// <ext>
use actix_web::{get, App, HttpRequest, HttpServer, Responder};

#[get("/")]
async fn index(req: HttpRequest) -> impl Responder {
    let url = req.url_for("youtube", ["oHg5SJYRHA0"]).unwrap();
    assert_eq!(url.as_str(), "https://youtube.com/watch/oHg5SJYRHA0");

    url.to_string()
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| {
        App::new()
            .service(index)
            .external_resource("youtube", "https://youtube.com/watch/{video_id}")
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}
// </ext>