Udp socket in Flutter does not receive anything

Question

I'm trying to use a udp socket as server in Flutter. I'd like to bind this socket on my localhost at 6868 port always in listening. Unfortunately when i try to send something from a client,it never prints the string "RECEIVED". Here's the code:

static Future openPortUdp(Share share) async {
        await RawDatagramSocket.bind(InternetAddress.anyIPv4,6868)
        .then(
          (RawDatagramSocket udpSocket) {
            udpSocket.listen((e) {
              switch (e) {
                case RawSocketEvent.read:
                  print("RECEIVED");
                  print(String.fromCharCodes(udpSocket.receive().data));
                  break;
                case RawSocketEvent.readClosed:
                    print("READCLOSED");
                    break;
                case RawSocketEvent.closed:
                  print("CLOSED");
                  break;
              }
            });
          },
        );
      }

Am I doing something wrong?

Anyway this is the client side, it is written is Lua:

local udp1 = socket.udp()
while true do
    udp1:setpeername("192.168.1.24", 6868)
    udp1:send("HI")
    local data1 = udp1:receive()
    if (not data1 == nil) then print(data1) break end
    udp1:close()
end

I tested it with another server and it works well, so i don't think the client is the problem.

Thanks!

Answer 1

If it can help you, here my code for my SocketUDP (as singleton) in my app. I used it in localhost and it works very well :

class SocketUDP {
  RawDatagramSocket _socket;

  // the port used by this socket
  int _port;

  // emit event when receive a new request. Emit the request
  StreamController<Request> _onRequestReceivedCtrl = StreamController<Request>.broadcast();

  // to give access of the Stream to listen when new request is received
  Stream<Request> get onRequestReceived => _onRequestReceivedCtrl.stream;

  // as singleton to maintain the connexion during the app life and be accessible everywhere
  static final SocketUDP _instance = SocketUDP._internal();

  factory SocketUDP() {
    return _instance;
  }

  SocketUDP._internal();

  void startSocket(int port) {

    _port = port;

    RawDatagramSocket.bind(InternetAddress.anyIPv4, _port)
        .then((RawDatagramSocket socket) {
      _socket = socket;
      // listen the request from server
      _socket.listen((e) {
        Datagram dg = _socket.receive();
        if (dg != null) {
          _onRequestReceivedCtrl.add(RequestConvert.decodeRequest(dg.data, dg.address));
        }
      });
    });
  }

  void send(Request requestToSend, {bool isBroadCast:false}) {

    _socket.broadcastEnabled = isBroadCast;

    final String requestEncoded = RequestConvert.encodeRequest(requestToSend);
     List<int> requestAsUTF8 = utf8.encode(requestEncoded);
    _socket.send(requestAsUTF8, requestToSend.address, _port);
  }
}

Edit : As asked below, here some details to use it.

At first, the Request definition :

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

import 'package:remotepcmultitouch/enumRequest.dart';

// describe a network request
class Request
{
  // the request ID
  final ERequest _id;
  // the request data list
  final List<String> _datas;
  // the request address (from/to)
  final InternetAddress _address;
  // binary data, optional
  final Uint8List binaryData;

  Request(this._id, this._datas, this._address, {this.binaryData});

  ERequest get id => _id;
  List<String> get datas => _datas;
  InternetAddress get address => _address;
}

To process a request received from the socket :

SocketUDP().onRequestReceived.listen(onRequestReceived);

void onRequestReceived(Request request) {
    switch (request.id) {
    // process the request
    }
}

To send a request with the SocketUDP : my example send touch position to server

// send request to server to send the new touch data
SocketUDP().send(Request(
    ERequest.SEND_TOUCH_DATA,
    [touchState.index.toString(), fingerID.toString(), percentX, percentY],
    this.address));

Then RequestConvert.encodeRequest and RequestConvert.decodeRequest are just utility functions to convert/decode the Request object to/from string, nothing special (many ways to doing this)