How can I output data before I end the response?

Question

Here is my snippet I tested it in Chrome 11, and Firefox 4:

var http = require('http');

http.createServer(function(request, response){
   // Write Headers
   response.writeHead(200);

   // Write Hello World!
   response.write("Hello World!");

   // End Response after 5 seconds
   setTimeout(function(){ 
        response.end(); 
   }, 5000);

}).listen(8000);

As you can see I timed out the response.end() so I can test if response.write is outputted before the response.end. In my experience though it is not.

Is there a way to output the data before ending the response, something like sending the data in packets?

Answer 1

If you change the content type to text/plain -- e.g:

// Write Headers
response.writeHead(200, {'Content-Type': 'text/plain'});

then firefox will show the content immediately. Chrome still seems to buffer (if you write a bunch more content, chrome will show it immediately).

Answer 2

There actually is a way that you can do this without setting Content-Type: text/plain and still use text/html as the Content-Type, but you need to tell the browser to expect chunks of data.

This can be done easily like this:

var http = require('http');

http.createServer(function(request, response) {

    response.setHeader('Connection', 'Transfer-Encoding');
    response.setHeader('Content-Type', 'text/html; charset=utf-8');
    response.setHeader('Transfer-Encoding', 'chunked');

    response.write('hello');

    setTimeout(function() {
        response.write(' world!');
        response.end();
    }, 10000);

}).listen(8888);

You should be aware though, that until response.end() is called the request is still taking place and blocking other requests to your nodejs server.
You can easily test this by opening calling this page (localhost:8888) on two different tabs. One of them will wait 10 seconds, and the other will only get the beginning of the response once the first response ends (meaning you'll wait 10 seconds for the beginning of the response and another 10 seconds till the end of the response, using this code).

You can probably pass this obstacle too by running a couple of nodejs processes and load balancing between them, but then this begins to get much more complicated, and is a thread that should be taken else where... :)

Answer 3

If you want to output chunked plain text in Chrome - just like what Firefox is doing by default - you need to use the 'X-Content-Type-Options': 'nosniff' header. See What is "X-Content-Type-Options=nosniff"?

var http = require('http');

http.createServer(function (req, res) {
    res.writeHead(200, {
        'Content-Type': 'text/plain; charset=utf-8',
        'Transfer-Encoding': 'chunked',
        'X-Content-Type-Options': 'nosniff'});
    res.write('Beginning\n');
    var count = 10;
    var io = setInterval(function() {
        res.write('Doing ' + count.toString() + '\n');
        count--;
        if (count === 0) {
            res.end('Finished\n');
            clearInterval(io);
        }
    }, 1000);
}).listen(8888);

You don't need this option if your output is text/html.

Solution found from this Chrome defect: Transfer-Encoding chunked not support on text/plain

Answer 4

Here are the primary points you need to take note of:

• specify a charset
• each "chunk" will be outputted by the browser (atleast, what I noticed in Chrome) through a new line (<br> if the charset is text/html)

Like so:

res.setHeader('Content-Type', 'text/html; charset=utf-8');
res.write('a<br>');
setTimeout(function() {
  res.write('b<br>');
  setTimeout(function() {
    res.write('c');
    res.end();
  }, 2000);
}, 2000);