FromData Failures cannot be caught by error catchers and are not debug-logged

[villem]

Hello,

Bug reports must include:

1. The version of Rocket you're using. Ensure it's the latest, if possible.

0.4.2, rustc --version
rustc 1.42.0-nightly (0de96d37f 2019-12-19)

2. The operating system (distribution and version) where the issue occurs.

OSX 10.5.2
3. A brief description of the bug that includes:
* The nature of the bug.

FromData and FromDataSimple ask (status, Error) for Failure. As far as I can see the Error is not populated any where.

* When the bug occurs.
* What you expected vs. what actually happened.

It would be good to get Error output to up to default catcher response Outputs.

4. How you uncovered the bug. Short, reproducible tests are especially useful.

Simplest FromDataSimple Guard do not show Error any where, not even debug level logs.

5. Ideas, if any, about what Rocket is doing incorrectly.

Rocket transforms rocket::request::Outcome to rocket::Outcome and just drops the addition E info all together.
It would be very convenient if the Error info could be populated from data parsers to above levels. Now I need to do FromDataSimple functionality in post route fn itself.

[jebrosen]

This is covered in the docs at https://api.rocket.rs/v0.4/rocket/data/trait.FromData.html#outcomes

Note that users can request types of Result<S, E> and Option<S> to catch Failures and retrieve the error value.

We do want to expand the functionality so that errors from just about anywhere could go to error catchers (#749 (comment)), but it needs some work in rustc.

[villem]

This is covered in the docs at https://api.rocket.rs/v0.4/rocket/data/trait.FromData.html#outcomes

Note that users can request types of Result<S, E> and Option<S> to catch Failures and retrieve the error value.

Do you have an example how I would do this? Or isn't rustc providing needed functionally currently.

Anyways I could easily workaround this with bit of Custom responder. Rocket is really nice! Thank you!

[jebrosen]

form_kitchen_sink has an example: https://github.com/SergioBenitez/Rocket/blob/v0.4/examples/form_kitchen_sink/src/main.rs#L31 - the error type here is FormError, which matches up with the Error type specified for Form (https://api.rocket.rs/v0.4/rocket/request/struct.Form.html#impl-FromData%3C%27f%3E)

[villem]

This example is great and I can now use types in a really simple way. Thank you!

[Scipi]

Hi all,

Using rocket = "0.4.6"

I'm having a similar issue here with Request Guards. I have a couple custom guards that can fail in various ways (the database connection fails, missing headers/cookies, etc) and even though I encapsulate these failures in an Error type and pass them back to Rocket, they never get logged as reasons for Outcome::Failure.

I could always get around this in my own code by writing my own logging in the Request Guard (which can sometimes hurt readability) or by wrapping the from_request method like so:

...
impl FromRequest for MyRequestGuard {
    fn from_request(r: Request) -> Outcome<Self, Self::Error> {
        match _from_request(r) {
            o@Outcome::Success(_) => o,
            Outcome::Failure((s,e)) => {
                info!("MyRequestGuard failed with: {} - {}", s, e);
                Outcome::Failure((s, e))
            }
            o@Outcome::Forward(_) => o
        }
    }
}


fn _from_request(r: Request) -> Outcome<MyRequestGuard, MyError> {
   // ...
}

But this seems like unnecessary boilerplate for something Rocket is able to handle.

This issue is exasperated for Data Guards, too. In order to do logging it seems like I have to use Result<S, E> on every endpoint that uses them and then I have to remember to do the actual logging in the endpoint. That's fine for a couple endpoints, but when you have a couple dozen scattered around across the API it becomes very easy to miss one. It also doesn't make sense that a user would have to log an error that occurred within Rocket's handling of a request on Rocket's behalf.

[SergioBenitez]

Errors and forwards from all guards are now being logged by Rocket.

[svenstaro]

I think logging is only part of the solution. I'd also like to be able to act on it in catchers which is probably the primary thing in this issue.

[SergioBenitez]

There is already an issue for handling typed errors in catchers. See #749.

[svenstaro]

Alright.