PPCoin: Automatic checkpoint

diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
index d20fe24..8898ca1 100644 (file)
--- a/src/checkpoints.cpp
+++ b/src/checkpoints.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2011 The Bitcoin developers
+// Copyright (c) 2011 The PPCoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
 
@@ -10,7 +11,7 @@
 
 namespace Checkpoints
 {
-    typedef std::map<int, uint256> MapCheckpoints;
+    typedef std::map<int, uint256> MapCheckpoints;   // hardened checkpoints
 
     //
     // What makes a good checkpoint block?
@@ -24,7 +25,10 @@ namespace Checkpoints
         ( 0, hashGenesisBlock )
         ; // ppcoin: no checkpoint yet; to be created in future releases
 
-    bool CheckBlock(int nHeight, const uint256& hash)
+    // ppcoin: automatic checkpoint (represented by height of checkpoint)
+    int nAutoCheckpoint = 0;
+
+    bool CheckHardened(int nHeight, const uint256& hash)
     {
         if (fTestNet) return true; // Testnet has no checkpoints
 
@@ -33,6 +37,84 @@ namespace Checkpoints
         return hash == i->second;
     }
 
+    // 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)
+    {
+        while (pindex)
+        {
+            if (pindex->IsInMainChain())
+            {
+                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);
+            }
+            else
+                pindex = pindex->pprev;
+        }
+        return error("Checkpoints: failed to find any ancestor on main chain for the new block - internal error");
+    }
+
+    // ppcoin: get next auto checkpoint in the chain
+    int GetNextChainCheckpoint(const CBlockIndex *pindexLast)
+    {
+        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 since checkpoint
+        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)
+        {
+            bnTarget.SetCompact(pindex->nBits);
+            if (bnTarget > bnTargetMax)
+                bnTargetMax = bnTarget;
+            if (nCheckpointMax > 0 && bnTarget < bnTargetMin)
+            {
+                bnTargetMin = bnTarget;
+                nMinTargetHeight = pindex->nHeight;
+            }
+            if (nCheckpointMax == 0 && pindexLast->GetBlockTime() - pindex->GetBlockTime() > AUTO_CHECKPOINT_MIN_SPAN)
+            {
+                nCheckpointMax = pindex->nHeight;
+                bnTargetMin.SetCompact(pindex->nBits);
+                nMinTargetHeight = pindex->nHeight;
+            }
+            if (pindexLast->GetBlockTime() - pindex->GetBlockTime() < AUTO_CHECKPOINT_MAX_SPAN)
+                nCheckpointMin = pindex->nHeight;
+            pindex = pindex->pprev;
+            nDepth--;
+        }
+
+        assert (nDepth == -1);  // arrive at chain checkpoint now
+
+        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;
+
+        if (bnTargetMin * 100 > bnTargetMax * 90)
+            return nCheckpointMax;
+        if (bnTarget * 100 > bnTargetMax * 90)
+            return std::min(nCheckpointMax, nMinTargetHeight);
+        else
+            return nCheckpointMin;
+    }
+
+    // ppcoin: advance to next automatic checkpoint
+    void AdvanceAutoCheckpoint(int nCheckpoint)
+    {
+        nAutoCheckpoint = std::max(nAutoCheckpoint, nCheckpoint);
+        printf("Checkpoints: auto checkpoint now at height=%d\n", nAutoCheckpoint);
+    }
+
     int GetTotalBlocksEstimate()
     {
         if (fTestNet) return 0;

diff --git a/src/checkpoints.h b/src/checkpoints.h
index 9d52da4..78ccce9 100644 (file)
--- a/src/checkpoints.h
+++ b/src/checkpoints.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2011 The Bitcoin developers
+// Copyright (c) 2011 The PPCoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
 #ifndef BITCOIN_CHECKPOINT_H
@@ -7,6 +8,10 @@
 #include <map>
 #include "util.h"
 
+// ppcoin: auto checkpoint min at 1 day; max at 1 week
+#define AUTO_CHECKPOINT_MIN_SPAN (60 * 60 * 24)
+#define AUTO_CHECKPOINT_MAX_SPAN (60 * 60 * 24 * 7)
+
 class uint256;
 class CBlockIndex;
 
@@ -16,8 +21,14 @@ class CBlockIndex;
 //
 namespace Checkpoints
 {
+    extern int nAutoCheckpoint;
+
     // Returns true if block passes checkpoint checks
-    bool CheckBlock(int nHeight, const uint256& hash);
+    bool CheckHardened(int nHeight, const uint256& hash);
+    bool CheckAuto(const CBlockIndex *pindex);
+
+    int  GetNextChainCheckpoint(const CBlockIndex *pindex);
+    void AdvanceAutoCheckpoint(int nCheckpoint);
 
     // Return conservative estimate of total number of blocks, 0 if unknown
     int GetTotalBlocksEstimate();

diff --git a/src/db.cpp b/src/db.cpp
index bb3c3b0..40cc35e 100644 (file)
--- a/src/db.cpp
+++ b/src/db.cpp
@@ -7,6 +7,7 @@
 #include "headers.h"
 #include "db.h"
 #include "net.h"
+#include "checkpoints.h"
 #include <boost/filesystem.hpp>
 #include <boost/filesystem/fstream.hpp>
 
@@ -469,6 +470,16 @@ bool CTxDB::WriteBestInvalidTrust(uint64 nBestInvalidTrust)
     return Write(string("nBestInvalidTrust"), nBestInvalidTrust);
 }
 
+bool CTxDB::ReadAutoCheckpoint(int& nAutoCheckpoint)
+{
+    return Read(string("nAutoCheckpoint"), nAutoCheckpoint);
+}
+
+bool CTxDB::WriteAutoCheckpoint(int nCheckpoint)
+{
+    return Write(string("nAutoCheckpoint"), max(Checkpoints::nAutoCheckpoint, nCheckpoint));
+}
+
 CBlockIndex static * InsertBlockIndex(uint256 hash)
 {
     if (hash == 0)
@@ -560,7 +571,12 @@ bool CTxDB::LoadBlockIndex()
     pindexBest = mapBlockIndex[hashBestChain];
     nBestHeight = pindexBest->nHeight;
     nBestChainTrust = pindexBest->nChainTrust;
-    printf("LoadBlockIndex(): hashBestChain=%s  height=%d\n", hashBestChain.ToString().substr(0,20).c_str(), nBestHeight);
+    printf("LoadBlockIndex(): hashBestChain=%s  height=%d  trust=%d\n", hashBestChain.ToString().substr(0,20).c_str(), nBestHeight, nBestChainTrust);
+
+    // Load nAutoCheckpoint
+    if (!ReadAutoCheckpoint(Checkpoints::nAutoCheckpoint))
+        return error("CTxDB::LoadBlockIndex() : nAutoCheckpoint not loaded");
+    printf("LoadBlockIndex(): automatic checkpoint at height=%d\n", Checkpoints::nAutoCheckpoint);
 
     // Load nBestInvalidTrust, OK if it doesn't exist
     ReadBestInvalidTrust(nBestInvalidTrust);

diff --git a/src/db.h b/src/db.h
index 578a497..06e8dbd 100644 (file)
--- a/src/db.h
+++ b/src/db.h
@@ -291,6 +291,8 @@ public:
     bool WriteHashBestChain(uint256 hashBestChain);
     bool ReadBestInvalidTrust(uint64& nBestInvalidTrust);
     bool WriteBestInvalidTrust(uint64 nBestInvalidTrust);
+    bool ReadAutoCheckpoint(int& nAutoCheckpoint);
+    bool WriteAutoCheckpoint(int nCheckpoint);
     bool LoadBlockIndex();
 };
 

diff --git a/src/main.cpp b/src/main.cpp
index 9df7584..71ce131 100644 (file)
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1102,6 +1102,8 @@ bool static Reorganize(CTxDB& txdb, CBlockIndex* pindexNew)
     }
     if (!txdb.WriteHashBestChain(pindexNew->GetBlockHash()))
         return error("Reorganize() : WriteHashBestChain failed");
+    if (!txdb.WriteAutoCheckpoint(pindexNew->nCheckpoint))
+        return error("Reorganize() : WriteAutoCheckpoint failed");
 
     // Make sure it's successfully written to disk before changing memory structure
     if (!txdb.TxnCommit())
@@ -1137,6 +1139,7 @@ bool CBlock::SetBestChain(CTxDB& txdb, CBlockIndex* pindexNew)
     if (pindexGenesisBlock == NULL && hash == hashGenesisBlock)
     {
         txdb.WriteHashBestChain(hash);
+        txdb.WriteAutoCheckpoint(pindexNew->nCheckpoint);
         if (!txdb.TxnCommit())
             return error("SetBestChain() : TxnCommit failed");
         pindexGenesisBlock = pindexNew;
@@ -1144,7 +1147,7 @@ bool CBlock::SetBestChain(CTxDB& txdb, CBlockIndex* pindexNew)
     else if (hashPrevBlock == hashBestChain)
     {
         // Adding to current best branch
-        if (!ConnectBlock(txdb, pindexNew) || !txdb.WriteHashBestChain(hash))
+        if (!ConnectBlock(txdb, pindexNew) || !txdb.WriteHashBestChain(hash) || !txdb.WriteAutoCheckpoint(pindexNew->nCheckpoint))
         {
             txdb.TxnAbort();
             InvalidChainFound(pindexNew);
@@ -1185,6 +1188,7 @@ bool CBlock::SetBestChain(CTxDB& txdb, CBlockIndex* pindexNew)
     nBestChainTrust = pindexNew->nChainTrust;
     nTimeBestReceived = GetTime();
     nTransactionsUpdated++;
+    Checkpoints::AdvanceAutoCheckpoint(pindexBest->nCheckpoint);
     printf("SetBestChain: new best=%s  height=%d  trust=%s\n", hashBestChain.ToString().substr(0,20).c_str(), nBestHeight, CBigNum(nBestChainTrust).ToString().c_str());
 
     return true;
@@ -1247,13 +1251,20 @@ bool CBlock::AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos)
     if (!pindexNew)
         return error("AddToBlockIndex() : new CBlockIndex failed");
     map<uint256, CBlockIndex*>::iterator mi = mapBlockIndex.insert(make_pair(hash, pindexNew)).first;
+
     pindexNew->phashBlock = &((*mi).first);
     map<uint256, CBlockIndex*>::iterator miPrev = mapBlockIndex.find(hashPrevBlock);
     if (miPrev != mapBlockIndex.end())
     {
         pindexNew->pprev = (*miPrev).second;
         pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
+
+        // ppcoin: compute chain checkpoint
+        pindexNew->nCheckpoint = Checkpoints::GetNextChainCheckpoint(pindexNew->pprev);
+        assert (pindexNew->nCheckpoint >= pindexNew->pprev->nCheckpoint);
     }
+
+    // ppcoin: compute chain trust score
     uint64 nCoinAge = GetBlockCoinAge();
     if (!nCoinAge)
         return error("AddToBlockIndex() : invalid or orphaned transaction in block");
@@ -1359,9 +1370,13 @@ bool CBlock::AcceptBlock()
         if (!tx.IsFinal(nHeight, GetBlockTime()))
             return DoS(10, error("AcceptBlock() : contains a non-final transaction"));
 
-    // Check that the block chain matches the known block chain up to a checkpoint
-    if (!Checkpoints::CheckBlock(nHeight, hash))
-        return DoS(100, error("AcceptBlock() : rejected by checkpoint lockin at %d", nHeight));
+    // Check that the block chain matches the known block chain up to a hardened checkpoint
+    if (!Checkpoints::CheckHardened(nHeight, hash))
+        return DoS(100, error("AcceptBlock() : rejected by hardened checkpoint lockin at %d", nHeight));
+
+    // ppcoin: check that the block satisfies automatic checkpoint
+    if (!Checkpoints::CheckAuto(pindexPrev))
+        return DoS(100, error("AcceptBlock() : rejected by automatic checkpoint at %d", Checkpoints::nAutoCheckpoint));
 
     // Write block to history file
     if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK)))

diff --git a/src/main.h b/src/main.h
index 32fbc39..1bcad19 100644 (file)
--- a/src/main.h
+++ b/src/main.h
@@ -1029,6 +1029,7 @@ public:
     unsigned int nBlockPos;
     uint64 nChainTrust;// ppcoin: trust score of chain, in the unit of coin-days
     int nHeight;
+    int nCheckpoint;    // ppcoin: chain auto checkpoint height
 
     // block header
     int nVersion;
@@ -1047,6 +1048,7 @@ public:
         nBlockPos = 0;
         nHeight = 0;
         nChainTrust = 0;
+        nCheckpoint = 0;
 
         nVersion       = 0;
         hashMerkleRoot = 0;
@@ -1064,6 +1066,7 @@ public:
         nBlockPos = nBlockPosIn;
         nHeight = 0;
         nChainTrust = 0;
+        nCheckpoint = 0;
 
         nVersion       = block.nVersion;
         hashMerkleRoot = block.hashMerkleRoot;
@@ -1157,8 +1160,8 @@ public:
 
     std::string ToString() const
     {
-        return strprintf("CBlockIndex(nprev=%08x, pnext=%08x, nFile=%d, nBlockPos=%-6d nChainTrust=%"PRI64d" nHeight=%d, merkle=%s, hashBlock=%s)",
-            pprev, pnext, nFile, nBlockPos, nChainTrust, nHeight,
+        return strprintf("CBlockIndex(nprev=%08x, pnext=%08x, nFile=%d, nBlockPos=%-6d nChainTrust=%"PRI64d" nHeight=%d, nCheckpoint=%d, merkle=%s, hashBlock=%s)",
+            pprev, pnext, nFile, nBlockPos, nChainTrust, nHeight, nCheckpoint,
             hashMerkleRoot.ToString().substr(0,10).c_str(),
             GetBlockHash().ToString().substr(0,20).c_str());
     }
@@ -1202,6 +1205,7 @@ public:
         READWRITE(nBlockPos);
         READWRITE(nChainTrust);
         READWRITE(nHeight);
+        READWRITE(nCheckpoint);
 
         // block header
         READWRITE(this->nVersion);