network: don't wait indefinitely for packet to be sent

Peers can be slow, very slow, slow enough to affect node's regular
operation. We can't wait for them indefinitely, there has to be a timeout for
send operations.

This patch uses TimePerBlock as a reference for its timeout. It's relatively
big and it doesn't affect tests much, 4+1 scenarios tend to perform a little
worse with while 7+2 scenarios work a little better. The difference is in some
percents, but all of these tests easily have 10-15% variations from run to
run.

It's an important step in making our gossip better because we can't have any
behavior where neighbors directly block the node forever, refs. #2678 and

pkg/network/server.go

@@ -1385,7 +1385,7 @@ func (s *Server) iteratePeersWithSendMsg(msg *Message, send func(Peer, bool, []b
 					peer.AddGetAddrSent()
 				}
 				sentN++
-			} else if errors.Is(err, errBusy) {
+			} else if !blocking && errors.Is(err, errBusy) {
 				// Can be retried.
 				continue
 			} else {

pkg/network/tcp_peer.go

@@ -87,11 +87,18 @@ func (p *TCPPeer) putPacketIntoQueue(queue chan<- []byte, block bool, msg []byte
 	if !p.Handshaked() {
 		return errStateMismatch
 	}
+	var ret error
 	if block {
+		timer := time.NewTimer(p.server.TimePerBlock / 2)
 		select {
 		case queue <- msg:
 		case <-p.done:
-			return errGone
+			ret = errGone
+		case <-timer.C:
+			ret = errBusy
+		}
+		if !errors.Is(ret, errBusy) && !timer.Stop() {
+			<-timer.C
 		}
 	} else {
 		select {
@@ -102,7 +109,7 @@ func (p *TCPPeer) putPacketIntoQueue(queue chan<- []byte, block bool, msg []byte
 			return errBusy
 		}
 	}
-	return nil
+	return ret
 }
 
 // EnqueuePacket implements the Peer interface.