src/checkpoints.cpp

   1 // Copyright (c) 2011 The Bitcoin developers
   2 // Copyright (c) 2011-2012 The PPCoin developers
   3 // Distributed under the MIT/X11 software license, see the accompanying
   4 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
   5
   6 #include <boost/assign/list_of.hpp> // for 'map_list_of()'
   7 #include <boost/foreach.hpp>
   8
   9 #include "headers.h"
  10 #include "checkpoints.h"
  11
  12 namespace Checkpoints
  13 {
  14     typedef std::map<int, uint256> MapCheckpoints;   // hardened checkpoints
  15
  16     //
  17     // What makes a good checkpoint block?
  18     // + Is surrounded by blocks with reasonable timestamps
  19     //   (no blocks before with a timestamp after, none after with
  20     //    timestamp before)
  21     // + Contains no strange transactions
  22     //
  23     static MapCheckpoints mapCheckpoints =
  24         boost::assign::map_list_of
  25         ( 0, hashGenesisBlock )
  26         ; // ppcoin: no checkpoint yet; to be created in future releases
  27
  28     bool CheckHardened(int nHeight, const uint256& hash)
  29     {
  30         if (fTestNet) return true; // Testnet has no checkpoints
  31
  32         MapCheckpoints::const_iterator i = mapCheckpoints.find(nHeight);
  33         if (i == mapCheckpoints.end()) return true;
  34         return hash == i->second;
  35     }
  36
  37     int GetTotalBlocksEstimate()
  38     {
  39         if (fTestNet) return 0;
  40
  41         return mapCheckpoints.rbegin()->first;
  42     }
  43
  44     CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex)
  45     {
  46         if (fTestNet) return NULL;
  47
  48         int64 nResult;
  49         BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, mapCheckpoints)
  50         {
  51             const uint256& hash = i.second;
  52             std::map<uint256, CBlockIndex*>::const_iterator t = mapBlockIndex.find(hash);
  53             if (t != mapBlockIndex.end())
  54                 return t->second;
  55         }
  56         return NULL;
  57     }
  58
  59     // ppcoin: synchronized checkpoint (centrally broadcasted)
  60     uint256 hashSyncCheckpoint;
  61     CSyncCheckpoint checkpointMessage;
  62     CSyncCheckpoint checkpointMessagePending;
  63     CCriticalSection cs_hashSyncCheckpoint;
  64
  65     bool CSyncCheckpoint::ProcessSyncCheckpoint()
  66     {
  67         if (!CheckSignature())
  68             return false;
  69
  70         CRITICAL_BLOCK(cs_hashSyncCheckpoint)
  71         {
  72             if (!mapBlockIndex.count(hashCheckpoint))
  73             {
  74                 // TODO: we don't have this block yet, so ask for it
  75                 checkpointMessagePending = *this;
  76                 return false;
  77             }
  78
  79             if (!mapBlockIndex.count(hashSyncCheckpoint))
  80                 return error("ProcessSyncCheckpoint: block index missing for synchronized checkpoint %s", hashSyncCheckpoint.ToString().c_str());
  81
  82             CBlockIndex* pindexSyncCheckpoint = mapBlockIndex[hashSyncCheckpoint];
  83             CBlockIndex* pindexCheckpointPending = mapBlockIndex[hashCheckpoint];
  84             if (pindexCheckpointPending->nHeight <= pindexSyncCheckpoint->nHeight)
  85                 return false;  // this is an older checkpoint, ignore
  86
  87             CBlockIndex* pindex = pindexCheckpointPending;
  88             while (pindex->nHeight > pindexSyncCheckpoint->nHeight)
  89                 pindex = pindex->pprev;
  90             if (pindex->GetBlockHash() != hashSyncCheckpoint)
  91                 return error("ProcessSyncCheckpoint: new sync-checkpoint %s is not a descendant of current sync-checkpoint %s", hashCheckpoint.ToString().c_str(), hashSyncCheckpoint.ToString().c_str());
  92             hashSyncCheckpoint = this->hashCheckpoint;
  93             checkpointMessage = *this;
  94         }
  95         return true;
  96     }
  97
  98     // ppcoin: automatic checkpoint (represented by height of checkpoint)
  99     int nAutoCheckpoint = 0;
 100     int nBranchPoint = 0;    // branch point to alternative branch
 101
 102     // ppcoin: check automatic checkpoint
 103     // To pass the check:
 104     //   - All ancestors (including the block itself) have block index already
 105     //   - The immediate ancestor in main chain must not have height less than
 106     //     checkpoint height
 107     bool CheckAuto(const CBlockIndex *pindex)
 108     {
 109         while (pindex)
 110         {
 111             if (pindex->IsInMainChain())
 112             {
 113                 if (pindex->nHeight >= nAutoCheckpoint)
 114                     return true;
 115                 else
 116                 {
 117                     nBranchPoint = pindex->nHeight;
 118                     return error("Checkpoints: new block on alternative branch at height=%d before auto checkpoint at height=%d", pindex->nHeight, nAutoCheckpoint);
 119                 }
 120             }
 121             else
 122                 pindex = pindex->pprev;
 123         }
 124         return error("Checkpoints: failed to find any ancestor on main chain for the new block - internal error");
 125     }
 126
 127     // ppcoin: get next chain checkpoint
 128     int GetNextChainCheckpoint(const CBlockIndex *pindexLast)
 129     {
 130         CBigNum bnTarget;
 131         CBigNum bnTargetMax = 0;  // max target of all blocks since checkpoint
 132         CBigNum bnTargetMin = 0;  // min target of all candidate checkpoints
 133         int nMinTargetHeight = 0; // min target height of candidate checkpoints
 134         int nCheckpointMin = 0;   // minimum candidate checkpoint
 135         int nCheckpointMax = 0;   // maximum candidate checkpoint
 136         int nDepth = pindexLast->nHeight - pindexLast->nCheckpoint;
 137         const CBlockIndex *pindex = pindexLast;
 138         while (nDepth >= 0 && pindex)
 139         {
 140             bnTarget.SetCompact(pindex->nBits);
 141             if (bnTarget > bnTargetMax)
 142                 bnTargetMax = bnTarget;
 143             if (nCheckpointMax > 0 && bnTarget < bnTargetMin)
 144             {
 145                 bnTargetMin = bnTarget;
 146                 nMinTargetHeight = pindex->nHeight;
 147             }
 148             if (nCheckpointMax == 0 && pindexLast->GetBlockTime() - pindex->GetBlockTime() > AUTO_CHECKPOINT_MIN_SPAN)
 149             {
 150                 nCheckpointMax = pindex->nHeight;
 151                 bnTargetMin.SetCompact(pindex->nBits);
 152                 nMinTargetHeight = pindex->nHeight;
 153             }
 154             if (pindexLast->GetBlockTime() - pindex->GetBlockTime() < AUTO_CHECKPOINT_MAX_SPAN)
 155                 nCheckpointMin = pindex->nHeight;
 156             pindex = pindex->pprev;
 157             nDepth--;
 158         }
 159
 160         assert (nDepth == -1);  // arrive at chain checkpoint now
 161
 162         printf("Checkpoints: min=%d max=%d tminheight=%d tmin=0x%08x tmax=0x%08x\n",
 163             nCheckpointMin, nCheckpointMax, nMinTargetHeight,
 164             bnTargetMin.GetCompact(), bnTargetMax.GetCompact());
 165         if (nCheckpointMax == 0) // checkpoint stays if max candidate not found
 166             return pindexLast->nCheckpoint;
 167
 168         if (bnTargetMin * 100 > bnTargetMax * 90)
 169             return nCheckpointMax;
 170         if (bnTarget * 100 > bnTargetMax * 90)
 171             return nMinTargetHeight;
 172         else
 173             return nCheckpointMin;
 174     }
 175
 176     // ppcoin: get next auto checkpoint from the new chain checkpoint
 177     int GetNextAutoCheckpoint(int nCheckpoint)
 178     {
 179         return (std::max(nAutoCheckpoint, nCheckpoint));
 180     }
 181
 182     // ppcoin: advance to next automatic checkpoint
 183     void AdvanceAutoCheckpoint(int nCheckpoint)
 184     {
 185         nAutoCheckpoint = GetNextAutoCheckpoint(nCheckpoint);
 186         printf("Checkpoints: auto checkpoint now at height=%d\n", nAutoCheckpoint);
 187     }
 188
 189     // ppcoin: reset auto checkpoint
 190     bool ResetAutoCheckpoint(int nCheckpoint)
 191     {
 192         if (nCheckpoint <= 0 || nCheckpoint > nBestHeight)
 193             return error("ResetAutoCheckpoint() : new checkpoint invalid");
 194         if (nCheckpoint >= nAutoCheckpoint)
 195             return error("ResetAutoCheckpoint() : new checkpoint not earlier than current auto checkpoint");
 196         CTxDB txdb;
 197         txdb.TxnBegin();
 198         if (!txdb.WriteAutoCheckpoint(nCheckpoint, true))
 199             return error("ResetAutoCheckpoint() : database write failed");
 200         if (!txdb.TxnCommit())
 201             return error("ResetAutoCheckpoint() : database commit failed");
 202         nAutoCheckpoint = nCheckpoint;
 203         nBranchPoint = 0;  // clear branch point
 204
 205         // clear ban list to accept alternative branches
 206         CRITICAL_BLOCK(cs_vNodes)
 207         {
 208             BOOST_FOREACH(CNode* pnode, vNodes)
 209                 pnode->ClearBanned();
 210         }
 211
 212         return true;
 213     }
 214 }