From 0bf431870e45d8e20c4671e51a782ebf97b75fac Mon Sep 17 00:00:00 2001
From: "Wladimir J. van der Laan" <laanwj@gmail.com>
Date: Wed, 2 May 2018 14:10:27 +0200
Subject: net: Serve blocks directly from disk when possible

In `ProcessGetBlockData`, send the block data directly from disk if
type MSG_WITNESS_BLOCK is requested. This is a valid shortcut as the
on-disk format matches the network format.

This is expected to increase performance because a deserialization and
subsequent serialization roundtrip is avoided.
---
 src/validation.cpp | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

(limited to 'src/validation.cpp')

diff --git a/src/validation.cpp b/src/validation.cpp
index 1b9e982753..69a201d988 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1125,6 +1125,52 @@ bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus
     return true;
 }
 
+bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CDiskBlockPos& pos, const CMessageHeader::MessageStartChars& message_start)
+{
+    CDiskBlockPos hpos = pos;
+    hpos.nPos -= 8; // Seek back 8 bytes for meta header
+    CAutoFile filein(OpenBlockFile(hpos, true), SER_DISK, CLIENT_VERSION);
+    if (filein.IsNull()) {
+        return error("%s: OpenBlockFile failed for %s", __func__, pos.ToString());
+    }
+
+    try {
+        CMessageHeader::MessageStartChars blk_start;
+        unsigned int blk_size;
+
+        filein >> blk_start >> blk_size;
+
+        if (memcmp(blk_start, message_start, CMessageHeader::MESSAGE_START_SIZE)) {
+            return error("%s: Block magic mismatch for %s: %s versus expected %s", __func__, pos.ToString(),
+                    HexStr(blk_start, blk_start + CMessageHeader::MESSAGE_START_SIZE),
+                    HexStr(message_start, message_start + CMessageHeader::MESSAGE_START_SIZE));
+        }
+
+        if (blk_size > MAX_SIZE) {
+            return error("%s: Block data is larger than maximum deserialization size for %s: %s versus %s", __func__, pos.ToString(),
+                    blk_size, MAX_SIZE);
+        }
+
+        block.resize(blk_size); // Zeroing of memory is intentional here
+        filein.read((char*)block.data(), blk_size);
+    } catch(const std::exception& e) {
+        return error("%s: Read from block file failed: %s for %s", __func__, e.what(), pos.ToString());
+    }
+
+    return true;
+}
+
+bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CBlockIndex* pindex, const CMessageHeader::MessageStartChars& message_start)
+{
+    CDiskBlockPos block_pos;
+    {
+        LOCK(cs_main);
+        block_pos = pindex->GetBlockPos();
+    }
+
+    return ReadRawBlockFromDisk(block, block_pos, message_start);
+}
+
 CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
 {
     int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
-- 
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