Fix: FileMeta Version Handling and Delete Operations

Summary

This PR fixes critical issues in file metadata version handling, specifically addressing:

1. Version sorting logic inconsistencies
2. Delete version operations with nil UUID handling
3. Directory object version ID assignment
4. Version ID validation and serialization improvements

Type of Change

• New Feature
• Bug Fix
• Documentation
• Performance Improvement
• Test/CI
• Refactor
• Other:

Related Issues

#844

Problem

The previous implementation had several version-related issues:

• Version sorting used a simple reverse() which didn't properly handle all version attributes
• Delete version operations failed when handling nil UUIDs (used for directory objects)
• Directory objects incorrectly used Uuid::max() instead of Uuid::nil() as default version ID
• Version ID validation was too strict, rejecting valid nil UUIDs for directory objects
• Version ID serialization filtered out nil UUIDs, causing inconsistencies

Changes

1. Fixed Version Sorting Logic (filemeta.rs)

• Replaced simple reverse() with comprehensive multi-field sorting
• Changed sort order to descending by mod_time, version_type, version_id, and flags
• Ensures consistent version ordering across all operations
• Applied to both sort_versions() and sort_versions_by_modtime() methods

2. Fixed Delete Version with Nil UUID (filemeta.rs)

• Added nil UUID handling in delete_version() method
• Fixed version matching logic to properly handle nil UUIDs
• Removed redundant version search loop, consolidating logic into single iteration
• Ensures delete operations work correctly for directory objects

3. Fixed Version ID Serialization (filemeta.rs)

• Removed nil UUID filtering in FileMetaVersionHeader::unmarshal()
• Changed to always store version_id as Some(Uuid), even for nil UUIDs
• Fixed into_fileinfo() to preserve nil UUIDs instead of filtering them out
• Maintains consistency between serialized and in-memory representations

4. Fixed Add Version with Nil UUID (filemeta.rs)

• Added nil UUID assignment in add_version() when version_id is None
• Ensures all versions have a valid UUID for internal operations

5. Fixed Directory Object Version ID (ecfs.rs, options.rs)

• Changed default version ID for directory objects from Uuid::max() to Uuid::nil()
• Applied to del_opts(), get_opts(), and put_opts() functions
• Consistent with nil UUID usage for directory objects

6. Fixed Version ID Validation (options.rs)

• Updated validation to allow nil UUID for directory objects
• Removed unnecessary versioned bucket check for version ID validation
• Allows nil UUID to pass validation when appropriate

7. Fixed Version Sorting in SetDisks (set_disk.rs)

• Removed unnecessary reverse() after sorting versions
• Sorting now produces correct order without reversal

8. Code Quality Improvements

• Changed Vec<FileInfo> to &[FileInfo] in delete_versions_internal() for better performance
• Updated to modern Rust string formatting ({err} instead of {}, err)
• Removed unnecessary comments and dead code
• Fixed clippy warnings

Checklist

• I have read and followed the CONTRIBUTING.md guidelines
• Passed make pre-commit
• Added/updated necessary tests
• Documentation updated (if needed)
• CI/CD passed (if applicable)

Impact

• Breaking change (compatibility)
  the version number generated for empty directory objects has been changed from uuid::max to uuid::nil. If there are previously created empty directories, they must be manually deleted from the data directory

here is a shell command to help delete existing empty directories:

#!/usr/bin/env bash
set -euo pipefail

DATA_DIR=${1:-}
if [[ -z "$DATA_DIR" || ! -d "$DATA_DIR" ]]; then
  echo "Usage: $0 <data_directory>"
  exit 1
fi

find "$DATA_DIR" -type d -name '*__XLDIR__' -prune -print -exec rm -rf {} +

• Requires doc/config/deployment update
• Other impact:

Additional Notes

Thank you for your contribution! Please ensure your PR follows the community standards (CODE_OF_CONDUCT.md) and sign the CLA if this is your first contribution.