Merge #9058: Fixes for p2p-compactblocks.py test timeouts on travis (#8842)

dac53b5 Modify getblocktxn handler not to drop requests for old blocks (Russell Yanofsky)
55bfddc [qa] Fix stale data bug in test_compactblocks_not_at_tip (Russell Yanofsky)
47e9659 [qa] Fix bug in compactblocks v2 merge (Russell Yanofsky)

src/main.cpp

@@ -5495,7 +5495,19 @@ 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 vInv;
+            vInv.type = State(pfrom->GetId())->fWantsCmpctWitness ? MSG_WITNESS_BLOCK : MSG_BLOCK;
+            vInv.hash = req.blockhash;
+            pfrom->vRecvGetData.push_back(vInv);
+            ProcessGetData(pfrom, chainparams.GetConsensus(), connman);
             return true;
         }