client: resume subs only if present

This patch only sends a PublishRequest after a reconnect when active
subscriptions are present. Sending a PublishRequest when no
subscriptions are present can confuse some servers.

client.go

@@ -320,9 +320,10 @@ func (c *Client) monitor(ctx context.Context) {
 			c.pauseSubscriptions(ctx)
 
 			var (
-				subsToRepublish []uint32 // subscription ids for which to send republish requests
-				subsToRecreate  []uint32 // subscription ids which need to be recreated as new subscriptions
-				availableSeqs   map[uint32][]uint32
+				subsToRepublish []uint32            // subscription ids for which to send republish requests
+				subsToRecreate  []uint32            // subscription ids which need to be recreated as new subscriptions
+				availableSeqs   map[uint32][]uint32 // available sequence numbers per subscription
+				activeSubs      int                 // number of active subscriptions to resume/recreate
 			)
 
 			for action != none {
@@ -485,11 +486,13 @@ func (c *Client) monitor(ctx context.Context) {
 						// Assume that subsToRecreate and subsToRepublish have been
 						// populated in the previous step.
 
+						activeSubs = 0
 						for _, id := range subsToRepublish {
 							if err := c.republishSubscription(ctx, id, availableSeqs[id]); err != nil {
 								dlog.Printf("republish of subscription %d failed", id)
 								subsToRecreate = append(subsToRecreate, id)
 							}
+							activeSubs++
 						}
 
 						for _, id := range subsToRecreate {
@@ -498,6 +501,7 @@ func (c *Client) monitor(ctx context.Context) {
 								action = recreateSession
 								continue
 							}
+							activeSubs++
 						}
 
 						c.setState(Connected)
@@ -521,9 +525,14 @@ func (c *Client) monitor(ctx context.Context) {
 				<-c.sechanErr
 			}
 
-			dlog.Printf("resuming subscriptions")
-			c.resumeSubscriptions(ctx)
-			dlog.Printf("resumed subscriptions")
+			switch {
+			case activeSubs > 0:
+				dlog.Printf("resuming %d subscriptions", activeSubs)
+				c.resumeSubscriptions(ctx)
+				dlog.Printf("resumed %d subscriptions", activeSubs)
+			default:
+				dlog.Printf("no subscriptions to resume")
+			}
 		}
 	}
 }

client_sub.go

@@ -376,6 +376,9 @@ publish:
 
 		default:
 			// send publish request and handle response
+			//
+			// publish() blocks until a PublishResponse
+			// is received or the context is cancelled.
 			if err := c.publish(ctx); err != nil {
 				dlog.Print("error: ", err.Error())
 				c.pauseSubscriptions(ctx)