fileutil

func WriteFileAtomic ¶

func WriteFileAtomic(path string, data []byte, perm os.FileMode) error

WriteFileAtomic atomically writes data to a file using a temp file + rename pattern.

This guarantees that the target file is either: - Completely written with the new data - Unchanged (if any step fails before rename)

The function: 1. Creates a temp file in the same directory (original untouched) 2. Writes data to temp file 3. Syncs data to disk (critical for SD cards/flash storage) 4. Sets file permissions 5. Syncs directory metadata (ensures rename is durable) 6. Atomically renames temp file to target path

Safety guarantees: - Original file is NEVER modified until successful rename - Temp file is always cleaned up on error - Data is flushed to physical storage before rename - Directory entry is synced to prevent orphaned inodes

Parameters:

• path: Target file path
• data: Data to write
• perm: File permission mode (e.g., 0o600 for secure, 0o644 for readable)

Returns:

• Error if any step fails, nil on success

Example:

// Secure config file (owner read/write only)
err := utils.WriteFileAtomic("config.json", data, 0o600)

// Public readable file
err := utils.WriteFileAtomic("public.txt", data, 0o644)