Error handling audit

[BrynCooke]

Create a comprehensive list of all errors. Ensure that error messages have:

1. Information about what happened in a user friendly language.
2. Information about what to do about the error in user friendly language.

Sensitive information must not be leaked. Consider metrics for infrastructure errors.

[Geal]

putting that in the api-1.0 effort, although I think it's mostly done?

[o0Ignition0o]

Not sure if it belongs in here, but error handling in native plugins is pretty cumbersome as well. Is there an issue tracking this specifically?

[abernix]

@o0Ignition0o I don't think there is an issue for that (at least not that I'm aware of)

[SimonSapin]

https://github.com/apollographql/router/pull/1487 make some error enums private, but the remaining ones are still in need of an audit. I think some variants are not used anymore. And the enums should probably be made #[non_exhaustive] so we can add variants after 1.0.

[SimonSapin]

In the spirit of https://github.com/apollographql/router/issues/1142#issuecomment-1211874799, we generally want to use a Vec<apollo_router::graphql::Error> in SomethingResponse value, rather than return Result::Err in Tower services.

~~What if we never used Result::Err, and make the error type std::convert::Infallible (an empty enum, impossible to construct) instead of BoxError?~~

[SimonSapin]

make the error type std::convert::Infallible

Let’s… not. tower::Buffer uses BoxError, tower_test::Mock uses BoxError. Building types from the http crate is fallible. and And probably more constraints I haven’t found yet

[garypen]

If we wish to improve the quality of our generated error documentation:

In case you want to have an independent doc comment, the #[displaydoc("...") atrribute may be used on the variant or struct to override it.

We could use this mechanism to, for instance, number all of our errors: e.g.: router000001, etc...

[SimonSapin]

https://github.com/apollographql/router/pull/1621 completes the audit of error-handling-related Rust APIs for 1.0. Removing the label and milestone, but leaving this issue open as in 1.x we’ll want to audit the presentation / formatting of errors in GraphQL responses and in logs, as well as maybe add error codes.