Most efficient way to store and access list of clients in Sockets.IO Node.JS

Question

I'm having this simple socket.io manager, where when a user connects, he will be added to a pool of online clients and when another client (say client B), sends a message to client A, It should try to send that message only if client is in the pool. Currently I have this:

var connectionMap = [];
const socketHandler = (io) => {
  io.on("connection", (socket) => {
    socket.id = "some_custom_id I define";
    connectionMap.push(socket);

    socket.on("textMessage", function (message) {
      connectionMap.forEach(function (connection, index) {
        if (connection.id == message.receiver_id)
          connection.emit("textMessage", message);
      });
    });

    socket.on("disconnect", function () {
      connectionMap.splice(connectionMap.indexOf(client), 1);
    });
  });
};

Although this might work on a use case with small number of users, I'm looking for a solution that could scale decently without throttling the performance much. (I can't imagine a foreach running across thousands of indexes on every message sent accross the platform.) Any ideas on how to approach this?

Answer 1

You can use an object instead of an array for connectionMap . On connection we set the socket.id as key in the object and value can be true . During message we can check directly in connectionMap if message.receiver_id is present. This is a significant improvement over using array as connectionMap because in the worst case array will take O(N) time and with object (map) you can have constant time O(1)

var connectionMap = {};
const socketHandler = (io) => {
  io.on("connection", (socket) => {
    socket.id = "some_custom_id I define";
    connectionMap[socket.id] = socket;

    socket.on("textMessage", function (message) {
        if (connectionMap[message.receiver_id]) {
            connectionMap[message.receiver_id].emit("textMessage", message);
        }
    });

    socket.on("disconnect", function () {
        delete connectionMap[client];
    });
  });
};

Or you can use a Map

var connectionMap = new Map();
const socketHandler = (io) => {
  io.on("connection", (socket) => {
    socket.id = "some_custom_id I define";
    connectionMap.set(socket.id, socket);

    socket.on("textMessage", function (message) {
        if (connectionMap.has(message.receiver_id)) {
          connectionMap.get(message.receiver_id).emit("textMessage", message);
        }
    });

    socket.on("disconnect", function () {
        connectionMap.delete(client);
    });
  });
};

Answer 2

Use an Object instead of Array , so you can access sockets directly by id instead of having to search through them until you find the one you want:

 const connectionMap = {}; const socketHandler = io => { io.on('connection', socket => { socket.id = 'some_custom_id I define'; connectionMap[socket.id] = socket; socket.on('textMessage', message => { connectionMap[message.receiver_id].emit('textMessage', message); }); socket.on('disconnect', message => { delete connectionMap[socket.id]; }); }); };