Dont remove a "preferred" cmpctblock peer if they provide a block

src/main.cpp

@@ -485,9 +485,13 @@ void MaybeSetPeerAsAnnouncingHeaderAndIDs(const CNodeState* nodestate, CNode* pf
         return;
     }
     if (nodestate->fProvidesHeaderAndIDs) {
-        BOOST_FOREACH(const NodeId nodeid, lNodesAnnouncingHeaderAndIDs)
-            if (nodeid == pfrom->GetId())
+        for (std::list<NodeId>::iterator it = lNodesAnnouncingHeaderAndIDs.begin(); it != lNodesAnnouncingHeaderAndIDs.end(); it++) {
+            if (*it == pfrom->GetId()) {
+                lNodesAnnouncingHeaderAndIDs.erase(it);
+                lNodesAnnouncingHeaderAndIDs.push_back(pfrom->GetId());
                 return;
+            }
+        }
         bool fAnnounceUsingCMPCTBLOCK = false;
         uint64_t nCMPCTBLOCKVersion = (pfrom->GetLocalServices() & NODE_WITNESS) ? 2 : 1;
         if (lNodesAnnouncingHeaderAndIDs.size() >= 3) {
@@ -5731,6 +5735,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     return true;
                 }
 
+                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);
+                }
+
                 BlockTransactionsRequest req;
                 for (size_t i = 0; i < cmpctblock.BlockTxCount(); i++) {
                     if (!partialBlock.IsTxAvailable(i))