我收到来自客户端的数据包，其中包含许多字段。我成功读取了所有字段，但是当涉及到最后一个字段 tag_end 时，python 给了我一个错误：
unpack_from 需要至少 4 个字节的缓冲区未找到。
这是代码：
def set_bin(self, buf):
"""Reads a vector of bytes (probably received from network or
read from file) and tries to construct the packet structure
from it, by reading each packet member from the buffer. This
is somehow like deserializing the packet.
"""
assert isinstance(buf, bytearray), 'buffer type is not valid'
offset = 0
print("$$$$$$$$$$$$$$$$ set bin $$$$$$$$$$$$$$$$$")
try:
(self._tag_start, self._version, self._checksum, self._connection_id,
self._packet_seq) = Packet.PACKER_1.unpack_from(str(buf), offset)
except struct.error as e:
print(e)
raise DeserializeError(e)
except ValueError as e:
print(e)
raise DeserializeError(e)
#I=4 H=2 B=1
offset = Packet.OFFSET_GUID #14 correct
self._guid = buf[offset:offset+Packet.UUID_SIZE] #14-16 correct
offset = Packet.OFFSET_GUID + Packet.UUID_SIZE
print("$$$$$$$$$$$$$$$$ GUID read successfully $$$$$$$$$$$$$$$$$")
try:
(self._timestamp_sec, self._timestamp_microsec, self._command,
self._command_seq, self._subcommand, self._data_seq,
self._data_length) = Packet.PACKER_3.unpack_from(str(buf), offset)
except struct.error as e:
print(e)
raise DeserializeError(e)
except ValueError as e:
print(e)
raise DeserializeError(e)
print("$$$$$$$$$$$$$$$$ timestamps read successfully $$$$$$$$$$$$$$$$$")
offset = Packet.OFFSET_AUTHENTICATE
self._username = buf[offset:offset + self.USERNAME_SIZE] #Saman
offset += self.USERNAME_SIZE
print("$$$$$$$$$$$$$$$$ username read successfully $$$$$$$$$$$$$$$$$")
self._password = buf[offset:offset+self.USERNAME_SIZE]
offset += self.PASSWORD_SIZE
print("$$$$$$$$$$$$$$$$ password read successfully $$$$$$$$$$$$$$$$$")
self._data = buf[offset:offset+self._data_length]
offset = offset + self._data_length
print("$$$$$$$$$$$$$$$$ data read successfully $$$$$$$$$$$$$$$$$")
try:
(self._tag_end,) = Packet.PACKER_4.unpack_from(str(buf), offset)
except struct.error as e:
print(e)
raise DeserializeError(e)
except ValueError as e:
print(e)
raise DeserializeError(e)
print("$$$$$$$$$$$$$$$$ tag end read successfully $$$$$$$$$$$$$$$$$")
if len(buf) != Packet.PACKER.size + self._data_length:
print('failed to deserialize binary data correctly and construct the packet due to extra data')
else:
print('@@@@@@@@@@@@@@@ Deserialized Successfully')
这是代码中使用的一些常量：
STRUCT_FORMAT_STR = r'=IHIHH 16B IIHHHHH I 6c 9c' #Saman
STRUCT_FORMAT_STR_1 = r'=IHIHH'
STRUCT_FORMAT_STR_2 = r'=16B'
STRUCT_FORMAT_STR_3 = r'=IIHHHHH'
STRUCT_FORMAT_STR_4 = r'=I'
STRUCT_FORMAT_STR_5 = r'=6c'
STRUCT_FORMAT_STR_6 = r'=9c'
UUID_SIZE = 16
OFFSET_GUID = 14
#OFFSET_DATA = 48 #shifting offset data by 15 char
OFFSET_AUTHENTICATE = 48
PACKER = struct.Struct(str(STRUCT_FORMAT_STR)) #Saman
PACKER_1 = struct.Struct(str(STRUCT_FORMAT_STR_1))
PACKER_2 = struct.Struct(str(STRUCT_FORMAT_STR_2))
PACKER_3 = struct.Struct(str(STRUCT_FORMAT_STR_3))
PACKER_4 = struct.Struct(str(STRUCT_FORMAT_STR_4))
PACKER_5 = struct.Struct(str(STRUCT_FORMAT_STR_5))
PACKER_6 = struct.Struct(str(STRUCT_FORMAT_STR_6))
BYTES_TAG_START = PACKER_4.pack(TAG_START)
BYTES_TAG_END = PACKER_4.pack(TAG_END)
以及数据包对象的初始化，其中初始化字段：
def init（自我，**kwargs）：
如果 kwargs 中的“buf”：
self.set_bin(kwargs['buf'])
别的：
在 Packet.RTCINET_COMMANDS.values() 中断言 kwargs['command'] 和 Packet.RTCINET_COMMANDS.values() 中的 kwargs['subcommand'], '未定义的协议命令'
断言 isinstance(kwargs['data'], bytearray), '数据字段类型无效'
对于（'命令'，'子命令'，'数据'）中的字段：
setattr(self, '_' + 字段, kwargs[字段])
self._tag_start = Packet.TAG_START
self._version = Packet.VERSION_CURRENT % (Packet.USHRT_MAX + 1)
self._checksum = Packet.CRC_INIT
self._connection_id = kwargs.get('connection_id', 0) % (Packet.USHRT_MAX + 1)
self._packet_seq = Packet.PACKET_SEQ
Packet.PACKET_SEQ = (Packet.PACKET_SEQ + 1) % (Packet.USHRT_MAX + 1)
self._guid = uuid.uuid4().bytes
dt = datetime.datetime.now()
self._timestamp_sec = int(time.mktime(dt.timetuple()))
self._timestamp_microsec = dt.microsecond
# self._command = kwargs['command']
self._command_seq = kwargs.get('command_seq', 0)
# self._subcommand = kwargs['subcommand']
self._data_seq = kwargs.get('data_seq', 0)
self._data_length = len(kwargs['data'])
self._username = Packet.USERNAME #Saman
self._password = Packet.PASSWORD
我已确保以正确的顺序读取所有字段，因为它是由客户端程序写入数据包中的。但我仍然无法解决这个问题。
您知道如何解决这个问题吗？
