Sending message to a specific connected users using webSocket?

Question

I wrote a code for broadcasting a message to all users:

// websocket and http servers
var webSocketServer = require('websocket').server;

...
...
var clients = [ ];

var server = http.createServer(function(request, response) {
    // Not important for us. We're writing WebSocket server, not HTTP server
});
server.listen(webSocketsServerPort, function() {
  ...
});

var wsServer = new webSocketServer({
    // WebSocket server is tied to a HTTP server. 
    httpServer: server
});

// This callback function is called every time someone
// tries to connect to the WebSocket server
wsServer.on('request', function(request) {
...
var connection = request.accept(null, request.origin); 
var index = clients.push(connection) - 1;
...

Please notice:

• I don't have any user reference but only a connection .
• All users connection are stored in an array.

Goal: Let's say that the Node.js server wants to send a message to a specific client (John). How would the NodeJs server know which connection John has? The Node.js server doesn't even know John. all it sees is the connections.

So, I believe that now, I shouldn't store users only by their connection, instead, I need to store an object, which will contain the userId and the connection object.

Idea:

• When the page finishes loading (DOM ready) - establish a connection to the Node.js server.

• When the Node.js server accept a connection - generate a unique string and send it to the client browser. Store the user connection and the unique string in an object. e.g. {UserID:"6", value: {connectionObject}}

• At client side, when this message arrives - store it in a hidden field or cookie. (for future requests to the NodeJs server )

---

When the server wants to send a message to John:

• Find john's UserID in the dictionary and send a message by the corresponding connection.

• please notice there is no asp.net server code invloced here (in the message mechanism). only NodeJs .*

Question:

Is this the right way to go?

Answer 1

This is not only the right way to go, but the only way. Basically each connection needs a unique ID. Otherwise you won't be able to identify them, it's as simple as that.

Now how you will represent it it's a different thing. Making an object with id and connection properties is a good way to do that ( I would definitely go for it ). You could also attach the id directly to connection object.

Also remember that if you want communication between users, then you have to send target user's ID as well, i.e. when user A wants to send a message to user B, then obviously A has to know the ID of B.

Answer 2

Here's a simple chat server private/direct messaging.

package.json

{
  "name": "chat-server",
  "version": "0.0.1",
  "description": "WebSocket chat server",
  "dependencies": {
    "ws": "0.4.x"
  }
}

server.js

var webSocketServer = new (require('ws')).Server({port: (process.env.PORT || 5000)}),
    webSockets = {} // userID: webSocket

// CONNECT /:userID
// wscat -c ws://localhost:5000/1
webSocketServer.on('connection', function (webSocket) {
  var userID = parseInt(webSocket.upgradeReq.url.substr(1), 10)
  webSockets[userID] = webSocket
  console.log('connected: ' + userID + ' in ' + Object.getOwnPropertyNames(webSockets))

  // Forward Message
  //
  // Receive               Example
  // [toUserID, text]      [2, "Hello, World!"]
  //
  // Send                  Example
  // [fromUserID, text]    [1, "Hello, World!"]
  webSocket.on('message', function(message) {
    console.log('received from ' + userID + ': ' + message)
    var messageArray = JSON.parse(message)
    var toUserWebSocket = webSockets[messageArray[0]]
    if (toUserWebSocket) {
      console.log('sent to ' + messageArray[0] + ': ' + JSON.stringify(messageArray))
      messageArray[0] = userID
      toUserWebSocket.send(JSON.stringify(messageArray))
    }
  })

  webSocket.on('close', function () {
    delete webSockets[userID]
    console.log('deleted: ' + userID)
  })
})

Instructions

To test it out, run npm install to install ws. Then, to start the chat server, run node server.js (or npm start) in one Terminal tab. Then, in another Terminal tab, run wscat -c ws://localhost:5000/1, where 1 is the connecting user's user ID. Then, in a third Terminal tab, run wscat -c ws://localhost:5000/2, and then, to send a message from user 2 to 1, enter ["1", "Hello, World!"].

Shortcomings

This chat server is very simple.

• Persistence

  It doesn't store messages to a database, such as PostgreSQL. So, the user you're sending a message to must be connected to the server to receive it. Otherwise, the message is lost.

• Security

  It is insecure.

  • If I know the server's URL and Alice's user ID, then I can impersonate Alice, ie, connect to the server as her, allowing me to receive her new incoming messages and send messages from her to any user whose user ID I also know. To make it more secure, modify the server to accept your access token (instead of your user ID) when connecting. Then, the server can get your user ID from your access token and authenticate you.

  • I'm not sure if it supports a WebSocket Secure (wss://) connection since I've only tested it on localhost, and I'm not sure how to connect securely from localhost.

Answer 3

For people using ws version 3 or above. If you want to use the answer provided by @ma11hew28, simply change this block as following.

webSocketServer.on('connection', function (webSocket) {
  var userID = parseInt(webSocket.upgradeReq.url.substr(1), 10)

webSocketServer.on('connection', function (webSocket, req) {
  var userID = parseInt(req.url.substr(1), 10)

ws package has moved upgradeReq to request object and you can check the following link for further detail.

Reference: https://github.com/websockets/ws/issues/1114

Answer 4

I would like to share what I have done. Hope it doesn't waste your time.

I created database table holding field ID, IP, username, logintime and logouttime. When a user logs in logintime will be currect unixtimestamp unix. And when connection is started in websocket database checks for largest logintime. It will be come user logged in.

And for when user logs out it will store currect logouttime. The user will become who left the app.

Whenever there is new message, Websocket ID and IP are compared and related username will be displayed. Following are sample code...

// when a client connects
function wsOnOpen($clientID) {
      global $Server;
      $ip = long2ip( $Server->wsClients[$clientID][6] );

      require_once('config.php');
      require_once CLASSES . 'class.db.php';
      require_once CLASSES . 'class.log.php';

      $db = new database();
      $loga = new log($db);

      //Getting the last login person time and username
      $conditions = "WHERE which = 'login' ORDER BY id DESC LIMIT 0, 1";
      $logs = $loga->get_logs($conditions);
      foreach($logs as $rows) {

              $destination = $rows["user"];
              $idh = md5("$rows[user]".md5($rows["time"]));

              if ( $clientID > $rows["what"]) {
                      $conditions = "ip = '$ip', clientID = '$clientID'  

                      WHERE logintime = '$rows[time]'";
                      $loga->update_log($conditions);
             }
      }
      ...//rest of the things
} 

Answer 5

interesting post (similar to what I am doing). We are making an API (in C#) to connect dispensers with WebSockets, for each dispenser we create a ConcurrentDictionary that stores the WebSocket and the DispenserId making it easy for each Dispenser to create a WebSocket and use it afterwards without thread problems (invoking specific functions on the WebSocket like GetSettings or RequestTicket). The difference for you example is the use of ConcurrentDictionary instead of an array to isolate each element (never attempted to do such in javascript). Best regards,