awserr: support errors.Is function

[jkawamoto]

It's helpful if we can compare the original error without casting. For example, this usually happens in our use case:

// An API call returns an error.
err := awserr.New("RequestTimeout", "RequestTimeout", context.DeadlineExceeded)

// The error can be wrapped in an upper layer to add more message.
err = fmt.Errorf("additional message: %w", err)

// Then, we need to check what is the original error.
if errors.Is(err, context.DeadlineExceeded){
  ...
}

Unfortunately, the current implementation doesn't support errors.Is. We need to cast the error before the comparision like this:

var e awserr.Error
if errors.As(err, &e) && errors.Is(e.OrigErr(), context.DeadlineExceeded){
  ...
}

However, the above only works if there is one original error. If it has multiple original errors, we need to use BatchedErrors.OrigErrs instead. It makes error handling complicated.

This PR solves this problem. Errors defined in awserr package can work with errors.Is function.

[jasdel]

Thanks for creating this Pr @jkawamoto there are two older (in progress) PRs covering similar topics, and would be helpful to pull these similar ideas together.

• Errors returned by awserr.New() work with errors.Unwrap() #3348
• Implement Wrapper interface for baseError #2872

Also, the AWS SDK for Go v2 has solved this problem from the start. It supports errors.Unwrap, and errors.As for all error types.

[jkawamoto]

@jasdel Thanks for your comment. I added two commits. Commit 0e2d6db adds errors.As support and it should cover #3348 and #2872. Commit 8a95855 also adds Is/As supports to other errors as #3348 (review) mentions.

We'd like to migrate to v2 at some point but some of our depending libraries still use v1. I hope this PR fixes the error issue.

[jasdel]

Thanks for updating this pr @jkawamoto . We'll review and post feedback!

[jasdel]

Thanks for updating this Pr @jkawamoto. We'll need to figure out a solution to the SDK's current support of older Go versions prior to Go1.13. Currently this PR's direct usage of errors.As and errors.Is will break with older versions of Go.

One way to handles this is to only add the As, Is functions to the for newer go versions, or alternatively back fill the modern errors As, Is behavior as an internal module to the SDK.

[jkawamoto]

Thanks for your review. I think it's fine to support Is and As functions only for Go 1.13 or later because those functions are mainly called from errors.Is and errors.As, which don't exist before Go 1.13.

[davidmerwin]

🎸🧬

…

________________________________ From: Junpei Kawamoto ***@***.***> Sent: Monday, August 30, 2021 3:26:11 PM To: aws/aws-sdk-go ***@***.***> Cc: Subscribed ***@***.***> Subject: Re: [aws/aws-sdk-go] awserr: support errors.Is function (#4010) Thanks for your review. I think it's fine to support Is and As functions only for Go 1.13 or later because those functions are mainly called from errors.Is and errors.As, which don't exist before Go 1.13. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub<#4010 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AMR4C53ICKHN4RTYIM7CQFLT7PLNHANCNFSM5AOL65GA>.

[andrewkroh]

Looks like a leftover debugging statement?

[jkawamoto]

Thanks! I've removed it.

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