BIP9 Implementation

Inspired by former implementations by Eric Lombrozo and Rusty Russell, and
based on code by Jorge Timon.

src/Makefile.am

@@ -152,6 +152,7 @@ BITCOIN_CORE_H = \
   utilmoneystr.h \
   utiltime.h \
   validationinterface.h \
+  versionbits.h \
   wallet/crypter.h \
   wallet/db.h \
   wallet/rpcwallet.h \
@@ -204,6 +205,7 @@ libbitcoin_server_a_SOURCES = \
   txdb.cpp \
   txmempool.cpp \
   validationinterface.cpp \
+  versionbits.cpp \
   $(BITCOIN_CORE_H)
 
 if ENABLE_ZMQ

src/chain.h

@@ -14,8 +14,6 @@
 
 #include <vector>
 
-#include <boost/foreach.hpp>
-
 struct CDiskBlockPos
 {
     int nFile;

src/chainparams.cpp

@@ -81,6 +81,8 @@ public:
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = false;
         consensus.fPowNoRetargeting = false;
+        consensus.nRuleChangeActivationThreshold = 1916; // 95% of 2016
+        consensus.nMinerConfirmationWindow = 2016; // nPowTargetTimespan / nPowTargetSpacing
         /** 
          * The message start string is designed to be unlikely to occur in normal data.
          * The characters are rarely used upper ASCII, not valid as UTF-8, and produce
@@ -162,6 +164,8 @@ public:
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
         consensus.fPowNoRetargeting = false;
+        consensus.nRuleChangeActivationThreshold = 1512; // 75% for testchains
+        consensus.nMinerConfirmationWindow = 2016; // nPowTargetTimespan / nPowTargetSpacing
         pchMessageStart[0] = 0x0b;
         pchMessageStart[1] = 0x11;
         pchMessageStart[2] = 0x09;
@@ -225,6 +229,8 @@ public:
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
         consensus.fPowNoRetargeting = true;
+        consensus.nRuleChangeActivationThreshold = 108; // 75% for testchains
+        consensus.nMinerConfirmationWindow = 144; // Faster than normal for regtest (144 instead of 2016)
 
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0xbf;

src/consensus/params.h

@@ -7,8 +7,28 @@
 #define BITCOIN_CONSENSUS_PARAMS_H
 
 #include "uint256.h"
+#include <map>
+#include <string>
 
 namespace Consensus {
+
+enum DeploymentPos
+{
+    MAX_VERSION_BITS_DEPLOYMENTS = 0,
+};
+
+/**
+ * Struct for each individual consensus rule change using BIP9.
+ */
+struct BIP9Deployment {
+    /** Bit position to select the particular bit in nVersion. */
+    int bit;
+    /** Start MedianTime for version bits miner confirmation. Can be a date in the past */
+    int64_t nStartTime;
+    /** Timeout/expiry MedianTime for the deployment attempt. */
+    int64_t nTimeout;
+};
+
 /**
  * Parameters that influence chain consensus.
  */
@@ -22,6 +42,14 @@ struct Params {
     /** Block height and hash at which BIP34 becomes active */
     int BIP34Height;
     uint256 BIP34Hash;
+    /**
+     * Minimum blocks including miner confirmation of the total of 2016 blocks in a retargetting period,
+     * (nPowTargetTimespan / nPowTargetSpacing) which is also used for BIP9 deployments.
+     * Examples: 1916 for 95%, 1512 for testchains.
+     */
+    uint32_t nRuleChangeActivationThreshold;
+    uint32_t nMinerConfirmationWindow;
+    BIP9Deployment vDeployments[MAX_VERSION_BITS_DEPLOYMENTS];
     /** Proof of work parameters */
     uint256 powLimit;
     bool fPowAllowMinDifficultyBlocks;

src/init.cpp

@@ -466,7 +466,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-blockmaxsize=<n>", strprintf(_("Set maximum block size in bytes (default: %d)"), DEFAULT_BLOCK_MAX_SIZE));
     strUsage += HelpMessageOpt("-blockprioritysize=<n>", strprintf(_("Set maximum size of high-priority/low-fee transactions in bytes (default: %d)"), DEFAULT_BLOCK_PRIORITY_SIZE));
     if (showDebug)
-        strUsage += HelpMessageOpt("-blockversion=<n>", strprintf("Override block version to test forking scenarios (default: %d)", (int)CBlock::CURRENT_VERSION));
+        strUsage += HelpMessageOpt("-blockversion=<n>", "Override block version to test forking scenarios");
 
     strUsage += HelpMessageGroup(_("RPC server options:"));
     strUsage += HelpMessageOpt("-server", _("Accept command line and JSON-RPC commands"));

src/main.cpp

@@ -34,6 +34,7 @@
 #include "utilmoneystr.h"
 #include "utilstrencodings.h"
 #include "validationinterface.h"
+#include "versionbits.h"
 
 #include <sstream>
 
@@ -2083,6 +2084,51 @@ void PartitionCheck(bool (*initialDownloadCheck)(), CCriticalSection& cs, const
     }
 }
 
+// Protected by cs_main
+static 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;
@@ -2452,27 +2498,45 @@ void static UpdateTip(CBlockIndex *pindexNew) {
 
     // Check the version of the last 100 blocks to see if we need to upgrade:
     static bool fWarned = false;
-    if (!IsInitialBlockDownload() && !fWarned)
+    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) {
+                        CAlert::Notify(strMiscWarning, true);
+                        fWarned = true;
+                    }
+                } else {
+                    LogPrintf("%s: unknown new rules are about to activate (versionbit %i)\n", __func__, bit);
+                }
+            }
+        }
         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("%s: %d of last 100 blocks above version %d\n", __func__, nUpgraded, (int)CBlock::CURRENT_VERSION);
+            LogPrintf("%s: %d of last 100 blocks have unexpected version\n", __func__, 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!");
+            strMiscWarning = _("Warning: Unknown block versions being mined! It's possible unknown rules are in effect");
+            if (!fWarned) {
                 CAlert::Notify(strMiscWarning, true);
                 fWarned = true;
             }
         }
     }
+}
 
 /** 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 Consensus::Params& consensusParams)
@@ -3763,6 +3827,10 @@ void UnloadBlockIndex()
     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;

src/main.h

@@ -537,6 +537,11 @@ extern CBlockTreeDB *pblocktree;
  */
 int GetSpendHeight(const CCoinsViewCache& inputs);
 
+/**
+ * Determine what nVersion a new block should use.
+ */
+int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params);
+
 /** Reject codes greater or equal to this can be returned by AcceptToMemPool
  * for transactions, to signal internal conditions. They cannot and should not
  * be sent over the P2P network.

src/miner.cpp

@@ -79,11 +79,6 @@ CBlockTemplate* CreateNewBlock(const CChainParams& chainparams, const CScript& s
         return NULL;
     CBlock *pblock = &pblocktemplate->block; // pointer for convenience
 
-    // -regtest only: allow overriding block.nVersion with
-    // -blockversion=N to test forking scenarios
-    if (chainparams.MineBlocksOnDemand())
-        pblock->nVersion = GetArg("-blockversion", pblock->nVersion);
-
     // Create coinbase tx
     CMutableTransaction txNew;
     txNew.vin.resize(1);
@@ -137,6 +132,12 @@ CBlockTemplate* CreateNewBlock(const CChainParams& chainparams, const CScript& s
         pblock->nTime = GetAdjustedTime();
         const int64_t nMedianTimePast = pindexPrev->GetMedianTimePast();
 
+        pblock->nVersion = ComputeBlockVersion(pindexPrev, chainparams.GetConsensus());
+        // -regtest only: allow overriding block.nVersion with
+        // -blockversion=N to test forking scenarios
+        if (chainparams.MineBlocksOnDemand())
+            pblock->nVersion = GetArg("-blockversion", pblock->nVersion);
+
         int64_t nLockTimeCutoff = (STANDARD_LOCKTIME_VERIFY_FLAGS & LOCKTIME_MEDIAN_TIME_PAST)
                                 ? nMedianTimePast
                                 : pblock->GetBlockTime();

src/primitives/block.h

@@ -21,7 +21,6 @@ class CBlockHeader
 {
 public:
     // header
-    static const int32_t CURRENT_VERSION=4;
     int32_t nVersion;
     uint256 hashPrevBlock;
     uint256 hashMerkleRoot;
@@ -49,7 +48,7 @@ public:
 
     void SetNull()
     {
-        nVersion = CBlockHeader::CURRENT_VERSION;
+        nVersion = 0;
         hashPrevBlock.SetNull();
         hashMerkleRoot.SetNull();
         nTime = 0;

src/test/miner_tests.cpp

@@ -247,13 +247,40 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
 
     // subsidy changing
     int nHeight = chainActive.Height();
-    chainActive.Tip()->nHeight = 209999;
+    // Create an actual 209999-long block chain (without valid blocks).
+    while (chainActive.Tip()->nHeight < 209999) {
+        CBlockIndex* prev = chainActive.Tip();
+        CBlockIndex* next = new CBlockIndex();
+        next->phashBlock = new uint256(GetRandHash());
+        pcoinsTip->SetBestBlock(next->GetBlockHash());
+        next->pprev = prev;
+        next->nHeight = prev->nHeight + 1;
+        next->BuildSkip();
+        chainActive.SetTip(next);
+    }
     BOOST_CHECK(pblocktemplate = CreateNewBlock(chainparams, scriptPubKey));
     delete pblocktemplate;
-    chainActive.Tip()->nHeight = 210000;
+    // Extend to a 210000-long block chain.
+    while (chainActive.Tip()->nHeight < 210000) {
+        CBlockIndex* prev = chainActive.Tip();
+        CBlockIndex* next = new CBlockIndex();
+        next->phashBlock = new uint256(GetRandHash());
+        pcoinsTip->SetBestBlock(next->GetBlockHash());
+        next->pprev = prev;
+        next->nHeight = prev->nHeight + 1;
+        next->BuildSkip();
+        chainActive.SetTip(next);
+    }
     BOOST_CHECK(pblocktemplate = CreateNewBlock(chainparams, scriptPubKey));
     delete pblocktemplate;
-    chainActive.Tip()->nHeight = nHeight;
+    // Delete the dummy blocks again.
+    while (chainActive.Tip()->nHeight > nHeight) {
+        CBlockIndex* del = chainActive.Tip();
+        chainActive.SetTip(del->pprev);
+        pcoinsTip->SetBestBlock(del->pprev->GetBlockHash());
+        delete del->phashBlock;
+        delete del;
+    }
 
     // non-final txs in mempool
     SetMockTime(chainActive.Tip()->GetMedianTimePast()+1);

src/versionbits.cpp

@@ -0,0 +1,133 @@
+// Copyright (c) 2016 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 "versionbits.h"
+
+ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
+{
+    int nPeriod = Period(params);
+    int nThreshold = Threshold(params);
+    int64_t nTimeStart = BeginTime(params);
+    int64_t nTimeTimeout = EndTime(params);
+
+    // A block's state is always the same as that of the first of its period, so it is computed based on a pindexPrev whose height equals a multiple of nPeriod - 1.
+    if (pindexPrev != NULL) {
+        pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
+    }
+
+    // Walk backwards in steps of nPeriod to find a pindexPrev whose information is known
+    std::vector<const CBlockIndex*> vToCompute;
+    while (cache.count(pindexPrev) == 0) {
+        if (pindexPrev == NULL) {
+            // The genesis block is by definition defined.
+            cache[pindexPrev] = THRESHOLD_DEFINED;
+            break;
+        }
+        if (pindexPrev->GetMedianTimePast() < nTimeStart) {
+            // Optimizaton: don't recompute down further, as we know every earlier block will be before the start time
+            cache[pindexPrev] = THRESHOLD_DEFINED;
+            break;
+        }
+        vToCompute.push_back(pindexPrev);
+        pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
+    }
+
+    // At this point, cache[pindexPrev] is known
+    assert(cache.count(pindexPrev));
+    ThresholdState state = cache[pindexPrev];
+
+    // Now walk forward and compute the state of descendants of pindexPrev
+    while (!vToCompute.empty()) {
+        ThresholdState stateNext = state;
+        pindexPrev = vToCompute.back();
+        vToCompute.pop_back();
+
+        switch (state) {
+            case THRESHOLD_DEFINED: {
+                if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
+                    stateNext = THRESHOLD_FAILED;
+                } else if (pindexPrev->GetMedianTimePast() >= nTimeStart) {
+                    stateNext = THRESHOLD_STARTED;
+                }
+                break;
+            }
+            case THRESHOLD_STARTED: {
+                if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
+                    stateNext = THRESHOLD_FAILED;
+                    break;
+                }
+                // We need to count
+                const CBlockIndex* pindexCount = pindexPrev;
+                int count = 0;
+                for (int i = 0; i < nPeriod; i++) {
+                    if (Condition(pindexCount, params)) {
+                        count++;
+                    }
+                    pindexCount = pindexCount->pprev;
+                }
+                if (count >= nThreshold) {
+                    stateNext = THRESHOLD_LOCKED_IN;
+                }
+                break;
+            }
+            case THRESHOLD_LOCKED_IN: {
+                // Always progresses into ACTIVE.
+                stateNext = THRESHOLD_ACTIVE;
+                break;
+            }
+            case THRESHOLD_FAILED:
+            case THRESHOLD_ACTIVE: {
+                // Nothing happens, these are terminal states.
+                break;
+            }
+        }
+        cache[pindexPrev] = state = stateNext;
+    }
+
+    return state;
+}
+
+namespace
+{
+/**
+ * Class to implement versionbits logic.
+ */
+class VersionBitsConditionChecker : public AbstractThresholdConditionChecker {
+private:
+    const Consensus::DeploymentPos id;
+
+protected:
+    int64_t BeginTime(const Consensus::Params& params) const { return params.vDeployments[id].nStartTime; }
+    int64_t EndTime(const Consensus::Params& params) const { return params.vDeployments[id].nTimeout; }
+    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 & Mask(params)) != 0);
+    }
+
+public:
+    VersionBitsConditionChecker(Consensus::DeploymentPos id_) : id(id_) {}
+    uint32_t Mask(const Consensus::Params& params) const { return ((uint32_t)1) << params.vDeployments[id].bit; }
+};
+
+}
+
+ThresholdState VersionBitsState(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache)
+{
+    return VersionBitsConditionChecker(pos).GetStateFor(pindexPrev, params, cache.caches[pos]);
+}
+
+uint32_t VersionBitsMask(const Consensus::Params& params, Consensus::DeploymentPos pos)
+{
+    return VersionBitsConditionChecker(pos).Mask(params);
+}
+
+void VersionBitsCache::Clear()
+{
+    for (unsigned int d = 0; d < Consensus::MAX_VERSION_BITS_DEPLOYMENTS; d++) {
+        caches[d].clear();
+    }
+}

src/versionbits.h

@@ -0,0 +1,59 @@
+// Copyright (c) 2016 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_CONSENSUS_VERSIONBITS
+#define BITCOIN_CONSENSUS_VERSIONBITS
+
+#include "chain.h"
+#include <map>
+
+/** What block version to use for new blocks (pre versionbits) */
+static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
+/** What bits to set in version for versionbits blocks */
+static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
+/** What bitmask determines whether versionbits is in use */
+static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
+/** Total bits available for versionbits */
+static const int32_t VERSIONBITS_NUM_BITS = 29;
+
+enum ThresholdState {
+    THRESHOLD_DEFINED,
+    THRESHOLD_STARTED,
+    THRESHOLD_LOCKED_IN,
+    THRESHOLD_ACTIVE,
+    THRESHOLD_FAILED,
+};
+
+// A map that gives the state for blocks whose height is a multiple of Period().
+// The map is indexed by the block's parent, however, so all keys in the map
+// will either be NULL or a block with (height + 1) % Period() == 0.
+typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;
+
+/**
+ * Abstract class that implements BIP9-style threshold logic, and caches results.
+ */
+class AbstractThresholdConditionChecker {
+protected:
+    virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;
+    virtual int64_t BeginTime(const Consensus::Params& params) const =0;
+    virtual int64_t EndTime(const Consensus::Params& params) const =0;
+    virtual int Period(const Consensus::Params& params) const =0;
+    virtual int Threshold(const Consensus::Params& params) const =0;
+
+public:
+    // Note that the function below takes a pindexPrev as input: they compute information for block B based on its parent.
+    ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
+};
+
+struct VersionBitsCache
+{
+    ThresholdConditionCache caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS];
+
+    void Clear();
+};
+
+ThresholdState VersionBitsState(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache);
+uint32_t VersionBitsMask(const Consensus::Params& params, Consensus::DeploymentPos pos);
+
+#endif