nest.md

Nest a [Service] at some path.

This allows you to break your application into smaller pieces and compose them together.

Example

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

let user_routes = Router::new().route("/:id", get(|| async {}));

let team_routes = Router::new().route("/", post(|| async {}));

let api_routes = Router::new()
    .nest("/users", user_routes)
    .nest("/teams", team_routes);

let app = Router::new().nest("/api", api_routes);

// Our app now accepts
// - GET /api/users/:id
// - POST /api/teams
# async {
# axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
# };

How the URI changes

Note that nested routes will not see the original request URI but instead have the matched prefix stripped. This is necessary for services like static file serving to work. Use OriginalUri if you need the original request URI.

Captures from outer routes

Take care when using nest together with dynamic routes as nesting also captures from the outer routes:

use axum::{
    extract::Path,
    routing::get,
    Router,
};
use std::collections::HashMap;

async fn users_get(Path(params): Path<HashMap<String, String>>) {
    // Both `version` and `id` were captured even though `users_api` only
    // explicitly captures `id`.
    let version = params.get("version");
    let id = params.get("id");
}

let users_api = Router::new().route("/users/:id", get(users_get));

let app = Router::new().nest("/:version/api", users_api);
# async {
# axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
# };

Differences to wildcard routes

Nested routes are similar to wildcard routes. The difference is that wildcard routes still see the whole URI whereas nested routes will have the prefix stripped:

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

let nested_router = Router::new()
    .route("/", get(|uri: Uri| async {
        // `uri` will _not_ contain `/bar`
    }));

let app = Router::new()
    .route("/foo/*rest", get(|uri: Uri| async {
        // `uri` will contain `/foo`
    }))
    .nest("/bar", nested_router);
# async {
# axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
# };

Fallbacks

If a nested router doesn't have its own fallback then it will inherit the fallback from the outer router:

use axum::{routing::get, http::StatusCode, handler::Handler, Router};

async fn fallback() -> (StatusCode, &'static str) {
    (StatusCode::NOT_FOUND, "Not Found")
}

let api_routes = Router::new().route("/users", get(|| async {}));

let app = Router::new()
    .nest("/api", api_routes)
    .fallback(fallback);
# let _: Router = app;

Here requests like GET /api/not-found will go into api_routes but because it doesn't have a matching route and doesn't have its own fallback it will call the fallback from the outer router, i.e. the fallback function.

If the nested router has its own fallback then the outer fallback will not be inherited:

use axum::{
    routing::get,
    http::StatusCode,
    handler::Handler,
    Json,
    Router,
};

async fn fallback() -> (StatusCode, &'static str) {
    (StatusCode::NOT_FOUND, "Not Found")
}

async fn api_fallback() -> (StatusCode, Json<serde_json::Value>) {
    (
        StatusCode::NOT_FOUND,
        Json(serde_json::json!({ "status": "Not Found" })),
    )
}

let api_routes = Router::new()
    .route("/users", get(|| async {}))
    .fallback(api_fallback);

let app = Router::new()
    .nest("/api", api_routes)
    .fallback(fallback);
# let _: Router = app;

Here requests like GET /api/not-found will go to api_fallback.

Panics

• If the route overlaps with another route. See [Router::route] for more details.
• If the route contains a wildcard (*).
• If path is empty.