From 8539361e66eace839060f77f39b770d045e7ce28 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Sun, 30 Dec 2012 23:41:41 +0100
Subject: [PATCH] Add checksums to undo data

This should be compatible with older code that didn't write checksums.
---
 src/main.cpp | 22 +++++++---------------
 src/main.h   | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index bb39f422f9..2619062a6b 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1474,19 +1474,11 @@ bool CBlock::DisconnectBlock(CBlockIndex *pindex, CCoinsViewCache &view, bool *p
     bool fClean = true;
 
     CBlockUndo blockUndo;
-    {
-        CDiskBlockPos pos = pindex->GetUndoPos();
-        if (pos.IsNull())
-            return error("DisconnectBlock() : no undo data available");
-        CAutoFile fileUndo(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
-        if (!fileUndo)
-            return error("DisconnectBlock() : cannot open undo file");
-        try {
-            fileUndo >> blockUndo;
-        } catch(std::exception &e) {
-            return error("DisconnectBlock() : deserialize or I/O error reading udno data");
-        }
-    }
+    CDiskBlockPos pos = pindex->GetUndoPos();
+    if (pos.IsNull())
+        return error("DisconnectBlock() : no undo data available");
+    if (!blockUndo.ReadFromDisk(pos, pindex->pprev->GetBlockHash()))
+        return error("DisconnectBlock() : failure reading undo data");
 
     if (blockUndo.vtxundo.size() + 1 != vtx.size())
         return error("DisconnectBlock() : block and undo data inconsistent");
@@ -1670,9 +1662,9 @@ bool CBlock::ConnectBlock(CBlockIndex* pindex, CCoinsViewCache &view, bool fJust
     {
         if (pindex->GetUndoPos().IsNull()) {
             CDiskBlockPos pos;
-            if (!FindUndoPos(pindex->nFile, pos, ::GetSerializeSize(blockundo, SER_DISK, CLIENT_VERSION) + 8))
+            if (!FindUndoPos(pindex->nFile, pos, ::GetSerializeSize(blockundo, SER_DISK, CLIENT_VERSION) + 40))
                 return error("ConnectBlock() : FindUndoPos failed");
-            if (!blockundo.WriteToDisk(pos))
+            if (!blockundo.WriteToDisk(pos, pindex->pprev->GetBlockHash()))
                 return error("ConnectBlock() : CBlockUndo::WriteToDisk failed");
 
             // update nUndoPos in block index
diff --git a/src/main.h b/src/main.h
index 80fd76452b..557df8bc5f 100644
--- a/src/main.h
+++ b/src/main.h
@@ -746,7 +746,7 @@ public:
         READWRITE(vtxundo);
     )
 
-    bool WriteToDisk(CDiskBlockPos &pos)
+    bool WriteToDisk(CDiskBlockPos &pos, const uint256 &hashBlock)
     {
         // Open history file to append
         CAutoFile fileout = CAutoFile(OpenUndoFile(pos), SER_DISK, CLIENT_VERSION);
@@ -764,6 +764,12 @@ public:
         pos.nPos = (unsigned int)fileOutPos;
         fileout << *this;
 
+        // calculate & write checksum
+        CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
+        hasher << hashBlock;
+        hasher << *this;
+        fileout << hasher.GetHash();
+
         // Flush stdio buffers and commit to disk before returning
         fflush(fileout);
         if (!IsInitialBlockDownload())
@@ -771,6 +777,44 @@ public:
 
         return true;
     }
+
+    bool ReadFromDisk(const CDiskBlockPos &pos, const uint256 &hashBlock)
+    {
+        // Open history file to read
+        CAutoFile filein = CAutoFile(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
+        if (!filein)
+            return error("CBlockUndo::ReadFromDisk() : OpenBlockFile failed");
+
+        // Read block
+        uint256 hashChecksum;
+        try {
+            filein >> *this;
+        }
+        catch (std::exception &e) {
+            return error("%s() : deserialize or I/O error", __PRETTY_FUNCTION__);
+        }
+
+        // for compatibility with pre-release code that didn't write checksums to undo data
+        // TODO: replace by a simply 'filein >> hashChecksum' in the above try block
+        try {
+            filein >> hashChecksum;
+        } catch (std::exception &e) {
+            hashChecksum = 0;
+        }
+        uint32_t hashInit = hashChecksum.Get64(0) & 0xFFFFFFFFUL;
+        if (hashChecksum == 0 || memcmp(&hashInit, pchMessageStart, 4) == 0)
+            return true;
+
+        // Verify checksum
+        CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
+        hasher << hashBlock;
+        hasher << *this;
+        if (hashChecksum != hasher.GetHash())
+            return error("CBlockUndo::ReadFromDisk() : checksum mismatch");
+
+        return true;
+    }
+
 };
 
 /** pruned version of CTransaction: only retains metadata and unspent transaction outputs