Add --tarball to crane digest

[jonjohnsonjr]

Fixes #895

[codecov-io]

Codecov Report

Merging #896 (c838fd6) into master (ec3c7a5) will decrease coverage by 0.07%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #896      +/-   ##
==========================================
- Coverage   72.53%   72.46%   -0.08%     
==========================================
  Files         108      108              
  Lines        4672     4677       +5     
==========================================
  Hits         3389     3389              
- Misses        773      778       +5     
  Partials      510      510              

Impacted Files	Coverage Δ
pkg/crane/push.go	54.54% <0.00%> (-45.46%)	⬇️

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[aelij]

Can you make the required tag argument optional? Our tarballs have "RepoTags": null in their manifest.

I've made this change and tested it - it works as expected (crane push and crane digest produce the same digest):

img, err := crane.Load(tarball)

[aelij]

@jonjohnsonjr Do you want me to finish this? I can create a sub-command as you suggested.

[jonjohnsonjr]

Ah I just forgot about it completely. I have some plans to add another crane layout subcommand for doing layout-y things, so adding a crane tarball command makes some sense to me, but I haven't thought it through.

At the same time, it's a bit weird to duplicate all the top-level commands a bunch of times instead of just having flags.

The main thing pushing me towards subcommands here is that the cobra stuff for parsing flags and args will be different depending on if you're interacting with a tarball, layout, or registry.

The other option would be overloading the reference string with schemes, e.g. tarball:// or layout://... it doesn't make sense to have both --tarball and --layout flags, this is kind of nice... also, anything that crane can do remotely still makes sense to do against a tarball or a layout, so I'm leaning this way.

It makes a lot of sense to support append, blob, config, copy, delete, digest, export, ls, manifest, rebase, tag, and validate for a tarball or layout. We could make catalog make a little bit of sense, but it would be a little weird...

@imjasonh what do you think about this?

# Roughly, `$ tar -Oxf ubuntu.tar manifest.json | jq .[].RepoTags | jq .[] -r`
$ crane ls tarball://ubuntu.tar
ubuntu

# Works for len(tarball) == 1
$ crane [digest|config|manifest] tarball://ubuntu.tar

# For len(tarball) > 1
# Not sure about the separator? How do we handle tarballs with `:` in the filename?
$ crane [digest|config|manifest] tarball://ubuntu.tar:latest

Maybe we need a -t flag for these? That makes me thing we should do a separate subcommand, but it's weird...

Similarly, for layout, we'd need some selector -- we could use -t and assume the OCI name annotation?

For layout, there are other commands that are interesting, like GC (see https://github.com/opencontainers/umoci). This could also apply to tarball, I guess... gcrane has a gc command, but it's a bit different (sorry).

tl;dr three options:

1. Flags, manual arg parsing
2. Schemes
3. Subcommands

Not sure which we want to go with. If we go the scheme route, we might want to adopt skopeo's conventions.

[aelij]

Ping :)
My vote is for the schemes approach. Makes all the commands simple to use.
Meanwhile, could merge the current PR with this minor fix to unblock us?

img, err := crane.Load(tarball)

[jonjohnsonjr]

Ended up just finessing this with some manual flag logic. If we want to do something fancier in the future, we can revisit this.

I should probably provide a big warning about how this doesn't do what most people would expect, but we can do that if it becomes an issue.

[codecov-commenter]

Codecov Report

Merging #896 (d2c9843) into main (7e30746) will increase coverage by 0.09%.
The diff coverage is 100.00%.

❗ Current head d2c9843 differs from pull request most recent head cb59bb1. Consider uploading reports for the commit cb59bb1 to get more accurate results

@@            Coverage Diff             @@
##             main     #896      +/-   ##
==========================================
+ Coverage   74.52%   74.61%   +0.09%     
==========================================
  Files         107      107              
  Lines        5020     5027       +7     
==========================================
+ Hits         3741     3751      +10     
+ Misses        723      721       -2     
+ Partials      556      555       -1     

Impacted Files	Coverage Δ
pkg/crane/push.go	100.00% <100.00%> (ø)
pkg/v1/daemon/write.go	46.15% <0.00%> (+11.53%)	⬆️

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[aelij]

Thanks all