Actix Web: Routes, Extractors & Shared State

Actix Web is a fast, popular web framework for building HTTP APIs in Rust, frequently near the top of cross-language performance benchmarks -- a combination of Rust's compile-time optimizations, async I/O, and a lean implementation.

Defining Routes

#[get("/users/{id}")]
async fn get_user(path: web::Path<u32>, pool: web::Data<PgPool>) -> impl Responder {
    let id = path.into_inner();
    let user = fetch_user(&pool, id).await;
    HttpResponse::Ok().json(user)
}

Extractors

#[post("/users")]
async fn create_user(body: web::Json<CreateUserInput>) -> impl Responder {
    // body is already parsed and typed -- Actix returns an
    // error response automatically if JSON parsing fails
    HttpResponse::Created().json(body.into_inner())
}

Shared Application State

HttpServer::new(move || {
    App::new()
        .app_data(web::Data::new(pool.clone()))
        .service(get_user)
        .service(create_user)
})
.bind("127.0.0.1:8080")?
.run()
.await

Why Async Matters Here

A handler awaiting I/O (a database query) yields control rather than blocking a whole OS thread, letting Actix Web handle many concurrent connections with a relatively small thread pool -- a key factor in its throughput.