追加数据帧时出现问题

import struct

# 假设数据帧格式为：2字节头部 + 4字节数据长度 + 数据部分
def create_data_frame(header, data):
    data_length = len(data)
    frame = struct.pack('!HH', header, data_length) + data.encode('utf-8')
    return frame

def append_data_frame(original_frame, new_data):
    # 解析原始数据帧
    header, data_length = struct.unpack('!HH', original_frame[:4])
    original_data = original_frame[6:6+data_length].decode('utf-8')
    
    # 创建新的数据帧
    new_frame = create_data_frame(header, original_data + new_data)
    
    return new_frame

# 示例使用
original_frame = create_data_frame(0x01, "Hello")
new_data = " World"
appended_frame = append_data_frame(original_frame, new_data)

print(appended_frame)