From efc135ff6dd3f9b7a599c4ed8ee72de70db6773c Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Wed, 1 Feb 2017 16:17:54 -0500
Subject: [PATCH] Use cached [compact] blocks to respond to getdata messages

---
 src/net_processing.cpp | 47 +++++++++++++++++++++++++++---------------
 1 file changed, 30 insertions(+), 17 deletions(-)

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index b9667eb6c..4bfa01606 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -979,6 +979,13 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
             {
                 bool send = false;
                 BlockMap::iterator mi = mapBlockIndex.find(inv.hash);
+                std::shared_ptr<const CBlock> a_recent_block;
+                std::shared_ptr<const CBlockHeaderAndShortTxIDs> a_recent_compact_block;
+                {
+                    LOCK(cs_most_recent_block);
+                    a_recent_block = most_recent_block;
+                    a_recent_compact_block = most_recent_compact_block;
+                }
                 if (mi != mapBlockIndex.end())
                 {
                     if (mi->second->nChainTx && !mi->second->IsValid(BLOCK_VALID_SCRIPTS) &&
@@ -988,11 +995,6 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                         // before ActivateBestChain but after AcceptBlock).
                         // In this case, we need to run ActivateBestChain prior to checking the relay
                         // conditions below.
-                        std::shared_ptr<const CBlock> a_recent_block;
-                        {
-                            LOCK(cs_most_recent_block);
-                            a_recent_block = most_recent_block;
-                        }
                         CValidationState dummy;
                         ActivateBestChain(dummy, Params(), a_recent_block);
                     }
@@ -1026,14 +1028,20 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                 // it's available before trying to send.
                 if (send && (mi->second->nStatus & BLOCK_HAVE_DATA))
                 {
-                    // Send block from disk
-                    CBlock block;
-                    if (!ReadBlockFromDisk(block, (*mi).second, consensusParams))
-                        assert(!"cannot load block from disk");
+                    std::shared_ptr<const CBlock> pblock;
+                    if (a_recent_block && a_recent_block->GetHash() == (*mi).second->GetBlockHash()) {
+                        pblock = a_recent_block;
+                    } else {
+                        // Send block from disk
+                        std::shared_ptr<CBlock> pblockRead = std::make_shared<CBlock>();
+                        if (!ReadBlockFromDisk(*pblockRead, (*mi).second, consensusParams))
+                            assert(!"cannot load block from disk");
+                        pblock = pblockRead;
+                    }
                     if (inv.type == MSG_BLOCK)
-                        connman.PushMessage(pfrom, msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCK, block));
+                        connman.PushMessage(pfrom, msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCK, *pblock));
                     else if (inv.type == MSG_WITNESS_BLOCK)
-                        connman.PushMessage(pfrom, msgMaker.Make(NetMsgType::BLOCK, block));
+                        connman.PushMessage(pfrom, msgMaker.Make(NetMsgType::BLOCK, *pblock));
                     else if (inv.type == MSG_FILTERED_BLOCK)
                     {
                         bool sendMerkleBlock = false;
@@ -1042,7 +1050,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                             LOCK(pfrom->cs_filter);
                             if (pfrom->pfilter) {
                                 sendMerkleBlock = true;
-                                merkleBlock = CMerkleBlock(block, *pfrom->pfilter);
+                                merkleBlock = CMerkleBlock(*pblock, *pfrom->pfilter);
                             }
                         }
                         if (sendMerkleBlock) {
@@ -1055,7 +1063,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                             // however we MUST always provide at least what the remote peer needs
                             typedef std::pair<unsigned int, uint256> PairType;
                             BOOST_FOREACH(PairType& pair, merkleBlock.vMatchedTxn)
-                                connman.PushMessage(pfrom, msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::TX, *block.vtx[pair.first]));
+                                connman.PushMessage(pfrom, msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::TX, *pblock->vtx[pair.first]));
                         }
                         // else
                             // no response
@@ -1069,10 +1077,15 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                         bool fPeerWantsWitness = State(pfrom->GetId())->fWantsCmpctWitness;
                         int nSendFlags = fPeerWantsWitness ? 0 : SERIALIZE_TRANSACTION_NO_WITNESS;
                         if (CanDirectFetch(consensusParams) && mi->second->nHeight >= chainActive.Height() - MAX_CMPCTBLOCK_DEPTH) {
-                            CBlockHeaderAndShortTxIDs cmpctblock(block, fPeerWantsWitness);
-                            connman.PushMessage(pfrom, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, cmpctblock));
-                        } else
-                            connman.PushMessage(pfrom, msgMaker.Make(nSendFlags, NetMsgType::BLOCK, block));
+                            if (fPeerWantsWitness && a_recent_compact_block && a_recent_compact_block->header.GetHash() == mi->second->GetBlockHash()) {
+                                connman.PushMessage(pfrom, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, *a_recent_compact_block));
+                            } else {
+                                CBlockHeaderAndShortTxIDs cmpctblock(*pblock, fPeerWantsWitness);
+                                connman.PushMessage(pfrom, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, cmpctblock));
+                            }
+                        } else {
+                            connman.PushMessage(pfrom, msgMaker.Make(nSendFlags, NetMsgType::BLOCK, *pblock));
+                        }
                     }
 
                     // Trigger the peer node to send a getblocks request for the next batch of inventory