Modify getblocktxn handler not to drop requests for old blocks

src/main.cpp

@@ -5453,7 +5453,19 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
 
         if (it->second->nHeight < chainActive.Height() - MAX_BLOCKTXN_DEPTH) {
+            // If an older block is requested (should never happen in practice,
+            // but can happen in tests) send a block response instead of a
+            // blocktxn response. Sending a full block response instead of a
+            // small blocktxn response is preferable in the case where a peer
+            // might maliciously send lots of getblocktxn requests to trigger
+            // expensive disk reads, because it will require the peer to
+            // actually receive all the data read from disk over the network.
             LogPrint("net", "Peer %d sent us a getblocktxn for a block > %i deep", pfrom->id, MAX_BLOCKTXN_DEPTH);
+            CInv inv;
+            inv.type = MSG_BLOCK;
+            inv.hash = req.blockhash;
+            pfrom->vRecvGetData.push_back(inv);
+            ProcessGetData(pfrom, chainparams.GetConsensus());
             return true;
         }
 
@@ -5768,7 +5780,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 if (!fAlreadyInFlight && mapBlocksInFlight.size() == 1 && pindex->pprev->IsValid(BLOCK_VALID_CHAIN)) {
                     // We seem to be rather well-synced, so it appears pfrom was the first to provide us
                     // with this block! Let's get them to announce using compact blocks in the future.
-                    MaybeSetPeerAsAnnouncingHeaderAndIDs(nodestate, pfrom, connman);
+                    MaybeSetPeerAsAnnouncingHeaderAndIDs(nodestate, pfrom);
                 }
 
                 BlockTransactionsRequest req;