Not able to close/release RawDatagramSocket after receiving a SocketException in Windows Desktop

[peqi-frontrow]

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Scanning a local network using UDP packets and the RawDatagramSocket, the socket resources are never released when the socket is seeing a SocketException.

Reproduced using a slightly modified example from the official docs: https://api.dart.dev/stable/3.5.0/dart-io/RawDatagramSocket-class.html

import 'dart:io';
import 'dart:typed_data';

void main() async {
  // Read the current time from an NTP server.
  final serverAddress = InternetAddress("192.168.130.92");
  final clientSocket = await RawDatagramSocket.bind(
      serverAddress.type == InternetAddressType.IPv6
          ? InternetAddress.anyIPv6
          : InternetAddress.anyIPv4,
      0);
  final ntpQuery = Uint8List(48);
  ntpQuery[0] = 0x23; // See RFC 5905 7.3


  clientSocket.listen((event) {
    switch (event) {
      case RawSocketEvent.read:
        final datagram = clientSocket.receive();
        // Parse `datagram.data`
        clientSocket.close();
        break;
      case RawSocketEvent.write:
        if (clientSocket.send(ntpQuery, serverAddress, 123) > 0) {
          clientSocket.writeEventsEnabled = false;
        }
        break;
      case RawSocketEvent.closed:
        break;
      default:
        throw "Unexpected event $event";
    }
  }).onError((e) {
    print(e);
  });

  Future.delayed(Duration(seconds: 1)).then((_) {
    print('Closing socket');
    clientSocket.close();
  });

}

At the specific server address I have a pixl8 device, but it may be any device and when I send a UDP to that address I'm seeing a SocketException from the RawDatagramSocket listener. Using wireshark I see an ICMP response with port unreachable:

The effect in the example code is that we print the exception to the console. Then I try to close the socket on a timer, but the session never exits:

$ dart --version Dart SDK version: 3.5.0 (stable) (Tue Jul 30 02:17:59 2024 -0700) on "windows_x64"

[dart-github-bot]

Summary: The RawDatagramSocket on Windows Desktop fails to close and release resources after receiving a SocketException, specifically a "Port Unreachable" ICMP response. This occurs when sending UDP packets to an unreachable address, causing the socket to remain open indefinitely.

[mraleph]

cc @brianquinlan