Streaming data with Node.js

Question

I want to know if it is possible to stream data from the server to the client with Node.js. I want to post a single AJAX request to Node.js, then leave the connection open a

Answer 1

Look at Sockets.io. It provides HTTP/HTTPS streaming and uses various transports to do so:

• WebSocket
• WebSocket over Flash (+ XML security policy support)
• XHR Polling
• XHR Multipart Streaming
• Forever Iframe
• JSONP Polling (for cross domain)

And! It works seamlessly with Node.JS. It's also an NPM package.

https://github.com/LearnBoost/Socket.IO

https://github.com/LearnBoost/Socket.IO-node

Answer 2

It is possible. Just use response.write() multiple times.

var body = ["hello world", "early morning", "richard stallman", "chunky bacon"];
// send headers
response.writeHead(200, {
  "Content-Type": "text/plain"
});

// send data in chunks
for (piece in body) {
    response.write(body[piece], "ascii");
}

// close connection
response.end();

You may have to close and reopen connection every 30 seconds or so.

EDIT: this is the code I actually tested:

var sys = require('sys'),
http = require('http');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    var currentTime = new Date();
    sys.puts('Starting sending time');
    setInterval(function(){
        res.write(
            currentTime.getHours()
            + ':' +
            currentTime.getMinutes()
            + ':' +
            currentTime.getSeconds() + "\n"
        );

        setTimeout(function() {
            res.end();
        }, 10000);

    },1000);
}).listen(8090, '192.168.175.128');

I connected to it by Telnet and its indeed gives out chunked response. But to use it in AJAX browser has to support XHR.readyState = 3 (partial response). Not all browsers support this, as far as I know. So you better use long polling (or Websockets for Chrome/Firefox).

EDIT2: Also, if you use nginx as reverse proxy to Node, it sometimes wants to gather all chunks and send it to user at once. You need to tweak it.

Answer 3

You can also abort the infinite loop:

app.get('/sse/events', function(req, res) {
    res.header('Content-Type', 'text/event-stream');

    var interval_id = setInterval(function() {
        res.write("some data");
    }, 50);

    req.socket.on('close', function() {
        clearInterval(interval_id);
    }); 
}); 

This is an example of expressjs. I believe that without expressjs will be something like.