feat(consistent symlink): changes for CreateSymlink flow for updated representation

[anushka567]

Description

This PR implements the creation phase of the updated GCS symlink representation in GCSFuse to align with the standard used by other GCS clients like Storage Transfer Service (STS) . When enabled via a flag, new symlinks will be created as GCS objects where the target path is stored in the object content and marked with the standard metadata key goog-reserved-file-is-symlink: true .

Context: go/sts-consistent-symlink-handling-in-gcsfuse

Link to the issue in case of a bug fix.

b/488952518

Testing details

1. Manual - Yes.
2. Unit tests - Included.
3. Integration tests - Automated.

Any backward incompatible change? If so, please explain.

No.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.30%. Comparing base (632897e) to head (ee858ec).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4424       +/-   ##
===========================================
+ Coverage        0   83.30%   +83.30%     
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  Files           0      163      +163     
  Lines           0    19997    +19997     
===========================================
+ Hits            0    16659    +16659     
- Misses          0     2718     +2718     
- Partials        0      620      +620     

Flag	Coverage Δ
unittests	83.30% <100.00%> (?)

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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 introduces a significant enhancement to how GCSFuse handles symlink creation, moving towards a standardized representation that is compatible with other Google Cloud Storage clients. The change allows symlink targets to be stored directly in the object content and marked with a specific metadata key, improving interoperability and consistency across GCS services. This new behavior is opt-in via a configuration flag, ensuring backward compatibility while enabling future-proof symlink management.

Highlights

• Standard Symlink Representation: Implemented the creation phase for a new standard GCS symlink representation, aligning GCSFuse with other GCS clients like Storage Transfer Service (STS). When enabled via a flag, new symlinks will store their target path in the object content and be marked with the goog-reserved-file-is-symlink: true metadata key.
• Configurable Symlink Behavior: Introduced a new configuration flag, ExperimentalEnableStandardSymlinks, to control whether the new standard symlink representation is used during creation. This allows for a gradual rollout and testing of the new behavior.
• Object Creation API Update: Modified the createNewObject function to accept content, enabling symlink targets to be stored directly within the GCS object's content when using the standard representation.
• New Test Coverage: Added a new unit test, TestCreateChildSymlink_StandardSymlinkEnabled, to verify the correct creation and metadata handling of symlinks using the new standard representation.

Changelog

• internal/fs/inode/dir.go
  • Added isStandardSymlinkRepresentationEnabled boolean field to the dirInode struct.
  • Updated NewDirInode to initialize isStandardSymlinkRepresentationEnabled from cfg.ExperimentalEnableStandardSymlinks.
  • Modified createNewObject function signature to include a content parameter.
  • Updated calls to createNewObject in CreateChildFile, CreateChildSymlink, and CreateChildDir to pass appropriate content.
  • Implemented conditional logic within CreateChildSymlink to use either the legacy gcsfuse_symlink_target metadata or the new goog-reserved-file-is-symlink: true metadata with target in content, based on the isStandardSymlinkRepresentationEnabled flag.
• internal/fs/inode/dir_test.go
  • Added TestCreateChildSymlink_StandardSymlinkEnabled test case to validate the creation of symlinks using the new standard representation, including checks for metadata and content.
• internal/fs/inode/symlink.go
  • Defined a new constant StandardSymlinkMetadataKey with the value goog-reserved-file-is-symlink.

Activity

• No activity (comments, reviews) has been recorded for this pull request yet.

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[gemini-code-assist]

Code Review

This pull request introduces support for creating symlinks using the standard GCS representation, controlled by the experimental-enable-standard-symlinks flag. The changes correctly modify the CreateChildSymlink flow to store the symlink target in the object's content and set the goog-reserved-file-is-symlink: true metadata key. The changes are logical and include a new unit test to verify the creation logic.

However, a critical piece of functionality is missing: the logic to read and identify these new symlinks is not implemented. Specifically, inode.IsSymlink and inode.NewSymlinkInode are not updated to handle the new format. This means that while gcsfuse can create these symlinks, it cannot recognize them when they are read back from GCS (e.g., during a directory listing or file lookup on a cold cache). They will be incorrectly treated as regular files.

I've added a comment to the new unit test suggesting an extension that would expose this issue. Addressing this is crucial for the feature to be complete and usable.