Question

我收到来自客户端的数据包，包含许多字段。我成功读取了所有字段，但是当涉及到tag_end的最后一个字段时，python给了我一个错误：

unpack_from需要至少4个字节的缓冲区。

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)

并初始化数据包对象，初始化字段：

def init （自我，** kwargs）：如果'buf'在kwargs： self.set_bin（kwargs [ 'BUF']）其他：在Packet.RTCINET_COMMANDS.values（）中的kwargs ['command']和Packet.RTCINET_COMMANDS.values（）中的kwargs ['subcommand']断言，'Undefined protocol command' assert isinstance（kwargs ['data']，bytearray），'数据字段的无效类型' for field in（'command'，'subcommand'，'data'）： setattr（self，'_'+ field，kwargs [field]）

    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的。但我仍然无法解决这个问题。

你知道如何解决这个问题吗？

Answer 1

问题似乎是你无缘无故地将事情转移到str。

在某些地方，例如PACKER_1 = struct.Struct(str(STRUCT_FORMAT_STR_1))，它会降低您的代码的可读性和可理解性，但不会影响实际输出。例如，STRUCT_FORMAT_STR_1已经是str，因此str(STRUCT_FORMAT_STR_1)与str相同。

但在其他地方，情况要糟糕得多。特别是，请查看Packet.PACKER_1.unpack_from(str(buf), offset)之类的所有行。在那里，buf是bytearray。（必须是这样，因为您assert它。）在str上调用bytearray会为您提供bytearray的字符串表示形式。例如：

>>> b = bytearray(b'abc')
>>> len(b)
3
>>> s = str(b)
>>> s
"bytearray(b'abc')"
>>> len(s)
17

该字符串表示通常不会与您所代表的实际缓冲区具有相同的长度。因此，难怪你得到错误的长度错误。（如果你真的不走运并且没有任何此类错误，那么你就是在阅读垃圾值。）

那么，您应该怎么做才能将bytearray转换为struct模块可以处理的内容？没有！正如the docs所说：

几个struct函数（和Struct的方法）采用缓冲区参数。这指的是实现缓冲区协议并提供可读或可读写缓冲区的对象。用于此目的的最常见类型是bytes和bytearray ...

unpack_from需要至少4个字节的缓冲区

1 个答案: