Fix nil pointer dereference during close

client.go

@@ -43,6 +43,7 @@ type Client struct {
 	token             string
 	data              protocol.Raw
 	transport         transport
+	disconnectedCh    chan struct{}
 	state             State
 	subs              map[string]*Subscription
 	serverSubs        map[string]*serverSub
@@ -138,7 +139,9 @@ func newClient(endpoint string, isProtobuf bool, config Config) *Client {
 	}
 
 	// Queue to run callbacks on.
-	client.cbQueue = &cbQueue{}
+	client.cbQueue = &cbQueue{
+		closeCh: make(chan struct{}),
+	}
 	client.cbQueue.cond = sync.NewCond(&client.cbQueue.mu)
 	go client.cbQueue.dispatch()
 
@@ -534,10 +537,20 @@ func (c *Client) moveToClosed() {
 		})
 	}
 
+	c.mu.RLock()
+	disconnectedCh := c.disconnectedCh
+	c.mu.RUnlock()
+	// At this point connection close was issued, so we wait until the reader goroutine
+	// finishes its work, after that it's safe to close the callback queue.
+	if disconnectedCh != nil {
+		<-disconnectedCh
+	}
+
 	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.disconnectedCh = nil
 	c.cbQueue.close()
 	c.cbQueue = nil
-	c.mu.Unlock()
 }
 
 func (c *Client) handleError(err error) {
@@ -959,6 +972,7 @@ func (c *Client) startReconnecting() error {
 	disconnectCh := make(chan struct{})
 	c.receive = make(chan []byte, 64)
 	c.transport = t
+	c.disconnectedCh = disconnectCh
 
 	go c.reader(t, disconnectCh)
 

queue.go

@@ -11,10 +11,12 @@ import (
 // https://github.com/nats-io/nats.go client released under Apache 2.0
 // license: see https://github.com/nats-io/nats.go/blob/master/LICENSE.
 type cbQueue struct {
-	mu   sync.Mutex
-	cond *sync.Cond
-	head *asyncCB
-	tail *asyncCB
+	mu      sync.Mutex
+	cond    *sync.Cond
+	head    *asyncCB
+	tail    *asyncCB
+	closeCh chan struct{}
+	closed  bool
 }
 
 type asyncCB struct {
@@ -43,6 +45,7 @@ func (q *cbQueue) dispatch() {
 		// This signals that the dispatcher has been closed and all
 		// previous callbacks have been dispatched.
 		if curr.fn == nil {
+			close(q.closeCh)
 			return
 		}
 		curr.fn(time.Since(curr.tm))
@@ -56,13 +59,22 @@ func (q *cbQueue) push(f func(duration time.Duration)) {
 }
 
 // Close signals that async queue must be closed.
+// Queue won't accept any more callbacks after that – ignoring them if pushed.
 func (q *cbQueue) close() {
 	q.pushOrClose(nil, true)
+	q.waitClose()
+}
+
+func (q *cbQueue) waitClose() {
+	<-q.closeCh
 }
 
 func (q *cbQueue) pushOrClose(f func(time.Duration), close bool) {
 	q.mu.Lock()
 	defer q.mu.Unlock()
+	if q.closed {
+		return
+	}
 	// Make sure that library is not calling push with nil function,
 	// since this is used to notify the dispatcher that it must stop.
 	if !close && f == nil {
@@ -76,6 +88,7 @@ func (q *cbQueue) pushOrClose(f func(time.Duration), close bool) {
 	}
 	q.tail = cb
 	if close {
+		q.closed = true
 		q.cond.Broadcast()
 	} else {
 		q.cond.Signal()

queue_test.go

@@ -0,0 +1,131 @@
+package centrifuge
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func assertTrue(t *testing.T, condition bool, msg string) {
+	if !condition {
+		t.Fatalf("Assertion failed: %s", msg)
+	}
+}
+
+func assertEqual(t *testing.T, expected, actual interface{}, msg string) {
+	if expected != actual {
+		t.Fatalf("Assertion failed: %s - expected: %v, got: %v", msg, expected, actual)
+	}
+}
+
+func newTestQueue() *cbQueue {
+	q := &cbQueue{
+		closeCh: make(chan struct{}),
+	}
+	q.cond = sync.NewCond(&q.mu)
+	return q
+}
+
+func TestCbQueue_PushAndDispatch(t *testing.T) {
+	q := newTestQueue()
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	// Start the dispatcher in a separate goroutine.
+	go q.dispatch()
+
+	startTime := time.Now()
+	q.push(func(d time.Duration) {
+		defer wg.Done()
+		assertTrue(t, d >= 0, "Callback duration should be positive")
+	})
+
+	// Wait for the callback to finish.
+	wg.Wait()
+
+	// Ensure the callback executed quickly.
+	elapsed := time.Since(startTime)
+	assertTrue(t, elapsed < 100*time.Millisecond, "Callback should be dispatched immediately")
+}
+
+func TestCbQueue_OrderPreservation(t *testing.T) {
+	q := newTestQueue()
+
+	// Start the dispatcher in a separate goroutine.
+	go q.dispatch()
+
+	var results []int
+	var mu sync.Mutex
+	expectedResults := []int{1, 2, 3}
+
+	for _, i := range expectedResults {
+		i := i
+		q.push(func(d time.Duration) {
+			mu.Lock()
+			defer mu.Unlock()
+			results = append(results, i)
+		})
+	}
+
+	// Allow time for the queue to process.
+	time.Sleep(100 * time.Millisecond)
+
+	mu.Lock()
+	defer mu.Unlock()
+
+	for i, r := range results {
+		assertEqual(t, expectedResults[i], r, "unexpected result")
+	}
+}
+
+func TestCbQueue_Close(t *testing.T) {
+	q := newTestQueue()
+
+	go q.dispatch()
+
+	var executed bool
+	q.push(func(d time.Duration) {
+		executed = true
+	})
+
+	q.close()
+
+	// Ensure the closeCh channel is closed.
+	select {
+	case <-q.closeCh:
+		// Channel was closed as expected.
+	case <-time.After(1 * time.Second):
+		t.Fatal("closeCh was not closed after queue close")
+	}
+
+	assertTrue(t, executed, "Callback should be executed before close")
+}
+
+func TestCbQueue_IgnorePushAfterClose(t *testing.T) {
+	q := newTestQueue()
+	go q.dispatch()
+	q.close()
+
+	var executed bool
+	q.push(func(d time.Duration) {
+		executed = true
+	})
+
+	// Allow some time to see if the callback is executed.
+	time.Sleep(100 * time.Millisecond)
+
+	assertTrue(t, !executed, "Callback should not be executed after queue close")
+}
+
+func TestCbQueue_PushNilCallbackPanics(t *testing.T) {
+	q := newTestQueue()
+
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatal("Expected panic when pushing nil callback with close set to false")
+		}
+	}()
+
+	q.pushOrClose(nil, false)
+}