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     // ppcoin: automatic checkpoint (represented by height of checkpoint)
  29     int nAutoCheckpoint = 0;
  30     int nBranchPoint = 0;    // branch point to alternative branch
  31
  32     bool CheckHardened(int nHeight, const uint256& hash)
  33     {
  34         if (fTestNet) return true; // Testnet has no checkpoints
  35
  36         MapCheckpoints::const_iterator i = mapCheckpoints.find(nHeight);
  37         if (i == mapCheckpoints.end()) return true;
  38         return hash == i->second;
  39     }
  40
  41     // ppcoin: check automatic checkpoint
  42     // To pass the check:
  43     //   - All ancestors (including the block itself) have block index already
  44     //   - The immediate ancestor in main chain must not have height less than
  45     //     checkpoint height
  46     bool CheckAuto(const CBlockIndex *pindex)
  47     {
  48         while (pindex)
  49         {
  50             if (pindex->IsInMainChain())
  51             {
  52                 if (pindex->nHeight >= nAutoCheckpoint)
  53                     return true;
  54                 else
  55                 {
  56                     nBranchPoint = pindex->nHeight;
  57                     return error("Checkpoints: new block on alternative branch at height=%d before auto checkpoint at height=%d", pindex->nHeight, nAutoCheckpoint);
  58                 }
  59             }
  60             else
  61                 pindex = pindex->pprev;
  62         }
  63         return error("Checkpoints: failed to find any ancestor on main chain for the new block - internal error");
  64     }
  65
  66     // ppcoin: get next chain checkpoint
  67     int GetNextChainCheckpoint(const CBlockIndex *pindexLast)
  68     {
  69         CBigNum bnTarget;
  70         CBigNum bnTargetMax = 0;  // max target of all blocks since checkpoint
  71         CBigNum bnTargetMin = 0;  // min target of all candidate checkpoints
  72         int nMinTargetHeight = 0; // min target height of candidate checkpoints
  73         int nCheckpointMin = 0;   // minimum candidate checkpoint
  74         int nCheckpointMax = 0;   // maximum candidate checkpoint
  75         int nDepth = pindexLast->nHeight - pindexLast->nCheckpoint;
  76         const CBlockIndex *pindex = pindexLast;
  77         while (nDepth >= 0 && pindex)
  78         {
  79             bnTarget.SetCompact(pindex->nBits);
  80             if (bnTarget > bnTargetMax)
  81                 bnTargetMax = bnTarget;
  82             if (nCheckpointMax > 0 && bnTarget < bnTargetMin)
  83             {
  84                 bnTargetMin = bnTarget;
  85                 nMinTargetHeight = pindex->nHeight;
  86             }
  87             if (nCheckpointMax == 0 && pindexLast->GetBlockTime() - pindex->GetBlockTime() > AUTO_CHECKPOINT_MIN_SPAN)
  88             {
  89                 nCheckpointMax = pindex->nHeight;
  90                 bnTargetMin.SetCompact(pindex->nBits);
  91                 nMinTargetHeight = pindex->nHeight;
  92             }
  93             if (pindexLast->GetBlockTime() - pindex->GetBlockTime() < AUTO_CHECKPOINT_MAX_SPAN)
  94                 nCheckpointMin = pindex->nHeight;
  95             pindex = pindex->pprev;
  96             nDepth--;
  97         }
  98
  99         assert (nDepth == -1);  // arrive at chain checkpoint now
 100
 101         printf("Checkpoints: min=%d max=%d tminheight=%d tmin=0x%08x tmax=0x%08x\n",
 102             nCheckpointMin, nCheckpointMax, nMinTargetHeight,
 103             bnTargetMin.GetCompact(), bnTargetMax.GetCompact());
 104         if (nCheckpointMax == 0) // checkpoint stays if max candidate not found
 105             return pindexLast->nCheckpoint;
 106
 107         if (bnTargetMin * 100 > bnTargetMax * 90)
 108             return nCheckpointMax;
 109         if (bnTarget * 100 > bnTargetMax * 90)
 110             return nMinTargetHeight;
 111         else
 112             return nCheckpointMin;
 113     }
 114
 115     // ppcoin: get next auto checkpoint from the new chain checkpoint
 116     int GetNextAutoCheckpoint(int nCheckpoint)
 117     {
 118         return (std::max(nAutoCheckpoint, nCheckpoint));
 119     }
 120
 121     // ppcoin: advance to next automatic checkpoint
 122     void AdvanceAutoCheckpoint(int nCheckpoint)
 123     {
 124         nAutoCheckpoint = GetNextAutoCheckpoint(nCheckpoint);
 125         printf("Checkpoints: auto checkpoint now at height=%d\n", nAutoCheckpoint);
 126     }
 127
 128     int GetTotalBlocksEstimate()
 129     {
 130         if (fTestNet) return 0;
 131
 132         return mapCheckpoints.rbegin()->first;
 133     }
 134
 135     // ppcoin: reset auto checkpoint
 136     bool ResetAutoCheckpoint(int nCheckpoint)
 137     {
 138         if (nCheckpoint <= 0 || nCheckpoint > nBestHeight)
 139             return error("ResetAutoCheckpoint() : new checkpoint invalid");
 140         if (nCheckpoint >= nAutoCheckpoint)
 141             return error("ResetAutoCheckpoint() : new checkpoint not earlier than current auto checkpoint");
 142         CTxDB txdb;
 143         txdb.TxnBegin();
 144         if (!txdb.WriteAutoCheckpoint(nCheckpoint, true))
 145             return error("ResetAutoCheckpoint() : database write failed");
 146         if (!txdb.TxnCommit())
 147             return error("ResetAutoCheckpoint() : database commit failed");
 148         nAutoCheckpoint = nCheckpoint;
 149         nBranchPoint = 0;  // clear branch point
 150
 151         // clear ban list to accept alternative branches
 152         CRITICAL_BLOCK(cs_vNodes)
 153         {
 154             BOOST_FOREACH(CNode* pnode, vNodes)
 155                 pnode->ClearBanned();
 156         }
 157
 158         return true;
 159     }
 160
 161     CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex)
 162     {
 163         if (fTestNet) return NULL;
 164
 165         int64 nResult;
 166         BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, mapCheckpoints)
 167         {
 168             const uint256& hash = i.second;
 169             std::map<uint256, CBlockIndex*>::const_iterator t = mapBlockIndex.find(hash);
 170             if (t != mapBlockIndex.end())
 171                 return t->second;
 172         }
 173         return NULL;
 174     }
 175 }