Merge pull request #3370 from sipa/headersfirst3

Prepare block connection logic for headers-first

3 files changed, 284 insertions, 229 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 7213477b22..8520d63c89 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -983,7 +983,7 @@ bool AppInit2(boost::thread_group& threadGroup)
 
     // scan for better chains in the block chain database, that are not yet connected in the active best chain
     CValidationState state;
-    if (!ConnectBestBlock(state))
+    if (!ActivateBestChain(state))
         strErrors << "Failed to connect best block";
 
     std::vector<boost::filesystem::path> vImportFiles;
diff --git a/src/main.cpp b/src/main.cpp
index 610efaf07d..3c174a4650 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -41,6 +41,7 @@ CTxMemPool mempool;
 
 map<uint256, CBlockIndex*> mapBlockIndex;
 CChain chainActive;
+CChain chainMostWork;
 int64_t nTimeBestReceived = 0;
 int nScriptCheckThreads = 0;
 bool fImporting = false;
@@ -77,13 +78,21 @@ namespace {
 struct CBlockIndexWorkComparator
 {
     bool operator()(CBlockIndex *pa, CBlockIndex *pb) {
+        // First sort by most total work, ...
         if (pa->nChainWork > pb->nChainWork) return false;
         if (pa->nChainWork < pb->nChainWork) return true;
 
-        if (pa->GetBlockHash() < pb->GetBlockHash()) return false;
-        if (pa->GetBlockHash() > pb->GetBlockHash()) return true;
+        // ... then by earliest time received, ...
+        if (pa->nSequenceId < pb->nSequenceId) return false;
+        if (pa->nSequenceId > pb->nSequenceId) return true;
 
-        return false; // identical blocks
+        // Use pointer address as tie breaker (should only happen with blocks
+        // loaded from disk, as those all have id 0).
+        if (pa < pb) return false;
+        if (pa > pb) return true;
+
+        // Identical blocks.
+        return false;
     }
 };
 
@@ -93,6 +102,16 @@ set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid; // may contain
 CCriticalSection cs_LastBlockFile;
 CBlockFileInfo infoLastBlockFile;
 int nLastBlockFile = 0;
+
+// Every received block is assigned a unique and increasing identifier, so we
+// know which one to give priority in case of a fork.
+CCriticalSection cs_nBlockSequenceId;
+// Blocks loaded from disk are assigned id 0, so start the counter at 1.
+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.
+map<uint256, NodeId> mapBlockSource;
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -156,14 +175,26 @@ void SyncWithWallets(const uint256 &hash, const CTransaction &tx, const CBlock *
 //
 
 namespace {
+
+struct CBlockReject {
+    unsigned char chRejectCode;
+    string strRejectReason;
+    uint256 hashBlock;
+};
+
 // Maintain validation-specific state about nodes, protected by cs_main, instead
 // by CNode's own locks. This simplifies asynchronous operation, where
 // processing of incoming data is done after the ProcessMessage call returns,
 // and we're no longer holding the node's locks.
 struct CNodeState {
+    // Accumulated misbehaviour score for this peer.
     int nMisbehavior;
+    // Whether this peer should be disconnected and banned.
     bool fShouldBan;
+    // String name of this peer (debugging/logging purposes).
     std::string name;
+    // List of asynchronously-determined block rejections to notify this peer about.
+    std::vector<CBlockReject> rejects;
 
     CNodeState() {
         nMisbehavior = 0;
@@ -171,6 +202,7 @@ struct CNodeState {
     }
 };
 
+// Map maintaining per-node state. Requires cs_main.
 map<NodeId, CNodeState> mapNodeState;
 
 // Requires cs_main.
@@ -1242,6 +1274,24 @@ void CheckForkWarningConditionsOnNewFork(CBlockIndex* pindexNewForkTip)
     CheckForkWarningConditions();
 }
 
+void Misbehaving(NodeId pnode, int howmuch)
+{
+    if (howmuch == 0)
+        return;
+
+    CNodeState *state = State(pnode);
+    if (state == NULL)
+        return;
+
+    state->nMisbehavior += howmuch;
+    if (state->nMisbehavior >= GetArg("-banscore", 100))
+    {
+        LogPrintf("Misbehaving: %s (%d -> %d) BAN THRESHOLD EXCEEDED\n", state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
+        state->fShouldBan = true;
+    } else
+        LogPrintf("Misbehaving: %s (%d -> %d)\n", state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
+}
+
 void static InvalidChainFound(CBlockIndex* pindexNew)
 {
     if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
@@ -1263,67 +1313,23 @@ void static InvalidChainFound(CBlockIndex* pindexNew)
     CheckForkWarningConditions();
 }
 
-void static InvalidBlockFound(CBlockIndex *pindex) {
-    pindex->nStatus |= BLOCK_FAILED_VALID;
-    pblocktree->WriteBlockIndex(CDiskBlockIndex(pindex));
-    setBlockIndexValid.erase(pindex);
-    InvalidChainFound(pindex);
-    if (chainActive.Next(pindex)) {
-        CValidationState stateDummy;
-        ConnectBestBlock(stateDummy); // reorganise away from the failed block
-    }
-}
-
-bool ConnectBestBlock(CValidationState &state) {
-    do {
-        CBlockIndex *pindexNewBest;
-
-        {
-            std::set<CBlockIndex*,CBlockIndexWorkComparator>::reverse_iterator it = setBlockIndexValid.rbegin();
-            if (it == setBlockIndexValid.rend())
-                return true;
-            pindexNewBest = *it;
+void static InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state) {
+    int nDoS = 0;
+    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(), pindex->GetBlockHash()};
+            State(it->second)->rejects.push_back(reject);
+            if (nDoS > 0)
+                Misbehaving(it->second, nDoS);
         }
-
-        if (pindexNewBest == chainActive.Tip() || (chainActive.Tip() && pindexNewBest->nChainWork == chainActive.Tip()->nChainWork))
-            return true; // nothing to do
-
-        // check ancestry
-        CBlockIndex *pindexTest = pindexNewBest;
-        std::vector<CBlockIndex*> vAttach;
-        do {
-            if (pindexTest->nStatus & BLOCK_FAILED_MASK) {
-                // mark descendants failed
-                CBlockIndex *pindexFailed = pindexNewBest;
-                while (pindexTest != pindexFailed) {
-                    pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
-                    setBlockIndexValid.erase(pindexFailed);
-                    pblocktree->WriteBlockIndex(CDiskBlockIndex(pindexFailed));
-                    pindexFailed = pindexFailed->pprev;
-                }
-                InvalidChainFound(pindexNewBest);
-                break;
-            }
-
-            if (chainActive.Tip() == NULL || pindexTest->nChainWork > chainActive.Tip()->nChainWork)
-                vAttach.push_back(pindexTest);
-
-            if (pindexTest->pprev == NULL || chainActive.Next(pindexTest)) {
-                reverse(vAttach.begin(), vAttach.end());
-                BOOST_FOREACH(CBlockIndex *pindexSwitch, vAttach) {
-                    boost::this_thread::interruption_point();
-                    try {
-                        if (!SetBestChain(state, pindexSwitch))
-                            return false;
-                    } catch(std::runtime_error &e) {
-                        return state.Abort(_("System error: ") + e.what());
-                    }
-                }
-                return true;
-            }
-            pindexTest = pindexTest->pprev;
-        } while(true);
-    } while(true);
+    }
+    if (!state.CorruptionPossible()) {
+        pindex->nStatus |= BLOCK_FAILED_VALID;
+        pblocktree->WriteBlockIndex(CDiskBlockIndex(pindex));
+        setBlockIndexValid.erase(pindex);
+        InvalidChainFound(pindex);
+    }
 }
 
 void UpdateTime(CBlockHeader& block, const CBlockIndex* pindexPrev)
@@ -1746,102 +1752,10 @@ bool ConnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex, C
     return true;
 }
 
-bool SetBestChain(CValidationState &state, CBlockIndex* pindexNew)
-{
-    mempool.check(pcoinsTip);
-
-    // All modifications to the coin state will be done in this cache.
-    // Only when all have succeeded, we push it to pcoinsTip.
-    CCoinsViewCache view(*pcoinsTip, true);
-
-    // Find the fork (typically, there is none)
-    std::map<uint256, CBlockIndex*>::iterator it = mapBlockIndex.find(view.GetBestBlock());
-    CBlockIndex* ptip = (it != mapBlockIndex.end()) ? it->second : NULL;
-    CBlockIndex* pfork = ptip;
-    CBlockIndex* plonger = pindexNew;
-    while (pfork && pfork != plonger)
-    {
-        while (plonger->nHeight > pfork->nHeight) {
-            plonger = plonger->pprev;
-            assert(plonger != NULL);
-        }
-        if (pfork == plonger)
-            break;
-        pfork = pfork->pprev;
-        assert(pfork != NULL);
-    }
-
-    // List of what to disconnect (typically nothing)
-    vector<CBlockIndex*> vDisconnect;
-    for (CBlockIndex* pindex = ptip; pindex != pfork; pindex = pindex->pprev)
-        vDisconnect.push_back(pindex);
-
-    // List of what to connect (typically only pindexNew)
-    vector<CBlockIndex*> vConnect;
-    for (CBlockIndex* pindex = pindexNew; pindex != pfork; pindex = pindex->pprev)
-        vConnect.push_back(pindex);
-    reverse(vConnect.begin(), vConnect.end());
-
-    if (vDisconnect.size() > 0) {
-        LogPrintf("REORGANIZE: Disconnect %"PRIszu" blocks; %s...\n", vDisconnect.size(), pfork->GetBlockHash().ToString());
-        LogPrintf("REORGANIZE: Connect %"PRIszu" blocks; ...%s\n", vConnect.size(), pindexNew->GetBlockHash().ToString());
-    }
-
-    // Disconnect shorter branch
-    list<CTransaction> vResurrect;
-    BOOST_FOREACH(CBlockIndex* pindex, vDisconnect) {
-        CBlock block;
-        if (!ReadBlockFromDisk(block, pindex))
-            return state.Abort(_("Failed to read block"));
-        int64_t nStart = GetTimeMicros();
-        if (!DisconnectBlock(block, state, pindex, view))
-            return error("SetBestBlock() : DisconnectBlock %s failed", pindex->GetBlockHash().ToString());
-        if (fBenchmark)
-            LogPrintf("- Disconnect: %.2fms\n", (GetTimeMicros() - nStart) * 0.001);
-
-        // Queue memory transactions to resurrect.
-        // We only do this for blocks after the last checkpoint (reorganisation before that
-        // point should only happen with -reindex/-loadblock, or a misbehaving peer.
-        BOOST_REVERSE_FOREACH(const CTransaction& tx, block.vtx)
-            if (!tx.IsCoinBase() && pindex->nHeight > Checkpoints::GetTotalBlocksEstimate())
-                vResurrect.push_front(tx);
-    }
-
-    // Connect longer branch
-    vector<CTransaction> vDelete;
-    BOOST_FOREACH(CBlockIndex *pindex, vConnect) {
-        CBlock block;
-        if (!ReadBlockFromDisk(block, pindex))
-            return state.Abort(_("Failed to read block"));
-        int64_t nStart = GetTimeMicros();
-        if (!ConnectBlock(block, state, pindex, view)) {
-            if (state.IsInvalid()) {
-                InvalidChainFound(pindexNew);
-                InvalidBlockFound(pindex);
-            }
-            return error("SetBestBlock() : ConnectBlock %s failed", pindex->GetBlockHash().ToString());
-        }
-        if (fBenchmark)
-            LogPrintf("- Connect: %.2fms\n", (GetTimeMicros() - nStart) * 0.001);
-
-        // Queue memory transactions to delete
-        BOOST_FOREACH(const CTransaction& tx, block.vtx)
-            vDelete.push_back(tx);
-    }
-
-    // Flush changes to global coin state
-    int64_t nStart = GetTimeMicros();
-    int nModified = view.GetCacheSize();
-    bool ret;
-    ret = view.Flush();
-    assert(ret);
-    int64_t nTime = GetTimeMicros() - nStart;
-    if (fBenchmark)
-        LogPrintf("- Flush %i transactions: %.2fms (%.4fms/tx)\n", nModified, 0.001 * nTime, 0.001 * nTime / nModified);
-
-    // Make sure it's successfully written to disk before changing memory structure
-    bool fIsInitialDownload = IsInitialBlockDownload();
-    if (!fIsInitialDownload || pcoinsTip->GetCacheSize() > nCoinCacheSize) {
+// Update the on-disk chain state.
+bool static WriteChainState(CValidationState &state) {
+    static int64_t nLastWrite = 0;
+    if (!IsInitialBlockDownload() || pcoinsTip->GetCacheSize() > nCoinCacheSize || GetTimeMicros() > nLastWrite + 600*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
@@ -1853,39 +1767,25 @@ bool SetBestChain(CValidationState &state, CBlockIndex* pindexNew)
         pblocktree->Sync();
         if (!pcoinsTip->Flush())
             return state.Abort(_("Failed to write to coin database"));
+        nLastWrite = GetTimeMicros();
     }
+    return true;
+}
 
-    // At this point, all changes have been done to the database.
-    // Proceed by updating the memory structures.
-
-    // Register new best chain
+// Update chainActive and related internal data structures.
+void static UpdateTip(CBlockIndex *pindexNew) {
     chainActive.SetTip(pindexNew);
 
-    // Resurrect memory transactions that were in the disconnected branch
-    BOOST_FOREACH(CTransaction& tx, vResurrect) {
-        // ignore validation errors in resurrected transactions
-        CValidationState stateDummy;
-        if (!AcceptToMemoryPool(mempool,stateDummy, tx, false, NULL))
-            mempool.remove(tx, true);
-    }
-
-    // Delete redundant memory transactions that are in the connected branch
-    BOOST_FOREACH(CTransaction& tx, vDelete) {
-        mempool.remove(tx);
-        mempool.removeConflicts(tx);
-    }
-
-    mempool.check(pcoinsTip);
-
     // Update best block in wallet (so we can detect restored wallets)
-    if ((pindexNew->nHeight % 20160) == 0 || (!fIsInitialDownload && (pindexNew->nHeight % 144) == 0))
-        g_signals.SetBestChain(chainActive.GetLocator(pindexNew));
+    bool fIsInitialDownload = IsInitialBlockDownload();
+    if ((chainActive.Height() % 20160) == 0 || (!fIsInitialDownload && (chainActive.Height() % 144) == 0))
+        g_signals.SetBestChain(chainActive.GetLocator());
 
     // New best block
     nTimeBestReceived = GetTime();
     mempool.AddTransactionsUpdated(1);
-    LogPrintf("SetBestChain: new best=%s  height=%d  log2_work=%.8g  tx=%lu  date=%s progress=%f\n",
-      chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(), log(chainActive.Tip()->nChainWork.getdouble())/log(2.0), (unsigned long)pindexNew->nChainTx,
+    LogPrintf("UpdateTip: new best=%s  height=%d  log2_work=%.8g  tx=%lu  date=%s progress=%f\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()));
 
@@ -1906,18 +1806,181 @@ bool SetBestChain(CValidationState &state, CBlockIndex* pindexNew)
             // 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!");
     }
+}
 
-    std::string strCmd = GetArg("-blocknotify", "");
-
-    if (!fIsInitialDownload && !strCmd.empty())
+// Disconnect chainActive's tip.
+bool static DisconnectTip(CValidationState &state) {
+    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"));
+    // Apply the block atomically to the chain state.
+    int64_t nStart = GetTimeMicros();
     {
-        boost::replace_all(strCmd, "%s", chainActive.Tip()->GetBlockHash().GetHex());
-        boost::thread t(runCommand, strCmd); // thread runs free
+        CCoinsViewCache view(*pcoinsTip, true);
+        if (!DisconnectBlock(block, state, pindexDelete, view))
+            return error("DisconnectTip() : DisconnectBlock %s failed", pindexDelete->GetBlockHash().ToString());
+        assert(view.Flush());
     }
+    if (fBenchmark)
+        LogPrintf("- Disconnect: %.2fms\n", (GetTimeMicros() - nStart) * 0.001);
+    // Write the chain state to disk, if necessary.
+    if (!WriteChainState(state))
+        return false;
+    // Ressurect mempool transactions from the disconnected block.
+    BOOST_FOREACH(const CTransaction &tx, block.vtx) {
+        // ignore validation errors in resurrected transactions
+        CValidationState stateDummy; 
+        if (!tx.IsCoinBase())
+            if (!AcceptToMemoryPool(mempool, stateDummy, tx, false, NULL))
+                mempool.remove(tx, true);
+    }
+    mempool.check(pcoinsTip);
+    // Update chainActive and related variables.
+    UpdateTip(pindexDelete->pprev);
+    return true;
+}
 
+// Connect a new block to chainActive.
+bool static ConnectTip(CValidationState &state, CBlockIndex *pindexNew) {
+    assert(pindexNew->pprev == chainActive.Tip());
+    mempool.check(pcoinsTip);
+    // Read block from disk.
+    CBlock block;
+    if (!ReadBlockFromDisk(block, pindexNew))
+        return state.Abort(_("Failed to read block"));
+    // Apply the block atomically to the chain state.
+    int64_t nStart = GetTimeMicros();
+    {
+        CCoinsViewCache view(*pcoinsTip, true);
+        CInv inv(MSG_BLOCK, pindexNew->GetBlockHash());
+        if (!ConnectBlock(block, state, pindexNew, view)) {
+            if (state.IsInvalid())
+                InvalidBlockFound(pindexNew, state);
+            return error("ConnectTip() : ConnectBlock %s failed", pindexNew->GetBlockHash().ToString());
+        }
+        mapBlockSource.erase(inv.hash);
+        assert(view.Flush());
+    }
+    if (fBenchmark)
+        LogPrintf("- Connect: %.2fms\n", (GetTimeMicros() - nStart) * 0.001);
+    // Write the chain state to disk, if necessary.
+    if (!WriteChainState(state))
+        return false;
+    // Remove conflicting transactions from the mempool.
+    BOOST_FOREACH(const CTransaction &tx, block.vtx) {
+        mempool.remove(tx);
+        mempool.removeConflicts(tx);
+    }
+    mempool.check(pcoinsTip);
+    // Update chainActive & related variables.
+    UpdateTip(pindexNew);
     return true;
 }
 
+// Make chainMostWork correspond to the chain with the most work in it, that isn't
+// known to be invalid (it's however far from certain to be valid).
+void static FindMostWorkChain() {
+    CBlockIndex *pindexNew = NULL;
+
+    // In case the current best is invalid, do not consider it.
+    while (chainMostWork.Tip() && (chainMostWork.Tip()->nStatus & BLOCK_FAILED_MASK)) {
+        setBlockIndexValid.erase(chainMostWork.Tip());
+        chainMostWork.SetTip(chainMostWork.Tip()->pprev);
+    }
+
+    do {
+        // Find the best candidate header.
+        {
+            std::set<CBlockIndex*, CBlockIndexWorkComparator>::reverse_iterator it = setBlockIndexValid.rbegin();
+            if (it == setBlockIndexValid.rend())
+                return;
+            pindexNew = *it;
+        }
+
+        // Check whether all blocks on the path between the currently active chain and the candidate are valid.
+        // Just going until the active chain is an optimization, as we know all blocks in it are valid already.
+        CBlockIndex *pindexTest = pindexNew;
+        bool fInvalidAncestor = false;
+        while (pindexTest && !chainActive.Contains(pindexTest)) {
+            if (pindexTest->nStatus & BLOCK_FAILED_MASK) {
+                // Candidate has an invalid ancestor, remove entire chain from the set.
+                if (pindexBestInvalid == NULL || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
+                    pindexBestInvalid = pindexNew;                CBlockIndex *pindexFailed = pindexNew;
+                while (pindexTest != pindexFailed) {
+                    pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
+                    setBlockIndexValid.erase(pindexFailed);
+                    pindexFailed = pindexFailed->pprev;
+                }
+                fInvalidAncestor = true;
+                break;
+            }
+            pindexTest = pindexTest->pprev;
+        }
+        if (fInvalidAncestor)
+            continue;
+
+        break;
+    } while(true);
+
+    // Check whether it's actually an improvement.
+    if (chainMostWork.Tip() && !CBlockIndexWorkComparator()(chainMostWork.Tip(), pindexNew))
+        return;
+
+    // We have a new best.
+    chainMostWork.SetTip(pindexNew);
+}
+
+// Try to activate to the most-work chain (thereby connecting it).
+bool ActivateBestChain(CValidationState &state) {
+    CBlockIndex *pindexOldTip = chainActive.Tip();
+    bool fComplete = false;
+    while (!fComplete) {
+        FindMostWorkChain();
+        fComplete = true;
+
+        // Check whether we have something to do.
+        if (chainMostWork.Tip() == NULL) break;
+
+        // Disconnect active blocks which are no longer in the best chain.
+        while (chainActive.Tip() && !chainMostWork.Contains(chainActive.Tip())) {
+            if (!DisconnectTip(state))
+                return false;
+        }
+
+        // Connect new blocks.
+        while (!chainActive.Contains(chainMostWork.Tip())) {
+            CBlockIndex *pindexConnect = chainMostWork[chainActive.Height() + 1];
+            if (!ConnectTip(state, pindexConnect)) {
+                if (state.IsInvalid()) {
+                    // The block violates a consensus rule.
+                    if (!state.CorruptionPossible())
+                        InvalidChainFound(chainMostWork.Tip());
+                    fComplete = false;
+                    state = CValidationState();
+                    break;
+                } else {
+                    // A system error occurred (disk space, database error, ...).
+                    return false;
+                }
+            }
+        }
+    }
+
+    if (chainActive.Tip() != pindexOldTip) {
+        std::string strCmd = GetArg("-blocknotify", "");
+        if (!IsInitialBlockDownload() && !strCmd.empty())
+        {
+            boost::replace_all(strCmd, "%s", chainActive.Tip()->GetBlockHash().GetHex());
+            boost::thread t(runCommand, strCmd); // thread runs free
+        }
+    }
+
+    return true;
+}
 
 bool AddToBlockIndex(CBlock& block, CValidationState& state, const CDiskBlockPos& pos)
 {
@@ -1928,7 +1991,12 @@ bool AddToBlockIndex(CBlock& block, CValidationState& state, const CDiskBlockPos
 
     // Construct new block index object
     CBlockIndex* pindexNew = new CBlockIndex(block);
+    {
+         LOCK(cs_nBlockSequenceId);
+         pindexNew->nSequenceId = nBlockSequenceId++;
+    }
     assert(pindexNew);
+    mapAlreadyAskedFor.erase(CInv(MSG_BLOCK, hash));
     map<uint256, CBlockIndex*>::iterator mi = mapBlockIndex.insert(make_pair(hash, pindexNew)).first;
     pindexNew->phashBlock = &((*mi).first);
     map<uint256, CBlockIndex*>::iterator miPrev = mapBlockIndex.find(block.hashPrevBlock);
@@ -1950,7 +2018,7 @@ bool AddToBlockIndex(CBlock& block, CValidationState& state, const CDiskBlockPos
         return state.Abort(_("Failed to write block index"));
 
     // New best?
-    if (!ConnectBestBlock(state))
+    if (!ActivateBestChain(state))
         return false;
 
     if (pindexNew == chainActive.Tip())
@@ -2274,8 +2342,11 @@ bool ProcessBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBl
         return state.Invalid(error("ProcessBlock() : already have block (orphan) %s", hash.ToString()));
 
     // Preliminary checks
-    if (!CheckBlock(*pblock, state))
+    if (!CheckBlock(*pblock, state)) {
+        if (state.CorruptionPossible())
+            mapAlreadyAskedFor.erase(CInv(MSG_BLOCK, hash));
         return error("ProcessBlock() : CheckBlock FAILED");
+    }
 
     CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(mapBlockIndex);
     if (pcheckpoint && pblock->hashPrevBlock != (chainActive.Tip() ? chainActive.Tip()->GetBlockHash() : uint256(0)))
@@ -3004,24 +3075,6 @@ bool static AlreadyHave(const CInv& inv)
 }
 
 
-void Misbehaving(NodeId pnode, int howmuch)
-{
-    if (howmuch == 0)
-        return;
-
-    CNodeState *state = State(pnode);
-    if (state == NULL)
-        return;
-
-    state->nMisbehavior += howmuch;
-    if (state->nMisbehavior >= GetArg("-banscore", 100))
-    {
-        LogPrintf("Misbehaving: %s (%d -> %d) BAN THRESHOLD EXCEEDED\n", state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
-        state->fShouldBan = true;
-    } else
-        LogPrintf("Misbehaving: %s (%d -> %d)\n", state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
-}
-
 void static ProcessGetData(CNode* pfrom)
 {
     std::deque<CInv>::iterator it = pfrom->vRecvGetData.begin();
@@ -3584,18 +3637,11 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
         pfrom->AddInventoryKnown(inv);
 
         LOCK(cs_main);
+        // Remember who we got this block from.
+        mapBlockSource[inv.hash] = pfrom->GetId();
 
         CValidationState state;
-        if (ProcessBlock(state, pfrom, &block) || state.CorruptionPossible())
-            mapAlreadyAskedFor.erase(inv);
-        int nDoS = 0;
-        if (state.IsInvalid(nDoS))
-        {
-            pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),
-                               state.GetRejectReason(), inv.hash);
-            if (nDoS > 0)
-                Misbehaving(pfrom->GetId(), nDoS);
-        }
+        ProcessBlock(state, pfrom, &block);
     }
 
 
@@ -4042,16 +4088,21 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
         if (!lockMain)
             return true;
 
-        if (State(pto->GetId())->fShouldBan) {
+        CNodeState &state = *State(pto->GetId());
+        if (state.fShouldBan) {
             if (pto->addr.IsLocal())
                 LogPrintf("Warning: not banning local node %s!\n", pto->addr.ToString());
             else {
                 pto->fDisconnect = true;
                 CNode::Ban(pto->addr);
             }
-            State(pto->GetId())->fShouldBan = false;
+            state.fShouldBan = false;
         }
 
+        BOOST_FOREACH(const CBlockReject& reject, state.rejects)
+            pto->PushMessage("reject", (string)"block", reject.chRejectCode, reject.strRejectReason, reject.hashBlock);
+        state.rejects.clear();
+
         // Start block sync
         if (pto->fStartSync && !fImporting && !fReindex) {
             pto->fStartSync = false;
diff --git a/src/main.h b/src/main.h
index 60e733b23a..ba353a885b 100644
--- a/src/main.h
+++ b/src/main.h
@@ -165,10 +165,8 @@ bool IsInitialBlockDownload();
 std::string GetWarnings(std::string strFor);
 /** Retrieve a transaction (from memory pool, or from disk, if possible) */
 bool GetTransaction(const uint256 &hash, CTransaction &tx, uint256 &hashBlock, bool fAllowSlow = false);
-/** Connect/disconnect blocks until pindexNew is the new tip of the active block chain */
-bool SetBestChain(CValidationState &state, CBlockIndex* pindexNew);
 /** Find the best known block, and make it the tip of the block chain */
-bool ConnectBestBlock(CValidationState &state);
+bool ActivateBestChain(CValidationState &state);
 int64_t GetBlockValue(int nHeight, int64_t nFees);
 unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock);
 
@@ -716,6 +714,8 @@ public:
     unsigned int nBits;
     unsigned int nNonce;
 
+    // (memory only) Sequencial id assigned to distinguish order in which blocks are received.
+    uint32_t nSequenceId;
 
     CBlockIndex()
     {
@@ -729,6 +729,7 @@ public:
         nTx = 0;
         nChainTx = 0;
         nStatus = 0;
+        nSequenceId = 0;
 
         nVersion       = 0;
         hashMerkleRoot = 0;
@@ -749,6 +750,7 @@ public:
         nTx = 0;
         nChainTx = 0;
         nStatus = 0;
+        nSequenceId = 0;
 
         nVersion       = block.nVersion;
         hashMerkleRoot = block.hashMerkleRoot;
@@ -958,23 +960,23 @@ public:
         AbortNode(msg);
         return Error();
     }
-    bool IsValid() {
+    bool IsValid() const {
         return mode == MODE_VALID;
     }
-    bool IsInvalid() {
+    bool IsInvalid() const {
         return mode == MODE_INVALID;
     }
-    bool IsError() {
+    bool IsError() const {
         return mode == MODE_ERROR;
     }
-    bool IsInvalid(int &nDoSOut) {
+    bool IsInvalid(int &nDoSOut) const {
         if (IsInvalid()) {
             nDoSOut = nDoS;
             return true;
         }
         return false;
     }
-    bool CorruptionPossible() {
+    bool CorruptionPossible() const {
         return corruptionPossible;
     }
     unsigned char GetRejectCode() const { return chRejectCode; }
@@ -1041,6 +1043,8 @@ public:
 /** The currently-connected chain of blocks. */
 extern CChain chainActive;
 
+/** The currently best known chain of headers (some of which may be invalid). */
+extern CChain chainMostWork;
 
 /** Global variable that points to the active CCoinsView (protected by cs_main) */
 extern CCoinsViewCache *pcoinsTip;