Adds support for truncating files after write operations, enabling proper
HTTP PUT semantics where the entire file content should be replaced.
Implementation:
- Added TOASTY_WRITE_TRUNCATE_AFTER flag (0x02) to ToastyFS API
- Updated file_tree_write() to accept truncate_after parameter:
* When true, sets file size to exactly offset+length
* Removes chunks beyond the new file size
* Marks removed chunks for garbage collection
- Metadata server extracts and passes truncate flag to file_tree_write()
- WAL replay passes false for truncate_after (already handled in original write)
- Web proxy PUT now uses both CREATE_IF_MISSING and TRUNCATE_AFTER flags
- Updated documentation in PROTOCOL.txt, DESIGN.txt, and web/DESIGN.txt
Benefits:
- Proper HTTP PUT semantics (replace entire file content)
- Efficient: single write operation truncates and updates file
- Works with both sync and async APIs
- Garbage collection automatically removes orphaned chunks
CRITICAL BUG FIX: The previous Windows implementation had a fatal flaw
where it deleted the old WAL file before renaming, creating a window
where all data could be lost if the rename failed.
Previous (BROKEN) Windows code:
remove_file_or_dir(wal->file_path); // Delete old file
rename(...); // <-- If this fails, we've lost all data!
New implementation uses MoveFileExW with MOVEFILE_REPLACE_EXISTING:
- Windows: MoveFileExW(..., MOVEFILE_REPLACE_EXISTING) atomically
replaces the destination file, matching Unix semantics
- Unix/Linux: rename() continues to atomically replace as before
- Both platforms now have atomic file replacement with no data loss window
This ensures durability on both platforms - if the operation fails at
any point, we still have either the old file or the new file, never
losing all data.
This commit addresses several important robustness issues in the WAL
implementation:
1. Fixed file_path lifetime issue:
- The file_path argument to wal_open() may not have the same lifetime
as the WAL structure
- Now allocate and copy the path string to ensure WAL owns its data
- Properly free the allocated path in wal_close()
- Added error cleanup path in wal_open() to prevent memory leaks
2. Replaced static arrays with dynamic allocation in next_entry():
- Static arrays were not thread-safe and had limited lifetimes
- Now dynamically allocate path buffer and hash buffers using sys_malloc
- Caller must free allocated fields after using the entry
- Added proper error cleanup to free allocations on failure
- Updated wal_open() to free entry fields after processing each entry
3. Improved swap_file() for cross-platform compatibility:
- On Unix/Linux: rename() atomically replaces the destination file
- On Windows: rename() doesn't overwrite, so delete old file first
- Added platform-specific handling with #ifdef _WIN32
- Ensures WAL rotation works correctly on both platforms
4. Added system.h include for sys_malloc/sys_free definitions
These changes ensure proper memory management, prevent leaks, and make
the WAL implementation more robust across different platforms.
This commit completes the Write-Ahead Log (WAL) implementation for the
metadata server, including all missing functionality and error fixes:
File System Changes (src/file_system.c):
- Implemented file_set_offset() using lseek (Linux) and SetFilePointer (Windows)
- Implemented file_get_offset() to get current file position
WAL Header Changes (src/wal.h):
- Added file_tree pointer to WAL structure for snapshot serialization
- Added file_path to WAL structure for rotation operations
WAL Implementation (src/wal.c):
- Fixed handle assignment bug in wal_open (was using wal->handle before assignment)
- Fixed missing return statement in append_begin()
- Implemented serialize_callback for writing file tree snapshots to WAL
- Implemented deserialize_callback for reading file tree snapshots from WAL
- Implemented next_entry() to read WAL entries from file during recovery
- Implemented wal_append_write() to write file modifications to WAL
- Implemented swap_file() for complete WAL file rotation:
* Creates temporary file with new snapshot
* Writes WAL header and serialized file tree
* Atomically replaces old WAL file
* Resets entry counter for new rotation cycle
- Added WAL file initialization for newly created files
- Added helper functions: read_exact, read_u8, read_u16, read_u32, read_u64, write_u32
- Fixed typo in comment (Not -> Now)
The WAL now supports:
- Full crash recovery by replaying logged operations
- Automatic file rotation when entry limit is reached
- Atomic file replacement to ensure durability
- Proper file locking throughout rotation process
cozis
Claude