Update s3manager's iface with missing methods

[alexieyizhe]

This addresses #2273 and adds some new methods on top of it:

• NewDownloader
• NewDownloaderWithClient
• NewUploader
• NewUploaderWithClient

that were missing in the interface before.

It was suggested in #2273 that since this interface was not autogenerated and had no warning, the methods should be added as separate interfaces that can be composed together by the user to avoid breaking when the API changes.

[jasdel]

Thanks for taking the time to create this PR @alexieyizhe. I think this is the right approach for this API. But I don't think we need to create interfaces for the constructor functions, just the methods.

Similar like the following.

type UploadWithIterator interface {
    UploadWithIterator(aws.Context, s3manager.BatchUploadIterator, ...func(*s3manager.Uploader)) error
}

type DownloadWithIterator interface {
    DownloadWithIterator(aws.Context, s3manager.BatchDownloadIterator, ...func(*s3manager.Downloader)) error
}

type BatchDeleter interface {
    Delete(aws.Context, s3manager.BatchDeleteIterator) error
}

[jasdel]

I think the CI tests are failing due to Go formatting issues. Maybe try using gofmt -w ./service/s3/s3manager before committing the change.

[alexieyizhe]

@jasdel that explains the tests, thank you :)

Are you referring to the NewDownloader/NewUploader interfaces when you say the constructor functions?

[jasdel]

Correct, I was referring to the NewDownloader/NewUploader interfaces. could you go more into the reasoning behind creating interfaces for these functions?

[alexieyizhe]

I was under the impression an interface would be needed for all the functions that were exposed in order to mock them out. Is this not the case? I'm not the most familiar with the sdk or Go so it may very well be that they're not needed.

[alexieyizhe]

Hey @jasdel I've addressed the feedback you've given (appreciate it!)

[jasdel]

Thanks for the update @alexieyizhe, we'll review this update and get back with your with our feedback. Thanks!