How to return either success or errors?

[tobymurray]

I'm just not getting this - it seems like I'm missing something obvious. I want to return either a successful rocket_dyn_templates::Template or an error (e.g. 401, 403, 500), and the slight twist is I want to add a custom header as well.

First:

Responders may fail instead of generating a response by returning an Err with a status code

What does this mean in practice? What's the response signature for this method?

a default error catcher will be used

If I declare e.g. Result<Template, String> and return Err("This is an error".to_string(), I get an HTTP 200 response with this content. The docs read as though I should expect Rocket to be doing something with the Err that I'm returning (maybe a 500 or some other default?). Does the default error handler catch errors and turn them into HTTP 200s?

Elsewhere the docs suggest:

If you're returning two different responses, use a Result<T, E> or an Either<A, B>.

If you need to return more than two kinds, derive a custom Responder enum:
rocket_dyn_templates::Template

use rocket::fs::NamedFile;
use rocket::http::ContentType;

#[derive(Responder)]
enum Error<'r, T> {
    #[response(status = 400)]
    Unauthorized(T),
    #[response(status = 404)]
    NotFound(NamedFile),
    #[response(status = 500)]
    A(&'r str, ContentType),
}

But this is just the error. Is this example showing how to implement an API (Responder) that exclusively returns errors? If so... that's a very confusing piece of documentation, as it seems unlikely anyone would practically use that.

I've seen the error handling example, #71, #72, #2155, and #2172 and for the life of me I can't put the pieces together.

[tobymurray]

Edit: There was a bunch of confusing code here that muddied the waters more than helping anything, removed because I don't think it's useful. Didn't delete because @myz-dev has a useful reply that I don't want to orphan

[myz-dev]

Hi,
I do not know if I understand what your goal is. I assume you want to achieve something like this:
Have a responder that does not only return different variations of an error type, but also, on success, return the type that the client expects on a successful request.

So what I have in my code base for this scenario:

#[derive(Responder, Debug)]
pub enum SomeResponder{
    #[response(status = 200, content_type = "Json")]
    Success(Json<MyPayloadType>),
    #[response(status = 400, content_type = "plain")]
    Failure(String),
    //there could be more here
}

And in my request that has a signature like: pub async fn get_payload(/**/ -> RollResponder {} I return these responses like this:

// success:
SomeResponder::Success(Json(some_payload))
// failure:
return SomeResponder::Failure(format!("ERROR!"));

Does this help you at all?