From 09ee8b7f278627b917f0784adf23cbc76cae5fa0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Mon, 12 May 2025 22:41:04 +0200
Subject: [PATCH] node: avoid recomputing block hash in `ReadBlock`
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Eliminate one SHA‑256 double‑hash computation of the header per block read by reusing the hash for:
* proof‑of‑work verification;
* (optional) integrity check against the supplied hash.
---
 src/node/blockstorage.cpp | 23 ++++++++++++-----------
 src/node/blockstorage.h   |  2 +-
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index f8cdd4ce08c..04936ec99da 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -38,6 +38,7 @@
 
 #include <cstddef>
 #include <map>
+#include <optional>
 #include <unordered_map>
 
 namespace kernel {
@@ -989,7 +990,7 @@ bool BlockManager::WriteBlockUndo(const CBlockUndo& blockundo, BlockValidationSt
     return true;
 }
 
-bool BlockManager::ReadBlock(CBlock& block, const FlatFilePos& pos) const
+bool BlockManager::ReadBlock(CBlock& block, const FlatFilePos& pos, const std::optional<uint256>& expected_hash) const
 {
     block.SetNull();
 
@@ -1007,8 +1008,10 @@ bool BlockManager::ReadBlock(CBlock& block, const FlatFilePos& pos) const
         return false;
     }
 
+    const auto block_hash{block.GetHash()};
+
     // Check the header
-    if (!CheckProofOfWork(block.GetHash(), block.nBits, GetConsensus())) {
+    if (!CheckProofOfWork(block_hash, block.nBits, GetConsensus())) {
         LogError("Errors in block header at %s while reading block", pos.ToString());
         return false;
     }
@@ -1019,21 +1022,19 @@ bool BlockManager::ReadBlock(CBlock& block, const FlatFilePos& pos) const
         return false;
     }
 
+    if (expected_hash && block_hash != *expected_hash) {
+        LogError("GetHash() doesn't match index at %s while reading block (%s != %s)",
+                 pos.ToString(), block_hash.ToString(), expected_hash->ToString());
+        return false;
+    }
+
     return true;
 }
 
 bool BlockManager::ReadBlock(CBlock& block, const CBlockIndex& index) const
 {
     const FlatFilePos block_pos{WITH_LOCK(cs_main, return index.GetBlockPos())};
-
-    if (!ReadBlock(block, block_pos)) {
-        return false;
-    }
-    if (block.GetHash() != index.GetBlockHash()) {
-        LogError("GetHash() doesn't match index for %s at %s while reading block", index.ToString(), block_pos.ToString());
-        return false;
-    }
-    return true;
+    return ReadBlock(block, block_pos, index.GetBlockHash());
 }
 
 bool BlockManager::ReadRawBlock(std::vector<uint8_t>& block, const FlatFilePos& pos) const
diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index 324f8e68605..9405f68c6cf 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -411,7 +411,7 @@ public:
     void UnlinkPrunedFiles(const std::set<int>& setFilesToPrune) const;
 
     /** Functions for disk access for blocks */
-    bool ReadBlock(CBlock& block, const FlatFilePos& pos) const;
+    bool ReadBlock(CBlock& block, const FlatFilePos& pos, const std::optional<uint256>& expected_hash = {}) const;
     bool ReadBlock(CBlock& block, const CBlockIndex& index) const;
     bool ReadRawBlock(std::vector<uint8_t>& block, const FlatFilePos& pos) const;