fix: update ZIP EOCD comment_length when signing#204
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tobinsouth merged 1 commit intomainfrom Mar 18, 2026
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The signMcpbFile function appended a signature block to the ZIP file but did not update the EOCD comment_length field. Strict ZIP parsers (like Claude Desktop's) rejected these files because the declared comment length didn't account for the appended signature data. Now scans backwards for the EOCD magic bytes, reads the current comment_length, and adds the signature block length before concatenating. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Review by Claude Code
Clean, focused bug fix. Observations:
findEocdOffset()correctly scans backwards frombuffer.length - 22for the EOCD magic bytes (0x06054b50). The search range and byte-order handling look correct.- When EOCD is not found (offset === -1), the code silently skips the
comment_lengthupdate. This preserves backward compatibility — the file was already a valid ZIP before signing, so failing to update this field is a safe fallback rather than a hard error. - The
comment_lengthfield at EOCD+20 is correctly written as a 16-bit little-endian value reflecting the size of the appended signature block. - Test coverage verifies both the before state (comment_length=0) and after state (comment_length equals appended data size), which are the two key assertions for this fix.
- The test reimplements EOCD-finding logic rather than importing from
sign.ts— reasonable since the function is private and the test needs independent verification.
No issues found. This should resolve the strict ZIP parser rejections observed in Claude Desktop.
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@claude please review for security |
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Enterprise HSM signers (GaraSign, SignServer, Venafi, Azure SignTool) append PKCS#7 signatures after the ZIP EOCD without updating comment_length. Claude Desktop's adm-zip parser rejects these files. PR #204 fixed this for `mcpb sign` but external signers remain broken. This adds `mcpb fix-signature` which applies the same EOCD fix post-hoc, so enterprises can add one step to their signing pipeline. Validated end-to-end with Autodesk's GaraSign-signed Fusion MCPB: - adm-zip, unzip, Python zipfile all accept the fixed bundle - Claude Desktop installs it successfully - Signature bytes (MCPB_SIG_V1 + PKCS#7 + MCPB_SIG_END) remain intact - Exactly 2 bytes changed (EOCD comment_length field) Relates to #204, #21, #194 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Fixes #194.
comment_lengthfield, causing strict ZIP parsers (including Claude Desktop's) to reject signed files.findEocdOffset()helper to locate the EOCD record by scanning backwards for magic bytes0x06054b50.comment_lengthis now updated to include the signature block size.Test plan
comment_lengthis correctly updated after signingyarn build:codecompiles cleanlyyarn lintpasses🤖 Generated with Claude Code