server.js

/**
* server.js
*
* Core server component that handles all realtime data transfer and static site hosting
*
* Created by Sameid Usmani on 08-05-17.
*/

// Simple constant files for identifying messages and errors
var MESSAGES = require("./public/js/messages");
var ERRORS = require("./public/js/errors");

// Libraries used to setup the static server and WebSocket server
var http = require('http');
var sockjs = require('sockjs');
var express = require("express");
var bodyParser = require("body-parser");
var path = require("path");

// Create an express app
var app = express();

// Add necessary middleware for encoding the URL and hosting the app from the public folder
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(express.static(path.join(__dirname, 'public')));

// Either set the port to an ENVIRONMENT_VARIABLE or 3000
var port = process.env.PORT || 3000;

// Create a new router for hosting the game
var router = express.Router();

// Host the game entry point (index.html) on the '/' endpoint
router.get('/', function(req, res) {
    res.status(200).sendFile(path.join(__dirname + '../public/index.html'));
});

// Use that router against the '/' endpoint
app.use('/', router);

// Listen for http request on the port specified
app.listen(port);
console.log("Shooty Roads hosting server started on", port);

// Create a json map for rooms where the key is the room name and the object holds the connections for both the client and server
var rooms = {};

// Create a json map for the connection id generated by SockJS and the value is the room name, this makes accessing the room via the connection id easy
var connectionRoomMap = {};

/**
* A helper function to send data to a SockJS connection
*
* @param conn {SockJSConnection}
* @param object {Object}
*/
var send = function(conn, object){
    // Convert the object to a string, and send on the SockJSConnection
    if (conn) {
        conn.write(JSON.stringify(object));
    }
}

/**
* Common pattern for relay messages to the opposite player in the room
*
* @param room {Room}
* @param message {Object}
*/
var relayMessage = function(room, message){
    if (!room) {
        return;
    }

    if (message.isHost) {
        if (room.client) {
            send(room.client, message);
        }
    } else {
        if (room.server) {
            send(room.server, message);
        }
    }
}

// Create a new SockJSServer
var webSocketServer = sockjs.createServer({ sockjs_url: 'http://cdn.jsdelivr.net/sockjs/1.0.1/sockjs.min.js' });

// Listen to connection events on the SockJS server
webSocketServer.on('connection', function(conn) {

    // Listen to the data events for any given connection
    conn.on('data', function(message) {

        // Since all messages for SockJS are sent via string, we need to parse the string into a JSON object
        //XXX: This assumes all strings sent on the socket are in JSON format
        var message = JSON.parse(message);

        // Handle the event when the host is requesting to host a room
        if (message.id == MESSAGES.HOSTING_GAME_REQUEST.id) {

            // Check if the roomName provided doesn't already exist
            if (!rooms[message.roomName]){

                // If the room doesn't exist then create it
                rooms[message.roomName] = {
                    server: conn, // Set the connection to the server key
                    serverName: message.serverName // Also append the serverName specified by the player
                };

                // Also add the roomName to the connection id mapping on the SockJSConnection object
                connectionRoomMap[conn.id] = message.roomName;

                console.log("Created room:", message.roomName);

                // Send a message to the hoster, that creating the room was successful
                send(conn, MESSAGES.SUCCESSFUL_ROOM_CREATION)
            } else {

                // Notify the host that the room already exists
                send(conn, ERRORS.ROOM_ALREADY_EXISTS);
            }
        }
        // Handle the event when the client is requesting to join a room
        else if (message.id == MESSAGES.JOINING_GAME_REQUEST.id) {

            // Check if the room exists, and if it's not already full
            if (rooms[message.roomName] && !rooms[message.roomName].client) {

                // If there is room in the room, then add the client to the room
                var r = rooms[message.roomName];
                r.client = conn;

                // Notify the host of the room that someone has successfully joined the room
                var serverMessage = MESSAGES.SUCCESSFUL_JOIN_RESPONSE;
                serverMessage.clientName = message.clientName;
                send(r.server, serverMessage);

                // Notifu the client that they have successfully joined the room
                var clientMessage = MESSAGES.SUCCESSFUL_JOIN_RESPONSE;
                clientMessage.serverName = r.serverName
                send(r.client, clientMessage);

                // Create a mapping from the client connection id to the room name that they are in
                connectionRoomMap[conn.id] = message.roomName;

            } else {
                // Notify the client that the room doesn't exist
                //XXX: This will also send if the room is full
                send(conn, ERRORS.ROOM_DOES_NOT_EXIST);
            }
        }
        // Handle the event when the host has started the game
        else if (message.id == MESSAGES.GAME_STARTED_BY_HOST.id) {
            // Get the room, and notify the client that the game has started
            var r = rooms[message.roomName];
            send(r.client, MESSAGES.GAME_STARTED_BY_HOST);
        }
        // Handle all events for in game data
        else if (message.id == MESSAGES.GAME_DATA.id) {
            // Simply get the room and push the data to the appropriate person in the room
            relayMessage(rooms[message.roomName], message);
        }
        // Handle the event if the host or client stopped the game (ie. they died)
        else if (message.id == MESSAGES.GAME_OVER.id) {
            // Notify the client or host directly
            relayMessage(rooms[message.roomName], message);
        }
        // Handle the vevent if the host or client cancel the joining or hosting process
        else if (message.id == MESSAGES.CANCEL.id) {
            relayMessage(rooms[message.roomName], message);
        }

    });

    // Listen to the close events on any given connection
    conn.on('close', function() {
        console.log("Client closed connection:", conn.id);

        // Using the connectionRoomMap get the roomName and from that get the room object
        var roomName = connectionRoomMap[conn.id] || null;
        var r = roomName ? rooms[roomName] : null;

        // If no room exists for the current connection, simply return
        if (!r || !r.client || !r.server) {
            return;
        }

        // Notify the host or client if either player has disconnected
        if (r.client && r.client.id == conn.id) {
            send(r.server, ERRORS.CLIENT_DISCONNECTED);
        } else {
            send(r.client, ERRORS.SERVER_DISCONNECTED);
        }

        // Expire the room afterwards
        delete rooms[connectionRoomMap[conn.id]];
    });

});

// Create an http server to host the SockJS server
var server = http.createServer();
// Install the handler to the webSocketServer, and listen on /multiplayer
webSocketServer.installHandlers(server, {prefix:'/multiplayer'});
// Start listening to SockJS request on 3001
server.listen(3001, '0.0.0.0');
console.log("SockJS server started on", 3001);