Request Routing

In web development, routing refers to the process of matching an incoming request with generating the appropriate response. For most web servers (and definitely for Node-based ones), we abstract the process of generating the response into a function. We often call these functions endpoints as their purpose is to serve the response, effectively ending the processing of an incoming request with an appropriate response.

With a Node webserver, endpoint functions typically take in a req (an instance of http.IncomingMessage) and res (an instance of http.ServerResponse) objects. These objects form an abstraction around the HTTP request and response.

Routing in a Node webserver therefore consists of examining the properties of the req object and determining which endpoint function to invoke. Up to this point, we’ve done this logic in a handleRequest() function, in a fairly ad-hoc way. Consider what we might need to do for a dynamically generated blog - we’d need to serve static files (like CSS and JS files), as well as dynamically generated pages for blog posts and the home page. What might our handleRequest() look like in that case?

Let’s assume we have a serveHome() function to serve the home page, a serveFile() function to serve static files, and a servePost() function to serve dynamically generated posts. Determining if the request is for the homepage is easy, as we know the path should just be a forward slash:

    // Determine if the request is for the index page
    if(req.url === '/') return serveHome(req, res);

But what about determining if a request is for a post or a static file? We could use fs.stat to determine if a file exists:

    // Determine if a corresponding file exists 
    fs.stat(path.join("public", req.url), (err, stat) => {
        if(err) {
            // Error reading file, might be a post?
            servePost(req, res);
        else {
            // File exists, serve it 
            serveFile(req, res);

This would work, but it’s a bit ugly. Also, using a filesystem method like fs.stat is potential bottleneck in our application; we’d like to avoid it if at all possible.

If we make all our posts use the url /posts, we could use the query string to determine which post we want to display. This approach is a bit cleaner, though it does mean we need to separate the pathname from our URL:

public handleRequest(req, res) {
    // Separate the pathname from the url 
    const pathname = new URL(req.url, "http://localhost").pathname;

    // Determine if the request is for the index page
    if(pathname === '/') return serveHome(req, res);

    // Determine if the request is for a post 
    if(pathname === '/post') return servePost(req, res);

    // Treat all other requests as a file 
    serveFile(req, res);

This is a bit cleaner of an approach, but it still has a very ad-hoc feel and requires us to incorporate query strings into some of our URLs.