Introduce CHashVerifier to hash read data

This is necessary later, when we drop the nVersion field from the undo
data. At that point deserializing and reserializing the data won't
roundtrip anymore, and thus that approach can't be used to verify
checksums anymore.

With this CHashVerifier approach, we can deserialize while hashing the
exact serialized form that was used. This is both more efficient and
more correct in that case.

1 files changed, 4 insertions, 5 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index ed94be5c2..fc7e129c0 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1210,8 +1210,10 @@ bool UndoReadFromDisk(CBlockUndo& blockundo, const CDiskBlockPos& pos, const uin
 
     // Read block
     uint256 hashChecksum;
+    CHashVerifier<CAutoFile> verifier(&filein); // We need a CHashVerifier as reserializing may lose data
     try {
-        filein >> blockundo;
+        verifier << hashBlock;
+        verifier >> blockundo;
         filein >> hashChecksum;
     }
     catch (const std::exception& e) {
@@ -1219,10 +1221,7 @@ bool UndoReadFromDisk(CBlockUndo& blockundo, const CDiskBlockPos& pos, const uin
     }
 
     // Verify checksum
-    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
-    hasher << hashBlock;
-    hasher << blockundo;
-    if (hashChecksum != hasher.GetHash())
+    if (hashChecksum != verifier.GetHash())
         return error("%s: Checksum mismatch", __func__);
 
     return true;