1 files changed, 21 insertions, 6 deletions

diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 601d0bdf58..04d46f4361 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -415,7 +415,7 @@ void CleanupBlockRevFiles()
     // Remove the rev files immediately and insert the blk file paths into an
     // ordered map keyed by block file index.
     LogPrintf("Removing unusable blk?????.dat and rev?????.dat files for -reindex with -prune\n");
-    fs::path blocksdir = gArgs.GetBlocksDirPath();
+    const fs::path& blocksdir = gArgs.GetBlocksDirPath();
     for (fs::directory_iterator it(blocksdir); it != fs::directory_iterator(); it++) {
         const std::string path = fs::PathToString(it->path().filename());
         if (fs::is_regular_file(*it) &&
@@ -524,6 +524,16 @@ void BlockManager::FlushUndoFile(int block_file, bool finalize)
 void BlockManager::FlushBlockFile(bool fFinalize, bool finalize_undo)
 {
     LOCK(cs_LastBlockFile);
+
+    if (m_blockfile_info.size() < 1) {
+        // Return if we haven't loaded any blockfiles yet. This happens during
+        // chainstate init, when we call ChainstateManager::MaybeRebalanceCaches() (which
+        // then calls FlushStateToDisk()), resulting in a call to this function before we
+        // have populated `m_blockfile_info` via LoadBlockIndexDB().
+        return;
+    }
+    assert(static_cast<int>(m_blockfile_info.size()) > m_last_blockfile);
+
     FlatFilePos block_pos_old(m_last_blockfile, m_blockfile_info[m_last_blockfile].nSize);
     if (!BlockFileSeq().Flush(block_pos_old, fFinalize)) {
         AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
@@ -789,19 +799,24 @@ bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, c
     return true;
 }
 
-/** Store block on disk. If dbp is non-nullptr, the file is known to already reside on disk */
 FlatFilePos BlockManager::SaveBlockToDisk(const CBlock& block, int nHeight, CChain& active_chain, const CChainParams& chainparams, const FlatFilePos* dbp)
 {
     unsigned int nBlockSize = ::GetSerializeSize(block, CLIENT_VERSION);
     FlatFilePos blockPos;
-    if (dbp != nullptr) {
+    const auto position_known {dbp != nullptr};
+    if (position_known) {
         blockPos = *dbp;
+    } else {
+        // when known, blockPos.nPos points at the offset of the block data in the blk file. that already accounts for
+        // the serialization header present in the file (the 4 magic message start bytes + the 4 length bytes = 8 bytes = BLOCK_SERIALIZATION_HEADER_SIZE).
+        // we add BLOCK_SERIALIZATION_HEADER_SIZE only for new blocks since they will have the serialization header added when written to disk.
+        nBlockSize += static_cast<unsigned int>(BLOCK_SERIALIZATION_HEADER_SIZE);
     }
-    if (!FindBlockPos(blockPos, nBlockSize + 8, nHeight, active_chain, block.GetBlockTime(), dbp != nullptr)) {
+    if (!FindBlockPos(blockPos, nBlockSize, nHeight, active_chain, block.GetBlockTime(), position_known)) {
         error("%s: FindBlockPos failed", __func__);
         return FlatFilePos();
     }
-    if (dbp == nullptr) {
+    if (!position_known) {
         if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart())) {
             AbortNode("Failed to write block");
             return FlatFilePos();
@@ -882,7 +897,7 @@ void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFile
         // We can't hold cs_main during ActivateBestChain even though we're accessing
         // the chainman unique_ptrs since ABC requires us not to be holding cs_main, so retrieve
         // the relevant pointers before the ABC call.
-        for (CChainState* chainstate : WITH_LOCK(::cs_main, return chainman.GetAll())) {
+        for (Chainstate* chainstate : WITH_LOCK(::cs_main, return chainman.GetAll())) {
             BlockValidationState state;
             if (!chainstate->ActivateBestChain(state, nullptr)) {
                 LogPrintf("Failed to connect best block (%s)\n", state.ToString());