feat: Implement Nix Binary Cache Index Protocol

[kalbasit]

This implements the Nix Binary Cache Index Protocol as outlined in RFC 0195.
The index provides a way for clients to efficiently determine if a NAR info
hash exists in the cache without querying the server for every hash.

Key changes:

• Added FileStore interface and implementations for local and S3 storage.
• Added GetAllNarInfos database query and implementation.
• Implemented nixcacheindex package for manifest, shard, and delta management.
• Wired up the index feature into pkg/cache and pkg/server.
• Added --experimental-cache-index flag to enable the feature.
• Implemented background index generation using cron.

[dosubot]

Related Documentation

Checked 1 published document(s) in 1 knowledge base(s). No updates required.

^{How did I do? Any feedback?}  

[kalbasit]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: Implement Nix Binary Cache Index Protocol #555 👈 (View in Graphite)
• feat: wire up new index feature into pkg/cache/upstream #554
• feat: implement delta logic for binary cache index protocol #553
• feat(nixcacheindex): implement RFC 0195 binary cache index protocol #552
• feat: introduce golomb-rice encoding package #564
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[gemini-code-assist]

Summary of Changes

Hello @kalbasit, 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 enhances the Nix cache by integrating the Nix Binary Cache Index Protocol. This new functionality allows for the creation and serving of a comprehensive index of all stored NAR infos, enabling Nix clients to perform highly efficient lookups. The change involves adding new storage abstractions for general files, a dedicated package for index management, database query extensions, and a background process for index generation, all configurable via an experimental flag.

Highlights

• Nix Binary Cache Index Protocol Implementation: This pull request fully implements the Nix Binary Cache Index Protocol (RFC 0195), enabling clients to efficiently determine if a NAR info hash exists in the cache without querying the server for every hash.
• New FileStore Interface and Implementations: A new FileStore interface has been introduced to handle arbitrary file storage, with concrete implementations for both local disk and S3 storage backends. This is used for storing the generated cache index files.
• Database Query for All NAR Infos: A new database query, GetAllNarInfos, has been added across MySQL, PostgreSQL, and SQLite to retrieve all NAR info hashes and their associated file metadata, which is crucial for building the cache index.
• Nix Cache Index Package and Management: A new nixcacheindex package has been created to manage the manifest, shards, and deltas of the cache index. The cache now includes logic to generate and store these index components.
• Integration and Experimental Flag: The cache index feature is wired into the pkg/cache and pkg/server components. It is controlled by a new --experimental-cache-index flag, allowing for opt-in usage. The server now exposes an endpoint for clients to fetch index files.
• Background Index Generation: The cache index is generated in the background using a cron job, scheduled to run hourly, ensuring the index remains up-to-date with the cache's contents.
• Optimized Cache Queries: When enabled, cache queries now leverage the generated index to quickly identify 'definite misses', avoiding unnecessary upstream checks and improving performance.

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[gemini-code-assist]

Code Review

This pull request introduces an implementation of the Nix Binary Cache Index Protocol, which is a significant feature for improving cache query performance. The changes are well-structured, introducing a FileStore interface, a new database query for index generation, and wiring everything up through the cache and server packages. The use of a background cron job for index generation is a good approach.

My review focuses on a critical security vulnerability, a performance and correctness issue in the database query, and an improvement for the feature toggle logic. All original comments have been retained as they align with the repository's best practices and do not contradict any provided rules. Overall, this is a great addition, and with these fixes, it will be even more robust and secure.

[kalbasit]

/gemini review

[gemini-code-assist]

Code Review

This pull request successfully implements the Nix Binary Cache Index Protocol as described in RFC 0195. The changes are well-structured, introducing the feature behind an experimental flag, adding a new FileStore interface with implementations for local and S3 storage, and integrating the index generation and querying into the existing cache logic. The background index generation via a cron job is a good approach.

My review includes one suggestion for a memory efficiency improvement in the shard generation process. Overall, this is a solid implementation of a significant new feature.

[kalbasit]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a significant new feature: the Nix Binary Cache Index Protocol, as described in RFC 0195. The implementation is well-structured, adding a new FileStore interface, implementing it for both local and S3 storage, and integrating the index generation and querying logic into the existing cache and server components. The use of a background cron job for index generation is a good approach. The changes are extensive but follow existing patterns in the codebase. I've identified a couple of areas for improvement related to scalability and robustness, which are detailed in the comments.

[kalbasit]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the Nix Binary Cache Index Protocol as outlined in RFC 0195, which is a great feature for improving client performance. The implementation is well-structured, introducing a FileStore interface for abstracting file storage, with implementations for both local and S3 backends. The cache index generation is handled by a background cron job, and the server is updated with a new endpoint to serve the index files. The code is clean and includes good test coverage, including security tests for path traversal. Overall, this is a solid implementation. The suggestion to improve error handling in the index generation logic is valid and should be considered.