skip signing/sbom if already present

[loosebazooka]

should keep images from have a ton of signatures when they don't change and reduce signing costs for reproduced images

[gemini-code-assist]

Summary of Changes

Hello @loosebazooka, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request optimizes the OCI image publishing workflow by implementing a conditional signing and SBOM attestation mechanism. It ensures that images are only signed and attested if they do not already possess a valid signature, thereby reducing unnecessary processing and associated costs, particularly for images that are rebuilt without changes.

Highlights

• Conditional Signing and SBOM Attestation: Introduced logic to check for existing signatures on OCI images before performing cosign attest and cosign sign operations. This prevents redundant signing and SBOM generation.
• Cost and Performance Optimization: The primary goal of this change is to reduce signing costs and avoid accumulating multiple signatures on images that have not changed, improving efficiency for reproduced images.
• Cosign Verification: Utilizes cosign verify with specific OIDC issuer and identity parameters to determine if an image already has a valid signature. If verification fails, signing and attestation proceed.

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[gemini-code-assist]

Code Review

This pull request introduces a check to see if an image is already signed before attempting to sign it and generate an SBOM. This is a good optimization to avoid redundant operations and costs. The implementation is mostly correct, but I have a suggestion to make the shell script logic more idiomatic and robust by simplifying the condition and ensuring all output from the verification command is silenced.

[github-actions]

🌳 🔧 Config Check

This pull request has not modified the root BUILD

[loosebazooka]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a useful optimization to skip signing and SBOM generation if an image is already signed, which can reduce redundant operations and costs. However, the implementation contains a critical shell syntax error that will cause the script to fail. I've also included suggestions to improve the script's clarity by managing output messages and to enhance its flexibility by parameterizing a hardcoded URL.

[github-actions]

🌳 🔄 Image Check
This pull request doesn't make any changes to the images. 👍
You can check the details in the report here