Custom 404 page

By default axum will return an empty page when the user accesses a path that is not handled by any of the routes.

We can add a special handler to be called by axum if no route was match. That function can create any response.

[package]
name = "custom-404-page"
version = "0.1.0"
edition = "2024"
publish = false

[dependencies]
axum = "0.8.8"
tokio = { version = "1.50.0", features = ["full"] }

[dev-dependencies]
headers = "0.4.1"
http-body-util = "0.1.3"
tower = { version = "0.5.3", features = ["util"] }

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

async fn main_page() -> Html<&'static str> {
    Html("<h1>Hello, World!</h1>")
}

async fn handler_404() -> impl IntoResponse {
    (StatusCode::NOT_FOUND, "Custom missing page")
}

fn create_router() -> Router {
    Router::new()
        .route("/", get(main_page))
        .fallback(handler_404)
    // add a fallback service for handling routes to unknown paths
}


#[tokio::main]
async fn main() {
    let listener = tokio::net::TcpListener::bind("127.0.0.1:3000")
        .await
        .unwrap();
    println!("listening on {}", listener.local_addr().unwrap());
    axum::serve(listener, create_router()).await.unwrap();
}

#[cfg(test)]
mod tests;

#![allow(unused)]
fn main() {
use axum::{body::Body, http::Request, http::StatusCode};
use http_body_util::BodyExt;
use tower::ServiceExt;

use super::*;

#[tokio::test]
async fn test_main_page() {
    let response = create_router()
        .oneshot(Request::builder().uri("/").body(Body::empty()).unwrap())
        .await
        .unwrap();

    assert_eq!(response.status(), StatusCode::OK);
    let body = response.into_body();
    let bytes = body.collect().await.unwrap().to_bytes();
    let html = String::from_utf8(bytes.to_vec()).unwrap();

    assert_eq!(html, "<h1>Hello, World!</h1>");
}

#[tokio::test]
async fn test_other_page() {
    let response = create_router()
        .oneshot(
            Request::builder()
                .uri("/other")
                .body(Body::empty())
                .unwrap(),
        )
        .await
        .unwrap();

    assert_eq!(response.status(), StatusCode::NOT_FOUND);
    let body = response.into_body();
    let bytes = body.collect().await.unwrap().to_bytes();
    let html = String::from_utf8(bytes.to_vec()).unwrap();

    assert_eq!(html, "Custom missing page");
}
}