[ADDED] Force reconnect (#1624)

Signed-off-by: Piotr Piotrowski <piotr@synadia.com>

example_test.go

@@ -89,6 +89,19 @@ func ExampleConn_Subscribe() {
 	})
 }
 
+func ExampleConn_ForceReconnect() {
+	nc, _ := nats.Connect(nats.DefaultURL)
+	defer nc.Close()
+
+	nc.Subscribe("foo", func(m *nats.Msg) {
+		fmt.Printf("Received a message: %s\n", string(m.Data))
+	})
+
+	// Reconnect to the server.
+	// the subscription will be recreated after the reconnect.
+	nc.ForceReconnect()
+}
+
 // This Example shows a synchronous subscriber.
 func ExampleConn_SubscribeSync() {
 	nc, _ := nats.Connect(nats.DefaultURL)

nats.go

@@ -2161,6 +2161,47 @@ func (nc *Conn) waitForExits() {
 	nc.wg.Wait()
 }
 
+// ForceReconnect forces a reconnect attempt to the server.
+// This is a non-blocking call and will start the reconnect
+// process without waiting for it to complete.
+//
+// If the connection is already in the process of reconnecting,
+// this call will force an immediate reconnect attempt (bypassing
+// the current reconnect delay).
+func (nc *Conn) ForceReconnect() error {
+	nc.mu.Lock()
+	defer nc.mu.Unlock()
+
+	if nc.isClosed() {
+		return ErrConnectionClosed
+	}
+	if nc.isReconnecting() {
+		// if we're already reconnecting, force a reconnect attempt
+		// even if we're in the middle of a backoff
+		if nc.rqch != nil {
+			close(nc.rqch)
+		}
+		return nil
+	}
+
+	// Clear any queued pongs
+	nc.clearPendingFlushCalls()
+
+	// Clear any queued and blocking requests.
+	nc.clearPendingRequestCalls()
+
+	// Stop ping timer if set.
+	nc.stopPingTimer()
+
+	// Go ahead and make sure we have flushed the outbound
+	nc.bw.flush()
+	nc.conn.Close()
+
+	nc.changeConnStatus(RECONNECTING)
+	go nc.doReconnect(nil, true)
+	return nil
+}
+
 // ConnectedUrl reports the connected server's URL
 func (nc *Conn) ConnectedUrl() string {
 	if nc == nil {
@@ -2420,7 +2461,7 @@ func (nc *Conn) connect() (bool, error) {
 		nc.setup()
 		nc.changeConnStatus(RECONNECTING)
 		nc.bw.switchToPending()
-		go nc.doReconnect(ErrNoServers)
+		go nc.doReconnect(ErrNoServers, false)
 		err = nil
 	} else {
 		nc.current = nil
@@ -2720,7 +2761,7 @@ func (nc *Conn) stopPingTimer() {
 
 // Try to reconnect using the option parameters.
 // This function assumes we are allowed to reconnect.
-func (nc *Conn) doReconnect(err error) {
+func (nc *Conn) doReconnect(err error, forceReconnect bool) {
 	// We want to make sure we have the other watchers shutdown properly
 	// here before we proceed past this point.
 	nc.waitForExits()
@@ -2776,7 +2817,8 @@ func (nc *Conn) doReconnect(err error) {
 			break
 		}
 
-		doSleep := i+1 >= len(nc.srvPool)
+		doSleep := i+1 >= len(nc.srvPool) && !forceReconnect
+		forceReconnect = false
 		nc.mu.Unlock()
 
 		if !doSleep {
@@ -2803,6 +2845,12 @@ func (nc *Conn) doReconnect(err error) {
 			select {
 			case <-rqch:
 				rt.Stop()
+
+				// we need to reset the rqch channel to avoid
+				// closing a closed channel in the next iteration
+				nc.mu.Lock()
+				nc.rqch = make(chan struct{})
+				nc.mu.Unlock()
 			case <-rt.C:
 			}
 		}
@@ -2872,9 +2920,6 @@ func (nc *Conn) doReconnect(err error) {
 		// Done with the pending buffer
 		nc.bw.doneWithPending()
 
-		// This is where we are truly connected.
-		nc.status = CONNECTED
-
 		// Queue up the correct callback. If we are in initial connect state
 		// (using retry on failed connect), we will call the ConnectedCB,
 		// otherwise the ReconnectedCB.
@@ -2930,7 +2975,7 @@ func (nc *Conn) processOpErr(err error) {
 		// Clear any queued pongs, e.g. pending flush calls.
 		nc.clearPendingFlushCalls()
 
-		go nc.doReconnect(err)
+		go nc.doReconnect(err, false)
 		nc.mu.Unlock()
 		return
 	}

test/conn_test.go

@@ -2946,16 +2946,6 @@ func TestRetryOnFailedConnectWithTLSError(t *testing.T) {
 }
 
 func TestConnStatusChangedEvents(t *testing.T) {
-	waitForStatus := func(t *testing.T, ch chan nats.Status, expected nats.Status) {
-		select {
-		case s := <-ch:
-			if s != expected {
-				t.Fatalf("Expected status: %s; got: %s", expected, s)
-			}
-		case <-time.After(5 * time.Second):
-			t.Fatalf("Timeout waiting for status %q", expected)
-		}
-	}
 	t.Run("default events", func(t *testing.T) {
 		s := RunDefaultServer()
 		nc, err := nats.Connect(s.ClientURL())
@@ -2978,15 +2968,15 @@ func TestConnStatusChangedEvents(t *testing.T) {
 		time.Sleep(50 * time.Millisecond)
 
 		s.Shutdown()
-		waitForStatus(t, newStatus, nats.RECONNECTING)
+		WaitOnChannel(t, newStatus, nats.RECONNECTING)
 
 		s = RunDefaultServer()
 		defer s.Shutdown()
 
-		waitForStatus(t, newStatus, nats.CONNECTED)
+		WaitOnChannel(t, newStatus, nats.CONNECTED)
 
 		nc.Close()
-		waitForStatus(t, newStatus, nats.CLOSED)
+		WaitOnChannel(t, newStatus, nats.CLOSED)
 
 		select {
 		case s := <-newStatus:
@@ -3019,7 +3009,7 @@ func TestConnStatusChangedEvents(t *testing.T) {
 		s = RunDefaultServer()
 		defer s.Shutdown()
 		nc.Close()
-		waitForStatus(t, newStatus, nats.CLOSED)
+		WaitOnChannel(t, newStatus, nats.CLOSED)
 
 		select {
 		case s := <-newStatus:

test/helper_test.go

@@ -54,6 +54,18 @@ func WaitTime(ch chan bool, timeout time.Duration) error {
 	return errors.New("timeout")
 }
 
+func WaitOnChannel[T comparable](t *testing.T, ch <-chan T, expected T) {
+	t.Helper()
+	select {
+	case s := <-ch:
+		if s != expected {
+			t.Fatalf("Expected result: %v; got: %v", expected, s)
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatalf("Timeout waiting for result %v", expected)
+	}
+}
+
 func stackFatalf(t tLogger, f string, args ...any) {
 	lines := make([]string, 0, 32)
 	msg := fmt.Sprintf(f, args...)