Building a Simple Web Server in Rust

As a JavaScript developer, you’re likely familiar with creating web servers using Node.js and Express. In this tutorial, we’ll build a simple HTTP server in Rust using the popular Actix Web framework, and compare it to a Node.js implementation.

Node.js Implementation

First, let’s look at how you’d build a simple server with Express:

server.js

const express = require('express');
const app = express();
const port = 3000;

// JSON middleware
app.use(express.json());

// In-memory "database"
let todos = [
  { id: 1, title: 'Learn Express', completed: true },
  { id: 2, title: 'Learn Rust', completed: false }
];

// Routes
app.get('/todos', (req, res) => {
  res.json(todos);
});

app.get('/todos/:id', (req, res) => {
  const id = parseInt(req.params.id);
  const todo = todos.find(todo => todo.id === id);

  if (!todo) {
    return res.status(404).json({ error: 'Todo not found' });
  }

  res.json(todo);
});

app.post('/todos', (req, res) => {
  const { title } = req.body;

  if (!title) {
    return res.status(400).json({ error: 'Title is required' });
  }

  const newId = todos.length > 0 ? Math.max(...todos.map(t => t.id)) + 1 : 1;
  const newTodo = { id: newId, title, completed: false };

  todos.push(newTodo);
  res.status(201).json(newTodo);
});

app.listen(port, () => {
  console.log(`Server running at http://localhost:${port}`);
});

Rust Implementation

Now, let’s build the same server in Rust using Actix Web.

Step 1: Create a New Rust Project

cargo new todo_server
cd todo_server

Step 2: Add Dependencies to Cargo.toml

Edit your Cargo.toml file to include the necessary dependencies:

[package]
name = "todo_server"
version = "0.1.0"
edition = "2021"

[dependencies]
actix-web = "4.3.0"
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0"
once_cell = "1.17.0"

Step 3: Implement the Server

Now, let’s implement our server in src/main.rs:

main.rs

use actix_web::{web, App, HttpResponse, HttpServer, Responder, get, post};
use once_cell::sync::Lazy;
use serde::{Deserialize, Serialize};
use std::sync::Mutex;

// Todo struct
#[derive(Debug, Serialize, Deserialize, Clone)]
struct Todo {
    id: u32,
    title: String,
    completed: bool,
}

// Create request struct
#[derive(Debug, Deserialize)]
struct CreateTodoRequest {
    title: String,
}

// In-memory "database" using a global variable with Mutex for safe concurrent access
static TODOS: Lazy<Mutex<Vec<Todo>>> = Lazy::new(|| {
    Mutex::new(vec![
        Todo { id: 1, title: "Learn Actix".to_string(), completed: true },
        Todo { id: 2, title: "Learn Rust".to_string(), completed: false },
    ])
});

// Get all todos
#[get("/todos")]
async fn get_todos() -> impl Responder {
    let todos = TODOS.lock().unwrap().clone();
    HttpResponse::Ok().json(todos)
}

// Get a specific todo by ID
#[get("/todos/{id}")]
async fn get_todo(path: web::Path<u32>) -> impl Responder {
    let id = path.into_inner();
    let todos = TODOS.lock().unwrap();

    match todos.iter().find(|t| t.id == id) {
        Some(todo) => HttpResponse::Ok().json(todo),
        None => HttpResponse::NotFound().json(("error", "Todo not found")),
    }
}

// Create a new todo
#[post("/todos")]
async fn create_todo(req: web::Json<CreateTodoRequest>) -> impl Responder {
    let mut todos = TODOS.lock().unwrap();

    // Validate request
    if req.title.is_empty() {
        return HttpResponse::BadRequest().json(("error", "Title is required"));
    }

    // Generate new ID
    let new_id = todos.iter().map(|t| t.id).max().unwrap_or(0) + 1;

    // Create new todo
    let new_todo = Todo {
        id: new_id,
        title: req.title.clone(),
        completed: false,
    };

    // Add to collection
    todos.push(new_todo.clone());

    HttpResponse::Created().json(new_todo)
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    println!("Server running at http://localhost:3000");

    HttpServer::new(|| {
        App::new()
            .service(get_todos)
            .service(get_todo)
            .service(create_todo)
    })
    .bind("127.0.0.1:3000")?
    .run()
    .await
}

Step 4: Run the Server

cargo run

Your server should now be running at http://localhost:3000.

Key Differences Between Node.js and Rust Implementations

Type Safety

• JavaScript: Dynamic typing means you might encounter runtime type errors.
• Rust: Static typing means the compiler catches type errors before your code runs.

// In Rust, you define the exact structure of your data:
#[derive(Debug, Serialize, Deserialize, Clone)]
struct Todo {
    id: u32,
    title: String,
    completed: bool,
}

Concurrency

• JavaScript: Single-threaded event loop with asynchronous callbacks.
• Rust: Multi-threaded by default with the async/await pattern.

// Rust's HTTP server runs multiple threads by default
HttpServer::new(|| {...})
    .bind("127.0.0.1:3000")?
    .run()
    .await

Data Handling

• JavaScript: Mutable objects without explicit thread safety.
• Rust: Uses Mutex to ensure thread-safe access to shared data.

// Thread-safe global state in Rust
static TODOS: Lazy<Mutex<Vec<Todo>>> = Lazy::new(|| {
    Mutex::new(vec![...])
});

Error Handling

• JavaScript: Uses exceptions and try/catch.
• Rust: Uses the Result type and pattern matching.

// Rust's ? operator for error handling
.bind("127.0.0.1:3000")?

Performance

The Rust version will generally:

• Have lower memory usage
• Have faster response times, especially under load
• Handle more concurrent connections

Testing the API

With curl

# Get all todos
curl http://localhost:3000/todos

# Get a specific todo
curl http://localhost:3000/todos/1

# Create a new todo
curl -X POST http://localhost:3000/todos \
  -H "Content-Type: application/json" \
  -d '{"title": "Learn Actix Web"}'

Taking It Further

Here are some improvements you could make to this server:

1. Add PUT and DELETE routes for updating and deleting todos
2. Implement persistence with a database like PostgreSQL using diesel or sqlx
3. Add authentication and user management
4. Implement middleware for logging, CORS, etc.
5. Add error handling middleware

Key Takeaways

1. Rust is more verbose: You need to define data structures explicitly.
2. Rust is more type-safe: The compiler catches errors that would only be found at runtime in JavaScript.
3. Rust has better concurrency: Multi-threading comes out of the box.
4. Rust is faster: Both in execution time and resource usage.

Comparison with JavaScript Ecosystem

Feature	JavaScript/Node.js	Rust
Web frameworks	Express, Koa, Fastify	Actix Web, Rocket, Warp
Request routing	Simple function-based	Macro-based or builder pattern
Middleware	Function-based middleware	Trait-based or function middleware
Performance	Good for I/O bound tasks	Excellent for CPU and I/O bound tasks
Learning curve	Gentle	Steep

Next Steps

Here are some extensions you can try on your own:

1. Add a database connection
2. Deploy your Rust application
3. Create a full-stack application with Rust backend and JavaScript frontend