Patterns for accessing state in error path.

[askreet]

Summary

I'm using a Result<Response, AppError> in order to make error paths quickly display an HTML error, like so:

struct AppError(anyhow::Error);

impl IntoResponse for AppError {
    fn into_response(self) -> Response {
        tracing::error!("AppError sending internal_server_error: {}", self.0);
        let msg = format!("error: {}", self.0);

        (StatusCode::INTERNAL_SERVER_ERROR, msg).into_response()
    }
}

impl<E> From<E> for AppError
    where
        E: Into<anyhow::Error>,
{
    fn from(err: E) -> Self {
        Self(err.into())
    }
}

Trouble is, my AppState that I pass into handlers holds a shared reference to both my template engine and the request's cookie jar (so I can identify the user). I'd like to render a pretty error page using these resources - any well documented patterns for this? Basically I want an AppError that can get the same extracts as handler functions, or some other (simple?) pattern.

axum version

0.7.4

[jplatte]

You can use tokio's task_local! macro and a middleware that sets the task-local to share state with your IntoResponse impl. #2769 has an example with the most important bits for this pattern.