Disconnect peers which are not catched up

Peers which stop sending us headers too early are very likely peers which
did not catch up before and stalled for some reason. We should disconnect
these peers and chose another one to continue.

src/net_processing.cpp

@@ -1775,11 +1775,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             ReadCompactSize(vRecv); // ignore tx count; assume it is 0.
         }
 
-        if (nCount == 0) {
-            // Nothing interesting. Stop asking this peers for more headers.
-            return true;
-        }
-
         CBlockIndex *pindexLast = NULL;
         {
         LOCK(cs_main);
@@ -1816,6 +1811,20 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // from there instead.
             LogPrint("net", "more getheaders (%d) to end to peer=%d (startheight:%d)\n", pindexLast->nHeight, pfrom->id, pfrom->nStartingHeight);
             connman.PushMessage(pfrom, NetMsgType::GETHEADERS, chainActive.GetLocator(pindexLast), uint256());
+        } else {
+            if (chainparams.DelayGetHeadersTime() != 0 && pindexBestHeader->GetBlockTime() < GetAdjustedTime() - chainparams.DelayGetHeadersTime()) {
+                // peer has sent us a HEADERS message below maximum size and we are still quite far from being fully
+                // synced, this means we probably got a bad peer for initial sync and need to continue with another one.
+                // By disconnecting we force to start a new iteration of initial headers sync in SendMessages
+                // TODO should we handle whitelisted peers here as we do in headers sync timeout handling?
+                pfrom->fDisconnect = true;
+                return error("detected bad peer for initial headers sync, disconnecting %d", pfrom->id);
+            }
+
+            if (nCount == 0) {
+                // Nothing interesting. Stop asking this peers for more headers.
+                return true;
+            }
         }
 
         bool fCanDirectFetch = CanDirectFetch(chainparams.GetConsensus());