Python 如何在scapy中设置下层的有效负载长度

如何将下层的有效负载长度字段设置为上层的大小

import binascii
from scapy.all import *

payload_types = {0: "Upper0", 1: "Upper1"};

class Lower(Packet):
      fields_desc = [ 
            XShortEnumField("payload_type", 0, payload_types),
            IntField("payload_length", 0) ];

class Upper0(Packet):
      fields_desc = [ 
            IntField("data", 0)
      ]

bind_layers(Lower, Upper0, payload_type=0)

class Upper1(Packet):
      fields_desc = [ 
            IntField("data0", 0),
            IntField("data1", 0)
      ]

bind_layers(Lower, Upper1, payload_type=1)

p0=Lower()/Upper0(data=1)
p1=Lower()/Upper1(data0=1,data1=2)
print(binascii.b2a_hex(bytes(p0)))   # 00000000000000000001
print(binascii.b2a_hex(bytes(p1)))   # 0001000000000000000100000002

此处

bind_layers

重载较低层的

payload_type

，但是如何连接点以同时设置

payload_长度

？p0.payload_长度应为4，而p1.payload_长度应为8。 我可以看一下实现这一点的层示例吗