fix: handle ancient empty docker layers

[rchincha]

Earlier versions of docker images had empty layers of 1024 zero-valued octets.

What type of PR is this?

Which issue does this PR fix:

What does this PR do / Why do we need it:

If an issue # is not available please add repro steps and logs showing the issue:

Testing done on this change:

Automation added to e2e:

Will this break upgrades or downgrades?

Does this PR introduce any user-facing change?:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[hallyn]

@rchincha the only file in the only patch is a .bats file. Did you forget some git-add action?

[codecov]

Codecov Report

Merging #522 (e761a50) into main (0cf2d70) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #522      +/-   ##
==========================================
- Coverage   13.34%   13.32%   -0.03%     
==========================================
  Files          40       40              
  Lines        5852     5863      +11     
==========================================
  Hits          781      781              
- Misses       4943     4954      +11     
  Partials      128      128              

Files	Coverage Δ
pkg/types/layer_type.go	0.00% <0.00%> (ø)
pkg/log/log.go	55.31% <0.00%> (-2.46%)	⬇️
pkg/stacker/base.go	0.00% <0.00%> (ø)
pkg/overlay/metadata.go	0.00% <0.00%> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[rchincha]

@rchincha the only file in the only patch is a .bats file. Did you forget some git-add action?

3 files right?

[rchincha]

Without this PR, the same test fails.
#525

A real-world image has been copied over to ghcr.io so should be internal without any dependency on dockerhub.

[raharper]

https://github.com/containers/image/blob/main/image/docker_schema2.go
https://github.com/containers/image/blob/main/internal/image/docker_schema2.go

I think this means it is a well-known type -- can we test if the image has the matching sha256?

I'm going to see if I can programmatically create a simple image with such a layer.

[rchincha]

https://github.com/containers/image/blob/main/image/docker_schema2.go https://github.com/containers/image/blob/main/internal/image/docker_schema2.go

I think this means it is a well-known type -- can we test if the image has the matching sha256?

I'm going to see if I can programmatically create a simple image with such a layer.

A single layer doesn't make sense IMO. What Dockerfile directive would make only that?

[rchincha]

https://github.com/containers/image/blob/main/internal/image/docker_schema2.go#L29

[raharper]

https://github.com/containers/image/blob/main/image/docker_schema2.go https://github.com/containers/image/blob/main/internal/image/docker_schema2.go
I think this means it is a well-known type -- can we test if the image has the matching sha256?
I'm going to see if I can programmatically create a simple image with such a layer.

A single layer doesn't make sense IMO. What Dockerfile directive would make only that?

ENV or RUN; any command that doesn't actually modify the rootfs. Why? I do not know.

[rchincha]

FROM scratch
ENV a=b

gives us

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "digest": "sha256:2b4a446f5ab37b5895b62507c572303f16ab4f8d9161a35799c994301722d3d5",
    "size": 334
  },
  "layers": []
}

[rchincha]

Included your example in the unit tests.

[rchincha]

Will move the ghcr test to a SLOW_TEST (nightly) once you review/approve

[raharper]

This PR should close #525 right?

[rchincha]

This PR should close #525 right?

Correct, PR #525 was only to demo that this PR is needed.