Socket.io began to support binary stream from 1.0,

Question

I'm a beginner on node.js and socket.io. Socket.io began to support binary stream from 1.0, is there a complete example especially for image push to client and show in canvas? thanks

Answer 1

The solution is a bit complicated but should work in Chrome, Firefox, and IE10+ (not sure about Opera and Safari):

Somewhere on the server-side:

io.on('connection', function(socket){
    fs.readFile('/path/to/image.png', function(err, buffer){
        socket.emit('image', { buffer: buffer });
    });
});

And here is how you handle it on a client:

socket.on('image', function(data) {
    var uint8Arr = new Uint8Array(data.buffer);
    var binary = '';
    for (var i = 0; i < uint8Arr.length; i++) {
        binary += String.fromCharCode(uint8Arr[i]);
    }
    var base64String = window.btoa(binary);

    var img = new Image();
    img.onload = function() {
        var canvas = document.getElementById('yourCanvasId');
        var ctx = canvas.getContext('2d');
        var x = 0, y = 0;
        ctx.drawImage(this, x, y);
    }
    img.src = 'data:image/png;base64,' + base64String;
});

Just replace yourCanvasId with your canvas id :)

Answer 2

thanks, @sovente, in this 1.0 introduction http://socket.io/blog/introducing-socket-io-1-0/ , this is code snippet on binary support.

var fs = require('fs');
var io = require('socket.io')(3000);
io.on('connection', function(socket){
  fs.readFile('image.png', function(err, buf){
    // it's possible to embed binary data
    // within arbitrarily-complex objects
    socket.emit('image', { image: true, buffer: buf });
  });
});

i want to know how to handle the buffer on client side, codes are like:

 socket.on("image", function(image, buffer) {
     if(image)
     {
         console.log(" image: ");
         **// code to handle buffer like drawing with canvas**
     }

 });

Answer 3

Starting from socket.io 1.0 it is possible to send binary data. http://socket.io/blog/introducing-socket-io-1-0/

How ever the way of sending and receiving binary data is not clear in the official documentation. The only documentation is:

var socket = new WebSocket('ws://localhost');
socket.binaryType = 'arraybuffer';
socket.send(new ArrayBuffer);

I suggest you to take a look at this answer, where you can find code implementation for server and client (javascript, java):

https://stackoverflow.com/questions/34056705/how-to-send-binary-data-with-socket-io/

The good part is that it also works on Android!

Cheers