Building a Single-Threaded Web Server

TCP Connection Handling

use std::net::TcpListener;

let listener = TcpListener::bind("127.0.0.1:7878")?;
for stream in listener.incoming() {
    let stream = stream?;
    handle_connection(stream);
}

Similar to Node.js server.listen(), but blocking by default.

HTTP Request Structure

GET / HTTP/1.1
Host: 127.0.0.1:7878
User-Agent: Mozilla/5.0...

[optional body]

Method + URI + Version
Headers until empty line
Optional body

Basic Response

fn handle_connection(mut stream: TcpStream) {
    let mut buffer = [0; 1024];
    stream.read(&mut buffer)?;
    
    let response = "HTTP/1.1 200 OK\r\n\r\nHello, World!";
    stream.write(response.as_bytes())?;
    stream.flush()?;
}

Serving Files

fn handle_connection(mut stream: TcpStream) {
    let mut buffer = [0; 1024];
    stream.read(&mut buffer)?;
    
    let get = b"GET / HTTP/1.1\r\n";
    let (status_line, filename) = if buffer.starts_with(get) {
        ("HTTP/1.1 200 OK", "hello.html")
    } else {
        ("HTTP/1.1 404 NOT FOUND", "404.html")
    };
    
    let contents = fs::read_to_string(filename)?;
    let response = format!(
        "{}\r\nContent-Length: {}\r\n\r\n{}",
        status_line,
        contents.len(),
        contents
    );
    
    stream.write(response.as_bytes())?;
    stream.flush()?;
}

Performance Limitation

// Simulate slow endpoint
if buffer.starts_with(b"GET /sleep HTTP/1.1\r\n") {
    thread::sleep(Duration::from_secs(5));
}

Problem: Single-threaded blocking - all requests wait for slow operations.

Node.js difference: Event loop handles I/O asynchronously on single thread, while this blocks the entire server.

Next: Thread pool for concurrent request handling.