distinguish throttled validation because of a full worker queue.

score.go

@@ -607,6 +607,12 @@ func (ps *peerScore) RejectMessage(msg *Message, reason string) {
 		fallthrough
 	case "blacklisted source":
 		return
+
+	case "validation queue full":
+		// the message was rejected before it entered the validation pipeline;
+		// we don't know if this message has a valid signature, and thus we also don't know if
+		// it has a valid message ID; all we can do is ignore it.
+		return
 	}
 
 	drec := ps.deliveries.getRecord(ps.msgID(msg.Message))

validation.go

@@ -151,8 +151,8 @@ func (v *validation) Push(src peer.ID, msg *Message) bool {
 		select {
 		case v.validateQ <- &validateReq{vals, src, msg}:
 		default:
-			log.Warningf("message validation throttled; dropping message from %s", src)
-			v.tracer.RejectMessage(msg, "validation throttled")
+			log.Warningf("message validation throttled: queue full; dropping message from %s", src)
+			v.tracer.RejectMessage(msg, "validation queue full")
 		}
 		return false
 	}