Better error handling story

[remexre]

Right now, I'm handling errors in an (HTMLful) warp app with the following helper:

https://github.com/remexre/nihctfplat/blob/e10ef2befe1bfa07373096b511e81e35284d708e/src/router/util.rs#L56-L96

I'm naturally not thrilled about this; #165 is largely about mitigating the need for the .map(Ok).recover(|e| Ok(Err(e))).unify().and(auth::opt_auth()); is there a nicer way to do something like this that I'm not seeing?

[seanmonstar]

I'm sorry, apparently I also can't quite understand what you're trying to do. Care to explain a little more?

[remexre]

Right off the bat, I'm converting a fallible filter to an infallible one that extracts a result...

self.map(Ok)
    .recover(|e| Ok(Err(e)))
    .unify()

...so that I can get authentication from the request.

    .and(auth::opt_auth())

Then to actually process the error, I match on the result...

    .and_then(move |res: Result<T, Rejection>, me| match res {

...with success continuing through...

        Ok(r) => Ok(Either::Left(r)),

...and errors being pulled out, with a passed-in func returning the HTTP status, error names, and messages to "flash" (i.e. show on a form when form validation fails).

        Err(r) => match r.find_cause() {
            Some(err) => match func(err) {
                Some((status, codes, flashes)) => {

The authentication object and the flashes are added to the context used to render the template...

                    let mut hm = hashmap! {
                        "flashes" => serde_json::to_value(flashes).unwrap(),
                        "me" => serde_json::to_value(me).unwrap(),
                    };

...and the corresponding errors are enabled...

                    for code in codes {
                        let _ = hm.insert(code, Value::Bool(true));
                    }

...then the error template page is rendered to a Response.

                    render_html(template, hm).map(|mut r| {
                        *r.status_mut() = status;
                        Either::Right(r)
                    })
                }

(If the function didn't handle the error, pass it along.)

                None => Err(r),
            },

(If the error was of the wrong type, pass it along.)

            None => Err(dbg!(r)),
        },
    })

Box<Filter<Extract=(impl Reply,)>> is the return type here.

    .boxed()

---

Really, my main gripes are:

• need to do .map().recover().unify() to chain more filters onto the failure
• need to be in a filter to do warp::ext::get()

[seanmonstar]

Thanks for the breakdown! I really understand what is going on now.

I'll give this problem some thought, but do you have any suggestions?

[remexre]

idk how much implementation effort it would be, but some way to get a Filter for recovery, like:

foo()
    .and(bar())
    .and_then(...)
    .or(recover().and_then(...))

and probably a get() free function, so render_html could have the auth put into it?