[refactor] Add deploymentstatus.h

Provides DeploymentEnabled, DeploymentActiveAt, and DeploymentActiveAfter
helpers for checking the status of buried deployments. Can be overloaded
so the same syntax works for non-buried deployments, allowing future
soft forks to be changed from signalled to buried deployments without
having to touch the implementation code.

Replaces IsWitnessEnabled and IsScriptWitnessEnabled.

9 files changed, 101 insertions, 53 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index e2ed70556d..a3248f3eab 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -145,6 +145,7 @@ BITCOIN_CORE_H = \
   core_memusage.h \
   cuckoocache.h \
   dbwrapper.h \
+  deploymentstatus.h \
   external_signer.h \
   flatfile.h \
   fs.h \
diff --git a/src/consensus/params.h b/src/consensus/params.h
index 28c95e0884..9b4139d76c 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -11,6 +11,17 @@
 
 namespace Consensus {
 
+enum BuriedDeployment : int16_t
+{
+    // buried deployments get negative values to avoid overlap with DeploymentPos
+    DEPLOYMENT_HEIGHTINCB = std::numeric_limits<int16_t>::min(),
+    DEPLOYMENT_CLTV,
+    DEPLOYMENT_DERSIG,
+    DEPLOYMENT_CSV,
+    DEPLOYMENT_SEGWIT,
+};
+constexpr bool ValidDeployment(BuriedDeployment dep) { return DEPLOYMENT_HEIGHTINCB <= dep && dep <= DEPLOYMENT_SEGWIT; }
+
 enum DeploymentPos
 {
     DEPLOYMENT_TESTDUMMY,
@@ -100,7 +111,25 @@ struct Params {
      */
     bool signet_blocks{false};
     std::vector<uint8_t> signet_challenge;
+
+    int DeploymentHeight(BuriedDeployment dep) const
+    {
+        switch (dep) {
+        case DEPLOYMENT_HEIGHTINCB:
+            return BIP34Height;
+        case DEPLOYMENT_CLTV:
+            return BIP65Height;
+        case DEPLOYMENT_DERSIG:
+            return BIP66Height;
+        case DEPLOYMENT_CSV:
+            return CSVHeight;
+        case DEPLOYMENT_SEGWIT:
+            return SegwitHeight;
+        } // no default case, so the compiler can warn about missing cases
+        return std::numeric_limits<int>::max();
+    }
 };
+
 } // namespace Consensus
 
 #endif // BITCOIN_CONSENSUS_PARAMS_H
diff --git a/src/deploymentstatus.h b/src/deploymentstatus.h
new file mode 100644
index 0000000000..32190e369d
--- /dev/null
+++ b/src/deploymentstatus.h
@@ -0,0 +1,33 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_DEPLOYMENTSTATUS_H
+#define BITCOIN_DEPLOYMENTSTATUS_H
+
+#include <chain.h>
+
+#include <limits>
+
+/** Determine if a deployment is active for the next block */
+inline bool DeploymentActiveAfter(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::BuriedDeployment dep)
+{
+    assert(Consensus::ValidDeployment(dep));
+    return (pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1) >= params.DeploymentHeight(dep);
+}
+
+/** Determine if a deployment is active for this block */
+inline bool DeploymentActiveAt(const CBlockIndex& index, const Consensus::Params& params, Consensus::BuriedDeployment dep)
+{
+    assert(Consensus::ValidDeployment(dep));
+    return index.nHeight >= params.DeploymentHeight(dep);
+}
+
+/** Determine if a deployment is enabled (can ever be active) */
+inline bool DeploymentEnabled(const Consensus::Params& params, Consensus::BuriedDeployment dep)
+{
+    assert(Consensus::ValidDeployment(dep));
+    return params.DeploymentHeight(dep) != std::numeric_limits<int>::max();
+}
+
+#endif // BITCOIN_DEPLOYMENTSTATUS_H
diff --git a/src/init.cpp b/src/init.cpp
index a88adbaa21..ae96f510bc 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -16,6 +16,7 @@
 #include <chain.h>
 #include <chainparams.h>
 #include <compat/sanity.h>
+#include <deploymentstatus.h>
 #include <fs.h>
 #include <hash.h>
 #include <httprpc.h>
@@ -1587,7 +1588,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         }
     }
 
-    if (chainparams.GetConsensus().SegwitHeight != std::numeric_limits<int>::max()) {
+    if (DeploymentEnabled(chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
         // Advertise witness capabilities.
         // The option to not set NODE_WITNESS is only used in the tests and should be removed.
         nLocalServices = ServiceFlags(nLocalServices | NODE_WITNESS);
diff --git a/src/miner.cpp b/src/miner.cpp
index 0cf303eb3c..c1a992b9e9 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -13,6 +13,7 @@
 #include <consensus/merkle.h>
 #include <consensus/tx_verify.h>
 #include <consensus/validation.h>
+#include <deploymentstatus.h>
 #include <policy/feerate.h>
 #include <policy/policy.h>
 #include <pow.h>
@@ -137,12 +138,12 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& sc
     // This is only needed in case the witness softfork activation is reverted
     // (which would require a very deep reorganization).
     // Note that the mempool would accept transactions with witness data before
-    // IsWitnessEnabled, but we would only ever mine blocks after IsWitnessEnabled
+    // the deployment is active, but we would only ever mine blocks after activation
     // unless there is a massive block reorganization with the witness softfork
     // not activated.
     // TODO: replace this with a call to main to assess validity of a mempool
     // transaction (which in most cases can be a no-op).
-    fIncludeWitness = IsWitnessEnabled(pindexPrev, chainparams.GetConsensus());
+    fIncludeWitness = DeploymentActiveAfter(pindexPrev, chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT);
 
     int nPackagesSelected = 0;
     int nDescendantsUpdated = 0;
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index ab9c41ca2b..315d2ac5cd 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -11,6 +11,7 @@
 #include <blockfilter.h>
 #include <chainparams.h>
 #include <consensus/validation.h>
+#include <deploymentstatus.h>
 #include <hash.h>
 #include <index/blockfilterindex.h>
 #include <merkleblock.h>
@@ -997,7 +998,7 @@ void PeerManagerImpl::FindNextBlocksToDownload(NodeId nodeid, unsigned int count
                 // We consider the chain that this peer is on invalid.
                 return;
             }
-            if (!State(nodeid)->fHaveWitness && IsWitnessEnabled(pindex->pprev, consensusParams)) {
+            if (!State(nodeid)->fHaveWitness && DeploymentActiveAt(*pindex, consensusParams, Consensus::DEPLOYMENT_SEGWIT)) {
                 // We wouldn't download this block or its descendants from this peer.
                 return;
             }
@@ -1467,7 +1468,7 @@ void PeerManagerImpl::NewPoWValidBlock(const CBlockIndex *pindex, const std::sha
         return;
     nHighestFastAnnounce = pindex->nHeight;
 
-    bool fWitnessEnabled = IsWitnessEnabled(pindex->pprev, m_chainparams.GetConsensus());
+    bool fWitnessEnabled = DeploymentActiveAt(*pindex, m_chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT);
     uint256 hashBlock(pblock->GetHash());
 
     {
@@ -2082,7 +2083,7 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
             while (pindexWalk && !m_chainman.ActiveChain().Contains(pindexWalk) && vToFetch.size() <= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
                 if (!(pindexWalk->nStatus & BLOCK_HAVE_DATA) &&
                         !IsBlockRequested(pindexWalk->GetBlockHash()) &&
-                        (!IsWitnessEnabled(pindexWalk->pprev, m_chainparams.GetConsensus()) || State(pfrom.GetId())->fHaveWitness)) {
+                        (!DeploymentActiveAt(*pindexWalk, m_chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT) || State(pfrom.GetId())->fHaveWitness)) {
                     // We don't have this block, and it's not yet in flight.
                     vToFetch.push_back(pindexWalk);
                 }
@@ -3397,7 +3398,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             return;
         }
 
-        if (IsWitnessEnabled(pindex->pprev, m_chainparams.GetConsensus()) && !nodestate->fSupportsDesiredCmpctVersion) {
+        if (DeploymentActiveAt(*pindex, m_chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT) && !nodestate->fSupportsDesiredCmpctVersion) {
             // Don't bother trying to process compact blocks from v1 peers
             // after segwit activates.
             return;
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 327f961196..f054c8b145 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -10,6 +10,7 @@
 #include <consensus/params.h>
 #include <consensus/validation.h>
 #include <core_io.h>
+#include <deploymentstatus.h>
 #include <key_io.h>
 #include <miner.h>
 #include <net.h>
@@ -774,7 +775,7 @@ static RPCHelpMan getblocktemplate()
     pblock->nNonce = 0;
 
     // NOTE: If at some point we support pre-segwit miners post-segwit-activation, this needs to take segwit support into consideration
-    const bool fPreSegWit = (pindexPrev->nHeight + 1 < consensusParams.SegwitHeight);
+    const bool fPreSegWit = !DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_SEGWIT);
 
     UniValue aCaps(UniValue::VARR); aCaps.push_back("proposal");
 
diff --git a/src/validation.cpp b/src/validation.cpp
index 1b0f881d14..b69faa54eb 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -15,6 +15,7 @@
 #include <consensus/tx_verify.h>
 #include <consensus/validation.h>
 #include <cuckoocache.h>
+#include <deploymentstatus.h>
 #include <flatfile.h>
 #include <hash.h>
 #include <index/blockfilterindex.h>
@@ -1649,15 +1650,6 @@ public:
 
 static ThresholdConditionCache warningcache[VERSIONBITS_NUM_BITS] GUARDED_BY(cs_main);
 
-// 0.13.0 was shipped with a segwit deployment defined for testnet, but not for
-// mainnet. We no longer need to support disabling the segwit deployment
-// except for testing purposes, due to limitations of the functional test
-// environment. See test/functional/p2p-segwit.py.
-static bool IsScriptWitnessEnabled(const Consensus::Params& params)
-{
-    return params.SegwitHeight != std::numeric_limits<int>::max();
-}
-
 static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& consensusparams)
 {
     unsigned int flags = SCRIPT_VERIFY_NONE;
@@ -1676,22 +1668,22 @@ static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consens
 
     // Enforce WITNESS rules whenever P2SH is in effect (and the segwit
     // deployment is defined).
-    if (flags & SCRIPT_VERIFY_P2SH && IsScriptWitnessEnabled(consensusparams)) {
+    if (flags & SCRIPT_VERIFY_P2SH && DeploymentEnabled(consensusparams, Consensus::DEPLOYMENT_SEGWIT)) {
         flags |= SCRIPT_VERIFY_WITNESS;
     }
 
-    // Start enforcing the DERSIG (BIP66) rule
-    if (pindex->nHeight >= consensusparams.BIP66Height) {
+    // Enforce the DERSIG (BIP66) rule
+    if (DeploymentActiveAt(*pindex, consensusparams, Consensus::DEPLOYMENT_DERSIG)) {
         flags |= SCRIPT_VERIFY_DERSIG;
     }
 
-    // Start enforcing CHECKLOCKTIMEVERIFY (BIP65) rule
-    if (pindex->nHeight >= consensusparams.BIP65Height) {
+    // Enforce CHECKLOCKTIMEVERIFY (BIP65)
+    if (DeploymentActiveAt(*pindex, consensusparams, Consensus::DEPLOYMENT_CLTV)) {
         flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
     }
 
-    // Start enforcing BIP112 (CHECKSEQUENCEVERIFY)
-    if (pindex->nHeight >= consensusparams.CSVHeight) {
+    // Enforce CHECKSEQUENCEVERIFY (BIP112)
+    if (DeploymentActiveAt(*pindex, consensusparams, Consensus::DEPLOYMENT_CSV)) {
         flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
     }
 
@@ -1700,8 +1692,8 @@ static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consens
         flags |= SCRIPT_VERIFY_TAPROOT;
     }
 
-    // Start enforcing BIP147 NULLDUMMY (activated simultaneously with segwit)
-    if (IsWitnessEnabled(pindex->pprev, consensusparams)) {
+    // Enforce BIP147 NULLDUMMY (activated simultaneously with segwit)
+    if (DeploymentActiveAt(*pindex, consensusparams, Consensus::DEPLOYMENT_SEGWIT)) {
         flags |= SCRIPT_VERIFY_NULLDUMMY;
     }
 
@@ -1891,9 +1883,9 @@ bool CChainState::ConnectBlock(const CBlock& block, BlockValidationState& state,
         }
     }
 
-    // Start enforcing BIP68 (sequence locks)
+    // Enforce BIP68 (sequence locks)
     int nLockTimeFlags = 0;
-    if (pindex->nHeight >= m_params.GetConsensus().CSVHeight) {
+    if (DeploymentActiveAt(*pindex, m_params.GetConsensus(), Consensus::DEPLOYMENT_CSV)) {
         nLockTimeFlags |= LOCKTIME_VERIFY_SEQUENCE;
     }
 
@@ -2986,7 +2978,7 @@ void CChainState::ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pi
     pindexNew->nDataPos = pos.nPos;
     pindexNew->nUndoPos = 0;
     pindexNew->nStatus |= BLOCK_HAVE_DATA;
-    if (IsWitnessEnabled(pindexNew->pprev, m_params.GetConsensus())) {
+    if (DeploymentActiveAt(*pindexNew, m_params.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
         pindexNew->nStatus |= BLOCK_OPT_WITNESS;
     }
     pindexNew->RaiseValidity(BLOCK_VALID_TRANSACTIONS);
@@ -3107,17 +3099,11 @@ bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensu
     return true;
 }
 
-bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)
-{
-    int height = pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1;
-    return (height >= params.SegwitHeight);
-}
-
 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 != NO_WITNESS_COMMITMENT && IsWitnessEnabled(pindexPrev, consensusParams) && !block.vtx[0]->HasWitness()) {
+    if (commitpos != NO_WITNESS_COMMITMENT && DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_SEGWIT) && !block.vtx[0]->HasWitness()) {
         CMutableTransaction tx(*block.vtx[0]);
         tx.vin[0].scriptWitness.stack.resize(1);
         tx.vin[0].scriptWitness.stack[0] = nonce;
@@ -3130,7 +3116,7 @@ std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBloc
     std::vector<unsigned char> commitment;
     int commitpos = GetWitnessCommitmentIndex(block);
     std::vector<unsigned char> ret(32, 0x00);
-    if (consensusParams.SegwitHeight != std::numeric_limits<int>::max()) {
+    if (DeploymentEnabled(consensusParams, Consensus::DEPLOYMENT_SEGWIT)) {
         if (commitpos == NO_WITNESS_COMMITMENT) {
             uint256 witnessroot = BlockWitnessMerkleRoot(block, nullptr);
             CHash256().Write(witnessroot).Write(ret).Finalize(witnessroot);
@@ -3208,13 +3194,13 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidatio
     if (block.GetBlockTime() > nAdjustedTime + MAX_FUTURE_BLOCK_TIME)
         return state.Invalid(BlockValidationResult::BLOCK_TIME_FUTURE, "time-too-new", "block timestamp too far in the future");
 
-    // Reject outdated version blocks when 95% (75% on testnet) of the network has upgraded:
-    // check for version 2, 3 and 4 upgrades
-    if((block.nVersion < 2 && nHeight >= consensusParams.BIP34Height) ||
-       (block.nVersion < 3 && nHeight >= consensusParams.BIP66Height) ||
-       (block.nVersion < 4 && nHeight >= consensusParams.BIP65Height))
+    // Reject blocks with outdated version
+    if ((block.nVersion < 2 && DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_HEIGHTINCB)) ||
+        (block.nVersion < 3 && DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_DERSIG)) ||
+        (block.nVersion < 4 && DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_CLTV))) {
             return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, strprintf("bad-version(0x%08x)", block.nVersion),
                                  strprintf("rejected nVersion=0x%08x block", block.nVersion));
+    }
 
     return true;
 }
@@ -3229,9 +3215,9 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat
 {
     const int nHeight = pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1;
 
-    // Start enforcing BIP113 (Median Time Past).
+    // Enforce BIP113 (Median Time Past).
     int nLockTimeFlags = 0;
-    if (nHeight >= consensusParams.CSVHeight) {
+    if (DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_CSV)) {
         assert(pindexPrev != nullptr);
         nLockTimeFlags |= LOCKTIME_MEDIAN_TIME_PAST;
     }
@@ -3248,7 +3234,7 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat
     }
 
     // Enforce rule that the coinbase starts with serialized block height
-    if (nHeight >= consensusParams.BIP34Height)
+    if (DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_HEIGHTINCB))
     {
         CScript expect = CScript() << nHeight;
         if (block.vtx[0]->vin[0].scriptSig.size() < expect.size() ||
@@ -3266,7 +3252,7 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat
     //   {0xaa, 0x21, 0xa9, 0xed}, and the following 32 bytes are SHA256^2(witness root, witness reserved value). In case there are
     //   multiple, the last one is used.
     bool fHaveWitness = false;
-    if (nHeight >= consensusParams.SegwitHeight) {
+    if (DeploymentActiveAfter(pindexPrev, consensusParams, Consensus::DEPLOYMENT_SEGWIT)) {
         int commitpos = GetWitnessCommitmentIndex(block);
         if (commitpos != NO_WITNESS_COMMITMENT) {
             bool malleated = false;
@@ -4096,9 +4082,8 @@ bool CChainState::NeedsRedownload() const
 
     // At and above m_params.SegwitHeight, segwit consensus rules must be validated
     CBlockIndex* block{m_chain.Tip()};
-    const int segwit_height{m_params.GetConsensus().SegwitHeight};
 
-    while (block != nullptr && block->nHeight >= segwit_height) {
+    while (block != nullptr && DeploymentActiveAt(*block, m_params.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
         if (!(block->nStatus & BLOCK_OPT_WITNESS)) {
             // block is insufficiently validated for a segwit client
             return true;
@@ -5000,7 +4985,7 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
 
         // Fake BLOCK_OPT_WITNESS so that CChainState::NeedsRedownload()
         // won't ask to rewind the entire assumed-valid chain on startup.
-        if (index->pprev && ::IsWitnessEnabled(index->pprev, ::Params().GetConsensus())) {
+        if (index->pprev && DeploymentActiveAt(*index, ::Params().GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
             index->nStatus |= BLOCK_OPT_WITNESS;
         }
     }
diff --git a/src/validation.h b/src/validation.h
index fc702b7183..50a8d7e575 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -345,10 +345,6 @@ bool TestBlockValidity(BlockValidationState& state,
                        bool fCheckPOW = true,
                        bool fCheckMerkleRoot = true) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
-/** Check whether witness commitments are required for a block, and whether to enforce NULLDUMMY (BIP 147) rules.
- *  Note that transaction witness validation rules are always enforced when P2SH is enforced. */
-bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params);
-
 /** Update uncommitted block structures (currently: only the witness reserved value). This is safe for submitted blocks. */
 void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams);