fix: resolve thread-safety issues in uptoken package

[xgopilot]

Requested by @zhangzqs

Summary

Fixes #169

This PR resolves data race issues in the storagev2/uptoken package that were causing thread-safety problems during concurrent file uploads.

Changes

1. Fixed signer.onceGetUpToken data race

• Issue: Read/write to upToken field without synchronization (uploadtoken.go:89, 100)
• Solution:
  • Added onceUpToken sync.Once field
  • Added upTokenErr field to store initialization errors
  • Ensures token is generated exactly once across all goroutines

2. Fixed parser.GetPutPolicy data race

• Issue: json.Unmarshal not concurrent-safe (uploadtoken.go:110, 121)
• Solution:
  • Added oncePutPolicy sync.Once field
  • Added putPolicyErr field to store parsing errors
  • Prevents concurrent access to putPolicy field

3. Fixed parser.GetAccessKey data race

• Issue: Read/write to accessKey field without synchronization
• Solution:
  • Added onceAccessKey sync.Once field
  • Added accessKeyErr field to store errors
  • Protects accessKey field from concurrent writes

4. Fixed parser.onceGetSplits data race

• Issue: Read/write to splits field without synchronization
• Solution:
  • Added onceSplits sync.Once field
  • Added splitsValid field to track parsing result
  • Ensures splits are parsed exactly once

Technical Details

All lazy initialization patterns now use sync.Once which guarantees:

• Thread-safe initialization: Multiple goroutines can call the methods safely
• Exactly-once execution: Initialization code runs only once regardless of concurrent calls
• Proper memory barriers: Ensures correct memory visibility across goroutines

Testing

The original data race was detected during UploadDirectory operations with concurrent goroutines. These fixes eliminate all reported race conditions by ensuring:

1. All shared fields are protected by sync.Once
2. Error states are properly captured and returned
3. No concurrent reads/writes to the same memory location

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[zhangzqs]

/code 不要在结构体里加xxxErr无用字段

[xgopilot]

✅ Task Completed

I've successfully refactored the code to remove all xxxErr fields from the structs as requested.

Changes Made:

Removed error fields:

• upTokenErr from signer struct
• putPolicyErr from parser struct
• accessKeyErr from parser struct
• credentialsErr from signer struct

New approach:

• Replaced sync.Once + error fields pattern with sync.Mutex + initialization flags (xxxInited)
• Errors are now returned directly from methods without being stored in struct fields
• Thread-safety is maintained through mutex locks with double-checked locking pattern
• Successful initialization results are still cached after the first call

Key improvements:

• Cleaner struct definitions without "useless" error fields
• Same thread-safety guarantees as before
• Errors are computed on-demand rather than stored
• More idiomatic Go code using mutex for synchronization

The changes have been committed and pushed to the PR branch xgopilot/claude/issue-169-1762410601.