From 42535b58bd40e14ea489dd595474c57ca73e52ea Mon Sep 17 00:00:00 2001
From: Scott Nadal <scott.nadal@gmail.com>
Date: Fri, 8 Jun 2012 16:21:54 +0100
Subject: [PATCH] PPCoin: Accept pending synchronized checkpoint

---
 src/checkpoints.cpp |   60 +++++++++++++++++++++++++++++++++++++++------------
 src/checkpoints.h   |    2 +
 src/main.cpp        |    3 ++
 3 files changed, 51 insertions(+), 14 deletions(-)

diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
index ac86c95..aeb0be7 100644
--- a/src/checkpoints.cpp
+++ b/src/checkpoints.cpp
@@ -62,6 +62,27 @@ namespace Checkpoints
     CSyncCheckpoint checkpointMessagePending;
     CCriticalSection cs_hashSyncCheckpoint;
 
+    // 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)
+            return false;  // this is an older checkpoint, ignore
+
+        CBlockIndex* pindex = pindexCheckpointRecv;
+        while (pindex->nHeight > pindexSyncCheckpoint->nHeight)
+            pindex = pindex->pprev;
+        if (pindex->GetBlockHash() != hashSyncCheckpoint)
+            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 CSyncCheckpoint::ProcessSyncCheckpoint(CNode* pfrom)
     {
         if (!CheckSignature())
@@ -78,26 +99,37 @@ namespace Checkpoints
                     pfrom->PushGetBlocks(pindexBest, hashCheckpoint);
                 return false;
             }
-
-            if (!mapBlockIndex.count(hashSyncCheckpoint))
-                return error("ProcessSyncCheckpoint: block index missing for synchronized checkpoint %s", hashSyncCheckpoint.ToString().c_str());
-
-            CBlockIndex* pindexSyncCheckpoint = mapBlockIndex[hashSyncCheckpoint];
-            CBlockIndex* pindexCheckpointPending = mapBlockIndex[hashCheckpoint];
-            if (pindexCheckpointPending->nHeight <= pindexSyncCheckpoint->nHeight)
-                return false;  // this is an older checkpoint, ignore
-
-            CBlockIndex* pindex = pindexCheckpointPending;
-            while (pindex->nHeight > pindexSyncCheckpoint->nHeight)
-                pindex = pindex->pprev;
-            if (pindex->GetBlockHash() != hashSyncCheckpoint)
-                return error("ProcessSyncCheckpoint: new sync-checkpoint %s is not a descendant of current sync-checkpoint %s", hashCheckpoint.ToString().c_str(), hashSyncCheckpoint.ToString().c_str());
+            if (!ValidateSyncCheckpoint(hashCheckpoint))
+                return false;
             hashSyncCheckpoint = this->hashCheckpoint;
             checkpointMessage = *this;
+            checkpointMessagePending.SetNull();
         }
         return true;
     }
 
+    bool AcceptPendingSyncCheckpoint(uint256 hashAcceptedBlock)
+    {
+        if (!mapBlockIndex.count(hashAcceptedBlock))
+            return false;
+
+        CRITICAL_BLOCK(cs_hashSyncCheckpoint)
+            if ((!checkpointMessagePending.IsNull()) && checkpointMessagePending.hashCheckpoint == hashAcceptedBlock)
+            {
+                if (!ValidateSyncCheckpoint(checkpointMessagePending.hashCheckpoint))
+                {
+                    checkpointMessagePending.SetNull();
+                    return false;
+                }
+                hashSyncCheckpoint = checkpointMessagePending.hashCheckpoint;
+                checkpointMessage = checkpointMessagePending;
+                checkpointMessagePending.SetNull();
+                return true;
+            }
+
+        return false;
+    }
+
     // ppcoin: automatic checkpoint (represented by height of checkpoint)
     int nAutoCheckpoint = 0;
     int nBranchPoint = 0;    // branch point to alternative branch
diff --git a/src/checkpoints.h b/src/checkpoints.h
index 372f32b..92c14b7 100644
--- a/src/checkpoints.h
+++ b/src/checkpoints.h
@@ -135,6 +135,8 @@ namespace Checkpoints
     extern CSyncCheckpoint checkpointMessage;
     extern CCriticalSection cs_hashSyncCheckpoint;
 
+    bool AcceptPendingSyncCheckpoint(uint256 hashAcceptedBlock);
+
     // ppcoin: automatic checkpoint
     extern int nAutoCheckpoint;
     extern int nBranchPoint;
diff --git a/src/main.cpp b/src/main.cpp
index 6839725..d6c10a4 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1595,6 +1595,9 @@ bool CBlock::AcceptBlock()
                 if (nBestHeight > (pnode->nStartingHeight != -1 ? pnode->nStartingHeight - 2000 : 140700))
                     pnode->PushInventory(CInv(MSG_BLOCK, hash));
 
+    // ppcoin: check pending sync-checkpoint
+    Checkpoints::AcceptPendingSyncCheckpoint(hash);
+
     return true;
 }
 
-- 
1.7.1