From 969c840db52da796c319f84c9a9a20b1de902ccf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Fri, 31 Oct 2025 15:41:35 +0100
Subject: [PATCH] log,blocks: avoid `ComputeTotalSize` and `GetHash` work when
 logging is disabled

`PartiallyDownloadedBlock::FillBlock()` computed the block header hash and summed missing transaction sizes for debug logging unconditionally, including when cmpctblock debug logging is disabled.

Guard the debug-only hash and size computations with `LogAcceptCategory`.
Since `txn_available` is invalidated after the first loop (needed for efficient moving), we compute `tx_missing_size` by iterating `vtx_missing` directly. This is safe because the later `tx_missing_offset` check guarantees `vtx_missing` was fully consumed during reconstruction.

Use `block.GetHash()` instead of `header.GetHash()`, since header is cleared before logging.

No behavior change when debug logging is enabled: the reported counts, hashes, and byte totals remain the same.
---
 src/blockencodings.cpp | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/src/blockencodings.cpp b/src/blockencodings.cpp
index eebf7bf466a..fd528309902 100644
--- a/src/blockencodings.cpp
+++ b/src/blockencodings.cpp
@@ -192,40 +192,44 @@ ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<
 {
     if (header.IsNull()) return READ_STATUS_INVALID;
 
-    uint256 hash = header.GetHash();
     block = header;
     block.vtx.resize(txn_available.size());
 
-    unsigned int tx_missing_size = 0;
     size_t tx_missing_offset = 0;
     for (size_t i = 0; i < txn_available.size(); i++) {
         if (!txn_available[i]) {
-            if (vtx_missing.size() <= tx_missing_offset)
+            if (tx_missing_offset >= vtx_missing.size()) {
                 return READ_STATUS_INVALID;
+            }
             block.vtx[i] = vtx_missing[tx_missing_offset++];
-            tx_missing_size += block.vtx[i]->ComputeTotalSize();
-        } else
+        } else {
             block.vtx[i] = std::move(txn_available[i]);
+        }
     }
 
     // Make sure we can't call FillBlock again.
     header.SetNull();
     txn_available.clear();
 
-    if (vtx_missing.size() != tx_missing_offset)
+    if (vtx_missing.size() != tx_missing_offset) {
         return READ_STATUS_INVALID;
+    }
 
     // Check for possible mutations early now that we have a seemingly good block
     IsBlockMutatedFn check_mutated{m_check_block_mutated_mock ? m_check_block_mutated_mock : IsBlockMutated};
-    if (check_mutated(/*block=*/block,
-                       /*check_witness_root=*/segwit_active)) {
+    if (check_mutated(/*block=*/block, /*check_witness_root=*/segwit_active)) {
         return READ_STATUS_FAILED; // Possible Short ID collision
     }
 
-    LogDebug(BCLog::CMPCTBLOCK, "Successfully reconstructed block %s with %u txn prefilled, %u txn from mempool (incl at least %u from extra pool) and %u txn (%u bytes) requested\n", hash.ToString(), prefilled_count, mempool_count, extra_count, vtx_missing.size(), tx_missing_size);
-    if (vtx_missing.size() < 5) {
-        for (const auto& tx : vtx_missing) {
-            LogDebug(BCLog::CMPCTBLOCK, "Reconstructed block %s required tx %s\n", hash.ToString(), tx->GetHash().ToString());
+    if (LogAcceptCategory(BCLog::CMPCTBLOCK, BCLog::Level::Debug)) {
+        const uint256 hash{block.GetHash()};
+        uint32_t tx_missing_size{0};
+        for (const auto& tx : vtx_missing) tx_missing_size += tx->ComputeTotalSize();
+        LogDebug(BCLog::CMPCTBLOCK, "Successfully reconstructed block %s with %u txn prefilled, %u txn from mempool (incl at least %u from extra pool) and %u txn (%u bytes) requested\n", hash.ToString(), prefilled_count, mempool_count, extra_count, vtx_missing.size(), tx_missing_size);
+        if (vtx_missing.size() < 5) {
+            for (const auto& tx : vtx_missing) {
+                LogDebug(BCLog::CMPCTBLOCK, "Reconstructed block %s required tx %s\n", hash.ToString(), tx->GetHash().ToString());
+            }
         }
     }