mysql-protocol中对编码长度整数型的规则

def read_lc_int(buf):
    """
    Takes a buffer and reads an length code string from the start.

    Returns a tuple with buffer less the integer and the integer read.
    """
    if not buf:
        raise ValueError("Empty buffer.")

    lcbyte = buf[0]
    if lcbyte == 251:
        return (buf[1:], None)
    elif lcbyte < 251:
        return (buf[1:], int(lcbyte))
    elif lcbyte == 252:
        return (buf[3:], struct_unpack(‘<xH‘, buf[0:3])[0])
    elif lcbyte == 253:
        return (buf[4:], struct_unpack(‘<I‘, buf[1:4] + b‘\x00‘)[0])
    elif lcbyte == 254:
        return (buf[9:], struct_unpack(‘<xQ‘, buf[0:9])[0])
    else:
        raise ValueError("Failed reading length encoded integer")