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 and continuously stream data to the client. The client will receive this stream and update the page continuously.

Update:

As an update to this answer - I cannot get this to work. The response.write is not sent before you call close. I have set up an example program that I use to achieve this:

Node.js:

var sys = require('sys'), 
http = require('http');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    var currentTime = new Date();
    setInterval(function(){
        res.write(
            currentTime.getHours()
            + ':' + 
            currentTime.getMinutes()
            + ':' +
            currentTime.getSeconds()
        );
    },1000);
}).listen(8000);

HTML:

<html>
    <head>
        <title>Testnode</title>
    </head>

    <body>
        <!-- This fields needs to be updated -->
        Server time: <span id="time">&nbsp;</span>

        <!-- import jQuery from google -->
        <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>

        <!-- import jQuery -->
        <script type="text/javascript">
            $(document).ready(function(){
            // I call here node.localhost nginx ports this to port 8000
                $('#time').load('http://node.localhost');
            });
        </script>
    </body>
</html>

Using this method I don't get anything back until I call close(). Is this possible or should I go with a long poll approach instead where I call the load function again as one comes in?

Also I don't think this is streaming, this is just chunking stuff in bits. Yes, node will send parts of an answer, but every html server does this. The streaming goodness you get from node refers to something else. — Zlatko
Also, in your example you don't have the pause, resume, flush methods. The (read) stream is something that is giving you data, as fast as it can (or as fast as you can). And you tell it to pause, then it pauses. And you tell it to continue etc. — Zlatko

Kuroki Kaze Kuroki Kaze · Accepted Answer · 2010-04-01T20:30:19

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.

Streaming data with Node.js

Update:

4 Answers