Gracefully close connecting channels

Fixes an issue where calling dataChannel.Close on
'connecting' state channels didn't work as expected.
When handling the `OnOpen` event detect if the
user has requested close.

Fixes #2659

datachannel.go

@@ -320,8 +320,13 @@ func (d *DataChannel) onMessage(msg DataChannelMessage) {
 
 func (d *DataChannel) handleOpen(dc *datachannel.DataChannel, isRemote, isAlreadyNegotiated bool) {
 	d.mu.Lock()
-	if d.isGracefulClosed {
+	if d.isGracefulClosed { // The channel was closed during the connecting state
 		d.mu.Unlock()
+		if err := dc.Close(); err != nil {
+			d.log.Errorf("Failed to close DataChannel that was closed during connecting state %v", err.Error())
+		}
+		d.onClose()
+
 		return
 	}
 	d.dataChannel = dc

datachannel_go_test.go

@@ -745,3 +745,80 @@ func TestDetachRemovesDatachannelReference(t *testing.T) {
 		}
 	}
 }
+
+func TestDataChannelClose(t *testing.T) {
+	// Test if onClose is fired for self and remote after Close is called
+	t.Run("close open channels", func(t *testing.T) {
+		options := &DataChannelInit{}
+
+		offerPC, answerPC, dc, done := setUpDataChannelParametersTest(t, options)
+
+		answerPC.OnDataChannel(func(dataChannel *DataChannel) {
+			// Make sure this is the data channel we were looking for. (Not the one
+			// created in signalPair).
+			if dataChannel.Label() != expectedLabel {
+				return
+			}
+
+			dataChannel.OnOpen(func() {
+				assert.NoError(t, dataChannel.Close())
+			})
+
+			dataChannel.OnClose(func() {
+				done <- true
+			})
+		})
+
+		dc.OnClose(func() {
+			done <- true
+		})
+
+		assert.NoError(t, signalPair(offerPC, answerPC))
+
+		// Offer and Answer OnClose
+		<-done
+		<-done
+
+		assert.NoError(t, offerPC.Close())
+		assert.NoError(t, answerPC.Close())
+	})
+
+	// Test if OnClose is fired for self and remote after Close is called on non-established channel
+	// https://github.com/pion/webrtc/issues/2659
+	t.Run("Close connecting channels", func(t *testing.T) {
+		options := &DataChannelInit{}
+
+		offerPC, answerPC, dc, done := setUpDataChannelParametersTest(t, options)
+
+		answerPC.OnDataChannel(func(dataChannel *DataChannel) {
+			// Make sure this is the data channel we were looking for. (Not the one
+			// created in signalPair).
+			if dataChannel.Label() != expectedLabel {
+				return
+			}
+
+			dataChannel.OnOpen(func() {
+				t.Fatal("OnOpen must not be fired after we call Close")
+			})
+
+			dataChannel.OnClose(func() {
+				done <- true
+			})
+
+			assert.NoError(t, dataChannel.Close())
+		})
+
+		dc.OnClose(func() {
+			done <- true
+		})
+
+		assert.NoError(t, signalPair(offerPC, answerPC))
+
+		// Offer and Answer OnClose
+		<-done
+		<-done
+
+		assert.NoError(t, offerPC.Close())
+		assert.NoError(t, answerPC.Close())
+	})
+}