Simple HTTP Web Server

An HTTP server is a software application that serves content over the web. It listens for incoming requests from clients (like web browsers) and sends back responses. HTTP servers are the backbone of the web, allowing you to access websites, download files, and interact with web services. In simple terms, HTTP servers deliver the content you see in your browser.

When you build your own HTTP server, you have complete control over its behavior and can tailor it to your specific needs. You may be using it for local development, to serve your HTML, CSS, and JavaScript files, or perhaps you're building a REST API - having your own server lets you define endpoints, handle requests and manage data.

Deno offers multiple ways to create an HTTP server. In this tutorial, we'll look at some of the most common methods.

Deno.serve Jump to heading#

The simplest way to create an HTTP server in Deno is by using Deno.serve.

We'll set up a basic HTTP server that responds to requests with the user-agent information. When you access the server at http://localhost:8080/, it will display the user-agent string from your browser or client.

Create a new file called server.ts and add the following code:

const port = 8080;

const handler = (request: Request): Response => {
  const body = `Your user-agent is:\n\n${
    request.headers.get("user-agent") ?? "Unknown"
  }`;

  return new Response(body, { status: 200 });
};

console.log(`HTTP server running. Access it at: http://localhost:${port}/`);
Deno.serve({ port }, handler);

This code defines a function called handler that takes a Request object and returns a Response object. The handler function extracts the user-agent string from the request headers and sends it back as the response body.

The Deno.serve function creates an HTTP server that listens on the suggested port and uses the handler function to process incoming requests.

You can run this code with:

deno run --allow-net server.ts

The server will start and display a message in the console. Open your browser and navigate to http://localhost:8080/ to see the user-agent information.

The --allow-net flag is required to allow the server to listen for incoming requests. This flag grants Deno permissions to access the network.

Default fetch export Jump to heading#

Another way to create an HTTP server in Deno is by exporting a default fetch function. The fetch API initiates an HTTP request to retrieve data from across a network and is built into the Deno runtime.

Create a new file called server.ts and add the following code:

export default {
  fetch(request) {
    const userAgent = request.headers.get("user-agent") || "Unknown";
    return new Response(`User Agent: ${userAgent}`);
  },
} satisfies Deno.ServeDefaultExport;

You can run this file with the deno serve command:

deno serve server.ts

The server will start and display a message in the console. Open your browser and navigate to http://localhost:8000/ to see the user-agent information.

Building on these examples Jump to heading#

You will likely want to expand on these examples to create more complex servers. Deno recommends using the Oak middleware framework for building web servers. Oak is a middleware framework for Deno's HTTP server, designed to be expressive and easy to use. It provides a simple way to create web servers with middleware support. Check out the Oak documentation for examples of how to define routes.

🦕 Now you can create your own HTTP server! You've learned how to set up a server, handle requests, and respond to clients. Now you have the basis to start building APIs, serving static files, or experimenting with server-side code.