move subscription check up in call chain, ref tinode#865

server/store/types/types.go

@@ -51,8 +51,6 @@ const (
 	ErrInvalidResponse = StoreError("invalid response")
 	// ErrRedirected means the subscription request was redirected to another topic.
 	ErrRedirected = StoreError("redirected")
-	// ErrAlreadySatisfied means the desired result, such as subscription, is already satisfied.
-	ErrAlreadySatisfied = StoreError("already satisfied")
 )
 
 // Uid is a database-specific record id, suitable to be used as a primary key.

server/topic.go

@@ -334,6 +334,12 @@ func (t *Topic) registerSession(msg *ClientComMessage) {
 	// Request to add a connection to this topic
 	if t.isInactive() {
 		msg.sess.queueOut(ErrLockedReply(msg, types.TimeNow()))
+	} else if msg.sess.getSub(t.name) != nil {
+		// Session is already subscribed to topic. Subscription is checked in session.go,
+		// but there is a gap between topic creation/un-pausing and processing the
+		// first subscription request, before the topic is linked to session: a client
+		// may send several subscription requests in that gap.
+		msg.sess.queueOut(InfoAlreadySubscribed(msg.Id, msg.Original, msg.Timestamp))
 	} else {
 		// The topic is alive, so stop the kill timer, if it's ticking. We don't want the topic to die
 		// while processing the call.
@@ -1330,16 +1336,6 @@ func (t *Topic) broadcastToSessions(msg *ServerComMessage) {
 func (t *Topic) subscriptionReply(asChan bool, msg *ClientComMessage) error {
 	// The topic is already initialized by the Hub
 
-	// Check if the session is already subscribed to topic.
-	// Subscription is checked in session.go, but there is a gap between topic
-	// creation + un-pausing and processing the first subscription request,
-	// before the topic is linked to session: a client may send several subscription
-	// requests in that gap.
-	if msg.sess.getSub(t.name) != nil {
-		msg.sess.queueOut(InfoAlreadySubscribed(msg.Id, msg.Original, msg.Timestamp))
-		return types.ErrAlreadySatisfied
-	}
-
 	msgsub := msg.Sub
 
 	// For newly created topics report topic creation time.

server/utils.go

@@ -271,8 +271,6 @@ func decodeStoreErrorExplicitTs(err error, id, topic string, serverTs, incomingR
 			errmsg = ErrInvalidResponse(id, topic, serverTs, incomingReqTs)
 		case types.ErrRedirected:
 			errmsg = InfoUseOther(id, topic, params["topic"].(string), serverTs, incomingReqTs)
-		case types.ErrAlreadySatisfied:
-			errmsg = InfoNoAction(id, topic, serverTs, incomingReqTs)
 		default:
 			errmsg = ErrUnknownExplicitTs(id, topic, serverTs, incomingReqTs)
 		}