Add compression option to tarball.Layer and stream.Layer

[jromero]

Resolves #572

Signed-off-by: Javier Romero jromero@pivotal.io

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[imjasonh]

lgtm but I'll wait for @jonjohnsonjr's review to merge

[codecov-io]

Codecov Report

Merging #574 into master will increase coverage by 0.05%.
The diff coverage is 93.1%.

@@           Coverage Diff            @@
##           master   #574      +/-   ##
========================================
+ Coverage   72.95%    73%   +0.05%     
========================================
  Files          99     99              
  Lines        4411   4420       +9     
========================================
+ Hits         3218   3227       +9     
  Misses        786    786              
  Partials      407    407

Impacted Files	Coverage Δ
pkg/v1/stream/layer.go	81.92% <100%> (+2.19%)	⬆️
pkg/v1/tarball/layer.go	77.77% <88.88%> (ø)	⬆️

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[jonjohnsonjr]

LGTM in general, a couple small nits.

This only fixes tarball.Layer and not stream.Layer -- I'd update the PR description to avoid closing this until we address both (or just fix stream in this PR as well?).

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[jromero]

Alright, think I've got everything squared away. I've implemented the change to stream.Layer as well to truly resolve the issue mentioned.

I did notice (and followed) the slightly different testing convention so the tests will look different between them.

[jonjohnsonjr]

Alright, think I've got everything squared away. I've implemented the change to stream.Layer as well to truly resolve the issue mentioned.

I have one small nit on the comments (sorry!), otherwise lgtm. I think we'll eventually want to deprecate this and move to a more general way to augment layer content and media type (see my comment here), but I don't want to block this on trying to design around that :)

I did notice (and followed) the slightly different testing convention so the tests will look different between them.

Yeah it's a bit of a mess.

[jromero]

@jonjohnsonjr I can totally see the need and use case of different compression algorithms but that goes a bit beyond our scope at the moment. I'd be happy to take a swing at it via a different PR.

[jonjohnsonjr]

Thanks!