Add platform option to crane copy and digest

[dvob]

Add platform option to crane copy and digest. If the remote reference is an index/list it only copies the image which matches the specified platform.

This would be a possible solution for #741

[codecov-commenter]

Codecov Report

Merging #742 into master will decrease coverage by 0.40%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #742      +/-   ##
==========================================
- Coverage   79.39%   78.99%   -0.41%     
==========================================
  Files         102      102              
  Lines        4683     4717      +34     
==========================================
+ Hits         3718     3726       +8     
- Misses        534      551      +17     
- Partials      431      440       +9     

Impacted Files	Coverage Δ
pkg/crane/options.go	76.47% <0.00%> (-23.53%)	⬇️
pkg/crane/copy.go	51.11% <16.66%> (-2.55%)	⬇️
pkg/crane/manifest.go	47.05% <53.33%> (-52.95%)	⬇️
pkg/crane/digest.go	56.52% <61.90%> (-43.48%)	⬇️
pkg/crane/get.go	100.00% <100.00%> (ø)

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[dvob]

I moved the logic to the Digest and Manifest function. Does not look super nice, but is probably easier to understand than the logic I used before with the interface.

[jonjohnsonjr]

This will still fail for schema 1 images, which we aren't able to satisfy the v1.Image interface for. If we keep the behavior the same here, but only try to resolve to an image when platform is specified, I think we can keep everything working, i.e.:

if o.platform != nil {
  img, err := desc.Image()
  if err != nil {
    return nil, err
  }
  return img.RawManifest()
}

return desc.Manifest, nil

Sorry for all the back and forth on this, I really appreciate your contribution!

[codecov-io]

Codecov Report

Merging #742 into master will decrease coverage by 0.38%.
The diff coverage is 11.11%.

@@            Coverage Diff             @@
##           master     #742      +/-   ##
==========================================
- Coverage   75.94%   75.55%   -0.39%     
==========================================
  Files         102      102              
  Lines        4144     4169      +25     
==========================================
+ Hits         3147     3150       +3     
- Misses        546      565      +19     
- Partials      451      454       +3     

Impacted Files	Coverage Δ
pkg/crane/options.go	75.00% <0.00%> (-25.00%)	⬇️
pkg/crane/digest.go	31.25% <8.33%> (-68.75%)	⬇️
pkg/crane/copy.go	48.78% <16.66%> (-2.58%)	⬇️
pkg/crane/manifest.go	50.00% <16.66%> (-50.00%)	⬇️

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[dvob]

Tried to change the logic according to your points in the last review, squashed the commits and rebased them on master.
Since in the meantime crane.Digest was changed and now only uses HEAD. I had to change the logic that it still gets the manifest if a platform is specified. Or is there another solution?

[jonjohnsonjr]

I had to change the logic that it still gets the manifest if a platform is specified. Or is there another solution?

I think what you've done is the best we can do.

[jonjohnsonjr]

LGTM, thanks!