(MSG_BLOCK, cmpctblock.header.GetHash());
+                pfrom->PushMessage(NetMsgType::GETDATA, vInv);
+                return true;
+            }
+        }
+
+        // If we're not close to tip yet, give up and let parallel block fetch work its magic
+        if (!fAlreadyInFlight && !CanDirectFetch(chainparams.GetConsensus()))
+            return true;
+
+        CNodeState *nodestate = State(pfrom->GetId());
+
+        // We want to be a bit conservative just to be extra careful about DoS
+        // possibilities in compact block processing...
+        if (pindex->nHeight <= chainActive.Height() + 2) {
+            if ((!fAlreadyInFlight && nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) ||
+                 (fAlreadyInFlight && blockInFlightIt->second.first == pfrom->GetId())) {
+                list<QueuedBlock>::iterator *queuedBlockIt = NULL;
+                if (!MarkBlockAsInFlight(pfrom->GetId(), pindex->GetBlockHash(), chainparams.GetConsensus(), pindex, &queuedBlockIt)) {
+                    if (!(*queuedBlockIt)->partialBlock)
+                        (*queuedBlockIt)->partialBlock.reset(new PartiallyDownloadedBlock(&mempool));
+                    else {
+                        // The block was already in flight using compact blocks from the same peer
+                        LogPrint("net", "Peer sent us compact block we were already syncing!\n");
+                        return true;
+                    }
+                }
+
+                PartiallyDownloadedBlock& partialBlock = *(*queuedBlockIt)->partialBlock;
+                ReadStatus status = partialBlock.InitData(cmpctblock);
+                if (status == READ_STATUS_INVALID) {
+                    MarkBlockAsReceived(pindex->GetBlockHash()); // Reset in-flight state in case of whitelist
+                    Misbehaving(pfrom->GetId(), 100);
+                    LogPrintf("Peer %d sent us invalid compact block\n", pfrom->id);
+                    return true;
+                } else if (status == READ_STATUS_FAILED) {
+                    // Duplicate txindexes, the block is now in-flight, so just request it
+                    std::vector<CInv> vInv(1);
+                    vInv[0] = CInv(MSG_BLOCK, cmpctblock.header.GetHash());
+                    pfrom->PushMessage(NetMsgType::GETDATA, vInv);
+                    return true;
+                }
+
+                BlockTransactionsRequest req;
+                for (size_t i = 0; i < cmpctblock.BlockTxCount(); i++) {
+                    if (!partialBlock.IsTxAvailable(i))
+                        req.indexes.push_back(i);
+                }
+                if (req.indexes.empty()) {
+                    // Dirty hack to jump to BLOCKTXN code (TODO: move message handling into their own functions)
+                    BlockTransactions txn;
+                    txn.blockhash = cmpctblock.header.GetHash();
+                    CDataStream blockTxnMsg(SER_NETWORK, PROTOCOL_VERSION);
+                    blockTxnMsg << txn;
+                    return ProcessMessage(pfrom, NetMsgType::BLOCKTXN, blockTxnMsg, nTimeReceived, chainparams);
+                } else {
+                    req.blockhash = pindex->GetBlockHash();
+                    pfrom->PushMessage(NetMsgType::GETBLOCKTXN, req);
+                }
+            }
+        } else {
+            if (fAlreadyInFlight) {
+                // We requested this block, but its far into the future, so our
+                // mempool will probably be useless - request the block normally
+                std::vector<CInv> vInv(1);
+                vInv[0] = CInv(MSG_BLOCK, cmpctblock.header.GetHash());
+                pfrom->PushMessage(NetMsgType::GETDATA, vInv);
+                return true;
+            } else {
+                // If this was an announce-cmpctblock, we want the same treatment as a header message
+                // Dirty hack to process as if it were just a headers message (TODO: move message handling into their own functions)
+                std::vector<CBlock> headers;
+                headers.push_back(cmpctblock.header);
+                CDataStream vHeadersMsg(SER_NETWORK, PROTOCOL_VERSION);
+                vHeadersMsg << headers;
+                return ProcessMessage(pfrom, NetMsgType::HEADERS, vHeadersMsg, nTimeReceived, chainparams);
+            }
+        }
+
+        CheckBlockIndex(chainparams.GetConsensus());
+    }
+
+    else if (strCommand == NetMsgType::BLOCKTXN && !fImporting && !fReindex) // Ignore blocks received while importing
+    {
+        BlockTransactions resp;
+        vRecv >> resp;
+
+        LOCK(cs_main);
+
+        map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator it = mapBlocksInFlight.find(resp.blockhash);
+        if (it == mapBlocksInFlight.end() || !it->second.second->partialBlock ||
+                it->second.first != pfrom->GetId()) {
+            LogPrint("net", "Peer %d sent us block transactions for block we weren't expecting\n", pfrom->id);
+            return true;
+        }
+
+        PartiallyDownloadedBlock& partialBlock = *it->second.second->partialBlock;
+        CBlock block;
+        ReadStatus status = partialBlock.FillBlock(block, resp.txn);
+        if (status == READ_STATUS_INVALID) {
+            MarkBlockAsReceived(resp.blockhash); // Reset in-flight state in case of whitelist
+            Misbehaving(pfrom->GetId(), 100);
+            LogPrintf("Peer %d sent us invalid compact block/non-matching block transactions\n", pfrom->id);
+            return true;
+        } else if (status == READ_STATUS_FAILED) {
+            // Might have collided, fall back to getdata now :(
+            std::vector<CInv> invs;
+            invs.push_back(CInv(MSG_BLOCK, resp.blockhash));
+            pfrom->PushMessage(NetMsgType::GETDATA, invs);
+        } else {
+            CValidationState state;
+            ProcessNewBlock(state, chainparams, pfrom, &block, false, NULL);
+            int nDoS;
+            if (state.IsInvalid(nDoS)) {
+                assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
+                pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
+                                   state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), block.GetHash());
+                if (nDoS > 0) {
+                    LOCK(cs_main);
+                    Misbehaving(pfrom->GetId(), nDoS);
+                }
+            }
+        }
+    }
+
+
+    else if (strCommand == NetMsgType::HEADERS && !fImporting && !fReindex) // Ignore headers received while importing
     {
         std::vector<CBlockHeader> headers;
 
         // Bypass the normal CBlock deserialization, as we don't want to risk deserializing 2000 full blocks.
         unsigned int nCount = ReadCompactSize(vRecv);
         if (nCount > MAX_HEADERS_RESULTS) {
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 20);
             return error("headers message size = %u", nCount);
         }
@@ -3862,6 +5768,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             ReadCompactSize(vRecv); // ignore tx count; assume it is 0.
         }
 
+        {
         LOCK(cs_main);
 
         if (nCount == 0) {
@@ -3869,6 +5776,35 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         }
 
+        CNodeState *nodestate = State(pfrom->GetId());
+
+        // If this looks like it could be a block announcement (nCount <
+        // MAX_BLOCKS_TO_ANNOUNCE), use special logic for handling headers that
+        // don't connect:
+        // - Send a getheaders message in response to try to connect the chain.
+        // - The peer can send up to MAX_UNCONNECTING_HEADERS in a row that
+        //   don't connect before giving DoS points
+        // - Once a headers message is received that is valid and does connect,
+        //   nUnconnectingHeaders gets reset back to 0.
+        if (mapBlockIndex.find(headers[0].hashPrevBlock) == mapBlockIndex.end() && nCount < MAX_BLOCKS_TO_ANNOUNCE) {
+            nodestate->nUnconnectingHeaders++;
+            pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), uint256());
+            LogPrint("net", "received header %s: missing prev block %s, sending getheaders (%d) to end (peer=%d, nUnconnectingHeaders=%d)\n",
+                    headers[0].GetHash().ToString(),
+                    headers[0].hashPrevBlock.ToString(),
+                    pindexBestHeader->nHeight,
+                    pfrom->id, nodestate->nUnconnectingHeaders);
+            // Set hashLastUnknownBlock for this peer, so that if we
+            // eventually get the headers - even from a different peer -
+            // we can use this peer to download.
+            UpdateBlockAvailability(pfrom->GetId(), headers.back().GetHash());
+
+            if (nodestate->nUnconnectingHeaders % MAX_UNCONNECTING_HEADERS == 0) {
+                Misbehaving(pfrom->GetId(), 20);
+            }
+            return true;
+        }
+
         CBlockIndex *pindexLast = NULL;
         BOOST_FOREACH(const CBlockHeader& header, headers) {
             CValidationState state;
@@ -3876,7 +5812,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 Misbehaving(pfrom->GetId(), 20);
                 return error("non-continuous headers sequence");
             }
-            if (!AcceptBlockHeader(header, state, &pindexLast)) {
+            if (!AcceptBlockHeader(header, state, chainparams, &pindexLast)) {
                 int nDoS;
                 if (state.IsInvalid(nDoS)) {
                     if (nDoS > 0)
@@ -3886,34 +5822,102 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             }
         }
 
-        if (pindexLast)
-            UpdateBlockAvailability(pfrom->GetId(), pindexLast->GetBlockHash());
+        if (nodestate->nUnconnectingHeaders > 0) {
+            LogPrint("net", "peer=%d: resetting nUnconnectingHeaders (%d -> 0)\n", pfrom->id, nodestate->nUnconnectingHeaders);
+        }
+        nodestate->nUnconnectingHeaders = 0;
+
+        assert(pindexLast);
+        UpdateBlockAvailability(pfrom->GetId(), pindexLast->GetBlockHash());
 
-        if (nCount == MAX_HEADERS_RESULTS && pindexLast) {
+        if (nCount == MAX_HEADERS_RESULTS) {
             // Headers message had its maximum size; the peer may have more headers.
             // TODO: optimize: if pindexLast is an ancestor of chainActive.Tip or pindexBestHeader, continue
             // from there instead.
             LogPrint("net", "more getheaders (%d) to end to peer=%d (startheight:%d)\n", pindexLast->nHeight, pfrom->id, pfrom->nStartingHeight);
-            pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexLast), uint256(0));
+            pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexLast), uint256());
+        }
+
+        bool fCanDirectFetch = CanDirectFetch(chainparams.GetConsensus());
+        // If this set of headers is valid and ends in a block with at least as
+        // much work as our tip, download as much as possible.
+        if (fCanDirectFetch && pindexLast->IsValid(BLOCK_VALID_TREE) && chainActive.Tip()->nChainWork <= pindexLast->nChainWork) {
+            vector<CBlockIndex *> vToFetch;
+            CBlockIndex *pindexWalk = pindexLast;
+            // Calculate all the blocks we'd need to switch to pindexLast, up to a limit.
+            while (pindexWalk && !chainActive.Contains(pindexWalk) && vToFetch.size() <= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
+                if (!(pindexWalk->nStatus & BLOCK_HAVE_DATA) &&
+                        !mapBlocksInFlight.count(pindexWalk->GetBlockHash()) &&
+                        (!IsWitnessEnabled(pindexWalk->pprev, chainparams.GetConsensus()) || State(pfrom->GetId())->fHaveWitness)) {
+                    // We don't have this block, and it's not yet in flight.
+                    vToFetch.push_back(pindexWalk);
+                }
+                pindexWalk = pindexWalk->pprev;
+            }
+            // If pindexWalk still isn't on our main chain, we're looking at a
+            // very large reorg at a time we think we're close to caught up to
+            // the main chain -- this shouldn't really happen.  Bail out on the
+            // direct fetch and rely on parallel download instead.
+            if (!chainActive.Contains(pindexWalk)) {
+                LogPrint("net", "Large reorg, won't direct fetch to %s (%d)\n",
+                        pindexLast->GetBlockHash().ToString(),
+                        pindexLast->nHeight);
+            } else {
+                vector<CInv> vGetData;
+                // Download as much as possible, from earliest to latest.
+                BOOST_REVERSE_FOREACH(CBlockIndex *pindex, vToFetch) {
+                    if (nodestate->nBlocksInFlight >= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
+                        // Can't download any more from this peer
+                        break;
+                    }
+                    uint32_t nFetchFlags = GetFetchFlags(pfrom, pindex->pprev, chainparams.GetConsensus());
+                    vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
+                    MarkBlockAsInFlight(pfrom->GetId(), pindex->GetBlockHash(), chainparams.GetConsensus(), pindex);
+                    LogPrint("net", "Requesting block %s from  peer=%d\n",
+                            pindex->GetBlockHash().ToString(), pfrom->id);
+                }
+                if (vGetData.size() > 1) {
+                    LogPrint("net", "Downloading blocks toward %s (%d) via headers direct fetch\n",
+                            pindexLast->GetBlockHash().ToString(), pindexLast->nHeight);
+                }
+                if (vGetData.size() > 0) {
+                    if (nodestate->fProvidesHeaderAndIDs && vGetData.size() == 1 && mapBlocksInFlight.size() == 1 && pindexLast->pprev->IsValid(BLOCK_VALID_CHAIN) && !(nLocalServices & NODE_WITNESS)) {
+                        // We seem to be rather well-synced, so it appears pfrom was the first to provide us
+                        // with this block! Let's get them to announce using compact blocks in the future.
+                        MaybeSetPeerAsAnnouncingHeaderAndIDs(nodestate, pfrom);
+                        // In any case, we want to download using a compact block, not a regular one
+                        vGetData[0] = CInv(MSG_CMPCT_BLOCK, vGetData[0].hash);
+                    }
+                    pfrom->PushMessage(NetMsgType::GETDATA, vGetData);
+                }
+            }
         }
+
+        CheckBlockIndex(chainparams.GetConsensus());
+        }
+
+        NotifyHeaderTip();
     }
 
-    else if (strCommand == "block" && !fImporting && !fReindex) // Ignore blocks received while importing
+    else if (strCommand == NetMsgType::BLOCK && !fImporting && !fReindex) // Ignore blocks received while importing
     {
         CBlock block;
         vRecv >> block;
 
-        CInv inv(MSG_BLOCK, block.GetHash());
-        LogPrint("net", "received block %s peer=%d\n", inv.hash.ToString(), pfrom->id);
-
-        pfrom->AddInventoryKnown(inv);
+        LogPrint("net", "received block %s peer=%d\n", block.GetHash().ToString(), pfrom->id);
 
         CValidationState state;
-        ProcessNewBlock(state, pfrom, &block);
+        // Process all blocks from whitelisted peers, even if not requested,
+        // unless we're still syncing with the network.
+        // Such an unrequested block may still be processed, subject to the
+        // conditions in AcceptBlock().
+        bool forceProcessing = pfrom->fWhitelisted && !IsInitialBlockDownload();
+        ProcessNewBlock(state, chainparams, pfrom, &block, forceProcessing, NULL);
         int nDoS;
         if (state.IsInvalid(nDoS)) {
-            pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),
-                               state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
+            assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
+                               state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), block.GetHash());
             if (nDoS > 0) {
                 LOCK(cs_main);
                 Misbehaving(pfrom->GetId(), nDoS);
@@ -3923,8 +5927,26 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "getaddr")
+    else if (strCommand == NetMsgType::GETADDR)
     {
+        // This asymmetric behavior for inbound and outbound connections was introduced
+        // to prevent a fingerprinting attack: an attacker can send specific fake addresses
+        // to users' AddrMan and later request them by sending getaddr messages.
+        // Making nodes which are behind NAT and can only make outgoing connections ignore
+        // the getaddr message mitigates the attack.
+        if (!pfrom->fInbound) {
+            LogPrint("net", "Ignoring \"getaddr\" from outbound connection. peer=%d\n", pfrom->id);
+            return true;
+        }
+
+        // Only send one GetAddr response per connection to reduce resource waste
+        //  and discourage addr stamping of INV announcements.
+        if (pfrom->fSentAddr) {
+            LogPrint("net", "Ignoring repeated \"getaddr\". peer=%d\n", pfrom->id);
+            return true;
+        }
+        pfrom->fSentAddr = true;
+
         pfrom->vAddrToSend.clear();
         vector<CAddress> vAddr = addrman.GetAddr();
         BOOST_FOREACH(const CAddress &addr, vAddr)
@@ -3932,32 +5954,28 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "mempool")
+    else if (strCommand == NetMsgType::MEMPOOL)
     {
-        LOCK2(cs_main, pfrom->cs_filter);
+        if (!(nLocalServices & NODE_BLOOM) && !pfrom->fWhitelisted)
+        {
+            LogPrint("net", "mempool request with bloom filters disabled, disconnect peer=%d\n", pfrom->GetId());
+            pfrom->fDisconnect = true;
+            return true;
+        }
 
-        std::vector<uint256> vtxid;
-        mempool.queryHashes(vtxid);
-        vector<CInv> vInv;
-        BOOST_FOREACH(uint256& hash, vtxid) {
-            CInv inv(MSG_TX, hash);
-            CTransaction tx;
-            bool fInMemPool = mempool.lookup(hash, tx);
-            if (!fInMemPool) continue; // another thread removed since queryHashes, maybe...
-            if ((pfrom->pfilter && pfrom->pfilter->IsRelevantAndUpdate(tx)) ||
-               (!pfrom->pfilter))
-                vInv.push_back(inv);
-            if (vInv.size() == MAX_INV_SZ) {
-                pfrom->PushMessage("inv", vInv);
-                vInv.clear();
-            }
+        if (CNode::OutboundTargetReached(false) && !pfrom->fWhitelisted)
+        {
+            LogPrint("net", "mempool request with bandwidth limit reached, disconnect peer=%d\n", pfrom->GetId());
+            pfrom->fDisconnect = true;
+            return true;
         }
-        if (vInv.size() > 0)
-            pfrom->PushMessage("inv", vInv);
+
+        LOCK(pfrom->cs_inventory);
+        pfrom->fSendMempool = true;
     }
 
 
-    else if (strCommand == "ping")
+    else if (strCommand == NetMsgType::PING)
     {
         if (pfrom->nVersion > BIP0031_VERSION)
         {
@@ -3974,12 +5992,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // it, if the remote node sends a ping once per second and this node takes 5
             // seconds to respond to each, the 5th ping the remote sends would appear to
             // return very quickly.
-            pfrom->PushMessage("pong", nonce);
+            pfrom->PushMessage(NetMsgType::PONG, nonce);
         }
     }
 
 
-    else if (strCommand == "pong")
+    else if (strCommand == NetMsgType::PONG)
     {
         int64_t pingUsecEnd = nTimeReceived;
         uint64_t nonce = 0;
@@ -3999,6 +6017,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     if (pingUsecTime > 0) {
                         // Successful ping time measurement, replace previous
                         pfrom->nPingUsecTime = pingUsecTime;
+                        pfrom->nMinPingUsecTime = std::min(pfrom->nMinPingUsecTime, pingUsecTime);
                     } else {
                         // This should never happen
                         sProblem = "Timing mishap";
@@ -4007,7 +6026,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     // Nonce mismatches are normal when pings are overlapping
                     sProblem = "Nonce mismatch";
                     if (nonce == 0) {
-                        // This is most likely a bug in another implementation somewhere, cancel this ping
+                        // This is most likely a bug in another implementation somewhere; cancel this ping
                         bPingFinished = true;
                         sProblem = "Nonce zero";
                     }
@@ -4016,15 +6035,14 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 sProblem = "Unsolicited pong without ping";
             }
         } else {
-            // This is most likely a bug in another implementation somewhere, cancel this ping
+            // This is most likely a bug in another implementation somewhere; cancel this ping
             bPingFinished = true;
             sProblem = "Short payload";
         }
 
         if (!(sProblem.empty())) {
-            LogPrint("net", "pong peer=%d %s: %s, %x expected, %x received, %u bytes\n",
+            LogPrint("net", "pong peer=%d: %s, %x expected, %x received, %u bytes\n",
                 pfrom->id,
-                pfrom->cleanSubVer,
                 sProblem,
                 pfrom->nPingNonceSent,
                 nonce,
@@ -4036,48 +6054,21 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "alert")
-    {
-        CAlert alert;
-        vRecv >> alert;
-
-        uint256 alertHash = alert.GetHash();
-        if (pfrom->setKnown.count(alertHash) == 0)
-        {
-            if (alert.ProcessAlert())
-            {
-                // Relay
-                pfrom->setKnown.insert(alertHash);
-                {
-                    LOCK(cs_vNodes);
-                    BOOST_FOREACH(CNode* pnode, vNodes)
-                        alert.RelayTo(pnode);
-                }
-            }
-            else {
-                // Small DoS penalty so peers that send us lots of
-                // duplicate/expired/invalid-signature/whatever alerts
-                // eventually get banned.
-                // This isn't a Misbehaving(100) (immediate ban) because the
-                // peer might be an older or different implementation with
-                // a different signature key, etc.
-                Misbehaving(pfrom->GetId(), 10);
-            }
-        }
-    }
-
-
-    else if (strCommand == "filterload")
+    else if (strCommand == NetMsgType::FILTERLOAD)
     {
         CBloomFilter filter;
         vRecv >> filter;
 
+        LOCK(pfrom->cs_filter);
+
         if (!filter.IsWithinSizeConstraints())
+        {
             // There is no excuse for sending a too-large filter
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 100);
+        }
         else
         {
-            LOCK(pfrom->cs_filter);
             delete pfrom->pfilter;
             pfrom->pfilter = new CBloomFilter(filter);
             pfrom->pfilter->UpdateEmptyFull();
@@ -4086,7 +6077,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "filteradd")
+    else if (strCommand == NetMsgType::FILTERADD)
     {
         vector<unsigned char> vData;
         vRecv >> vData;
@@ -4095,18 +6086,22 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         // and thus, the maximum size any matched object can have) in a filteradd message
         if (vData.size() > MAX_SCRIPT_ELEMENT_SIZE)
         {
+            LOCK(cs_main);
             Misbehaving(pfrom->GetId(), 100);
         } else {
             LOCK(pfrom->cs_filter);
             if (pfrom->pfilter)
                 pfrom->pfilter->insert(vData);
             else
+            {
+                LOCK(cs_main);
                 Misbehaving(pfrom->GetId(), 100);
+            }
         }
     }
 
 
-    else if (strCommand == "filterclear")
+    else if (strCommand == NetMsgType::FILTERCLEAR)
     {
         LOCK(pfrom->cs_filter);
         delete pfrom->pfilter;
@@ -4115,7 +6110,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "reject")
+    else if (strCommand == NetMsgType::REJECT)
     {
         if (fDebug) {
             try {
@@ -4125,32 +6120,38 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 ostringstream ss;
                 ss << strMsg << " code " << itostr(ccode) << ": " << strReason;
 
-                if (strMsg == "block" || strMsg == "tx")
+                if (strMsg == NetMsgType::BLOCK || strMsg == NetMsgType::TX)
                 {
                     uint256 hash;
                     vRecv >> hash;
                     ss << ": hash " << hash.ToString();
                 }
                 LogPrint("net", "Reject %s\n", SanitizeString(ss.str()));
-            } catch (std::ios_base::failure& e) {
+            } catch (const std::ios_base::failure&) {
                 // Avoid feedback loops by preventing reject messages from triggering a new reject message.
                 LogPrint("net", "Unparseable reject message received\n");
             }
         }
     }
 
-    else
-    {
+    else if (strCommand == NetMsgType::FEEFILTER) {
+        CAmount newFeeFilter = 0;
+        vRecv >> newFeeFilter;
+        if (MoneyRange(newFeeFilter)) {
+            {
+                LOCK(pfrom->cs_feeFilter);
+                pfrom->minFeeFilter = newFeeFilter;
+            }
+            LogPrint("net", "received: feefilter of %s from peer=%d\n", CFeeRate(newFeeFilter).ToString(), pfrom->id);
+        }
+    }
+
+    else {
         // Ignore unknown commands for extensibility
         LogPrint("net", "Unknown command \"%s\" from peer=%d\n", SanitizeString(strCommand), pfrom->id);
     }
 
 
-    // Update the last seen time for this node's address
-    if (pfrom->fNetworkNode)
-        if (strCommand == "version" || strCommand == "addr" || strCommand == "inv" || strCommand == "getdata" || strCommand == "ping")
-            AddressCurrentlyConnected(pfrom->addr);
-
 
     return true;
 }
@@ -4158,8 +6159,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 // requires LOCK(cs_vRecvMsg)
 bool ProcessMessages(CNode* pfrom)
 {
+    const CChainParams& chainparams = Params();
     //if (fDebug)
-    //    LogPrintf("ProcessMessages(%u messages)\n", pfrom->vRecvMsg.size());
+    //    LogPrintf("%s(%u messages)\n", __func__, pfrom->vRecvMsg.size());
 
     //
     // Message format
@@ -4172,7 +6174,7 @@ bool ProcessMessages(CNode* pfrom)
     bool fOk = true;
 
     if (!pfrom->vRecvGetData.empty())
-        ProcessGetData(pfrom);
+        ProcessGetData(pfrom, chainparams.GetConsensus());
 
     // this maintains the order of responses
     if (!pfrom->vRecvGetData.empty()) return fOk;
@@ -4187,7 +6189,7 @@ bool ProcessMessages(CNode* pfrom)
         CNetMessage& msg = *it;
 
         //if (fDebug)
-        //    LogPrintf("ProcessMessages(message %u msgsz, %u bytes, complete:%s)\n",
+        //    LogPrintf("%s(message %u msgsz, %u bytes, complete:%s)\n", __func__,
         //            msg.hdr.nMessageSize, msg.vRecv.size(),
         //            msg.complete() ? "Y" : "N");
 
@@ -4199,17 +6201,17 @@ bool ProcessMessages(CNode* pfrom)
         it++;
 
         // Scan for message start
-        if (memcmp(msg.hdr.pchMessageStart, Params().MessageStart(), MESSAGE_START_SIZE) != 0) {
-            LogPrintf("PROCESSMESSAGE: INVALID MESSAGESTART %s peer=%d\n", msg.hdr.GetCommand(), pfrom->id);
+        if (memcmp(msg.hdr.pchMessageStart, chainparams.MessageStart(), MESSAGE_START_SIZE) != 0) {
+            LogPrintf("PROCESSMESSAGE: INVALID MESSAGESTART %s peer=%d\n", SanitizeString(msg.hdr.GetCommand()), pfrom->id);
             fOk = false;
             break;
         }
 
         // Read header
         CMessageHeader& hdr = msg.hdr;
-        if (!hdr.IsValid())
+        if (!hdr.IsValid(chainparams.MessageStart()))
         {
-            LogPrintf("PROCESSMESSAGE: ERRORS IN HEADER %s peer=%d\n", hdr.GetCommand(), pfrom->id);
+            LogPrintf("PROCESSMESSAGE: ERRORS IN HEADER %s peer=%d\n", SanitizeString(hdr.GetCommand()), pfrom->id);
             continue;
         }
         string strCommand = hdr.GetCommand();
@@ -4220,12 +6222,11 @@ bool ProcessMessages(CNode* pfrom)
         // Checksum
         CDataStream& vRecv = msg.vRecv;
         uint256 hash = Hash(vRecv.begin(), vRecv.begin() + nMessageSize);
-        unsigned int nChecksum = 0;
-        memcpy(&nChecksum, &hash, sizeof(nChecksum));
+        unsigned int nChecksum = ReadLE32((unsigned char*)&hash);
         if (nChecksum != hdr.nChecksum)
         {
-            LogPrintf("ProcessMessages(%s, %u bytes) : CHECKSUM ERROR nChecksum=%08x hdr.nChecksum=%08x\n",
-               strCommand, nMessageSize, nChecksum, hdr.nChecksum);
+            LogPrintf("%s(%s, %u bytes): CHECKSUM ERROR nChecksum=%08x hdr.nChecksum=%08x\n", __func__,
+               SanitizeString(strCommand), nMessageSize, nChecksum, hdr.nChecksum);
             continue;
         }
 
@@ -4233,38 +6234,43 @@ bool ProcessMessages(CNode* pfrom)
         bool fRet = false;
         try
         {
-            fRet = ProcessMessage(pfrom, strCommand, vRecv, msg.nTime);
+            fRet = ProcessMessage(pfrom, strCommand, vRecv, msg.nTime, chainparams);
             boost::this_thread::interruption_point();
         }
-        catch (std::ios_base::failure& e)
+        catch (const std::ios_base::failure& e)
         {
-            pfrom->PushMessage("reject", strCommand, REJECT_MALFORMED, string("error parsing message"));
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_MALFORMED, string("error parsing message"));
             if (strstr(e.what(), "end of data"))
             {
                 // Allow exceptions from under-length message on vRecv
-                LogPrintf("ProcessMessages(%s, %u bytes) : Exception '%s' caught, normally caused by a message being shorter than its stated length\n", strCommand, nMessageSize, e.what());
+                LogPrintf("%s(%s, %u bytes): Exception '%s' caught, normally caused by a message being shorter than its stated length\n", __func__, SanitizeString(strCommand), nMessageSize, e.what());
             }
             else if (strstr(e.what(), "size too large"))
             {
                 // Allow exceptions from over-long size
-                LogPrintf("ProcessMessages(%s, %u bytes) : Exception '%s' caught\n", strCommand, nMessageSize, e.what());
+                LogPrintf("%s(%s, %u bytes): Exception '%s' caught\n", __func__, SanitizeString(strCommand), nMessageSize, e.what());
+            }
+            else if (strstr(e.what(), "non-canonical ReadCompactSize()"))
+            {
+                // Allow exceptions from non-canonical encoding
+                LogPrintf("%s(%s, %u bytes): Exception '%s' caught\n", __func__, SanitizeString(strCommand), nMessageSize, e.what());
             }
             else
             {
                 PrintExceptionContinue(&e, "ProcessMessages()");
             }
         }
-        catch (boost::thread_interrupted) {
+        catch (const boost::thread_interrupted&) {
             throw;
         }
-        catch (std::exception& e) {
+        catch (const std::exception& e) {
             PrintExceptionContinue(&e, "ProcessMessages()");
         } catch (...) {
             PrintExceptionContinue(NULL, "ProcessMessages()");
         }
 
         if (!fRet)
-            LogPrintf("ProcessMessage(%s, %u bytes) FAILED peer=%d\n", strCommand, nMessageSize, pfrom->id);
+            LogPrintf("%s(%s, %u bytes) FAILED peer=%d\n", __func__, SanitizeString(strCommand), nMessageSize, pfrom->id);
 
         break;
     }
@@ -4276,11 +6282,28 @@ bool ProcessMessages(CNode* pfrom)
     return fOk;
 }
 
+class CompareInvMempoolOrder
+{
+    CTxMemPool *mp;
+public:
+    CompareInvMempoolOrder(CTxMemPool *mempool)
+    {
+        mp = mempool;
+    }
+
+    bool operator()(std::set<uint256>::iterator a, std::set<uint256>::iterator b)
+    {
+        /* As std::make_heap produces a max-heap, we want the entries with the
+         * fewest ancestors/highest fee to sort later. */
+        return mp->CompareDepthAndScore(*b, *a);
+    }
+};
 
-bool SendMessages(CNode* pto, bool fSendTrickle)
+bool SendMessages(CNode* pto)
 {
+    const Consensus::Params& consensusParams = Params().GetConsensus();
     {
-        // Don't send anything until we get their version message
+        // Don't send anything until we get its version message
         if (pto->nVersion == 0)
             return true;
 
@@ -4305,11 +6328,11 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             pto->nPingUsecStart = GetTimeMicros();
             if (pto->nVersion > BIP0031_VERSION) {
                 pto->nPingNonceSent = nonce;
-                pto->PushMessage("ping", nonce);
+                pto->PushMessage(NetMsgType::PING, nonce);
             } else {
                 // Peer is too old to support ping command with nonce, pong will never arrive.
                 pto->nPingNonceSent = 0;
-                pto->PushMessage("ping");
+                pto->PushMessage(NetMsgType::PING);
             }
         }
 
@@ -4318,47 +6341,39 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             return true;
 
         // Address refresh broadcast
-        static int64_t nLastRebroadcast;
-        if (!IsInitialBlockDownload() && (GetTime() - nLastRebroadcast > 24 * 60 * 60))
-        {
-            LOCK(cs_vNodes);
-            BOOST_FOREACH(CNode* pnode, vNodes)
-            {
-                // Periodically clear setAddrKnown to allow refresh broadcasts
-                if (nLastRebroadcast)
-                    pnode->setAddrKnown.clear();
-
-                // Rebroadcast our address
-                AdvertizeLocal(pnode);
-            }
-            if (!vNodes.empty())
-                nLastRebroadcast = GetTime();
+        int64_t nNow = GetTimeMicros();
+        if (!IsInitialBlockDownload() && pto->nNextLocalAddrSend < nNow) {
+            AdvertiseLocal(pto);
+            pto->nNextLocalAddrSend = PoissonNextSend(nNow, AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL);
         }
 
         //
         // Message: addr
         //
-        if (fSendTrickle)
-        {
+        if (pto->nNextAddrSend < nNow) {
+            pto->nNextAddrSend = PoissonNextSend(nNow, AVG_ADDRESS_BROADCAST_INTERVAL);
             vector<CAddress> vAddr;
             vAddr.reserve(pto->vAddrToSend.size());
             BOOST_FOREACH(const CAddress& addr, pto->vAddrToSend)
             {
-                // returns true if wasn't already contained in the set
-                if (pto->setAddrKnown.insert(addr).second)
+                if (!pto->addrKnown.contains(addr.GetKey()))
                 {
+                    pto->addrKnown.insert(addr.GetKey());
                     vAddr.push_back(addr);
                     // receiver rejects addr messages larger than 1000
                     if (vAddr.size() >= 1000)
                     {
-                        pto->PushMessage("addr", vAddr);
+                        pto->PushMessage(NetMsgType::ADDR, vAddr);
                         vAddr.clear();
                     }
                 }
             }
             pto->vAddrToSend.clear();
             if (!vAddr.empty())
-                pto->PushMessage("addr", vAddr);
+                pto->PushMessage(NetMsgType::ADDR, vAddr);
+            // we only send the big addr message once
+            if (pto->vAddrToSend.capacity() > 40)
+                pto->vAddrToSend.shrink_to_fit();
         }
 
         CNodeState &state = *State(pto->GetId());
@@ -4371,28 +6386,37 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                     LogPrintf("Warning: not banning local peer %s!\n", pto->addr.ToString());
                 else
                 {
-                    CNode::Ban(pto->addr);
+                    CNode::Ban(pto->addr, BanReasonNodeMisbehaving);
                 }
             }
             state.fShouldBan = false;
         }
 
         BOOST_FOREACH(const CBlockReject& reject, state.rejects)
-            pto->PushMessage("reject", (string)"block", reject.chRejectCode, reject.strRejectReason, reject.hashBlock);
+            pto->PushMessage(NetMsgType::REJECT, (string)NetMsgType::BLOCK, reject.chRejectCode, reject.strRejectReason, reject.hashBlock);
         state.rejects.clear();
 
         // Start block sync
         if (pindexBestHeader == NULL)
             pindexBestHeader = chainActive.Tip();
         bool fFetch = state.fPreferredDownload || (nPreferredDownload == 0 && !pto->fClient && !pto->fOneShot); // Download if this is a nice peer, or we have no nice peers and this one might do.
-        if (!state.fSyncStarted && !pto->fClient && fFetch && !fImporting && !fReindex) {
+        if (!state.fSyncStarted && !pto->fClient && !fImporting && !fReindex) {
             // Only actively request headers from a single peer, unless we're close to today.
-            if (nSyncStarted == 0 || pindexBestHeader->GetBlockTime() > GetAdjustedTime() - 24 * 60 * 60) {
+            if ((nSyncStarted == 0 && fFetch) || pindexBestHeader->GetBlockTime() > GetAdjustedTime() - 24 * 60 * 60) {
                 state.fSyncStarted = true;
                 nSyncStarted++;
-                CBlockIndex *pindexStart = pindexBestHeader->pprev ? pindexBestHeader->pprev : pindexBestHeader;
+                const CBlockIndex *pindexStart = pindexBestHeader;
+                /* If possible, start at the block preceding the currently
+                   best known header.  This ensures that we always get a
+                   non-empty list of headers back as long as the peer
+                   is up-to-date.  With a non-empty response, we can initialise
+                   the peer's known best block.  This wouldn't be possible
+                   if we requested starting at pindexBestHeader and
+                   got back an empty response.  */
+                if (pindexStart->pprev)
+                    pindexStart = pindexStart->pprev;
                 LogPrint("net", "initial getheaders (%d) to peer=%d (startheight:%d)\n", pindexStart->nHeight, pto->id, pto->nStartingHeight);
-                pto->PushMessage("getheaders", chainActive.GetLocator(pindexStart), uint256(0));
+                pto->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexStart), uint256());
             }
         }
 
@@ -4401,59 +6425,268 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
         // transactions become unconfirmed and spams other nodes.
         if (!fReindex && !fImporting && !IsInitialBlockDownload())
         {
-            g_signals.Broadcast();
+            GetMainSignals().Broadcast(nTimeBestReceived);
+        }
+
+        //
+        // Try sending block announcements via headers
+        //
+        {
+            // If we have less than MAX_BLOCKS_TO_ANNOUNCE in our
+            // list of block hashes we're relaying, and our peer wants
+            // headers announcements, then find the first header
+            // not yet known to our peer but would connect, and send.
+            // If no header would connect, or if we have too many
+            // blocks, or if the peer doesn't want headers, just
+            // add all to the inv queue.
+            LOCK(pto->cs_inventory);
+            vector<CBlock> vHeaders;
+            bool fRevertToInv = ((!state.fPreferHeaders &&
+                                 (!state.fPreferHeaderAndIDs || pto->vBlockHashesToAnnounce.size() > 1)) ||
+                                pto->vBlockHashesToAnnounce.size() > MAX_BLOCKS_TO_ANNOUNCE);
+            CBlockIndex *pBestIndex = NULL; // last header queued for delivery
+            ProcessBlockAvailability(pto->id); // ensure pindexBestKnownBlock is up-to-date
+
+            if (!fRevertToInv) {
+                bool fFoundStartingHeader = false;
+                // Try to find first header that our peer doesn't have, and
+                // then send all headers past that one.  If we come across any
+                // headers that aren't on chainActive, give up.
+                BOOST_FOREACH(const uint256 &hash, pto->vBlockHashesToAnnounce) {
+                    BlockMap::iterator mi = mapBlockIndex.find(hash);
+                    assert(mi != mapBlockIndex.end());
+                    CBlockIndex *pindex = mi->second;
+                    if (chainActive[pindex->nHeight] != pindex) {
+                        // Bail out if we reorged away from this block
+                        fRevertToInv = true;
+                        break;
+                    }
+                    if (pBestIndex != NULL && pindex->pprev != pBestIndex) {
+                        // This means that the list of blocks to announce don't
+                        // connect to each other.
+                        // This shouldn't really be possible to hit during
+                        // regular operation (because reorgs should take us to
+                        // a chain that has some block not on the prior chain,
+                        // which should be caught by the prior check), but one
+                        // way this could happen is by using invalidateblock /
+                        // reconsiderblock repeatedly on the tip, causing it to
+                        // be added multiple times to vBlockHashesToAnnounce.
+                        // Robustly deal with this rare situation by reverting
+                        // to an inv.
+                        fRevertToInv = true;
+                        break;
+                    }
+                    pBestIndex = pindex;
+                    if (fFoundStartingHeader) {
+                        // add this to the headers message
+                        vHeaders.push_back(pindex->GetBlockHeader());
+                    } else if (PeerHasHeader(&state, pindex)) {
+                        continue; // keep looking for the first new block
+                    } else if (pindex->pprev == NULL || PeerHasHeader(&state, pindex->pprev)) {
+                        // Peer doesn't have this header but they do have the prior one.
+                        // Start sending headers.
+                        fFoundStartingHeader = true;
+                        vHeaders.push_back(pindex->GetBlockHeader());
+                    } else {
+                        // Peer doesn't have this header or the prior one -- nothing will
+                        // connect, so bail out.
+                        fRevertToInv = true;
+                        break;
+                    }
+                }
+            }
+            if (!fRevertToInv && !vHeaders.empty()) {
+                if (vHeaders.size() == 1 && state.fPreferHeaderAndIDs) {
+                    // We only send up to 1 block as header-and-ids, as otherwise
+                    // probably means we're doing an initial-ish-sync or they're slow
+                    LogPrint("net", "%s sending header-and-ids %s to peer %d\n", __func__,
+                            vHeaders.front().GetHash().ToString(), pto->id);
+                    //TODO: Shouldn't need to reload block from disk, but requires refactor
+                    CBlock block;
+                    assert(ReadBlockFromDisk(block, pBestIndex, consensusParams));
+                    CBlockHeaderAndShortTxIDs cmpctblock(block);
+                    pto->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::CMPCTBLOCK, cmpctblock);
+                    state.pindexBestHeaderSent = pBestIndex;
+                } else if (state.fPreferHeaders) {
+                    if (vHeaders.size() > 1) {
+                        LogPrint("net", "%s: %u headers, range (%s, %s), to peer=%d\n", __func__,
+                                vHeaders.size(),
+                                vHeaders.front().GetHash().ToString(),
+                                vHeaders.back().GetHash().ToString(), pto->id);
+                    } else {
+                        LogPrint("net", "%s: sending header %s to peer=%d\n", __func__,
+                                vHeaders.front().GetHash().ToString(), pto->id);
+                    }
+                    pto->PushMessage(NetMsgType::HEADERS, vHeaders);
+                    state.pindexBestHeaderSent = pBestIndex;
+                } else
+                    fRevertToInv = true;
+            }
+            if (fRevertToInv) {
+                // If falling back to using an inv, just try to inv the tip.
+                // The last entry in vBlockHashesToAnnounce was our tip at some point
+                // in the past.
+                if (!pto->vBlockHashesToAnnounce.empty()) {
+                    const uint256 &hashToAnnounce = pto->vBlockHashesToAnnounce.back();
+                    BlockMap::iterator mi = mapBlockIndex.find(hashToAnnounce);
+                    assert(mi != mapBlockIndex.end());
+                    CBlockIndex *pindex = mi->second;
+
+                    // Warn if we're announcing a block that is not on the main chain.
+                    // This should be very rare and could be optimized out.
+                    // Just log for now.
+                    if (chainActive[pindex->nHeight] != pindex) {
+                        LogPrint("net", "Announcing block %s not on main chain (tip=%s)\n",
+                            hashToAnnounce.ToString(), chainActive.Tip()->GetBlockHash().ToString());
+                    }
+
+                    // If the peer's chain has this block, don't inv it back.
+                    if (!PeerHasHeader(&state, pindex)) {
+                        pto->PushInventory(CInv(MSG_BLOCK, hashToAnnounce));
+                        LogPrint("net", "%s: sending inv peer=%d hash=%s\n", __func__,
+                            pto->id, hashToAnnounce.ToString());
+                    }
+                }
+            }
+            pto->vBlockHashesToAnnounce.clear();
         }
 
         //
         // Message: inventory
         //
         vector<CInv> vInv;
-        vector<CInv> vInvWait;
         {
             LOCK(pto->cs_inventory);
-            vInv.reserve(pto->vInventoryToSend.size());
-            vInvWait.reserve(pto->vInventoryToSend.size());
-            BOOST_FOREACH(const CInv& inv, pto->vInventoryToSend)
-            {
-                if (pto->setInventoryKnown.count(inv))
-                    continue;
+            vInv.reserve(std::max<size_t>(pto->vInventoryBlockToSend.size(), INVENTORY_BROADCAST_MAX));
+
+            // Add blocks
+            BOOST_FOREACH(const uint256& hash, pto->vInventoryBlockToSend) {
+                vInv.push_back(CInv(MSG_BLOCK, hash));
+                if (vInv.size() == MAX_INV_SZ) {
+                    pto->PushMessage(NetMsgType::INV, vInv);
+                    vInv.clear();
+                }
+            }
+            pto->vInventoryBlockToSend.clear();
+
+            // Check whether periodic sends should happen
+            bool fSendTrickle = pto->fWhitelisted;
+            if (pto->nNextInvSend < nNow) {
+                fSendTrickle = true;
+                // Use half the delay for outbound peers, as there is less privacy concern for them.
+                pto->nNextInvSend = PoissonNextSend(nNow, INVENTORY_BROADCAST_INTERVAL >> !pto->fInbound);
+            }
+
+            // Time to send but the peer has requested we not relay transactions.
+            if (fSendTrickle) {
+                LOCK(pto->cs_filter);
+                if (!pto->fRelayTxes) pto->setInventoryTxToSend.clear();
+            }
 
-                // trickle out tx inv to protect privacy
-                if (inv.type == MSG_TX && !fSendTrickle)
+            // Respond to BIP35 mempool requests
+            if (fSendTrickle && pto->fSendMempool) {
+                auto vtxinfo = mempool.infoAll();
+                pto->fSendMempool = false;
+                CAmount filterrate = 0;
                 {
-                    // 1/4 of tx invs blast to all immediately
-                    static uint256 hashSalt;
-                    if (hashSalt == 0)
-                        hashSalt = GetRandHash();
-                    uint256 hashRand = inv.hash ^ hashSalt;
-                    hashRand = Hash(BEGIN(hashRand), END(hashRand));
-                    bool fTrickleWait = ((hashRand & 3) != 0);
-
-                    if (fTrickleWait)
-                    {
-                        vInvWait.push_back(inv);
-                        continue;
+                    LOCK(pto->cs_feeFilter);
+                    filterrate = pto->minFeeFilter;
+                }
+
+                LOCK(pto->cs_filter);
+
+                for (const auto& txinfo : vtxinfo) {
+                    const uint256& hash = txinfo.tx->GetHash();
+                    CInv inv(MSG_TX, hash);
+                    pto->setInventoryTxToSend.erase(hash);
+                    if (filterrate) {
+                        if (txinfo.feeRate.GetFeePerK() < filterrate)
+                            continue;
+                    }
+                    if (pto->pfilter) {
+                        if (!pto->pfilter->IsRelevantAndUpdate(*txinfo.tx)) continue;
+                    }
+                    pto->filterInventoryKnown.insert(hash);
+                    vInv.push_back(inv);
+                    if (vInv.size() == MAX_INV_SZ) {
+                        pto->PushMessage(NetMsgType::INV, vInv);
+                        vInv.clear();
                     }
                 }
+                pto->timeLastMempoolReq = GetTime();
+            }
 
-                // returns true if wasn't already contained in the set
-                if (pto->setInventoryKnown.insert(inv).second)
+            // Determine transactions to relay
+            if (fSendTrickle) {
+                // Produce a vector with all candidates for sending
+                vector<std::set<uint256>::iterator> vInvTx;
+                vInvTx.reserve(pto->setInventoryTxToSend.size());
+                for (std::set<uint256>::iterator it = pto->setInventoryTxToSend.begin(); it != pto->setInventoryTxToSend.end(); it++) {
+                    vInvTx.push_back(it);
+                }
+                CAmount filterrate = 0;
                 {
-                    vInv.push_back(inv);
-                    if (vInv.size() >= 1000)
+                    LOCK(pto->cs_feeFilter);
+                    filterrate = pto->minFeeFilter;
+                }
+                // Topologically and fee-rate sort the inventory we send for privacy and priority reasons.
+                // A heap is used so that not all items need sorting if only a few are being sent.
+                CompareInvMempoolOrder compareInvMempoolOrder(&mempool);
+                std::make_heap(vInvTx.begin(), vInvTx.end(), compareInvMempoolOrder);
+                // No reason to drain out at many times the network's capacity,
+                // especially since we have many peers and some will draw much shorter delays.
+                unsigned int nRelayedTransactions = 0;
+                LOCK(pto->cs_filter);
+                while (!vInvTx.empty() && nRelayedTransactions < INVENTORY_BROADCAST_MAX) {
+                    // Fetch the top element from the heap
+                    std::pop_heap(vInvTx.begin(), vInvTx.end(), compareInvMempoolOrder);
+                    std::set<uint256>::iterator it = vInvTx.back();
+                    vInvTx.pop_back();
+                    uint256 hash = *it;
+                    // Remove it from the to-be-sent set
+                    pto->setInventoryTxToSend.erase(it);
+                    // Check if not in the filter already
+                    if (pto->filterInventoryKnown.contains(hash)) {
+                        continue;
+                    }
+                    // Not in the mempool anymore? don't bother sending it.
+                    auto txinfo = mempool.info(hash);
+                    if (!txinfo.tx) {
+                        continue;
+                    }
+                    if (filterrate && txinfo.feeRate.GetFeePerK() < filterrate) {
+                        continue;
+                    }
+                    if (pto->pfilter && !pto->pfilter->IsRelevantAndUpdate(*txinfo.tx)) continue;
+                    // Send
+                    vInv.push_back(CInv(MSG_TX, hash));
+                    nRelayedTransactions++;
                     {
-                        pto->PushMessage("inv", vInv);
+                        // Expire old relay messages
+                        while (!vRelayExpiration.empty() && vRelayExpiration.front().first < nNow)
+                        {
+                            mapRelay.erase(vRelayExpiration.front().second);
+                            vRelayExpiration.pop_front();
+                        }
+
+                        auto ret = mapRelay.insert(std::make_pair(hash, std::move(txinfo.tx)));
+                        if (ret.second) {
+                            vRelayExpiration.push_back(std::make_pair(nNow + 15 * 60 * 1000000, ret.first));
+                        }
+                    }
+                    if (vInv.size() == MAX_INV_SZ) {
+                        pto->PushMessage(NetMsgType::INV, vInv);
                         vInv.clear();
                     }
+                    pto->filterInventoryKnown.insert(hash);
                 }
             }
-            pto->vInventoryToSend = vInvWait;
         }
         if (!vInv.empty())
-            pto->PushMessage("inv", vInv);
+            pto->PushMessage(NetMsgType::INV, vInv);
 
         // Detect whether we're stalling
-        int64_t nNow = GetTimeMicros();
+        nNow = GetTimeMicros();
         if (!pto->fDisconnect && state.nStallingSince && state.nStallingSince < nNow - 1000000 * BLOCK_STALLING_TIMEOUT) {
             // Stalling only triggers when the block download window cannot move. During normal steady state,
             // the download window should be much larger than the to-be-downloaded set of blocks, so disconnection
@@ -4461,20 +6694,36 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             LogPrintf("Peer=%d is stalling block download, disconnecting\n", pto->id);
             pto->fDisconnect = true;
         }
+        // In case there is a block that has been in flight from this peer for 2 + 0.5 * N times the block interval
+        // (with N the number of peers from which we're downloading validated blocks), disconnect due to timeout.
+        // We compensate for other peers to prevent killing off peers due to our own downstream link
+        // being saturated. We only count validated in-flight blocks so peers can't advertise non-existing block hashes
+        // to unreasonably increase our timeout.
+        if (!pto->fDisconnect && state.vBlocksInFlight.size() > 0) {
+            QueuedBlock &queuedBlock = state.vBlocksInFlight.front();
+            int nOtherPeersWithValidatedDownloads = nPeersWithValidatedDownloads - (state.nBlocksInFlightValidHeaders > 0);
+            if (nNow > state.nDownloadingSince + consensusParams.nPowTargetSpacing * (BLOCK_DOWNLOAD_TIMEOUT_BASE + BLOCK_DOWNLOAD_TIMEOUT_PER_PEER * nOtherPeersWithValidatedDownloads)) {
+                LogPrintf("Timeout downloading block %s from peer=%d, disconnecting\n", queuedBlock.hash.ToString(), pto->id);
+                pto->fDisconnect = true;
+            }
+        }
 
         //
         // Message: getdata (blocks)
         //
         vector<CInv> vGetData;
-        if (!pto->fDisconnect && !pto->fClient && fFetch && state.nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
+        if (!pto->fDisconnect && !pto->fClient && (fFetch || !IsInitialBlockDownload()) && state.nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
             vector<CBlockIndex*> vToDownload;
             NodeId staller = -1;
             FindNextBlocksToDownload(pto->GetId(), MAX_BLOCKS_IN_TRANSIT_PER_PEER - state.nBlocksInFlight, vToDownload, staller);
             BOOST_FOREACH(CBlockIndex *pindex, vToDownload) {
-                vGetData.push_back(CInv(MSG_BLOCK, pindex->GetBlockHash()));
-                MarkBlockAsInFlight(pto->GetId(), pindex->GetBlockHash(), pindex);
-                LogPrint("net", "Requesting block %s (%d) peer=%d\n", pindex->GetBlockHash().ToString(),
-                    pindex->nHeight, pto->id);
+                if (State(pto->GetId())->fHaveWitness || !IsWitnessEnabled(pindex->pprev, consensusParams)) {
+                    uint32_t nFetchFlags = GetFetchFlags(pto, pindex->pprev, consensusParams);
+                    vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
+                    MarkBlockAsInFlight(pto->GetId(), pindex->GetBlockHash(), consensusParams, pindex);
+                    LogPrint("net", "Requesting block %s (%d) peer=%d\n", pindex->GetBlockHash().ToString(),
+                        pindex->nHeight, pto->id);
+                }
             }
             if (state.nBlocksInFlight == 0 && staller != -1) {
                 if (State(staller)->nStallingSince == 0) {
@@ -4497,71 +6746,42 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 vGetData.push_back(inv);
                 if (vGetData.size() >= 1000)
                 {
-                    pto->PushMessage("getdata", vGetData);
+                    pto->PushMessage(NetMsgType::GETDATA, vGetData);
                     vGetData.clear();
                 }
+            } else {
+                //If we're not going to ask, don't expect a response.
+                pto->setAskFor.erase(inv.hash);
             }
             pto->mapAskFor.erase(pto->mapAskFor.begin());
         }
         if (!vGetData.empty())
-            pto->PushMessage("getdata", vGetData);
-
-    }
-    return true;
-}
-
-
-bool CBlockUndo::WriteToDisk(CDiskBlockPos &pos, const uint256 &hashBlock)
-{
-    // Open history file to append
-    CAutoFile fileout(OpenUndoFile(pos), SER_DISK, CLIENT_VERSION);
-    if (fileout.IsNull())
-        return error("CBlockUndo::WriteToDisk : OpenUndoFile failed");
-
-    // Write index header
-    unsigned int nSize = fileout.GetSerializeSize(*this);
-    fileout << FLATDATA(Params().MessageStart()) << nSize;
-
-    // Write undo data
-    long fileOutPos = ftell(fileout.Get());
-    if (fileOutPos < 0)
-        return error("CBlockUndo::WriteToDisk : ftell failed");
-    pos.nPos = (unsigned int)fileOutPos;
-    fileout << *this;
-
-    // calculate & write checksum
-    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
-    hasher << hashBlock;
-    hasher << *this;
-    fileout << hasher.GetHash();
+            pto->PushMessage(NetMsgType::GETDATA, vGetData);
 
-    return true;
-}
-
-bool CBlockUndo::ReadFromDisk(const CDiskBlockPos &pos, const uint256 &hashBlock)
-{
-    // Open history file to read
-    CAutoFile filein(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
-    if (filein.IsNull())
-        return error("CBlockUndo::ReadFromDisk : OpenBlockFile failed");
-
-    // Read block
-    uint256 hashChecksum;
-    try {
-        filein >> *this;
-        filein >> hashChecksum;
-    }
-    catch (std::exception &e) {
-        return error("%s : Deserialize or I/O error - %s", __func__, e.what());
+        //
+        // Message: feefilter
+        //
+        // We don't want white listed peers to filter txs to us if we have -whitelistforcerelay
+        if (pto->nVersion >= FEEFILTER_VERSION && GetBoolArg("-feefilter", DEFAULT_FEEFILTER) &&
+            !(pto->fWhitelisted && GetBoolArg("-whitelistforcerelay", DEFAULT_WHITELISTFORCERELAY))) {
+            CAmount currentFilter = mempool.GetMinFee(GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000).GetFeePerK();
+            int64_t timeNow = GetTimeMicros();
+            if (timeNow > pto->nextSendTimeFeeFilter) {
+                CAmount filterToSend = filterRounder.round(currentFilter);
+                if (filterToSend != pto->lastSentFeeFilter) {
+                    pto->PushMessage(NetMsgType::FEEFILTER, filterToSend);
+                    pto->lastSentFeeFilter = filterToSend;
+                }
+                pto->nextSendTimeFeeFilter = PoissonNextSend(timeNow, AVG_FEEFILTER_BROADCAST_INTERVAL);
+            }
+            // If the fee filter has changed substantially and it's still more than MAX_FEEFILTER_CHANGE_DELAY
+            // until scheduled broadcast, then move the broadcast to within MAX_FEEFILTER_CHANGE_DELAY.
+            else if (timeNow + MAX_FEEFILTER_CHANGE_DELAY * 1000000 < pto->nextSendTimeFeeFilter &&
+                     (currentFilter < 3 * pto->lastSentFeeFilter / 4 || currentFilter > 4 * pto->lastSentFeeFilter / 3)) {
+                pto->nextSendTimeFeeFilter = timeNow + (insecure_rand() % MAX_FEEFILTER_CHANGE_DELAY) * 1000000;
+            }
+        }
     }
-
-    // Verify checksum
-    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
-    hasher << hashBlock;
-    hasher << *this;
-    if (hashChecksum != hasher.GetHash())
-        return error("CBlockUndo::ReadFromDisk : Checksum mismatch");
-
     return true;
 }
 
@@ -4569,7 +6789,11 @@ bool CBlockUndo::ReadFromDisk(const CDiskBlockPos &pos, const uint256 &hashBlock
      return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, DateTimeStrFormat("%Y-%m-%d", nTimeFirst), DateTimeStrFormat("%Y-%m-%d", nTimeLast));
  }
 
-
+ThresholdState VersionBitsTipState(const Consensus::Params& params, Consensus::DeploymentPos pos)
+{
+    LOCK(cs_main);
+    return VersionBitsState(chainActive.Tip(), params, pos, versionbitscache);
+}
 
 class CMainCleanup
 {