The goal of this assignment is to start to use Node.js and some of its built-in modules to build a very simple web server that serves static content.

You are provided with several files in public/ implementing the Tweeter site we've been working on throughout the course, with the exception of index.js. If you opened the index.html file in your browser, you'd see the site you're familiar with by now, with all of its styling and, when you add your own index.js file, its interactions. In addition to your familiar files, you're also provided with a file 404.html, whose purpose we'll get to in a bit.

The file server.js is the file you'll work on for this assignment. Your job is to complete that file to implement a very basic Node-based web server that satisfies the following requirements:

The server can only use Node's built-in modules (e.g. http, fs, path, etc.), no third-party modules.

The server should listen for requests on the port specified by the environment variable PORT. If PORT is not present in the environment, the server should listen on port 3000 by default.

When someone requests a path from your server that corresponds to the name of one of the files in public/, your server should respond with the contents of that file and a status code of 200. For example, if you run your server on port 3000 on your laptop, you should be able to access the following files by entering the following URLs into your browser:

public/index.html - http://localhost:3000/index.html

public/index.js - http://localhost:3000/index.js

public/style.css - http://localhost:3000/style.css

public/404.html - http://localhost:3000/404.html Note that if everything is hooked up correctly, your index.html and 404.html pages will automatically have styles and interactions from style.css and index.js because the browser will see those files referenced from the HTML and make additional requests for those files.

When someone requests the root path (i.e. /) from your server, it should respond with the contents of public/index.html and a status code of 200. For example, if you run your server on port 3000 on your laptop and visit http://localhost:3000 in your laptop's browser, your server should send the contents of public/index.html.

If someone visits a path on your site that does not correspond to the name of any of the files in public/, your server should respond with the contents of public/404.html and a status code of 404. For example, if you run your server on port 3000 on your laptop and visit http://localhost:3000/thispagedoesnotexist in your laptop's browser, your server should serve the contents of public/404.html.

Your server should read any given file in public/ from disk only once. In other words, the contents of each file should be cached in the server's memory after the first read, and the server should use this cache when responding with a file's contents.