node.js and IPv6

Sat, 13 Aug 2011 09:46:35 +0000
node.js ipv6 tech

tl;dr

OK, my last few posts on node.js may have seemed a little negative. While there are some things in node.js that seem a little more complicated than necessary, there are some things that are nice and simple, such as getting your server to run on both IPv4 and IPv6. This post is a little late for World IPv6 Day, but better late than never!

So this post isn’t about configuring IPv6 on your machine in general. I’m going to assume that your local network interface has an IPv6 address. You can probably check this with the output of ifconfig. On my Darwin box it looks something like:

benno@ff:~% ifconfig lo0
lo0: flags=8049 mtu 16384
	inet6 ::1 prefixlen 128 
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
	inet 127.0.0.1 netmask 0xff000000 

You should see the local interface bound to the IPv6 localhost address ::1 as well the IPv4 localhost address 127.0.0.1. So lets get started with a simple little IPv4 server.

var http = require('http')
var server

function onRequest(req, res) {
    console.log(req.method, req.url)
    res.writeHead(200, {'Content-Type': 'text/plain'})
    res.end('Hello World\n')
}

function onListening() {
    console.log('Listening at http://' + this.address().address + ':' + this.address().port + '/')
}

server = http.createServer()
server.on('request', onRequest)
server.on('listening', onListening)
server.listen(1337, '127.0.0.1')

This is a slight variation on the canonical node.js Hello World example. A few things worth noting:

So, apart from my stylistic quirks, the above should be fairly straight forward. The only new thing functionality wise compared to the normal node.js example is the addition of some trivial logging in the request handler.

So our quest is going to be to add support for IPv6. Before we do that though, I’m going to improve our logging a bit. Just because we are supporting IPv6, doesn’t mean we want to stop our server running on IPv4, so we are going to end up with multiple servers running at once. Once this happens, our logging might get a bit confusing. So we’re going to give our servers a name, and include that in the logging.

var http = require('http')
var server

function onRequest(req, res) {
    console.log('[' + this.name + ']', req.method, req.url)
    res.writeHead(200, {'Content-Type': 'text/plain'})
    res.end('Hello World\n')
}

function onListening() {
    console.log('[' + this.name + '] Listening at http://' + this.address().address + ':' + this.address().port + '/')
}

server = http.createServer()
server.name = 'ipv4server'
server.on('request', onRequest)
server.on('listening', onListening)
server.listen(1337, '127.0.0.1')

Because Javascript objects are open we can trivially add a name field to our objects, and then use this when logging. In general I avoid messing with objects created by other modules, but it is the quick and easy approach in this case.

OK, so on to IPv6. As a first stab at it, we get something like this:

var http = require('http')
var server

function onRequest(req, res) {
    console.log('[' + this.name + ']', req.method, req.url)
    res.writeHead(200, {'Content-Type': 'text/plain'})
    res.end('Hello World\n')
}

function onListening() {
    console.log('[' + this.name + '] Listening at http://' + this.address().address + ':' + this.address().port + '/')
}

ipv4server = http.createServer()
ipv6server = http.createServer()

ipv4server.name = 'ipv4server'
ipv6server.name = 'ipv6server'

ipv4server.on('request', onRequest)
ipv6server.on('request', onRequest)

ipv4server.on('listening', onListening)
ipv6server.on('listening', onListening)

ipv4server.listen(1337, '127.0.0.1')
ipv6server.listen(1337, '::1')

Basically, creating an IPv6 server is exactly the same as creating an IPv4 server, except you use an IPv6 address literal (i.e: ::1) to specify the local address to bind to, rather than an IPv4 address literal. You can see that there is absolutely no problem sharing the event handlers between the two different servers. The this variable in each event handler function refers to the server itself, so you can handle cases that are server specific if necessary.

When you run this you should get some output like:

[ipv4server] Listening at http://127.0.0.1:1337/
[ipv6server] Listening at http://::1:1337/

Which looks pretty good. You can try going to the IPv4 server URL in your browser. If you try the IPv6 URL, you will probably run in to some problems. This is because you need some escaping of the IPv6 literal address in the URL, or it can’t be parsed correctly (what with there being all those colons which are usually used for separating the port number). So the correct URL should be: http://[::1]:1337/. We better fix this bug in the code:

function onListening() {
    var hostname = this.type === 'tcp4' ? this.address().address : '[' + this.address().address + ']'

    console.log('[' + this.name + '] Listening at http://' + hostname + ':' + this.address().port + '/')
}

OK, that’s looking pretty good now, if you start hitting those URLs on the different address you should get some useful output such as:

[ipv4server] Listening at http://127.0.0.1:1337/
[ipv6server] Listening at http://[::1]:1337/
[ipv4server] GET /
[ipv4server] GET /favicon.ico
[ipv6server] GET /
[ipv6server] GET /favicon.ico

Now, I mentioned earlier I don’t like duplicating data. I also don’t like duplicating code either, so let’s refactor this a little:

function startServer(name, address, port) {
    var server = http.createServer()
    server.name = name
    server.on('request', onRequest)
    server.on('listening', onListening)
    server.listen(port, address)
    return server
}

startServer('ipv4server', '127.0.0.1', 1337)
startServer('ipv6server', '::1', 1337)

So, in conclusion it is easy-peasy to run your web application on IPv6, and even on IPv4 and IPv6 using the exact same script.

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