[POC] Adding initial comparison b/w rust and python for standard bucket

[raj-prince]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces an optional Rust-based read backend for gcsfs using the official google-cloud-storage SDK via PyO3 to improve object read performance. It includes the PyO3 extension bindings, a Python wrapper, integration into GCSFileSystem, and benchmark tools. The code review identified several critical issues and optimization opportunities: the global static Rust client ignores instance-specific configurations and should be refactored into a per-instance class; negative offsets are not resolved before being passed to Rust, which will cause conversion errors; missing object errors (404) should be mapped to FileNotFoundError to maintain compatibility with fsspec; read_backend needs fail-fast validation during initialization; memory allocations in Rust can be optimized using Vec::with_capacity; the double-thread-hop overhead should be eliminated by using PyO3's async integration; and a potential division-by-zero panic in the benchmark tool must be prevented.

[codecov]

Codecov Report

❌ Patch coverage is 56.52174% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.98%. Comparing base (211f484) to head (3bc06c5).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
gcsfs/rust_backend.py	58.82%	7 Missing ⚠️
gcsfs/core.py	50.00%	3 Missing ⚠️

❌ Your patch check has failed because the patch coverage (56.52%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1017      +/-   ##
==========================================
- Coverage   90.05%   89.98%   -0.08%     
==========================================
  Files          16       17       +1     
  Lines        3641     3764     +123     
==========================================
+ Hits         3279     3387     +108     
- Misses        362      377      +15     

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