feat(consistent symlink): create openReader helper method on symlink inode to read the object contents to decipher target

[anushka567]

Description

The PR adds a helper method, openReader, to the SymlinkInode struct to allow reading the content of the backing GCS object . This is necessary because, in the new consistent symlink design, the symlink target is stored as the object's content rather than in custom metadata .

For more context, refer to go/sts-consistent-symlink-handling-in-gcsfuse

Link to the issue in case of a bug fix.

b/489246084

Testing details

1. Manual - Yes.
2. Unit tests - Added
3. Integration tests - NA. Will be covered once implementation is complete.

Any backward incompatible change? If so, please explain.

No.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.73%. Comparing base (1484b06) to head (af5110d).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4432      +/-   ##
==========================================
+ Coverage   83.67%   83.73%   +0.05%     
==========================================
  Files         163      163              
  Lines       20077    20092      +15     
==========================================
+ Hits        16800    16824      +24     
+ Misses       2652     2645       -7     
+ Partials      625      623       -2     

Flag	Coverage Δ
unittests	83.73% <100.00%> (+0.05%)	⬆️

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[gemini-code-assist]

Summary of Changes

Hello, 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 enhances the SymlinkInode structure by introducing a new openReader helper method. This method is designed to read the content of the GCS object that represents a symlink, which is a critical component for the new consistent symlink design. By storing symlink targets directly within the object's content, this change streamlines how symlink data is accessed and managed, laying the groundwork for more robust symlink functionality.

Highlights

• Symlink Content Reading: Introduced openReader helper method to SymlinkInode for reading the content of the backing GCS object.
• Consistent Symlink Design: This change supports the new consistent symlink design where the symlink target is stored as the object's content instead of custom metadata.

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[gemini-code-assist]

Code Review

This pull request introduces a new openReader method for SymlinkInode to facilitate reading the target of a symlink from GCS. This method includes specific error handling to detect and wrap gcs.NotFoundError into a gcsfuse_errors.FileClobberedError when a file clobbering scenario is identified. Corresponding internal tests have been added to validate the functionality of openReader, including cases for successful reads and clobbered files. A review comment points out that the error handling logic in openReader involves redundant wrapping, which can lead to verbose and confusing error messages, and suggests a simplification to improve clarity.