REST APIs with Actix-web/Rocket

What are REST APIs?

Why Rust for Web Services?

Meet Actix-web

Project Setup & Dependencies

[dependencies]
actix-web = "4"
serde = { version = "1.0", features = ["derive"] }

Your First Actix-web Server

use actix_web::{App, HttpServer};

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    println!("Server running at http://127.0.0.1:8080");
    HttpServer::new(|| {
        // Our application instance, where we'll add routes
        App::new()
    })
    .bind(("127.0.0.1", 8080))? // Bind to an IP address and port
    .run() // Start the server
    .await // Await its completion
}

Defining a GET Route

use actix_web::{web, App, HttpServer, Responder};

// A handler function that returns a simple string response
async fn hello_world() -> impl Responder {
    "Hello, Actix-web!"
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    println!("Server running at http://127.0.0.1:8080");
    HttpServer::new(|| {
        App::new()
            // Register our route: GET /hello maps to hello_world()
            .route("/hello", web::get().to(hello_world))
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}

Path Parameters for Dynamic Routes

use actix_web::{web, App, HttpServer, Responder};

// Handler function with a path parameter 'name'
async fn greet_name(name: web::Path<String>) -> impl Responder {
    format!("Hello, {}!", name.into_inner())
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    println!("Server running at http://127.0.0.1:8080");
    HttpServer::new(|| {
        App::new()
            // Route with a dynamic path segment for a name
            .route("/greet/{name}", web::get().to(greet_name))
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}

Handling POST Requests & JSON

use actix_web::{web, App, HttpServer, Responder};
use serde::{Deserialize, Serialize};

// Define a struct to represent our incoming JSON data
#[derive(Deserialize, Serialize)]
struct User {
    username: String,
    email: String,
}

// Handler for POST requests that accepts a JSON User object
async fn create_user(user: web::Json<User>) -> impl Responder {
    // In a real app, you'd save this user to a database
    format!("User created: {} ({})", user.username, user.email)
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    println!("Server running at http://127.0.0.1:8080");
    HttpServer::new(|| {
        App::new()
            // POST /users expects a JSON body and maps to create_user()
            .route("/users", web::post().to(create_user))
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}

Building a Simple API with State

use actix_web::{web, App, HttpServer, Responder, HttpResponse};
use serde::{Deserialize, Serialize};
use std::sync::Mutex; // For shared mutable state

// Define a User struct that can be serialized/deserialized and cloned
#[derive(Deserialize, Serialize, Clone)]
struct User {
    id: u32,
    username: String,
    email: String,
}

// Application state to hold our users and track next ID
struct AppState {
    users: Mutex<Vec<User>>,
    next_id: Mutex<u32>,
}

// Handler to get all users
async fn get_users(data: web::Data<AppState>) -> impl Responder {
    let users = data.users.lock().unwrap(); // Acquire a lock
    web::Json(users.clone()) // Return users as JSON
}

// Handler to create a new user
async fn create_user(
    data: web::Data<AppState>,
    new_user: web::Json<User>,
) -> impl Responder {
    let mut users = data.users.lock().unwrap();
    let mut next_id = data.next_id.lock().unwrap();

    let user = User {
        id: *next_id,
        username: new_user.username.clone(),
        email: new_user.email.clone(),
    };
    users.push(user.clone());
    *next_id += 1; // Increment for the next user
    HttpResponse::Created().json(user) // Return 201 Created status and user
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    println!("Server running at http://127.0.0.1:8080");
    // Create shared application state
    let app_state = web::Data::new(AppState {
        users: Mutex::new(vec![]), // Initialize with an empty user list
        next_id: Mutex::new(1),    // Start IDs from 1
    });

    HttpServer::new(move || { // 'move' closure to capture app_state
        App::new()
            .app_data(app_state.clone()) // Register shared state with the app
            .route("/users", web::get().to(get_users))
            .route("/users", web::post().to(create_user))
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}

API Concepts Quick Check

Recap & Next Steps