Remove BOOST_FOREACH macro
[novacoin.git] / src / checkpoints.cpp
index 69024e2..a9728ff 100644 (file)
@@ -1,17 +1,21 @@
-// Copyright (c) 2011 The Bitcoin developers
-// Copyright (c) 2011 The PPCoin developers
+// Copyright (c) 2009-2012 The Bitcoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
-// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <boost/assign/list_of.hpp> // for 'map_list_of()'
 #include <boost/foreach.hpp>
+#include <algorithm>
 
-#include "headers.h"
 #include "checkpoints.h"
 
+#include "txdb.h"
+#include "main.h"
+#include "uint256.h"
+
 namespace Checkpoints
 {
-    typedef std::map<int, uint256> MapCheckpoints;   // hardened checkpoints
+    typedef std::map<int, std::pair<uint256, unsigned int> > MapCheckpoints;
+    typedef std::list<uint256> ListBannedBlocks;
 
     //
     // What makes a good checkpoint block?
@@ -22,124 +26,437 @@ namespace Checkpoints
     //
     static MapCheckpoints mapCheckpoints =
         boost::assign::map_list_of
-        ( 0, hashGenesisBlock )
-        ; // ppcoin: no checkpoint yet; to be created in future releases
+        ( 0,     std::make_pair(hashGenesisBlock, 1360105017) )
+        ( 13560, std::make_pair(uint256("0xa1591a0fcbf11f282d671581edb9f0aadcd06fee69761081e0a3245914c13729"), 1364674052) )
+        ( 143990, std::make_pair(uint256("0x00000000001ff5c3940a9f73ad4a990f64955179bde0f743c76dbf0031429efc"), 1418953493) )
+        ( 149000, std::make_pair(uint256("0x7a24acfcadcf43054e7f7d9f273522c0dfc5791ba4006e0273e7521a8d36c525"), 1420872125) )
+        ( 160000, std::make_pair(uint256("0x000000000001cb1133043d38d077c0e93f66c8b2566779f10f182137d1e34a68"), 1425150237) )
+        ( 200000, std::make_pair(uint256("0x0000000000029f8bbf66e6ea6f3e5db55009404aae0fe395a53dd33142b2bff2"), 1441127233) )
+        ( 221047, std::make_pair(uint256("0xa28aef712e7aa0c285bfe29351ca21ed416689139e3063ef770fc826a8b9e9da"), 1449431646) )
+        ( 243100, std::make_pair(uint256("0x000000000006522d1ebc0734cb0e6b83f5d4da0c3cbc72bd91b82016f611c4f0"), 1458215793) )
+    ;
+
+    static ListBannedBlocks listBanned =
+        boost::assign::list_of
+        // Invalid block #221047 with future timestamp of 2016/02/23 09:24:17 UTC
+        ( uint256("0x46223e5432ceffe650d5729b4bb8479dcdf0ca1e534fa8e69382dc87b42ea94b") )
+    ;
 
-    // ppcoin: automatic checkpoint (represented by height of checkpoint)
-    int nAutoCheckpoint = 0;
+    // TestNet has no checkpoints
+    static MapCheckpoints mapCheckpointsTestnet =
+        boost::assign::map_list_of
+        ( 0, std::make_pair(hashGenesisBlockTestNet, 1360105017) )
+        ;
 
     bool CheckHardened(int nHeight, const uint256& hash)
     {
-        if (fTestNet) return true; // Testnet has no checkpoints
+        MapCheckpoints& checkpoints = (fTestNet ? mapCheckpointsTestnet : mapCheckpoints);
 
-        MapCheckpoints::const_iterator i = mapCheckpoints.find(nHeight);
-        if (i == mapCheckpoints.end()) return true;
-        return hash == i->second;
+        MapCheckpoints::const_iterator i = checkpoints.find(nHeight);
+        if (i == checkpoints.end()) return true;
+        return hash == i->second.first;
     }
 
-    // ppcoin: check automatic checkpoint
-    // To pass the check:
-    //   - All ancestors (including the block itself) have block index already
-    //   - The immediate ancestor in main chain must not have height less than
-    //     checkpoint height
-    bool CheckAuto(const CBlockIndex *pindex)
+    bool CheckBanned(const uint256 &nHash)
+    {
+        if (fTestNet) // Testnet has no banned blocks
+            return true;
+        ListBannedBlocks::const_iterator it = std::find(listBanned.begin(), listBanned.end(), nHash);
+        return it == listBanned.end();
+    }
+
+    int GetTotalBlocksEstimate()
     {
-        while (pindex)
+        MapCheckpoints& checkpoints = (fTestNet ? mapCheckpointsTestnet : mapCheckpoints);
+
+        return checkpoints.rbegin()->first;
+    }
+
+    unsigned int GetLastCheckpointTime()
+    {
+        MapCheckpoints& checkpoints = (fTestNet ? mapCheckpointsTestnet : mapCheckpoints);
+
+        return checkpoints.rbegin()->second.second;
+    }
+
+    CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex)
+    {
+        MapCheckpoints& checkpoints = (fTestNet ? mapCheckpointsTestnet : mapCheckpoints);
+
+        BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, checkpoints)
         {
-            if (pindex->IsInMainChain())
+            const uint256& hash = i.second.first;
+            std::map<uint256, CBlockIndex*>::const_iterator t = mapBlockIndex.find(hash);
+            if (t != mapBlockIndex.end())
+                return t->second;
+        }
+        return NULL;
+    }
+
+    // ppcoin: synchronized checkpoint (centrally broadcasted)
+    uint256 hashSyncCheckpoint = 0;
+    uint256 hashPendingCheckpoint = 0;
+    CSyncCheckpoint checkpointMessage;
+    CSyncCheckpoint checkpointMessagePending;
+    uint256 hashInvalidCheckpoint = 0;
+    CCriticalSection cs_hashSyncCheckpoint;
+
+    // ppcoin: get last synchronized checkpoint
+    CBlockIndex* GetLastSyncCheckpoint()
+    {
+        LOCK(cs_hashSyncCheckpoint);
+        if (!mapBlockIndex.count(hashSyncCheckpoint))
+            error("GetSyncCheckpoint: block index missing for current sync-checkpoint %s", hashSyncCheckpoint.ToString().c_str());
+        else
+            return mapBlockIndex[hashSyncCheckpoint];
+        return NULL;
+    }
+
+    // ppcoin: only descendant of current sync-checkpoint is allowed
+    bool ValidateSyncCheckpoint(uint256 hashCheckpoint)
+    {
+        if (!mapBlockIndex.count(hashSyncCheckpoint))
+            return error("ValidateSyncCheckpoint: block index missing for current sync-checkpoint %s", hashSyncCheckpoint.ToString().c_str());
+        if (!mapBlockIndex.count(hashCheckpoint))
+            return error("ValidateSyncCheckpoint: block index missing for received sync-checkpoint %s", hashCheckpoint.ToString().c_str());
+
+        CBlockIndex* pindexSyncCheckpoint = mapBlockIndex[hashSyncCheckpoint];
+        CBlockIndex* pindexCheckpointRecv = mapBlockIndex[hashCheckpoint];
+
+        if (pindexCheckpointRecv->nHeight <= pindexSyncCheckpoint->nHeight)
+        {
+            // Received an older checkpoint, trace back from current checkpoint
+            // to the same height of the received checkpoint to verify
+            // that current checkpoint should be a descendant block
+            CBlockIndex* pindex = pindexSyncCheckpoint;
+            while (pindex->nHeight > pindexCheckpointRecv->nHeight)
+                if ((pindex = pindex->pprev) == NULL)
+                    return error("ValidateSyncCheckpoint: pprev null - block index structure failure");
+            if (pindex->GetBlockHash() != hashCheckpoint)
             {
-                if (pindex->nHeight >= nAutoCheckpoint)
-                    return true;
-                else
-                    return error("Checkpoints: new block on alternative branch at height=%d before auto checkpoint at height=%d", pindex->nHeight, nAutoCheckpoint);
+                hashInvalidCheckpoint = hashCheckpoint;
+                return error("ValidateSyncCheckpoint: new sync-checkpoint %s is conflicting with current sync-checkpoint %s", hashCheckpoint.ToString().c_str(), hashSyncCheckpoint.ToString().c_str());
             }
-            else
-                pindex = pindex->pprev;
+            return false; // ignore older checkpoint
+        }
+
+        // Received checkpoint should be a descendant block of the current
+        // checkpoint. Trace back to the same height of current checkpoint
+        // to verify.
+        CBlockIndex* pindex = pindexCheckpointRecv;
+        while (pindex->nHeight > pindexSyncCheckpoint->nHeight)
+            if ((pindex = pindex->pprev) == NULL)
+                return error("ValidateSyncCheckpoint: pprev2 null - block index structure failure");
+        if (pindex->GetBlockHash() != hashSyncCheckpoint)
+        {
+            hashInvalidCheckpoint = hashCheckpoint;
+            return error("ValidateSyncCheckpoint: new sync-checkpoint %s is not a descendant of current sync-checkpoint %s", hashCheckpoint.ToString().c_str(), hashSyncCheckpoint.ToString().c_str());
+        }
+        return true;
+    }
+
+    bool WriteSyncCheckpoint(const uint256& hashCheckpoint)
+    {
+        CTxDB txdb;
+        txdb.TxnBegin();
+        if (!txdb.WriteSyncCheckpoint(hashCheckpoint))
+        {
+            txdb.TxnAbort();
+            return error("WriteSyncCheckpoint(): failed to write to db sync checkpoint %s", hashCheckpoint.ToString().c_str());
         }
-        return error("Checkpoints: failed to find any ancestor on main chain for the new block - internal error");
+        if (!txdb.TxnCommit())
+            return error("WriteSyncCheckpoint(): failed to commit to db sync checkpoint %s", hashCheckpoint.ToString().c_str());
+
+#ifndef USE_LEVELDB
+        txdb.Close();
+#endif
+
+        Checkpoints::hashSyncCheckpoint = hashCheckpoint;
+        return true;
     }
 
-    // ppcoin: get next chain checkpoint
-    int GetNextChainCheckpoint(const CBlockIndex *pindexLast)
+    bool AcceptPendingSyncCheckpoint()
     {
-        CBigNum bnTarget;
-        CBigNum bnTargetMax = 0;  // max target of all blocks since checkpoint
-        CBigNum bnTargetMin = 0;  // min target of all candidate checkpoints
-        int nMinTargetHeight = 0; // min target height of candidate checkpoints
-        int nCheckpointMin = 0;   // minimum candidate checkpoint
-        int nCheckpointMax = 0;   // maximum candidate checkpoint
-        int nDepth = pindexLast->nHeight - pindexLast->nCheckpoint;
-        const CBlockIndex *pindex = pindexLast;
-        while (nDepth >= 0 && pindex)
+        LOCK(cs_hashSyncCheckpoint);
+        if (hashPendingCheckpoint != 0 && mapBlockIndex.count(hashPendingCheckpoint))
         {
-            bnTarget.SetCompact(pindex->nBits);
-            if (bnTarget > bnTargetMax)
-                bnTargetMax = bnTarget;
-            if (nCheckpointMax > 0 && bnTarget < bnTargetMin)
+            if (!ValidateSyncCheckpoint(hashPendingCheckpoint))
             {
-                bnTargetMin = bnTarget;
-                nMinTargetHeight = pindex->nHeight;
+                hashPendingCheckpoint = 0;
+                checkpointMessagePending.SetNull();
+                return false;
             }
-            if (nCheckpointMax == 0 && pindexLast->GetBlockTime() - pindex->GetBlockTime() > AUTO_CHECKPOINT_MIN_SPAN)
+
+            CTxDB txdb;
+            CBlockIndex* pindexCheckpoint = mapBlockIndex[hashPendingCheckpoint];
+            if (!pindexCheckpoint->IsInMainChain())
             {
-                nCheckpointMax = pindex->nHeight;
-                bnTargetMin.SetCompact(pindex->nBits);
-                nMinTargetHeight = pindex->nHeight;
+                CBlock block;
+                if (!block.ReadFromDisk(pindexCheckpoint))
+                    return error("AcceptPendingSyncCheckpoint: ReadFromDisk failed for sync checkpoint %s", hashPendingCheckpoint.ToString().c_str());
+                if (!block.SetBestChain(txdb, pindexCheckpoint))
+                {
+                    hashInvalidCheckpoint = hashPendingCheckpoint;
+                    return error("AcceptPendingSyncCheckpoint: SetBestChain failed for sync checkpoint %s", hashPendingCheckpoint.ToString().c_str());
+                }
             }
-            if (pindexLast->GetBlockTime() - pindex->GetBlockTime() < AUTO_CHECKPOINT_MAX_SPAN)
-                nCheckpointMin = pindex->nHeight;
+
+#ifndef USE_LEVELDB
+            txdb.Close();
+#endif
+            if (!WriteSyncCheckpoint(hashPendingCheckpoint))
+                return error("AcceptPendingSyncCheckpoint(): failed to write sync checkpoint %s", hashPendingCheckpoint.ToString().c_str());
+            hashPendingCheckpoint = 0;
+            checkpointMessage = checkpointMessagePending;
+            checkpointMessagePending.SetNull();
+            printf("AcceptPendingSyncCheckpoint : sync-checkpoint at %s\n", hashSyncCheckpoint.ToString().c_str());
+            // relay the checkpoint
+            if (!checkpointMessage.IsNull())
+            {
+                for (std::vector<CNode*>::iterator it = vNodes.begin(); it != vNodes.end(); ++it)
+                    checkpointMessage.RelayTo(*it);
+            }
+            return true;
+        }
+        return false;
+    }
+
+    // Automatically select a suitable sync-checkpoint 
+    uint256 AutoSelectSyncCheckpoint()
+    {
+        const CBlockIndex *pindex = pindexBest;
+        // Search backward for a block within max span and maturity window
+        while (pindex->pprev && (pindex->GetBlockTime() + CHECKPOINT_MAX_SPAN > pindexBest->GetBlockTime() || pindex->nHeight + 8 > pindexBest->nHeight))
             pindex = pindex->pprev;
-            nDepth--;
+        return pindex->GetBlockHash();
+    }
+
+    // Check against synchronized checkpoint
+    bool CheckSync(const uint256& hashBlock, const CBlockIndex* pindexPrev)
+    {
+        if (fTestNet) return true; // Testnet has no checkpoints
+        int nHeight = pindexPrev->nHeight + 1;
+
+        LOCK(cs_hashSyncCheckpoint);
+        // sync-checkpoint should always be accepted block
+        assert(mapBlockIndex.count(hashSyncCheckpoint));
+        const CBlockIndex* pindexSync = mapBlockIndex[hashSyncCheckpoint];
+
+        if (nHeight > pindexSync->nHeight)
+        {
+            // trace back to same height as sync-checkpoint
+            const CBlockIndex* pindex = pindexPrev;
+            while (pindex->nHeight > pindexSync->nHeight)
+                if ((pindex = pindex->pprev) == NULL)
+                    return error("CheckSync: pprev null - block index structure failure");
+            if (pindex->nHeight < pindexSync->nHeight || pindex->GetBlockHash() != hashSyncCheckpoint)
+                return false; // only descendant of sync-checkpoint can pass check
         }
+        if (nHeight == pindexSync->nHeight && hashBlock != hashSyncCheckpoint)
+            return false; // same height with sync-checkpoint
+        if (nHeight < pindexSync->nHeight && !mapBlockIndex.count(hashBlock))
+            return false; // lower height than sync-checkpoint
+        return true;
+    }
+
+    bool WantedByPendingSyncCheckpoint(uint256 hashBlock)
+    {
+        LOCK(cs_hashSyncCheckpoint);
+        if (hashPendingCheckpoint == 0)
+            return false;
+        if (hashBlock == hashPendingCheckpoint)
+            return true;
+        if (mapOrphanBlocks.count(hashPendingCheckpoint) 
+            && hashBlock == WantedByOrphan(mapOrphanBlocks[hashPendingCheckpoint]))
+            return true;
+        return false;
+    }
 
-        assert (nDepth == -1);  // arrive at chain checkpoint now
+    // ppcoin: reset synchronized checkpoint to last hardened checkpoint
+    bool ResetSyncCheckpoint()
+    {
+        LOCK(cs_hashSyncCheckpoint);
+        const uint256& hash = mapCheckpoints.rbegin()->second.first;
+        if (mapBlockIndex.count(hash) && !mapBlockIndex[hash]->IsInMainChain())
+        {
+            // checkpoint block accepted but not yet in main chain
+            printf("ResetSyncCheckpoint: SetBestChain to hardened checkpoint %s\n", hash.ToString().c_str());
+            CTxDB txdb;
+            CBlock block;
+            if (!block.ReadFromDisk(mapBlockIndex[hash]))
+                return error("ResetSyncCheckpoint: ReadFromDisk failed for hardened checkpoint %s", hash.ToString().c_str());
+            if (!block.SetBestChain(txdb, mapBlockIndex[hash]))
+            {
+                return error("ResetSyncCheckpoint: SetBestChain failed for hardened checkpoint %s", hash.ToString().c_str());
+            }
 
-        printf("Checkpoints: min=%d max=%d tminheight=%d tmin=0x%08x tmax=0x%08x\n",
-            nCheckpointMin, nCheckpointMax, nMinTargetHeight,
-            bnTargetMin.GetCompact(), bnTargetMax.GetCompact());
-        if (nCheckpointMax == 0) // checkpoint stays if max candidate not found
-            return pindexLast->nCheckpoint;
+#ifndef USE_LEVELDB
+            txdb.Close();
+#endif
 
-        if (bnTargetMin * 100 > bnTargetMax * 90)
-            return nCheckpointMax;
-        if (bnTarget * 100 > bnTargetMax * 90)
-            return nMinTargetHeight;
-        else
-            return nCheckpointMin;
+        }
+        else if(!mapBlockIndex.count(hash))
+        {
+            // checkpoint block not yet accepted
+            hashPendingCheckpoint = hash;
+            checkpointMessagePending.SetNull();
+            printf("ResetSyncCheckpoint: pending for sync-checkpoint %s\n", hashPendingCheckpoint.ToString().c_str());
+        }
+
+        BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, mapCheckpoints)
+        {
+            const uint256& hash = i.second.first;
+            if (mapBlockIndex.count(hash) && mapBlockIndex[hash]->IsInMainChain())
+            {
+                if (!WriteSyncCheckpoint(hash))
+                    return error("ResetSyncCheckpoint: failed to write sync checkpoint %s", hash.ToString().c_str());
+                printf("ResetSyncCheckpoint: sync-checkpoint reset to %s\n", hashSyncCheckpoint.ToString().c_str());
+                return true;
+            }
+        }
+
+        return false;
     }
 
-    // ppcoin: get next auto checkpoint from the new chain checkpoint
-    int GetNextAutoCheckpoint(int nCheckpoint)
+    void AskForPendingSyncCheckpoint(CNode* pfrom)
     {
-        return (std::max(nAutoCheckpoint, nCheckpoint));
+        LOCK(cs_hashSyncCheckpoint);
+        if (pfrom && hashPendingCheckpoint != 0 && (!mapBlockIndex.count(hashPendingCheckpoint)) && (!mapOrphanBlocks.count(hashPendingCheckpoint)))
+            pfrom->AskFor(CInv(MSG_BLOCK, hashPendingCheckpoint));
     }
 
-    // ppcoin: advance to next automatic checkpoint
-    void AdvanceAutoCheckpoint(int nCheckpoint)
+    bool SetCheckpointPrivKey(std::string strPrivKey)
     {
-        nAutoCheckpoint = GetNextAutoCheckpoint(nCheckpoint);
-        printf("Checkpoints: auto checkpoint now at height=%d\n", nAutoCheckpoint);
+        // Test signing a sync-checkpoint with genesis block
+        CSyncCheckpoint checkpoint;
+        checkpoint.hashCheckpoint = !fTestNet ? hashGenesisBlock : hashGenesisBlockTestNet;
+        CDataStream sMsg(SER_NETWORK, PROTOCOL_VERSION);
+        sMsg << (CUnsignedSyncCheckpoint)checkpoint;
+        checkpoint.vchMsg = std::vector<unsigned char>(sMsg.begin(), sMsg.end());
+
+        std::vector<unsigned char> vchPrivKey = ParseHex(strPrivKey);
+        CKey key;
+        key.SetPrivKey(CPrivKey(vchPrivKey.begin(), vchPrivKey.end())); // if key is not correct openssl may crash
+        if (!key.Sign(Hash(checkpoint.vchMsg.begin(), checkpoint.vchMsg.end()), checkpoint.vchSig))
+            return false;
+
+        // Test signing successful, proceed
+        CSyncCheckpoint::strMasterPrivKey = strPrivKey;
+        return true;
     }
 
-    int GetTotalBlocksEstimate()
+    bool SendSyncCheckpoint(uint256 hashCheckpoint)
     {
-        if (fTestNet) return 0;
+        CSyncCheckpoint checkpoint;
+        checkpoint.hashCheckpoint = hashCheckpoint;
+        CDataStream sMsg(SER_NETWORK, PROTOCOL_VERSION);
+        sMsg << (CUnsignedSyncCheckpoint)checkpoint;
+        checkpoint.vchMsg = std::vector<unsigned char>(sMsg.begin(), sMsg.end());
+
+        if (CSyncCheckpoint::strMasterPrivKey.empty())
+            return error("SendSyncCheckpoint: Checkpoint master key unavailable.");
+        std::vector<unsigned char> vchPrivKey = ParseHex(CSyncCheckpoint::strMasterPrivKey);
+        CKey key;
+        key.SetPrivKey(CPrivKey(vchPrivKey.begin(), vchPrivKey.end())); // if key is not correct openssl may crash
+        if (!key.Sign(Hash(checkpoint.vchMsg.begin(), checkpoint.vchMsg.end()), checkpoint.vchSig))
+            return error("SendSyncCheckpoint: Unable to sign checkpoint, check private key?");
+
+        if(!checkpoint.ProcessSyncCheckpoint(NULL))
+        {
+            printf("WARNING: SendSyncCheckpoint: Failed to process checkpoint.\n");
+            return false;
+        }
 
-        return mapCheckpoints.rbegin()->first;
+        // Relay checkpoint
+        {
+            LOCK(cs_vNodes);
+            for (std::vector<CNode*>::iterator it = vNodes.begin(); it != vNodes.end(); ++it)
+                checkpoint.RelayTo(*it);
+        }
+        return true;
     }
 
-    CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex)
+    // Is the sync-checkpoint outside maturity window?
+    bool IsMatureSyncCheckpoint()
     {
-        if (fTestNet) return NULL;
+        LOCK(cs_hashSyncCheckpoint);
+        // sync-checkpoint should always be accepted block
+        assert(mapBlockIndex.count(hashSyncCheckpoint));
+        const CBlockIndex* pindexSync = mapBlockIndex[hashSyncCheckpoint];
+        return (nBestHeight >= pindexSync->nHeight + nCoinbaseMaturity ||
+                pindexSync->GetBlockTime() + nStakeMinAge < GetAdjustedTime());
+    }
+}
 
-        int64 nResult;
-        BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, mapCheckpoints)
+// ppcoin: sync-checkpoint master key
+const std::string CSyncCheckpoint::strMasterPubKey = "04a51b735f816de4ec3f891d5b38bbc91e1f7245c7c08d17990760b86b4d8fc3910a850ffecf73bfa8886f01739a0c4c4322201282d07b6e48ce931cc92af94850";
+
+std::string CSyncCheckpoint::strMasterPrivKey = "";
+
+// ppcoin: verify signature of sync-checkpoint message
+bool CSyncCheckpoint::CheckSignature()
+{
+    CPubKey key(ParseHex(CSyncCheckpoint::strMasterPubKey));
+    if (!key.Verify(Hash(vchMsg.begin(), vchMsg.end()), vchSig))
+        return error("CSyncCheckpoint::CheckSignature() : verify signature failed");
+
+    // Now unserialize the data
+    CDataStream sMsg(vchMsg, SER_NETWORK, PROTOCOL_VERSION);
+    sMsg >> *(CUnsignedSyncCheckpoint*)this;
+    return true;
+}
+
+// process synchronized checkpoint
+bool CSyncCheckpoint::ProcessSyncCheckpoint(CNode* pfrom)
+{
+    if (!CheckSignature())
+        return false;
+
+    LOCK(Checkpoints::cs_hashSyncCheckpoint);
+    if (!mapBlockIndex.count(hashCheckpoint))
+    {
+        // We haven't received the checkpoint chain, keep the checkpoint as pending
+        Checkpoints::hashPendingCheckpoint = hashCheckpoint;
+        Checkpoints::checkpointMessagePending = *this;
+        printf("ProcessSyncCheckpoint: pending for sync-checkpoint %s\n", hashCheckpoint.ToString().c_str());
+        // Ask this guy to fill in what we're missing
+        if (pfrom)
         {
-            const uint256& hash = i.second;
-            std::map<uint256, CBlockIndex*>::const_iterator t = mapBlockIndex.find(hash);
-            if (t != mapBlockIndex.end())
-                return t->second;
+            pfrom->PushGetBlocks(pindexBest, hashCheckpoint);
+            // ask directly as well in case rejected earlier by duplicate
+            // proof-of-stake because getblocks may not get it this time
+            pfrom->AskFor(CInv(MSG_BLOCK, mapOrphanBlocks.count(hashCheckpoint)? WantedByOrphan(mapOrphanBlocks[hashCheckpoint]) : hashCheckpoint));
+        }
+        return false;
+    }
+
+    if (!Checkpoints::ValidateSyncCheckpoint(hashCheckpoint))
+        return false;
+
+    CTxDB txdb;
+    CBlockIndex* pindexCheckpoint = mapBlockIndex[hashCheckpoint];
+    if (!pindexCheckpoint->IsInMainChain())
+    {
+        // checkpoint chain received but not yet main chain
+        CBlock block;
+        if (!block.ReadFromDisk(pindexCheckpoint))
+            return error("ProcessSyncCheckpoint: ReadFromDisk failed for sync checkpoint %s", hashCheckpoint.ToString().c_str());
+        if (!block.SetBestChain(txdb, pindexCheckpoint))
+        {
+            Checkpoints::hashInvalidCheckpoint = hashCheckpoint;
+            return error("ProcessSyncCheckpoint: SetBestChain failed for sync checkpoint %s", hashCheckpoint.ToString().c_str());
         }
-        return NULL;
     }
+
+#ifndef USE_LEVELDB
+    txdb.Close();
+#endif
+
+    if (!Checkpoints::WriteSyncCheckpoint(hashCheckpoint))
+        return error("ProcessSyncCheckpoint(): failed to write sync checkpoint %s", hashCheckpoint.ToString().c_str());
+    Checkpoints::checkpointMessage = *this;
+    Checkpoints::hashPendingCheckpoint = 0;
+    Checkpoints::checkpointMessagePending.SetNull();
+    printf("ProcessSyncCheckpoint: sync-checkpoint at %s\n", hashCheckpoint.ToString().c_str());
+    return true;
 }