Connection/Channel.NotifyClose: allow only buffered channel=1

see knative-extensions/eventing-rabbitmq#1369

_examples/consumer/consumer.go

@@ -96,7 +96,7 @@ func NewConsumer(amqpURI, exchange, exchangeType, queueName, key, ctag string) (
 	}
 
 	go func() {
-		Log.Printf("closing: %s", <-c.conn.NotifyClose(make(chan *amqp.Error)))
+		Log.Printf("closing: %s", <-c.conn.NotifyClose(make(chan *amqp.Error, 1)))
 	}()
 
 	Log.Printf("got Connection, getting Channel")

channel.go

@@ -504,8 +504,14 @@ graceful close, no error will be sent.
 
 In case of a non graceful close the error will be notified synchronously by the library
 so that it will be necessary to consume the Channel from the caller in order to avoid deadlocks
+
+The chan provided must be a buffered channel of size 1.
 */
 func (ch *Channel) NotifyClose(c chan *Error) chan *Error {
+	if cap(c) != 1 {
+		panic("channel.NotifyClose expectes cap=1 buffered channel")
+	}
+
 	ch.notifyM.Lock()
 	defer ch.notifyM.Unlock()
 

client_test.go

@@ -632,7 +632,40 @@ func TestNotifyClosesReusedPublisherConfirmChan(t *testing.T) {
 	}
 }
 
-func TestNotifyClosesAllChansAfterConnectionClose(t *testing.T) {
+func TestConnectionNotifyCloseAcceptsOnlyBufferedChannels(t *testing.T) {
+	rwc, srv := newSession(t)
+	t.Cleanup(func() { rwc.Close() })
+
+	go func() {
+		srv.connectionOpen()
+
+		srv.recv(0, &connectionClose{})
+		srv.send(0, &connectionCloseOk{})
+	}()
+
+	c, err := Open(rwc, defaultConfig())
+	if err != nil {
+		t.Fatalf("could not create connection: %v (%s)", c, err)
+	}
+
+	if err := c.Close(); err != nil {
+		t.Fatalf("could not close connection: %v (%s)", c, err)
+	}
+
+	defer func() {
+		_ = recover()
+	}()
+
+	select {
+	case <-c.NotifyClose(make(chan *Error)):
+	case <-time.After(time.Millisecond):
+		t.Errorf("expected to close NotifyClose chan after Connection.Close")
+	}
+
+	t.Errorf("connection.NotifyClose shouldn't accept unbuffered channels")
+}
+
+func TestChannelNotifyClosesAllChansAfterConnectionClose(t *testing.T) {
 	rwc, srv := newSession(t)
 
 	go func() {
@@ -657,8 +690,10 @@ func TestNotifyClosesAllChansAfterConnectionClose(t *testing.T) {
 		t.Fatalf("could not close connection: %v (%s)", c, err)
 	}
 
+	defer func() { _ = recover() }()
+
 	select {
-	case <-c.NotifyClose(make(chan *Error)):
+	case <-c.NotifyClose(make(chan *Error, 1)):
 	case <-time.After(time.Millisecond):
 		t.Errorf("expected to close NotifyClose chan after Connection.Close")
 	}
@@ -669,6 +704,46 @@ func TestNotifyClosesAllChansAfterConnectionClose(t *testing.T) {
 		t.Errorf("expected to close Connection.NotifyClose chan after Connection.Close")
 	}
 
+	t.Errorf("connection.NotifyClose shouldn't accept unbuffered channels")
+}
+
+func TestNotifyClosesAllChansAfterConnectionClose(t *testing.T) {
+	rwc, srv := newSession(t)
+
+	go func() {
+		srv.connectionOpen()
+		srv.channelOpen(1)
+
+		srv.recv(0, &connectionClose{})
+		srv.send(0, &connectionCloseOk{})
+	}()
+
+	c, err := Open(rwc, defaultConfig())
+	if err != nil {
+		t.Fatalf("could not create connection: %v (%s)", c, err)
+	}
+
+	ch, err := c.Channel()
+	if err != nil {
+		t.Fatalf("could not open channel: %v (%s)", ch, err)
+	}
+
+	if err := c.Close(); err != nil {
+		t.Fatalf("could not close connection: %v (%s)", c, err)
+	}
+
+	select {
+	case <-c.NotifyClose(make(chan *Error, 1)):
+	case <-time.After(time.Millisecond):
+		t.Errorf("expected to close NotifyClose chan after Connection.Close")
+	}
+
+	select {
+	case <-ch.NotifyClose(make(chan *Error, 1)):
+	case <-time.After(time.Millisecond):
+		t.Errorf("expected to close Connection.NotifyClose chan after Connection.Close")
+	}
+
 	select {
 	case <-ch.NotifyFlow(make(chan bool)):
 	case <-time.After(time.Millisecond):

connection.go

@@ -368,8 +368,14 @@ so that it will be necessary to consume the Channel from the caller in order to
 
 To reconnect after a transport or protocol error, register a listener here and
 re-run your setup process.
+
+The chan provided must be a buffered channel of size 1.
 */
 func (c *Connection) NotifyClose(receiver chan *Error) chan *Error {
+	if cap(receiver) != 1 {
+		panic("channel.NotifyClose expectes cap=1 buffered channel")
+	}
+
 	c.m.Lock()
 	defer c.m.Unlock()
 

doc.go

@@ -110,40 +110,11 @@ In order to be notified when a connection or channel gets closed, both
 structures offer the possibility to register channels using
 [Channel.NotifyClose] and [Connection.NotifyClose] functions:
 
-	notifyConnCloseCh := conn.NotifyClose(make(chan *amqp.Error))
+	notifyConnCloseCh := conn.NotifyClose(make(chan *amqp.Error, 1))
 
 No errors will be sent in case of a graceful connection close. In case of a
 non-graceful closure due to e.g. network issue, or forced connection closure
-from the Management UI, the error will be notified synchronously by the library.
-
-The error is sent synchronously to the channel, so that the flow will wait until
-the receiver consumes from the channel. To avoid deadlocks in the library, it is
-necessary to consume from the channels. This could be done inside a
-different goroutine with a select listening on the two channels inside a for
-loop like:
-
-	go func() {
-	  for notifyConnClose != nil || notifyChanClose != nil {
-	    select {
-	      case err, ok := <-notifyConnClose:
-	        if !ok {
-	          notifyConnClose = nil
-	        } else {
-	          fmt.Printf("connection closed, error %s", err)
-	        }
-	      case err, ok := <-notifyChanClose:
-	        if !ok {
-	          notifyChanClose = nil
-	        } else {
-	          fmt.Printf("channel closed, error %s", err)
-	        }
-	      }
-	  }
-	}()
-
-Another approach is to use buffered channels:
-
-	notifyConnCloseCh := conn.NotifyClose(make(chan *amqp.Error, 1))
+from the Management UI, the error will be notified by the library.
 
 The library sends to notification channels just once. After sending a notification
 to all channels, the library closes all registered notification channels. After

integration_test.go

@@ -1644,7 +1644,7 @@ func TestChannelExceptionWithCloseIssue43(t *testing.T) {
 		t.Cleanup(func() { conn.Close() })
 
 		go func() {
-			for err := range conn.NotifyClose(make(chan *Error)) {
+			for err := range conn.NotifyClose(make(chan *Error, 1)) {
 				t.Log(err.Error())
 			}
 		}()
@@ -1655,7 +1655,7 @@ func TestChannelExceptionWithCloseIssue43(t *testing.T) {
 		}
 
 		go func() {
-			for err := range c1.NotifyClose(make(chan *Error)) {
+			for err := range c1.NotifyClose(make(chan *Error, 1)) {
 				t.Log("Channel1 Close: " + err.Error())
 			}
 		}()
@@ -1666,7 +1666,7 @@ func TestChannelExceptionWithCloseIssue43(t *testing.T) {
 		}
 
 		go func() {
-			for err := range c2.NotifyClose(make(chan *Error)) {
+			for err := range c2.NotifyClose(make(chan *Error, 1)) {
 				t.Log("Channel2 Close: " + err.Error())
 			}
 		}()