the_paint/lib/src/connection/ws.dart

import 'dart:async';
import 'dart:convert';

import 'package:the_paint/src/generated/client.pbgrpc.dart';
import 'package:flutter_webrtc/flutter_webrtc.dart';
import 'package:web_socket_channel/web_socket_channel.dart';


class WebRTCChannels {
  bool _inCalling = false;
  RTCPeerConnection? _pc;
  RTCDataChannel? _dc;
  PaintClient? _grpcClient;

  WebRTCChannels();

  final Map<String, dynamic> _iceServers = {
    'iceServers': [
      {
        'url': 'stun:melvans.com:3478',
        'username': 'b84e4232f84505e3c3967184df374f2cdaa954f1',
        'credential': 'afc39ae0591c132292f73a87f6f3725311fbafa0'
        // 'url': 'stun:stun.l.google.com:19302'
      },
    ]
  };

  final Map<String, dynamic> _config = {
    'mandatory': {},
    'optional': [
      {'DtlsSrtpKeyAgreement': true},
    ],
  };

  final Map<String, dynamic> _constraints = {
    'mandatory': {},
    'optional': [],
  };

  final _channel = WebSocketChannel.connect(
    Uri.parse('ws://localhost:8081/ws'),
  );

  Future<void> connect(Function callback) async {
    print("Connecting WEBSOCKET...");

    _pc = await createPeerConnection(
      _iceServers,
    );

    _pc!.onIceCandidate = (candidate) async {
      print('pc2: onIceCandidate: ${candidate.candidate}');
      await sendCandidate(candidate);
    };

    _pc!.onDataChannel = (channel) {
      RTCDataChannel dc = channel;
      print('\nnew channel');
      dc.onDataChannelState = (state) {
        print('\ndc2: change state: ${state.toString()}');
      };
      dc.onMessage = (data) {
        callback(MonitorReply.fromBuffer(data.binary));
        // dc.send(
        // RTCDataChannelMessage('(dc2 ==> dc1) Hello from dc2 echo !!!'));
      };
    };

    final rtcData = _channel.stream.map((event) => RTCData.fromBuffer(event));
    await for (var msg in rtcData) {
      print(msg.event);
      switch (msg.event) {
        case "offer":
          await _pc!
              .setRemoteDescription(RTCSessionDescription(msg.data, msg.event));
          var answer = await _pc!.createAnswer();
          await _pc!.setLocalDescription(answer);
          await sendLocalDescription();
          break;
        default:
          print("invalid event");
      }
    }
  }

  sendLocalDescription() async {
    RTCSessionDescription? answer = await _pc!.getLocalDescription();
    if (answer == null) {
      return;
    }
    final encodedData =
        RTCData(data: answer.sdp, event: answer.type).writeToBuffer();
    _channel.sink.add(encodedData);
  }

  sendCandidate(RTCIceCandidate candidate) async {
    final encodedData =
        RTCData(data: jsonEncode(candidate.toMap()), event: "candidate")
            .writeToBuffer();
    _channel.sink.add(encodedData);
  }
}