[英]Scapy: Adding more fields to fields_desc
我正在嘗試創建一個新協議。 問題是,需要向 fields_desc 動態添加更多字段,但我不確定如何實現。 在 Scapy 文檔中,我讀到 Scapy 中的圖層實際上只是一個可以操作的字段列表,但 Scapy 似乎不喜歡以下內容:
>>> class SomePacket(Packet):
...
... name = "SomePacket"
... fields_desc = [ IntField("Number",0) ]
...
... def add_IntField(self, name, value):
... self.fields_desc.append(IntField(name, value))
...
>>> packet = SomePacket()
>>> ls(packet)
Number : IntField = 0 (0)
>>> packet.add_IntField("X",1)
>>> ls(packet)
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/usr/lib/python2.7/dist-packages/scapy/packet.py", line 1212, in ls
print "%-10s : %-20s = %-15s (%s)" % (f.name, f.__class__.__name__, repr(getattr(obj,f.name)), repr(f.default))
File "/usr/lib/python2.7/dist-packages/scapy/packet.py", line 176, in __getattr__
fld,v = self.getfield_and_val(attr)
File "/usr/lib/python2.7/dist-packages/scapy/packet.py", line 172, in getfield_and_val
return self.payload.getfield_and_val(attr)
File "/usr/lib/python2.7/dist-packages/scapy/packet.py", line 1057, in getfield_and_val
raise AttributeError(attr)
AttributeError: X
>>> packet = SomePacket()
>>> ls(packet)
Number : IntField = 0 (0)
X : IntField = 1 (1)
因此,當我在添加字段后第一次嘗試顯示數據包內容時,它不起作用。 但是,如果我再次創建數據包,該屬性會突然出現。 我究竟做錯了什么?
你不應該那樣做。 當你創建一個新的SomePacket
對象時, Packet
的__init__()
函數會使用fields_desc
列表來初始化很多其他的東西。 向fields_desc
動態添加新值會導致不一致,從而產生給定的錯誤。
一種解決方案是將add_IntField
函數更改為classmethod
並在創建新對象之前添加所需的字段,如下所示:
>>> class SomePacket(Packet):
...
... name = "SomePacket"
... fields_desc = [ IntField("Number",0) ]
...
... @classmethod
... def add_IntField(cls, name, value):
... cls.fields_desc.append(IntField(name, value))
>>> SomePacket.add_IntField('X', 1)
>>> packet = SomePacket()
>>> ls(packet)
Number : IntField = 0 (0)
X : IntField = 1 (1)
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