Gateway: Fixed a race condition on ReconnectOP

gateway/op.go

@@ -30,6 +30,11 @@ const (
 	GuildSubscriptionsOP  OPCode = 14
 )
 
+// ErrReconnectRequest is returned by HandleOP if a ReconnectOP is given. This
+// is used mostly internally to signal the heartbeat loop to reconnect, if
+// needed. It is not a fatal error.
+var ErrReconnectRequest = errors.New("ReconnectOP received")
+
 func (g *Gateway) HandleOP(op *wsutil.OP) error {
 	switch op.Code {
 	case HeartbeatAckOP:
@@ -47,13 +52,9 @@ func (g *Gateway) HandleOP(op *wsutil.OP) error {
 		// Server requests to reconnect, die and retry.
 		wsutil.WSDebug("ReconnectOP received.")
 
-		// We must reconnect in another goroutine, as running Reconnect
-		// synchronously would prevent the main event loop from exiting.
-		go g.Reconnect()
-
-		// Gracefully exit with a nil let the event handler take the signal from
-		// the pacemaker.
-		return nil
+		// Exit with the ReconnectOP error to force the heartbeat event loop to
+		// reconnect synchronously. Not really a fatal error.
+		return ErrReconnectRequest
 
 	case InvalidSessionOP:
 		// Discord expects us to sleep for no reason
@@ -101,7 +102,7 @@ func (g *Gateway) HandleOP(op *wsutil.OP) error {
 			g.SessionID = ev.SessionID
 		}
 
-		// Throw the event into a channel, it's valid now.
+		// Throw the event into a channel; it's valid now.
 		g.Events <- ev
 		return nil
 

utils/wsutil/heart.go

@@ -108,7 +108,7 @@ func (p *PacemakerLoop) startLoop() error {
 
 			// Handle the event
 			if err := p.handler(o); err != nil {
-				p.errorLog(errors.Wrap(err, "handler failed"))
+				return errors.Wrap(err, "handler failed")
 			}
 		}
 	}