refactor(cache): replace xattr-based caching with file-based cache

[chlins]

This pull request introduces a new caching mechanism for file digests, replacing the previous use of extended attributes (xattrs) with a file-based cache. The cache stores metadata about files (such as modification time, size, and digest) to avoid redundant digest calculations, improving build performance and reliability. The changes also include dependency updates and code cleanup related to this refactor.

Caching mechanism refactor:

• Added a new file-based cache implementation in internal/cache/cache.go using the gofrs/flock library for safe concurrent access. This cache stores file metadata and digests in a JSON file and prunes expired entries.
• Refactored the builder logic in pkg/backend/build/builder.go to use the new cache for storing and retrieving file digests, replacing the previous xattrs-based approach. This includes new methods for cache retrieval and update, and integration into the build process. [1] [2] [3] [4] [5] [6]

Dependency updates:

• Added github.com/gofrs/flock and updated golang.org/x/sys to v0.40.0 in go.mod to support the new cache implementation. [1] [2]

Code cleanup:

• Removed the now-unused xattrs-based digest caching logic and related imports from pkg/backend/build/builder.go. [1] [2]
• Removed the unused IsRawMediaType helper from pkg/codec/codec.go since raw media type detection is now handled directly in the builder.

[gemini-code-assist]

Summary of Changes

Hello @chlins, 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 significantly overhauls the file digest caching strategy, moving from a system reliant on extended file attributes to a more robust and portable file-based approach. This change aims to improve the consistency and performance of build processes by efficiently storing and retrieving file metadata, ensuring that digest calculations are only performed when necessary. The refactor centralizes caching logic and removes dependencies on platform-specific file system features.

Highlights

• Caching Mechanism Refactor: Replaced the extended attributes (xattrs) based caching for file digests with a new file-based caching system. This new system stores file metadata (modification time, size, digest) in a JSON file and prunes expired entries.
• New Cache Implementation: Introduced a new internal/cache/cache.go file which provides a file-based cache implementation using the gofrs/flock library for safe concurrent access to the cache file.
• Builder Integration: The pkg/backend/build/builder.go logic has been refactored to integrate and utilize the new file-based cache for storing and retrieving file digests, enhancing build performance and reliability.
• Dependency Updates: Added github.com/gofrs/flock to go.mod to support the new file locking mechanism for the cache, and updated golang.org/x/sys to v0.40.0.
• Code Cleanup: Removed the deprecated xattrs-based digest caching logic and related imports from pkg/backend/build/builder.go, and removed the unused IsRawMediaType helper from pkg/codec/codec.go.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request is a great step towards improving build performance by introducing a file-based caching mechanism. The new cache implementation in internal/cache/cache.go is well-structured and the integration into pkg/backend/build/builder.go is clean.

I have a few suggestions to improve the robustness and configurability of the new cache:

• The file locking in the cache should be context-aware to prevent processes from hanging.
• The cache directory should be configurable instead of being hardcoded to the system's temporary directory.
• Error checking for cache misses could be made more robust.

Overall, this is a solid refactoring. Addressing these points will make the new caching feature even better.

[aftersnow]

lgtm