axum

Axum (Rust) - Production Web APIs

Overview

Axum is a Rust web framework built on Hyper and Tower. Use it for type-safe request handling with composable middleware, structured errors, and excellent testability.

Quick Start

Minimal server

✅ Correct: typed handler + JSON response

use axum::{routing::get, Json, Router};
use serde::Serialize;
use std::net::SocketAddr;

#[derive(Serialize)]
struct Health {
    status: &'static str,
}

async fn health() -> Json<Health> {
    Json(Health { status: "ok" })
}

#[tokio::main]
async fn main() {
    let app = Router::new().route("/health", get(health));

    let addr: SocketAddr = "0.0.0.0:3000".parse().unwrap();
    let listener = tokio::net::TcpListener::bind(addr).await.unwrap();
    axum::serve(listener, app).await.unwrap();
}

❌ Wrong: block the async runtime

async fn handler() {
    std::thread::sleep(std::time::Duration::from_secs(1)); // blocks executor
}

Core Concepts

Router + handlers

Handlers are async functions that return something implementing IntoResponse.

✅ Correct: route nesting

use axum::{routing::get, Router};

fn router() -> Router {
    let api = Router::new()
        .route("/users", get(list_users))
        .route("/users/:id", get(get_user));

    Router::new().nest("/api/v1", api)
}

async fn list_users() -> &'static str { "[]" }
async fn get_user() -> &'static str { "{}" }

Extractors

Prefer extractors for parsing and validation at the boundary:

• Path<T>: typed path params
• Query<T>: query strings
• Json<T>: JSON bodies
• State<T>: shared application state

✅ Correct: typed path + JSON

use axum::{extract::Path, Json};
use serde::{Deserialize, Serialize};

#[derive(Deserialize)]
struct CreateUser {
    email: String,
}

#[derive(Serialize)]
struct User {
    id: String,
    email: String,
}

async fn create_user(Json(body): Json<CreateUser>) -> Json<User> {
    Json(User { id: "1".into(), email: body.email })
}

async fn get_user(Path(id): Path<String>) -> Json<User> {
    Json(User { id, email: "[email protected]".into() })
}