Remove block-request logic from INV message processing

Author: TheBlueMatt

src/main.cpp

@@ -5364,28 +5364,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             if (inv.type == MSG_BLOCK) {
                 UpdateBlockAvailability(pfrom->GetId(), inv.hash);
                 if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
-                    // First request the headers preceding the announced block. In the normal fully-synced
-                    // case where a new block is announced that succeeds the current tip (no reorganization),
-                    // there are no such headers.
-                    // Secondly, and only when we are close to being synced, we request the announced block directly,
-                    // to avoid an extra round-trip. Note that we must *first* ask for the headers, so by the
-                    // time the block arrives, the header chain leading up to it is already validated. Not
-                    // doing this will result in the received block being rejected as an orphan in case it is
-                    // not a direct successor.
+                    // We used to request the full block here, but since headers-announcements are now the
+                    // primary method of announcement on the network, and since, in the case that a node
+                    // fell back to inv we probably have a reorg which we should get the headers for first,
+                    // we now only provide a getheaders response here. When we receive the headers, we will
+                    // then ask for the blocks we need.
                     connman.PushMessage(pfrom, NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), inv.hash);
-                    CNodeState *nodestate = State(pfrom->GetId());
-                    if (CanDirectFetch(chainparams.GetConsensus()) &&
-                        nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER &&
-                        (!IsWitnessEnabled(chainActive.Tip(), chainparams.GetConsensus()) || State(pfrom->GetId())->fHaveWitness)) {
-                        inv.type |= nFetchFlags;
-                        if (nodestate->fSupportsDesiredCmpctVersion)
-                            vToFetch.push_back(CInv(MSG_CMPCT_BLOCK, inv.hash));
-                        else
-                            vToFetch.push_back(inv);
-                        // Mark block as in flight already, even though the actual "getdata" message only goes out
-                        // later (within the same cs_main lock, though).
-                        MarkBlockAsInFlight(pfrom->GetId(), inv.hash, chainparams.GetConsensus());
-                    }
                     LogPrint("net", "getheaders (%d) %s to peer=%d\n", pindexBestHeader->nHeight, inv.hash.ToString(), pfrom->id);
                 }
             }