I'm using Tera templates with axum to generate pages for a user-facing web app. The Tera instance is passed around in Arc<State> for use by handlers.

I've implemented IntoResponse for my custom error type. However, I'd like to generate a nicer error page for users. I could instantiate a new Tera instance in the IntoResponse impl, but that seems wasteful.

The solution I landed on was a middleware that checks for server error in the response, and renders a Tera template there, as middleware has access to state. But, this seems sub-optimal. Is there a better way?

// to be used with middleware::from_fn_with_state
pub async fn error_page(
    State(tera): State<tera::Tera>,
    request: Request,
    next: Next,
) -> Result<Response, WebappError> {
    let response = next.run(request).await;

    let status_code = response.status();

    if status_code.is_server_error() {
        let mut context = tera::Context::new();

        context.insert("content", "Something broke");

        let rendered = tera.render("error.html", &context)?;

        Ok(Html(rendered).into_response())
    } else {
        Ok(response)
    }
}

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