Fix race condition on confirms

channel.go

@@ -1435,6 +1435,11 @@ func (ch *Channel) PublishWithDeferredConfirmWithContext(ctx context.Context, ex
 	ch.m.Lock()
 	defer ch.m.Unlock()
 
+	var dc *DeferredConfirmation
+	if ch.confirming {
+		dc = ch.confirms.publish()
+	}
+
 	if err := ch.send(&basicPublish{
 		Exchange:   exchange,
 		RoutingKey: key,
@@ -1457,14 +1462,13 @@ func (ch *Channel) PublishWithDeferredConfirmWithContext(ctx context.Context, ex
 			AppId:           msg.AppId,
 		},
 	}); err != nil {
+		if ch.confirming {
+			ch.confirms.unpublish()
+		}
 		return nil, err
 	}
 
-	if ch.confirming {
-		return ch.confirms.Publish(), nil
-	}
-
-	return nil, nil
+	return dc, nil
 }
 
 /*

confirms.go

@@ -39,14 +39,23 @@ func (c *confirms) Listen(l chan Confirmation) {
 }
 
 // Publish increments the publishing counter
-func (c *confirms) Publish() *DeferredConfirmation {
+func (c *confirms) publish() *DeferredConfirmation {
 	c.publishedMut.Lock()
 	defer c.publishedMut.Unlock()
 
 	c.published++
 	return c.deferredConfirmations.Add(c.published)
 }
 
+// unpublish decrements the publishing counter and removes the
+// DeferredConfirmation. It must be called immediately after a publish fails.
+func (c *confirms) unpublish() {
+	c.publishedMut.Lock()
+	defer c.publishedMut.Unlock()
+	c.deferredConfirmations.remove(c.published)
+	c.published--
+}
+
 // confirm confirms one publishing, increments the expecting delivery tag, and
 // removes bookkeeping for that delivery tag.
 func (c *confirms) confirm(confirmation Confirmation) {
@@ -135,6 +144,18 @@ func (d *deferredConfirmations) Add(tag uint64) *DeferredConfirmation {
 	return dc
 }
 
+// remove is only used to drop a tag whose publish failed
+func (d *deferredConfirmations) remove(tag uint64) {
+	d.m.Lock()
+	defer d.m.Unlock()
+	dc, found := d.confirmations[tag]
+	if !found {
+		return
+	}
+	close(dc.done)
+	delete(d.confirmations, tag)
+}
+
 func (d *deferredConfirmations) Confirm(confirmation Confirmation) {
 	d.m.Lock()
 	defer d.m.Unlock()

confirms_test.go

@@ -26,7 +26,7 @@ func TestConfirmOneResequences(t *testing.T) {
 	c.Listen(l)
 
 	for i := range fixtures {
-		if want, got := uint64(i+1), c.Publish(); want != got.DeliveryTag {
+		if want, got := uint64(i+1), c.publish(); want != got.DeliveryTag {
 			t.Fatalf("expected publish to return the 1 based delivery tag published, want: %d, got: %d", want, got.DeliveryTag)
 		}
 	}
@@ -64,7 +64,7 @@ func TestConfirmAndPublishDoNotDeadlock(t *testing.T) {
 	}()
 
 	for i := 0; i < iterations; i++ {
-		c.Publish()
+		c.publish()
 		<-l
 	}
 }
@@ -82,7 +82,7 @@ func TestConfirmMixedResequences(t *testing.T) {
 	c.Listen(l)
 
 	for range fixtures {
-		c.Publish()
+		c.publish()
 	}
 
 	c.One(fixtures[0])
@@ -117,7 +117,7 @@ func TestConfirmMultipleResequences(t *testing.T) {
 	c.Listen(l)
 
 	for range fixtures {
-		c.Publish()
+		c.publish()
 	}
 
 	c.Multiple(fixtures[len(fixtures)-1])
@@ -141,7 +141,7 @@ func BenchmarkSequentialBufferedConfirms(t *testing.B) {
 		if i > cap(l)-1 {
 			<-l
 		}
-		c.One(Confirmation{c.Publish().DeliveryTag, true})
+		c.One(Confirmation{c.publish().DeliveryTag, true})
 	}
 }
 
@@ -159,7 +159,7 @@ func TestConfirmsIsThreadSafe(t *testing.T) {
 	c.Listen(l)
 
 	for i := 0; i < count; i++ {
-		go func() { pub <- Confirmation{c.Publish().DeliveryTag, true} }()
+		go func() { pub <- Confirmation{c.publish().DeliveryTag, true} }()
 	}
 
 	for i := 0; i < count; i++ {