axum — Hello World HTTP Server

// Cargo.toml:
// axum  = "0.7"
// tokio = { version = "1", features = ["full"] }

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

#[derive(Serialize)]
struct Greeting { message: String }

async fn root() -> &'static str { "Hello, world!" }

async fn greet() -> Json<Greeting> {
    Json(Greeting { message: "Hello from JSON".into() })
}

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

    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    let listener = tokio::net::TcpListener::bind(addr).await.unwrap();
    println!("Listening on http://{addr}");
    axum::serve(listener, app).await.unwrap();
}