Setting up a router

In order to deliver web content we need to make a URI available. This recipe walks us through the creation of an HTTP server that exposes routes to the user.

Getting ready

First, let's create our server file. If our main purpose is to expose server functionality, it's general practice to call the file server.js, which we could put in a new folder. It's also a good idea to install and use hotnode:

sudo npm -g install hotnode
hotnode server.js

Hotnode will conveniently auto-restart the server when we save changes.

How to do it...

In order to create the server we need the http module, so let's load it and use the http.createServer method:

var http = require('http');
http.createServer(function (request, response) {
response.writeHead(200, {'Content-Type': 'text/html'});
response.end('Woohoo!');
}).listen(8080);

Note

Downloading the example code

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Now, if we save our file and access localhost:8080 on a web browser or using curl, our browser (or curl) will exclaim:'Woohoo!'. However, the same will occur at localhost:8080/foo. Indeed, any path will render the same behavior, so let's build in some routing. We can use the path module to extract basename of the path (the final part of the path), and reverse any URI encoding from the client with decodeURI:

var http = require('http');
var path = require('path');

http.createServer(function (request, response) {
var lookup = path.basename(decodeURI(request.url));

We now need a way to define our routes. One option is to use an array of objects:

var pages = [
{route: '', output: 'Woohoo!'},
{route: 'about', output: 'A simple routing with Node example'},
{route: 'another page', output: function() {return 'Here\'s '+this.route;}},
];

Our pages array should be placed above the http.createServer call.

Within our server, we need to loop through our array and see if the lookup variable matches any of our routes. If it does we can supply the output. We'll also implement some 404 handling:

http.createServer(function (request, response) {
var lookup = path.basename(decodeURI(request.url));
pages.forEach(function(page) {
if (page.route === lookup) {
response.writeHead(200, {'Content-Type': 'text/html'});
response.end(typeof page.output === 'function'
? page.output() : page.output);
}
});
if (!response.finished) {
response.writeHead(404);
response.end('Page Not Found!');
}
}).listen(8080);

How it works...

The callback function we provide to http.createServer gives us all the functionality we need to interact with our server through the request and response objects. We use request to obtain the requested URL and then we acquire its basename with path. We also use decodeURI which our another page route would fail without as our code would try to match another%20page against our pages array and return false.

Once we have our basename, we can match it in any way we want. We could send it in a database query to retrieve content, use regular expressions to effectuate partial matches, or we could match it to a file name and load its contents.

We could have used a switch statement to handle routing but our pages array has several advantages. It's easier to read and extend, and it can be seamlessly converted to JSON. We loop through our pages array using forEach.

Node is built on Google's V8 engine, which provides us with a number of ECMAScript 5 features. These features can't be used in all browsers as they're not yet universally implemented, but using them in Node is no problem! forEach is an ES5 implementation, but the ES3 way is to use the less convenient for loop.

While looping through each object, we check its route property. If we get a match, we write the 200 OK status and content-type headers. We then end the response with the object's output property.

response.end allows us to pass a parameter to it, which it writes just before finishing the response. In response.end, we used a ternary operator (?:) to conditionally call page.output as a function or simply pass it as a string. Notice that the another page route contains a function instead of a string. The function has access to its parent object through the this variable, and allows for greater flexibility in assembling the output we want to provide. In the event that there is no match in our forEach loop, response.end would never be called. Therefore, the client would continue to wait for a response until it times out. To avoid this, we check the response.finished property and if it's false, we write a 404 header and end the response.

response.finished depends on the forEach callback, yet it's not nested within the callback. Callback functions are mostly used for asynchronous operations. So on the surface this looks like a potential race condition, however forEach does not operate asynchronously. It continues to block until all loops are complete.

There's more...

There are many ways to extend and alter this example. There's also some great non-core modules available that do the leg work for us.

Simple multilevel routing

So far, our routing only deals with a single-level path. A multilevel path (for example, /about/node) will simply return a 404. We can alter our object to reflect a subdirectory-like structure, remove path, and use request.url for our routes instead of path.basename:

var http=require('http');
var pages = [
{route: '/', output: 'Woohoo!'},
{route: '/about/this', output: 'Multilevel routing with Node'},
{route: '/about/node', output: 'Evented I/O for V8 JavaScript.'},

{route: '/another page', output: function () {return 'Here\'s ' + this.route; }}
];
http.createServer(function (request, response) {
var lookup = decodeURI(request.url);

Note

When serving static files, request.url must be cleaned prior to fetching a given file. Check out the Securing against filesystem hacking exploits section discussed in this chapter.

Multilevel routing could be taken further, allowing us to build and then traverse a more complex object.

{route: 'about', childRoutes: [
{route: 'node', output: 'Evented I/O for V8 Javascript'},
{route: 'this', output: 'Complex Multilevel Example'}
]}

After the third or fourth level, this object would become a leviathan to look at. We could instead create a helper function to define our routes that essentially pieces our object together for us. Alternatively, we could use one of the excellent non-core routing modules provided by the open source Node community. Excellent solutions already exist which provide helper methods to handle the increasing complexity of scalable multilevel routing (see Routing modules discussed in this chapter andChapter 6, Accelerating Development with Express).

Parsing the querystring

Two other useful core modules are url and querystring. The url.parse method allows two parameters. First the URL string (in our case, this will be request.url) and second a Boolean parameter named parseQueryString. If set to true, it lazy loads the querystring module, saving us the need to require it, to parse the query into an object. This makes it easy for us to interact with the query portion of a URL.

var http = require('http');
var url = require('url');
var pages = [
{id: '1', route: '', output: 'Woohoo!'},
{id: '2', route: 'about', output: 'A simple routing with Node example'},
{id: '3', route: 'another page', output: function () {return 'Here\'s ' + this.route; }},
];
http.createServer(function (request, response) {
var id = url.parse(decodeURI(request.url), true).query.id;
if (id) {
pages.forEach(function (page) {
if (page.id === id) {
response.writeHead(200, {'Content-Type': 'text/html'});
response.end(typeof page.output === 'function'
? page.output() : page.output);
}
});
}
if (!response.finished) {
response.writeHead(404);
response.end('Page Not Found');
}
}).listen(8080);

With the added id properties we can access our object data by, for instance, localhost:8080?id=2.

Routing modules

There's an up-to-date list of various routing modules for Node at https://www.github.com/joyent/node/wiki/modules#wiki-web-frameworks-routers. These community-made routers cater to various scenarios. It's important to research the activity and maturity of a module before taking it into a production environment. In Chapter 6, Accelerating Development with Express, we will go into greater detail on using the built-in Express/Connect router for more comprehensive routing solutions.

See also

• Serving static files and Securing against filesystem hacking exploits discussed in this chapter

• Dynamic Routing discussed In Chapter 6, Accelerating Development with Express.