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Enhance TemporaryFile to match C's tmpfile() security and functionality #90

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Enhance TemporaryFile to match C's tmpfile() security and functionality #90

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@konard konard commented Sep 12, 2025 •
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Summary

This pull request enhances the TemporaryFile class to provide security features equivalent to C's tmpfile() function or better, addressing issue #82.

Key Improvements

🔒 Enhanced Security

  • Eliminates race conditions: Replaced insecure Path.GetTempFileName() with secure random filename generation using Path.GetRandomFileName()
  • Prevents file hijacking: Uses FileMode.CreateNew to ensure files don't already exist
  • Restrictive permissions: Implements Windows ACL (current user only) and Unix 600-equivalent permissions
  • Exclusive access: Uses FileShare.None to prevent concurrent access while file is open

🚀 Better Functionality

  • Direct stream access: Added FileStream Stream property for direct I/O operations like C's tmpfile()
  • Implicit conversions: Support for both string (filename) and FileStream implicit operators
  • Automatic cleanup: Uses FileOptions.DeleteOnClose for reliable deletion
  • Finalizer support: Ensures cleanup even during abnormal termination

🔧 Improved Reliability

  • Race condition handling: Retry logic (up to 1000 attempts) for unique file creation
  • Robust disposal: Enhanced error handling during cleanup operations
  • Registry tracking: Improved temporary file registry management with add/remove functionality

Technical Details

Before (Issues)

  • Used Path.GetTempFileName() which has known security vulnerabilities
  • Only provided filename access, requiring separate file operations
  • Relied on manual cleanup without proper error handling
  • Vulnerable to race conditions and predictable filename attacks

After (Improvements)

  • Secure random filename generation with collision avoidance
  • Direct FileStream access providing tmpfile-like functionality
  • Multiple layers of automatic cleanup (DeleteOnClose + finalizer)
  • Comprehensive error handling and security measures

Test Coverage

Added comprehensive tests covering:

  • ✅ Basic temporary file creation and cleanup
  • ✅ Direct stream access and I/O operations
  • ✅ Unique filename generation
  • ✅ Secure file creation verification
  • ✅ Proper disposal and cleanup behavior
  • ✅ Stream properties matching tmpfile behavior

Compatibility

  • Fully backward compatible - existing code continues to work unchanged
  • Additional functionality - new Stream property provides enhanced capabilities
  • Cross-platform - Works on both Windows (with ACL) and Unix-like systems

Performance

  • Minimal performance impact from security improvements
  • Efficient retry mechanism for filename collision handling
  • Optimized disposal path with proper resource management

Test Results

All tests pass successfully:

  • 7 total tests: 7 passed, 0 failed
  • Comprehensive coverage of new functionality and security features

🤖 Generated with Claude Code

Resolves #82

@konard
Initial commit with task details for issue #82
57e2892 
Adding CLAUDE.md with task information for AI processing.
This file will be removed when the task is complete.

Issue: #82
@konard konard self-assigned this Sep 12, 2025
@konard @claude
Enhance TemporaryFile to match C's tmpfile() security and functionality
a032a6b 
Major improvements:
- Replace insecure Path.GetTempFileName() with secure random filename generation
- Add direct FileStream access like C's tmpfile() for better usability
- Implement FileOptions.DeleteOnClose for automatic cleanup
- Add restrictive file permissions (Windows ACL, Unix 600 equivalent)
- Improve race condition handling with retry logic for unique file creation
- Add finalizer for cleanup during abnormal termination
- Enhanced test coverage with tmpfile-like behavior verification

Security benefits:
- Eliminates race conditions from predictable filenames
- Uses CreateNew mode to prevent file hijacking attacks
- Sets restrictive permissions accessible only to current user
- Automatic deletion on both normal and abnormal termination

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
@konard konard changed the title [WIP] Make sure is as good as from C/C++ or better. Enhance TemporaryFile to match C's tmpfile() security and functionality Sep 12, 2025
@konard konard marked this pull request as ready for review September 12, 2025 21:26
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Make sure TemproryFile is as good as tmpfile from C/C++ or better.

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