Fix crash when loading buildpack from OCI archive with relative paths

[phil9909]

Summary

• tar files can be absolute (/my/path) or relative (my/path).
• The OCI Image spec does not specify which style to use
• Some tools (like skopeo for example) use the relative style
• When reading buildpacks from an archive, pack assumes the absolute style

Output

Prepare

Download a buildpack with skopeo

skopeo copy docker://gcr.io/paketo-buildpacks/java oci-archive:java.cnb --format v2s2

Prepare some.jar as an executable jar file.

Before

$ pack build --builder paketobuildpacks/builder-jammy-buildpackless-base --buildpack java.cnb --path some.jar dev-null --trust-builder
latest: Pulling from paketobuildpacks/builder-jammy-buildpackless-base
Digest: sha256:5517fc3198bbfa84d3f31509c2bc3a14087e5aa718790bdfe9c561b0a19cf91b
Status: Image is up to date for paketobuildpacks/builder-jammy-buildpackless-base:latest
latest: Pulling from paketobuildpacks/run-jammy-base
Digest: sha256:36eddd3a51d37b4e11e7ff958b5c2568f4160e432dd526806a3940ec9369697b
Status: Image is up to date for paketobuildpacks/run-jammy-base:latest
ERROR: failed to build: downloading buildpack: extracting from file:///home/d060677/workspace/pack/java.cnb: reading buildpack: reading buildpack.toml: could not find entry path 'buildpack.toml': not exist

After

$ pack build --builder paketobuildpacks/builder-jammy-buildpackless-base --buildpack java.cnb --path some.jar dev-null --trust-builder                                                                                                                                          
latest: Pulling from paketobuildpacks/builder-jammy-buildpackless-base                                                                                                                                                                                                                                                                                
Digest: sha256:5517fc3198bbfa84d3f31509c2bc3a14087e5aa718790bdfe9c561b0a19cf91b                                                                                                                                                                                                                                                                       
Status: Image is up to date for paketobuildpacks/builder-jammy-buildpackless-base:latest                                                                                                                                                                                                                                                              
latest: Pulling from paketobuildpacks/run-jammy-base                                                                                                                                                                                                                                                                                                  
Digest: sha256:36eddd3a51d37b4e11e7ff958b5c2568f4160e432dd526806a3940ec9369697b                                                                                                                                                                                                                                                                       
Status: Image is up to date for paketobuildpacks/run-jammy-base:latest                                                                                                                                                                                                                                                                                
Restoring data for SBOM from previous image                                                                                                                                                                                                                                                                                                           
===> DETECTING                                                                                                                                                                                                                                                                                                                                        
6 of 24 buildpacks participating                                                                                                                                                                                                                                                                                                                      
paketo-buildpacks/ca-certificates   3.3.0                                                                                                                                                                                                                                                                                                             
paketo-buildpacks/bellsoft-liberica 9.6.1                                                                                                                                                                                                                                                                                                             
paketo-buildpacks/syft              1.18.0                                                                                                                                                                                                                                                                                                            
paketo-buildpacks/executable-jar    6.4.0                                                                                                                                                                                                                                                                                                             
paketo-buildpacks/dist-zip          5.3.0                                                                                                                                                                                                                                                                                                             
paketo-buildpacks/spring-boot       5.18.0
[...]
Successfully built image dev-null

Documentation

• Should this change be documented?
  • Yes, see #___
  • No

[codecov]

Codecov Report

Merging #1506 (75a0d6b) into main (651b9a7) will increase coverage by 1.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1506      +/-   ##
==========================================
+ Coverage   80.24%   81.26%   +1.03%     
==========================================
  Files         154      154              
  Lines       10018    10021       +3     
==========================================
+ Hits         8038     8143     +105     
+ Misses       1499     1397     -102     
  Partials      481      481              

Flag	Coverage Δ
os_linux	80.02% <100.00%> (+0.01%)	⬆️
os_macos	77.48% <100.00%> (+0.04%)	⬆️
os_windows	81.14% <100.00%> (+1.03%)	⬆️
unit	81.26% <100.00%> (+1.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[jromero]

This post/book section educated me a little further.

Thank you @phil9909. LGTM!