Relay compact block messages prior to full block connection

Author: TheBlueMatt

src/net_processing.cpp

@@ -752,6 +752,39 @@ void PeerLogicValidation::SyncTransaction(const CTransaction& tx, const CBlockIn
     }
 }
 
+void PeerLogicValidation::NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr<const CBlock>& pblock) {
+    CBlockHeaderAndShortTxIDs cmpctblock(*pblock, true);
+    CNetMsgMaker msgMaker(PROTOCOL_VERSION);
+
+    LOCK(cs_main);
+
+    static int nHighestFastAnnounce = 0;
+    if (pindex->nHeight <= nHighestFastAnnounce)
+        return;
+    nHighestFastAnnounce = pindex->nHeight;
+
+    bool fWitnessEnabled = IsWitnessEnabled(pindex->pprev, Params().GetConsensus());
+    uint256 hashBlock(pblock->GetHash());
+
+    connman->ForEachNode([this, &cmpctblock, pindex, &msgMaker, fWitnessEnabled, &hashBlock](CNode* pnode) {
+        // TODO: Avoid the repeated-serialization here
+        if (pnode->nVersion < INVALID_CB_NO_BAN_VERSION || pnode->fDisconnect)
+            return;
+        ProcessBlockAvailability(pnode->GetId());
+        CNodeState &state = *State(pnode->GetId());
+        // If the peer has, or we announced to them the previous block already,
+        // but we don't think they have this one, go ahead and announce it
+        if (state.fPreferHeaderAndIDs && (!fWitnessEnabled || state.fWantsCmpctWitness) &&
+                !PeerHasHeader(&state, pindex) && PeerHasHeader(&state, pindex->pprev)) {
+
+            LogPrint("net", "%s sending header-and-ids %s to peer %d\n", "PeerLogicValidation::NewPoWValidBlock",
+                    hashBlock.ToString(), pnode->id);
+            connman->PushMessage(pnode, msgMaker.Make(NetMsgType::CMPCTBLOCK, cmpctblock));
+            state.pindexBestHeaderSent = pindex;
+        }
+    });
+}
+
 void PeerLogicValidation::UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) {
     const int nNewHeight = pindexNew->nHeight;
     connman->SetBestHeight(nNewHeight);

src/net_processing.h

@@ -24,6 +24,7 @@ class PeerLogicValidation : public CValidationInterface {
     virtual void SyncTransaction(const CTransaction& tx, const CBlockIndex* pindex, int nPosInBlock);
     virtual void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload);
     virtual void BlockChecked(const CBlock& block, const CValidationState& state);
+    virtual void NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr<const CBlock>& pblock);
 };
 
 struct CNodeStateStats {