# Step 3: Write uploaded data data = request.get_data() os.write(fd, data)
# Step 4: Atomic rename over existing? No – we must ensure final doesn't exist if os.path.exists(final_path): os.close(fd) os.unlink(temp_path) abort(409, "Final destination file already exists – exclusive violation") httpsfiledottofolder exclusive
# Step 2: Acquire exclusive advisory lock on temp file fcntl.flock(fd, fcntl.LOCK_EX) # Step 3: Write uploaded data data = request
@app.route('/exclusive-upload/<filename>', methods=['PUT']) def exclusive_upload(filename): # Security: ensure no path traversal safe_filename = os.path.basename(filename) final_path = os.path.join(TARGET_BASE, safe_filename) temp_path = final_path + ".tmp_exclusive" os.O_CREAT | os.O_EXCL | os.O_WRONLY
# Step 1: Try to create temp file with exclusive flag try: fd = os.open(temp_path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600) except FileExistsError: abort(409, "Temporary conflict – retry")