Method Not Allowed Fallback - Axum

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 [MethodRouter]s, to be called when no matching method handler is set.

rust,no_run

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;
}

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.