Socket library for creating real-time multiplayer games

Game socket

The library was published in early access and is not stable, as it is being developed in parallel with other solutions. English is not a native language so there are no comments. At this stage, the library is for those who want to understand the source code and get a starting point for their solution or help me 🙂

Features

• One library contains both Server and Client parts.
• The API communication library is similar to Socket.io, but not compatible with this solution.
• Contains a built-in binary protocol so you don’t have to work at the byte level.
• The transport layer uses TCP. To send game messages, it is planned to implement parallel work with UDP.
• It implements such concepts as Multiplexing – interaction with several spaces through a single channel.

Support for WebSocket is not planned for the current day (but everything can change with the support of the community)

Example

Examples:

• example/client/main.dart
• example/server/main.dart

Usage

Create client:

import 'package:game_socket/client.dart';

void main() {
  var client = GameClientExample();
  client.connect('localhost', 3103);
}

class GameClientExample extends GameSocketClient {
  GameClientExample() {
    on(Event.handshake, (packet) => _onHandshake(packet));
    on(Event.roomPacket, (packet) => _onRoomPacket(packet));
  }

  void _onHandshake(Packet packet) {
    if (packet.namespace == '/') {
      sendMessage(ConnectRequest('/home'));
    } else if (packet.namespace == '/home') {
      sendMessage(JoinRoomRequest('lobby', namespace: '/home'));
    }
  }

  void _onRoomPacket(RoomPacket packet) {
    var roomName = packet.roomName;
    if (packet.joinRoom && roomName == 'lobby') {
      var msg = RoomEvent(roomName!, namespace: '/home', event: 'hello', message: 'hello all');
      sendMessage(msg);
    }
  }
}

This client connects to the main / namespace on the server, then to the /home namespace. Then it sends a request to enter the lobby room, after which it dispatches a hello event containing the message text hello all.

Create server:

import 'package:game_socket/server.dart';

void main() {
  var service = SocketServiceExample();
  service.listen();
}

class SocketServiceExample {
  late GameSocketServer server;
  late Namespace home;

  SocketServiceExample() {
    server = GameSocketServer(options: ServerOptions.byDefault()..supportRawData = true);
    home = server.of('/home');
    home.on(ServerEvent.connect, (data) => _onHomeConnect(data));
    home.on('hello', (packet) => _onHomeData(packet));
    //
    server.on(ServerEvent.connection, (socket) {
      print('/: connection $socket');
      socket.on(ServerEvent.connect, (data) => _onConnect(data[0], data[1]));
      socket.on(Event.disconnecting, (data) => _onDisconnecting(data));
      socket.on(Event.disconnect, (data) => _onDisconnect(data[0], data[1]));
      socket.on(Event.error, (data) => _onError(data));
      socket.on(Event.data, (data) => _onData(data));
      socket.on(Event.close, (data) => {_onClose(data)});
    });
    server.on(ServerEvent.error, (data) => {print('/: eventError $data')});
    server.on(ServerEvent.close, (data) => {print('/: serverClose $data')});
    server.on(ServerEvent.raw, (data) => {print('/: raw $data')});
    server.on(ServerEvent.createRoom, (data) => {print('/: createRoom $data')});
    server.on(ServerEvent.joinRoom, (data) => {print('/: joinRoom $data')});
    server.on(ServerEvent.leaveRoom, (data) => {print('/: leaveRoom $data')});
    server.on(ServerEvent.deleteRoom, (data) => {print('/: deleteRoom $data')});
  }

  void listen() {
    server.listen();
  }

  void _onHomeConnect(dynamic data) {
    print('/home: connect $data');
  }

  void _onHomeData(dynamic data) {
    print('/home: $data');
    if (data is RoomPacket && data.roomName != null) {
      home.broadcast(data, rooms: {data.roomName!});
    }
  }

  void _onConnect(String namespace, String socketId) {
    print('/: connect $socketId');
  }

  void _onDisconnecting(dynamic data) {
    print('/: disconnecting $data');
  }

  void _onDisconnect(String namespace, String reason) {
    print('$namespace: disconnect reason:$reason');
  }

  void _onError(dynamic data) {
    print('/: error $data');
  }

  void _onData(dynamic data) {
    print('/: $data');
  }

  void _onClose(dynamic data) {
    print('/: close $data');
  }
}

Server log

listen null Options{ port:3103 raw:true closeOnError:false }
/: connection GameClient{ 15466abe2006464e99b6c8b36f7f4ed8 ReadyState.open [137545126]}
/: createRoom 15466abe2006464e99b6c8b36f7f4ed8
/: joinRoom [15466abe2006464e99b6c8b36f7f4ed8, 15466abe2006464e99b6c8b36f7f4ed8]
Home: connect [/home, 15466abe2006464e99b6c8b36f7f4ed8]

Client log

open InternetAddress('127.0.0.1', IPv4) ReadyState.open
handshake Packet{[0.0 /], bit:516, bool:16, int:[0, 0, 60, 0, 0, 0], string:{3: 15466abe2006464e99b6c8b36f7f4ed8}}
>> Message{[/home] boolMask:4, int:[0, 0, 0, 0, 0, 0], string:{} null}
handshake Packet{[0.0 /home], bit:516, bool:16, int:[0, 0, 60, 0, 0, 0], string:{3: 15466abe2006464e99b6c8b36f7f4ed8}}
>> Message{[/home] boolMask:16, int:[0, 0, 0], string:{0: lobby} null}
>> Message{[/home] boolMask:512, int:[0, 0, 0], string:{0: lobby, 5: hello, 1: hello all} null}

Protocol

The protocol is schematic based. This approach allows you to save the amount of data transferred, since the data type is not transferred with the message, and the length of the numbers is not serialized.

Data types used in the schema

Schema creation

import 'package:game_socket/protocol.dart';
typedef PS = PlayerStateSchema;
class PlayerStateSchema extends SimpleSchema {
  @override
  int get code => 10; // unique schema code 10..255 
  @override
  int get version => 1; // version 0..255 to support game clients with different versions
  
  // bool
  static const int reserved = 0; // reserved
  @override
  int get boolCount => 1;

  // int8
  static const int speed = 0; // 0.000..1.000
  static const int health = 1; // max(100)
  @override
  int get int8Count => 2;
  // int16
  static const int uid = 2; // max(65535)
  static const int angle = 3; // radians
  static const int score = 4; // max(65535)
  @override
  int get int16Count => 3;
  // int32
  static const int elapsedTime = 5; // time for internal synchronization
  static const int x = 6; // x-coordinate
  static const int y = 7; // y-coordinate
  @override
  int get int32Count => 3;

  // strings
  static const int name = 0; // player name
  @override
  int get stringsCount => 1;
}

When you create a schema, you do two things: you take the named cell number of the array and determine the length of the array to one of the five schema data types.

Creating a message class

class PlayerStateMessage extends Message {
  PlayerStateMessage(Player player, {required double elapsedTime}) : super(PS()) {
    putUInt(PS.uid, player.uid);
    putInt(PS.x, (player.positionBody.x * 1000).toInt()); // ~ -2000000.0000..+2000000.0000
    putInt(PS.y, (player.positionBody.y * 1000).toInt());
    putInt(PS.score, player.score);
    putSingle(PS.speed, player.speed);
    putRadians(PS.angle, player.rotationBody);
    putUInt(PS.elapsedTime, (elapsedTime * 1000).toInt()); // double ms
  }
}

Data types when writing or reading messages

Plans

• Initialization for sending UPD diagrams.
• Automatic connections and reconnections.
• Expanding the possibilities for working with rooms.
• Conducting stress tests.

Tips for Beginners

• If you are developing a browser game, then you need a WebSocket solution.
• When designing a game for real-time communication, UDP should be preferred, sinceTCP will cause a delay in the event of packet loss.

GitHub

https://github.com/QiXi/game_socket