fix: make gzip compression deterministic #262
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Gzip includes timestamps by default, making compression non-deterministic. This causes SLSA attestation verification failures when artifacts are re-compressed or re-uploaded, as the digest changes even with identical content. Changes: - Add -n flag to gzip commands to exclude timestamps - Add -n flag to pigz commands for parallel compression - Update getCompressionCommand to use -n with custom compression levels This ensures: - Deterministic builds (same content = same digest) - SLSA attestations remain valid across re-uploads - Reproducible builds align with SLSA best practices Fixes digest mismatch issues in sign-cache workflow where artifacts may be re-uploaded after attestation creation. Co-authored-by: Ona <no-reply@ona.com>
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kylos101
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Problem
Gzip includes timestamps by default, making compression non-deterministic. This causes SLSA attestation verification failures when artifacts are re-compressed or re-uploaded, as the digest changes even with identical content.
Example of the Issue
This breaks SLSA verification when:
Solution
Add the
-nflag to all gzip/pigz commands to exclude timestamps from compressed output.Changes
-nflag to defaultgzipcompressor-nflag topigzcompressor (parallel gzip)-nflag when custom compression levels are specifiedVerification
Benefits
Testing
Related
This fix is particularly important for the
sign-cacheworkflow where artifacts may be re-uploaded after attestation creation, causing digest mismatches during verification.Part of https://linear.app/ona-team/issue/CLC-2062/ensure-leeway-does-not-uploads-again-cache-artifact