Flutter websocket connects to wrong port - flutter

Question

In my app, I created a Route for communicating with a socket.
class _SocketRouteState extends State<SocketRoute> {
#override
void initState() {
super.initState();
try {
WebSocketChannel _channel = IOWebSocketChannel.connect(
Uri.parse('ws://192.168.1.90:9998'),
);
///
/// Start listening to new notifications / messages
///
_channel.stream.listen(
(data) {
debugPrint(data);
},
onDone: () {
debugPrint('ws channel closed');
},
onError: (error) {
debugPrint('ws error $error');
},
);
_channel.sink.add('testing');
} catch (e) {
///
/// General error handling
/// TODO handle connection failure
///
debugPrint('Connection exception $e');
}
}
}
When I run this code, it fails to connect to the socket, though. After waiting for ~2 minutes, Xcode shows me the following error:
flutter: ws error WebSocketChannelException: WebSocketChannelException: SocketException: OS Error: Operation timed out, errno = 60, address = 192.168.1.90, port = 52168
This clearly shows a different port. Could that be the issue? Anyone know why it's connecting on port 52168 instead of 9998?

Answer 1

The problem with the confusing port number is, that the error message is not that great, since it shows the local port being used on your own machine and not the remote port you are trying to connect to. TCP requires a port to be open on both the server and the client so they can communicate both ways. But normally, you are mostly interested in the remote port.
There are an old github issue here about this issue:
https://github.com/dart-lang/sdk/issues/12693