Struct Router

struct Router<S = ()> { ... }

The router type for composing handlers and services.

Router<S> means a router that is missing a state of type S to be able to handle requests. Thus, only Router<()> (i.e. without missing state) can be passed to serve. See Router::with_state for more details.

Implementations

impl Router

fn into_make_service(self: Self) -> IntoMakeService<Self>

Convert this router into a MakeService, that is a Service whose response is another service.

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

let app = Router::new().route("/", get(|| async { "Hi!" }));

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app).await.unwrap();
# };

fn into_make_service_with_connect_info<C>(self: Self) -> IntoMakeServiceWithConnectInfo<Self, C>

Convert this router into a MakeService, that will store C's associated ConnectInfo in a request extension such that ConnectInfo can extract it.

This enables extracting things like the client's remote address.

Extracting std::net::SocketAddr is supported out of the box:

use axum::{
    extract::ConnectInfo,
    routing::get,
    Router,
};
use std::net::SocketAddr;

let app = Router::new().route("/", get(handler));

async fn handler(ConnectInfo(addr): ConnectInfo<SocketAddr>) -> String {
    format!("Hello {addr}")
}

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app.into_make_service_with_connect_info::<SocketAddr>()).await.unwrap();
# };

You can implement custom a Connected like so:

use axum::{
    extract::connect_info::{ConnectInfo, Connected},
    routing::get,
    serve::IncomingStream,
    Router,
};
use tokio::net::TcpListener;

let app = Router::new().route("/", get(handler));

async fn handler(
    ConnectInfo(my_connect_info): ConnectInfo<MyConnectInfo>,
) -> String {
    format!("Hello {my_connect_info:?}")
}

#[derive(Clone, Debug)]
struct MyConnectInfo {
    // ...
}

impl Connected<IncomingStream<'_, TcpListener>> for MyConnectInfo {
    fn connect_info(target: IncomingStream<'_, TcpListener>) -> Self {
        MyConnectInfo {
            // ...
        }
    }
}

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app.into_make_service_with_connect_info::<MyConnectInfo>()).await.unwrap();
# };

See the unix domain socket example for an example of how to use this to collect UDS connection info.

impl<S> Router<S>

fn new() -> Self

Create a new Router.

Unless you add additional routes this will respond with 404 Not Found to all requests.

fn without_v07_checks(self: Self) -> Self

Turn off checks for compatibility with route matching syntax from 0.7.

This allows usage of paths starting with a colon : or an asterisk * which are otherwise prohibited.

Example

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

let app = Router::<()>::new()
    .without_v07_checks()
    .route("/:colon", get(|| async {}))
    .route("/*asterisk", get(|| async {}));

// Our app now accepts
// - GET /:colon
// - GET /*asterisk
# let _: Router = app;

Adding such routes without calling this method first will panic.

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

// This panics...
let app = Router::<()>::new()
    .route("/:colon", get(|| async {}));

Merging

When two routers are merged, v0.7 checks are disabled for route registrations on the resulting router if both of the two routers had them also disabled.

Nesting

Each router needs to have the checks explicitly disabled. Nesting a router with the checks either enabled or disabled has no effect on the outer router.

fn route(self: Self, path: &str, method_router: MethodRouter<S>) -> Self

Add another route to the router.

path is a string of path segments separated by /. Each segment can be either static, a capture, or a wildcard.

method_router is the MethodRouter that should receive the request if the path matches path. Usually, method_router will be a handler wrapped in a method router like get. See handler for more details on handlers.

Static paths

Examples:

  • /
  • /foo
  • /users/123

If the incoming request matches the path exactly the corresponding service will be called.

Captures

Paths can contain segments like /{key} which matches any single segment and will store the value captured at key. The value captured can be zero-length except for in the invalid path //.

Examples:

  • /{key}
  • /users/{id}
  • /users/{id}/tweets

Captures can be extracted using Path. See its documentation for more details.

It is not possible to create segments that only match some types like numbers or regular expression. You must handle that manually in your handlers.

MatchedPath can be used to extract the matched path rather than the actual path.

Wildcards

Paths can end in /{*key} which matches all segments and will store the segments captured at key.

Examples:

  • /{*key}
  • /assets/{*path}
  • /{id}/{repo}/{*tree}

Note that /{*key} doesn't match empty segments. Thus:

  • /{*key} doesn't match / but does match /a, /a/, etc.
  • /x/{*key} doesn't match /x or /x/ but does match /x/a, /x/a/, etc.

Wildcard captures can also be extracted using Path:

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

let app: Router = Router::new().route("/{*key}", get(handler));

async fn handler(Path(path): Path<String>) -> String {
    path
}

Note that the leading slash is not included, i.e. for the route /foo/{*rest} and the path /foo/bar/baz the value of rest will be bar/baz.

Accepting multiple methods

To accept multiple methods for the same route you can add all handlers at the same time:

use axum::{Router, routing::{get, delete}, extract::Path};

let app = Router::new().route(
    "/",
    get(get_root).post(post_root).delete(delete_root),
);

async fn get_root() {}

async fn post_root() {}

async fn delete_root() {}
# let _: Router = app;

Or you can add them one by one:

# use axum::Router;
# use axum::routing::{get, post, delete};
#
let app = Router::new()
    .route("/", get(get_root))
    .route("/", post(post_root))
    .route("/", delete(delete_root));
#
# let _: Router = app;
# async fn get_root() {}
# async fn post_root() {}
# async fn delete_root() {}

More examples

use axum::{Router, routing::{get, delete}, extract::Path};

let app = Router::new()
    .route("/", get(root))
    .route("/users", get(list_users).post(create_user))
    .route("/users/{id}", get(show_user))
    .route("/api/{version}/users/{id}/action", delete(do_users_action))
    .route("/assets/{*path}", get(serve_asset));

async fn root() {}

async fn list_users() {}

async fn create_user() {}

async fn show_user(Path(id): Path<u64>) {}

async fn do_users_action(Path((version, id)): Path<(String, u64)>) {}

async fn serve_asset(Path(path): Path<String>) {}
# let _: Router = app;

Panics

Panics if the route overlaps with another route:

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

let app = Router::new()
    .route("/", get(|| async {}))
    .route("/", get(|| async {}));
# let _: Router = app;

The static route /foo and the dynamic route /{key} are not considered to overlap and /foo will take precedence.

Also panics if path is empty.

fn route_service<T>(self: Self, path: &str, service: T) -> Self
where
    T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
    <T as >::Response: IntoResponse,
    <T as >::Future: Send + 'static

Add another route to the router that calls a Service.

Example

use axum::{
    Router,
    body::Body,
    routing::{any_service, get_service},
    extract::Request,
    http::StatusCode,
    error_handling::HandleErrorLayer,
};
use tower_http::services::ServeFile;
use http::Response;
use std::{convert::Infallible, io};
use tower::service_fn;

let app = Router::new()
    .route(
        // Any request to `/` goes to a service
        "/",
        // Services whose response body is not `axum::body::BoxBody`
        // can be wrapped in `axum::routing::any_service` (or one of the other routing filters)
        // to have the response body mapped
        any_service(service_fn(|_: Request| async {
            let res = Response::new(Body::from("Hi from `GET /`"));
            Ok::<_, Infallible>(res)
        }))
    )
    .route_service(
        "/foo",
        // This service's response body is `axum::body::BoxBody` so
        // it can be routed to directly.
        service_fn(|req: Request| async move {
            let body = Body::from(format!("Hi from `{} /foo`", req.method()));
            let res = Response::new(body);
            Ok::<_, Infallible>(res)
        })
    )
    .route_service(
        // GET `/static/Cargo.toml` goes to a service from tower-http
        "/static/Cargo.toml",
        ServeFile::new("Cargo.toml"),
    );
# let _: Router = app;

Routing to arbitrary services in this way has complications for backpressure (Service::poll_ready). See the Routing to services and backpressure module for more details.

Panics

Panics for the same reasons as Router::route or if you attempt to route to a Router:

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

let app = Router::new().route_service(
    "/",
    Router::new().route("/foo", get(|| async {})),
);
# let _: Router = app;

Use Router::nest instead.

fn nest(self: Self, path: &str, router: Router<S>) -> Self

Nest a Router 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
# let _: Router = app;

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);
# let _: Router = app;

Differences from 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);
# let _: Router = app;

Additionally, while the wildcard route /foo/*rest will not match the paths /foo or /foo/, a nested router at /foo will match the path /foo (but not /foo/), and a nested router at /foo/ will match the path /foo/ (but not /foo).

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.

Nesting routers with state

When combining Routers with this method, each Router must have the same type of state. If your routers have different types you can use Router::with_state to provide the state and make the types match:

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

#[derive(Clone)]
struct InnerState {}

#[derive(Clone)]
struct OuterState {}

async fn inner_handler(state: State<InnerState>) {}

let inner_router = Router::new()
    .route("/bar", get(inner_handler))
    .with_state(InnerState {});

async fn outer_handler(state: State<OuterState>) {}

let app = Router::new()
    .route("/", get(outer_handler))
    .nest("/foo", inner_router)
    .with_state(OuterState {});
# let _: axum::Router = app;

Note that the inner router will still inherit the fallback from the outer router.

Panics

  • If the route overlaps with another route. See Router::route for more details.
  • If the route contains a wildcard (*).
  • If path is empty.
fn nest_service<T>(self: Self, path: &str, service: T) -> Self
where
    T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
    <T as >::Response: IntoResponse,
    <T as >::Future: Send + 'static

Like nest, but accepts an arbitrary Service.

fn merge<R>(self: Self, other: R) -> Self
where
    R: Into<Router<S>>

Merge the paths and fallbacks of two routers into a single Router.

This is useful for breaking apps into smaller pieces and combining them into one.

use axum::{
    routing::get,
    Router,
};
#
# async fn users_list() {}
# async fn users_show() {}
# async fn teams_list() {}

// define some routes separately
let user_routes = Router::new()
    .route("/users", get(users_list))
    .route("/users/{id}", get(users_show));

let team_routes = Router::new()
    .route("/teams", get(teams_list));

// combine them into one
let app = Router::new()
    .merge(user_routes)
    .merge(team_routes);

// could also do `user_routes.merge(team_routes)`

// Our app now accepts
// - GET /users
// - GET /users/{id}
// - GET /teams
# let _: Router = app;

Merging routers with state

When combining Routers with this method, each Router must have the same type of state. If your routers have different types you can use Router::with_state to provide the state and make the types match:

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

#[derive(Clone)]
struct InnerState {}

#[derive(Clone)]
struct OuterState {}

async fn inner_handler(state: State<InnerState>) {}

let inner_router = Router::new()
    .route("/bar", get(inner_handler))
    .with_state(InnerState {});

async fn outer_handler(state: State<OuterState>) {}

let app = Router::new()
    .route("/", get(outer_handler))
    .merge(inner_router)
    .with_state(OuterState {});
# let _: axum::Router = app;

Merging routers with fallbacks

When combining Routers with this method, the fallback is also merged. However only one of the routers can have a fallback.

Panics

  • If two routers that each have a fallback are merged. This is because Router only allows a single fallback.
fn layer<L>(self: Self, layer: L) -> Router<S>
where
    L: Layer<Route> + Clone + Send + Sync + 'static,
    <L as >::Service: Service<Request> + Clone + Send + Sync + 'static,
    <<L as >::Service as Service<Request>>::Response: IntoResponse + 'static,
    <<L as >::Service as Service<Request>>::Error: Into<Infallible> + 'static,
    <<L as >::Service as Service<Request>>::Future: Send + 'static

Apply a tower::Layer to all routes in the router.

This can be used to add additional processing to a request for a group of routes.

Note that the middleware is only applied to existing routes. So you have to first add your routes (and / or fallback) and then call layer afterwards. Additional routes added after layer is called will not have the middleware added.

If you want to add middleware to a single handler you can either use MethodRouter::layer or Handler::layer.

Example

Adding the [tower_http::trace::TraceLayer]:

use axum::{routing::get, Router};
use tower_http::trace::TraceLayer;

let app = Router::new()
    .route("/foo", get(|| async {}))
    .route("/bar", get(|| async {}))
    .layer(TraceLayer::new_for_http());
# let _: Router = app;

If you need to write your own middleware see "Writing middleware" for the different options.

If you only want middleware on some routes you can use [Router::merge]:

use axum::{routing::get, Router};
use tower_http::{trace::TraceLayer, compression::CompressionLayer};

let with_tracing = Router::new()
    .route("/foo", get(|| async {}))
    .layer(TraceLayer::new_for_http());

let with_compression = Router::new()
    .route("/bar", get(|| async {}))
    .layer(CompressionLayer::new());

// Merge everything into one `Router`
let app = Router::new()
    .merge(with_tracing)
    .merge(with_compression);
# let _: Router = app;

Multiple middleware

It's recommended to use tower::ServiceBuilder when applying multiple middleware. See middleware for more details.

Runs after routing

Middleware added with this method will run after routing and thus cannot be used to rewrite the request URI. See "Rewriting request URI in middleware" for more details and a workaround.

Error handling

See middleware for details on how error handling impacts middleware.

fn route_layer<L>(self: Self, layer: L) -> Self
where
    L: Layer<Route> + Clone + Send + Sync + 'static,
    <L as >::Service: Service<Request> + Clone + Send + Sync + 'static,
    <<L as >::Service as Service<Request>>::Response: IntoResponse + 'static,
    <<L as >::Service as Service<Request>>::Error: Into<Infallible> + 'static,
    <<L as >::Service as Service<Request>>::Future: Send + 'static

Apply a tower::Layer to the router that will only run if the request matches a route.

Note that the middleware is only applied to existing routes. So you have to first add your routes (and / or fallback) and then call route_layer afterwards. Additional routes added after route_layer is called will not have the middleware added.

This works similarly to Router::layer except the middleware will only run if the request matches a route. This is useful for middleware that return early (such as authorization) which might otherwise convert a 404 Not Found into a 401 Unauthorized.

This function will panic if no routes have been declared yet on the router, since the new layer will have no effect, and this is typically a bug. In generic code, you can test if that is the case first, by calling Router::has_routes.

Example

use axum::{
    routing::get,
    Router,
};
use tower_http::validate_request::ValidateRequestHeaderLayer;

let app = Router::new()
    .route("/foo", get(|| async {}))
    .route_layer(ValidateRequestHeaderLayer::bearer("password"));

// `GET /foo` with a valid token will receive `200 OK`
// `GET /foo` with a invalid token will receive `401 Unauthorized`
// `GET /not-found` with a invalid token will receive `404 Not Found`
# let _: Router = app;

fn has_routes(self: &Self) -> bool

True if the router currently has at least one route added.

fn fallback<H, T>(self: Self, handler: H) -> Self
where
    H: Handler<T, S>,
    T: 'static

Add a fallback Handler to the router.

This service will be called if no routes matches the incoming request.

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

let app = Router::new()
    .route("/foo", get(|| async { /* ... */ }))
    .fallback(fallback);

async fn fallback(uri: Uri) -> (StatusCode, String) {
    (StatusCode::NOT_FOUND, format!("No route for {uri}"))
}
# let _: Router = app;

Fallbacks only apply to routes that aren't matched by anything in the router. If a handler is matched by a request but returns 404 the fallback is not called. Note that this applies to MethodRouters too: if the request hits a valid path but the MethodRouter does not have an appropriate method handler installed, the fallback is not called (use MethodRouter::fallback for this purpose instead).

Handling all requests without other routes

Using Router::new().fallback(...) to accept all request regardless of path or method, if you don't have other routes, isn't optimal:

use axum::Router;

async fn handler() {}

let app = Router::new().fallback(handler);

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app).await.unwrap();
# };

Running the handler directly is faster since it avoids the overhead of routing:

use axum::handler::HandlerWithoutStateExt;

async fn handler() {}

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, handler.into_make_service()).await.unwrap();
# };

fn fallback_service<T>(self: Self, service: T) -> Self
where
    T: Service<Request, Error = Infallible> + Clone + Send + Sync + 'static,
    <T as >::Response: IntoResponse,
    <T as >::Future: Send + 'static

Add a fallback Service to the router.

See Router::fallback for more details.

fn method_not_allowed_fallback<H, T>(self: Self, handler: H) -> Self
where
    H: Handler<T, S>,
    T: 'static

Add a fallback Handler for the case where a route exists, but the method of the request is not supported.

Sets a fallback on all previously registered MethodRouters, to be called when no matching method handler is set.

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

async fn hello_world() -> impl IntoResponse {
    "Hello, world!\n"
}

async fn default_fallback() -> impl IntoResponse {
    "Default fallback\n"
}

async fn handle_405() -> impl IntoResponse {
    "Method not allowed fallback"
}

#[tokio::main]
async fn main() {
    let router = Router::new()
        .route("/", get(hello_world))
        .fallback(default_fallback)
        .method_not_allowed_fallback(handle_405);

    let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();

    axum::serve(listener, router).await.unwrap();
}

The fallback only applies if there is a MethodRouter registered for a given path, but the method used in the request is not specified. In the example, a GET on http://localhost:3000 causes the hello_world handler to react, while issuing a POST triggers handle_405. Calling an entirely different route, like http://localhost:3000/hello causes default_fallback to run.

fn reset_fallback(self: Self) -> Self

Reset the fallback to its default.

Useful to merge two routers with fallbacks, as merge doesn't allow both routers to have an explicit fallback. Use this method to remove the one you want to discard before merging.

fn with_state<S2>(self: Self, state: S) -> Router<S2>

Provide the state for the router. State passed to this method is global and will be used for all requests this router receives. That means it is not suitable for holding state derived from a request, such as authorization data extracted in a middleware. Use Extension instead for such data.

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

#[derive(Clone)]
struct AppState {}

let routes = Router::new()
    .route("/", get(|State(state): State<AppState>| async {
        // use state
    }))
    .with_state(AppState {});

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, routes).await.unwrap();
# };

Returning routers with states from functions

When returning Routers from functions, it is generally recommended not to set the state directly:

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

#[derive(Clone)]
struct AppState {}

// Don't call `Router::with_state` here
fn routes() -> Router<AppState> {
    Router::new()
        .route("/", get(|_: State<AppState>| async {}))
}

// Instead do it before you run the server
let routes = routes().with_state(AppState {});

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, routes).await.unwrap();
# };

If you do need to provide the state, and you're not nesting/merging the router into another router, then return Router without any type parameters:

# use axum::{Router, routing::get, extract::State};
# #[derive(Clone)]
# struct AppState {}
#
// Don't return `Router<AppState>`
fn routes(state: AppState) -> Router {
    Router::new()
        .route("/", get(|_: State<AppState>| async {}))
        .with_state(state)
}

let routes = routes(AppState {});

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, routes).await.unwrap();
# };

This is because we can only call Router::into_make_service on Router<()>, not Router<AppState>. See below for more details about why that is.

Note that the state defaults to () so Router and Router<()> is the same.

If you are nesting/merging the router it is recommended to use a generic state type on the resulting router:

# use axum::{Router, routing::get, extract::State};
# #[derive(Clone)]
# struct AppState {}
#
fn routes<S>(state: AppState) -> Router<S> {
    Router::new()
        .route("/", get(|_: State<AppState>| async {}))
        .with_state(state)
}

let routes = Router::new().nest("/api", routes(AppState {}));

# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, routes).await.unwrap();
# };

What S in Router<S> means

Router<S> means a router that is missing a state of type S to be able to handle requests. It does not mean a Router that has a state of type S.

For example:

# use axum::{Router, routing::get, extract::State};
# #[derive(Clone)]
# struct AppState {}
# 
// A router that _needs_ an `AppState` to handle requests
let router: Router<AppState> = Router::new()
    .route("/", get(|_: State<AppState>| async {}));

// Once we call `Router::with_state` the router isn't missing
// the state anymore, because we just provided it
//
// Therefore the router type becomes `Router<()>`, i.e a router
// that is not missing any state
let router: Router<()> = router.with_state(AppState {});

// Only `Router<()>` has the `into_make_service` method.
//
// You cannot call `into_make_service` on a `Router<AppState>`
// because it is still missing an `AppState`.
# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, router).await.unwrap();
# };

Perhaps a little counter intuitively, Router::with_state doesn't always return a Router<()>. Instead you get to pick what the new missing state type is:

# use axum::{Router, routing::get, extract::State};
# #[derive(Clone)]
# struct AppState {}
# 
let router: Router<AppState> = Router::new()
    .route("/", get(|_: State<AppState>| async {}));

// When we call `with_state` we're able to pick what the next missing state type is.
// Here we pick `String`.
let string_router: Router<String> = router.with_state(AppState {});

// That allows us to add new routes that uses `String` as the state type
let string_router = string_router
    .route("/needs-string", get(|_: State<String>| async {}));

// Provide the `String` and choose `()` as the new missing state.
let final_router: Router<()> = string_router.with_state("foo".to_owned());

// Since we have a `Router<()>` we can run it.
# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, final_router).await.unwrap();
# };

This why this returning Router<AppState> after calling with_state doesn't work:

# use axum::{Router, routing::get, extract::State};
# #[derive(Clone)]
# struct AppState {}
# 
// This won't work because we're returning a `Router<AppState>`
// i.e. we're saying we're still missing an `AppState`
fn routes(state: AppState) -> Router<AppState> {
    Router::new()
        .route("/", get(|_: State<AppState>| async {}))
        .with_state(state)
}

let app = routes(AppState {});

// We can only call `Router::into_make_service` on a `Router<()>`
// but `app` is a `Router<AppState>`
# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app).await.unwrap();
# };

Instead return Router<()> since we have provided all the state needed:

# use axum::{Router, routing::get, extract::State};
# #[derive(Clone)]
# struct AppState {}
# 
// We've provided all the state necessary so return `Router<()>`
fn routes(state: AppState) -> Router<()> {
    Router::new()
        .route("/", get(|_: State<AppState>| async {}))
        .with_state(state)
}

let app = routes(AppState {});

// We can now call `Router::into_make_service`
# async {
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app).await.unwrap();
# };

A note about performance

If you need a Router that implements Service but you don't need any state (perhaps you're making a library that uses axum internally) then it is recommended to call this method before you start serving requests:

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

let app = Router::new()
    .route("/", get(|| async { /* ... */ }))
    // even though we don't need any state, call `with_state(())` anyway
    .with_state(());
# let _: Router = app;

This is not required but it gives axum a chance to update some internals in the router which may impact performance and reduce allocations.

Note that Router::into_make_service and Router::into_make_service_with_connect_info do this automatically.

fn as_service<B>(self: &mut Self) -> RouterAsService<'_, B, S>

Convert the router into a borrowed Service with a fixed request body type, to aid type inference.

In some cases when calling methods from tower::ServiceExt on a Router you might get type inference errors along the lines of

let response = router.ready().await?.call(request).await?;
                      ^^^^^ cannot infer type for type parameter `B`

This happens because Router implements Service with impl<B> Service<Request<B>> for Router<()>.

For example:

use axum::{
    Router,
    routing::get,
    http::Request,
    body::Body,
};
use tower::{Service, ServiceExt};

# async fn async_main() -> Result<(), Box<dyn std::error::Error>> {
let mut router = Router::new().route("/", get(|| async {}));
let request = Request::new(Body::empty());
let response = router.ready().await?.call(request).await?;
# Ok(())
# }

Calling Router::as_service fixes that:

use axum::{
    Router,
    routing::get,
    http::Request,
    body::Body,
};
use tower::{Service, ServiceExt};

# async fn async_main() -> Result<(), Box<dyn std::error::Error>> {
let mut router = Router::new().route("/", get(|| async {}));
let request = Request::new(Body::empty());
let response = router.as_service().ready().await?.call(request).await?;
# Ok(())
# }

This is mainly used when calling Router in tests. It shouldn't be necessary when running the Router normally via Router::into_make_service.

fn into_service<B>(self: Self) -> RouterIntoService<B, S>

Convert the router into an owned Service with a fixed request body type, to aid type inference.

This is the same as Router::as_service instead it returns an owned Service. See that method for more details.

impl<B> Service for Router<()>

fn poll_ready(self: &mut Self, _: &mut Context<'_>) -> Poll<Result<(), <Self as >::Error>>
fn call(self: &mut Self, req: Request<B>) -> <Self as >::Future

impl<L> Service for Router<()>

fn poll_ready(self: &mut Self, _cx: &mut Context<'_>) -> Poll<Result<(), <Self as >::Error>>
fn call(self: &mut Self, _req: serve::IncomingStream<'_, L>) -> <Self as >::Future

impl<M, S, Target, Request> MakeService for Router<S>

fn poll_ready(self: &mut Self, cx: &mut Context<'_>) -> Poll<Result<(), <M as MakeService<Target, Request>>::MakeError>>
fn make_service(self: &mut Self, target: Target) -> <M as MakeService<Target, Request>>::Future

impl<S = ()> RefUnwindSafe for Router<S>

impl<S = ()> UnwindSafe for Router<S>

impl<S> Clone for Router<S>

fn clone(self: &Self) -> Self

impl<S> Debug for Router<S>

fn fmt(self: &Self, f: &mut fmt::Formatter<'_>) -> fmt::Result

impl<S> Default for Router<S>

fn default() -> Self

impl<S> Freeze for Router<S>

impl<S> Send for Router<S>

impl<S> Sync for Router<S>

impl<S> Unpin for Router<S>

impl<S, R> ServiceExt for Router<S>

fn into_make_service(self: Self) -> IntoMakeService<S>
fn into_make_service_with_connect_info<C>(self: Self) -> IntoMakeServiceWithConnectInfo<S, C>

impl<T> Any for Router<S>

fn type_id(self: &Self) -> TypeId

impl<T> Borrow for Router<S>

fn borrow(self: &Self) -> &T

impl<T> BorrowMut for Router<S>

fn borrow_mut(self: &mut Self) -> &mut T

impl<T> CloneToUninit for Router<S>

unsafe fn clone_to_uninit(self: &Self, dest: *mut u8)

impl<T> From for Router<S>

fn from(t: T) -> T

Returns the argument unchanged.

impl<T> FromRef for Router<S>

fn from_ref(input: &T) -> T

impl<T> Instrument for Router<S>

impl<T> Same for Router<S>

impl<T> ToOwned for Router<S>

fn to_owned(self: &Self) -> T
fn clone_into(self: &Self, target: &mut T)

impl<T> WithSubscriber for Router<S>

impl<T, Request> ServiceExt for Router<S>

impl<T, U> Into for Router<S>

fn into(self: Self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

impl<T, U> TryFrom for Router<S>

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto for Router<S>

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>

impl<V, T> VZip for Router<S>

fn vzip(self: Self) -> V