The Big Build: A Web Server

This is it — the grand finale! 🎉 Today we build something real: a tiny web server. A web server is a program that waits patiently for visitors, and when someone shows up, it hands them a web page. It’s like a friendly shopkeeper who greets everyone who walks through the door. 🏪

How does a web server work?

When you type a website address into a browser, your browser sends a little message called a request — basically, “Hey, can I see your page, please?” The server reads that request and sends back a response — the actual page!

The plan

Our server needs to do three things, over and over:

1. Listen at an address (like the stand’s street corner).
2. Read each visitor’s request.
3. Write back a response that says “Hello!”

In Rust, we use a tool called TcpListener to listen for visitors. Here is a sketch of the idea. Read it like a story — you don’t need every detail!

use std::io::Write;
use std::net::TcpListener;

fn main() {
    // 1. Listen at this address on our computer
    let listener = TcpListener::bind("127.0.0.1:7878").unwrap();
    println!("Listening on 127.0.0.1:7878");

    // 2. Wait for visitors, one at a time
    for stream in listener.incoming() {
        let mut stream = stream.unwrap();
        println!("Got a connection! Sending the hello page.");

        // 3. Write back a simple web page that says Hello!
        let response = "HTTP/1.1 200 OK\r\n\r\nHello!";
        stream.write_all(response.as_bytes()).unwrap();
    }
}

When you start this server, your terminal would print a log like this. Each time a browser visits http://127.0.0.1:7878, a new line pops up!

That funny-looking 127.0.0.1 means “this very computer,” and 7878 is like a door number where our server waits. 🚪

Quick quiz