actix

Actix Web

Actix Web is one of the fastest web frameworks in the world (TechEmpower benchmarks). It uses the Actor Model (though less visible in v4) for concurrency.

When to Use

• Ultra-High Throughput Rust Microservices: Systems demanding sub-millisecond response times and millions of requests per second.
• Actor-Based Asynchronous Workloads: Applications utilizing the Actix actor model alongside HTTP routing.
• Low-Latency WebSockets & Streaming: Real-time telemetry, chat engines, and financial quote tickers.
• Resource-Constrained Edge Services: Zero-cost abstraction web services requiring minimal resident memory.

Quick Start

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

#[derive(Serialize, Deserialize)]
struct User {
    id: u32,
    name: String,
}

#[get("/api/users/{id}")]
async fn get_user(path: web::Path<u32>) -> impl Responder {
    let user_id = path.into_inner();
    HttpResponse::Ok().json(User { id: user_id, name: "Alice".into() })
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| App::new().service(get_user))
        .bind(("127.0.0.1", 8080))?
        .run()
        .await
}

Core Concepts

Application State & Scoped Handlers

Thread-safe shared mutable and immutable state injected via extractors:

use actix_web::{web, App, HttpResponse, HttpServer, Responder};
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;

struct AppState {
    request_counter: Arc<AtomicUsize>,
    app_version: &'static str,
}

async fn metrics_handler(data: web::Data<AppState>) -> impl Responder {
    let count = data.request_counter.fetch_add(1, Ordering::SeqCst);
    HttpResponse::Ok().json(serde_json::json!({
        "version": data.app_version,
        "total_requests": count + 1
    }))
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    let state = web::Data::new(AppState {
        request_counter: Arc::new(AtomicUsize::new(0)),
        app_version: "2026.1.0",
    });

    HttpServer::new(move || {
        App::new()
            .app_data(state.clone())
            .route("/metrics", web::get().to(metrics_handler))
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}