class Protocol:
 """
 规定：
 数据包头部占4字节
 整型占4字节
 字符串长度位占2字节
 字符串不定长
 """
 
 def __init__(self, bs=None):
 """
 如果bs为None则代表需要创建一个数据包
 否则代表需要解析一个数据包
 """
 if bs:
  self.bs = bytearray(bs)
 else:
  self.bs = bytearray(0)
 
 def get_int32(self):
 try:
  ret = self.bs[:4]
  self.bs = self.bs[4:]
  return int.from_bytes(ret, byteorder='little')
 except:
  raise Exception("数据异常！")
 
 def get_str(self):
 try:
  # 拿到字符串字节长度(字符串长度位2字节)
  length = int.from_bytes(self.bs[:2], byteorder='little')
  # 再拿字符串
  ret = self.bs[2:length + 2]
  # 删掉取出来的部分
  self.bs = self.bs[2 + length:]
  return ret.decode(encoding='utf8')
 except:
  raise Exception("数据异常！")
 
 def add_int32(self, val):
 bytes_val = bytearray(val.to_bytes(4, byteorder='little'))
 self.bs += bytes_val
 
 def add_str(self, val):
 bytes_val = bytearray(val.encode(encoding='utf8'))
 bytes_length = bytearray(len(bytes_val).to_bytes(2, byteorder='little'))
 self.bs += (bytes_length + bytes_val)
 
 def get_pck_not_head(self):
 return self.bs
 
 def get_pck_has_head(self):
 bytes_pck_length = bytearray(len(self.bs).to_bytes(4, byteorder='little'))
 return bytes_pck_length + self.bs
 
 
if __name__ == '__main__':
 p = Protocol()
 
 p.add_int32(666)
 p.add_str("你好啊")
 p.add_str("hello")
 p.add_int32(888)
 
 r = Protocol(p.get_pck_not_head())
 
 print(r.get_int32())
 print(r.get_str())
 print(r.get_str())
 print(r.get_int32())