SocketException: The semaphore timeout period has expired

[ali-1989]

I take this exception and my app killed.

• The Dart version : 3.9.2
• Windows 10

Unhandled exception:
SocketException: The semaphore timeout period has expired.
 (OS Error: The semaphore timeout period has expired.
, errno = 121), address = tbox.trip.dotone.ir, port = 57527

my ways:

try{
      _mqt ??= MqttService(option);

      final connected = await _mqt!.connect();

      if(connected){
        _subscribeTopic();
      }
    }
    catch (e){}

AND

try{
      _mqt ??= MqttService(option);

      final connected = await _mqt!.connect().catchError((e)=> false));

      if(connected){
        _subscribeTopic();
      }
    }
    catch (e){}

Main:

void main(List<String> arguments) async {
  await runZonedGuarded(() async {
    try{
      await mainApp();
    }
    catch (e, s){
      print('');
    }
  }, zonedGuardedCatch);
}

but I can not catch error.

[lrhn]

Could be bad error handling anywhere in the stack.

I'd check the mqtt_client project first to see if it's a known issue. (Doesn't seem so from a very quick search, but Github search isn't known to be awesome.)

It could also be in the socket handling, if it (for some reason) reports the error in the root zone.
That's possible if the error comes in on the event loop, and gets reported as unhandled immediately
without going into any user code first. (If possible, it would be better to report it in the zone that the
socket was created in, if there is no other relevant zone around.)

My guess would that the error comes from socket_patch.dart line 1742:

                reportError(osError, null, osError.message);

which is the place I could find where a SocketException is created with the message of an OSError.
The text "semaphore timeout" does not exist in the Dart SDK source, so it must be OS provided.

You can try wrapping the code in:

import 'dart:isolate';
import 'dart:async';

void main() async {
  var port = await _installErrorHandler(Isolate.current);
  port.handler = (dynamic message) {
    var error = RemoteError(message[0], message[1]); // List of two strings.
    print("$error\n${error.stackTrace}");
  };
  await mainApp();
  port.close();
}

Future<RawReceivePort> _installErrorHandler(Isolate isolate) async {
  var installed = Completer<void>();
  var port = RawReceivePort();
  port.handler = installed.complete;
  isolate.setErrorsFatal(false);
  isolate.addErrorListener(port.sendPort);
  isolate.ping(port.sendPort); // Responds when prior commands have completed.
  await installed.future;
  port.handler = null;
  return port;
}

This should capture all unhandled errors, even those sent directly to the root zone.
The stack trace may suggest where the problem is.