protocol.py 文件源码

def pack_into(self, buff, offset):
        """Serialize and write to ``buff`` starting at offset ``offset``.

        Intentionally follows the pattern of ``struct.pack_into``

        :param buff: The buffer to write into
        :param offset: The offset to start the write at
        """
        # NB a length of 0 means an empty string, whereas -1 means null
        len_key = -1 if self.partition_key is None else len(self.partition_key)
        len_value = -1 if self.value is None else len(self.value)
        fmt = '!BBi%dsi%ds' % (max(len_key, 0), max(len_value, 0))
        args = (self.MAGIC,
                self.compression_type,
                len_key,
                self.partition_key or b"",
                len_value,
                self.value or b"")
        struct.pack_into(fmt, buff, offset + 4, *args)
        fmt_size = struct.calcsize(fmt)
        data = buffer(buff[(offset + 4):(offset + 4 + fmt_size)])
        crc = crc32(data) & 0xffffffff
        struct.pack_into('!I', buff, offset, crc)