Proper way to render custom error pages

[Elizafox]

Hello!

I want to change the default Axum error "pages" (just empty bodies) into custom templates.

I have this code, which works, but I feel like it's an absolutely major hack. Is there a better way?

use askama::Template;
use axum::{
    http::{header::CONTENT_LENGTH, StatusCode},
    middleware::map_response,
    response::{IntoResponse, Response},
    Router,
};
use itertools::Itertools;

#[derive(Template)]
#[template(source = "{{ error_code }}: {{ reason }}", ext = "txt")]
pub struct ErrorTemplate<'a> {
    pub error_code: &'a str,
    pub reason: &'a str,
}

async fn transform_error(response: Response) -> impl IntoResponse {
    let (parts, body) = response.into_parts();

    let status_num = parts.status.as_u16();
    if status_num < 400 {
        // We only care about client or server errors
        return Response::from_parts(parts, body);
    }

    // Sniff the content-length and see if we have any data
    if let Some(content_length) = parts.headers.get(CONTENT_LENGTH) {
        if let Ok(len) = std::str::from_utf8(content_length.as_bytes())
            .unwrap_or("0")
            .parse::<usize>()
        {
            if len > 0 {
                return Response::from_parts(parts, body);
            }
        }
    }

    let (error_code, reason) = parts
        .status
        .to_string()
        .splitn(2, ' ')
        .collect_tuple()
        .map_or(
            (format!("{:03}", status_num), parts.status.to_string()),
            |(x, y)| (x.to_owned(), y.to_owned()),
        );

    let t = ErrorTemplate {
        error_code: &error_code,
        reason: &reason,
    };
    (parts.status, t).into_response()
}

#[tokio::main]
fn main() {
    let router = Router::new()
        .layer(map_response(transform_error))
        // ...
    // ...
}

[davidpdrsn]

That looks fine to me.

[Elizafox]

I could see this being an issue if I wanted to do this with JSON endpoints, but I don't have any in this app. It's good to know that this is an okay way to do it.

Is there a preferred way to doing it that I don't know about?