Re: TLV based protocols

Hi,


> Anybody done any work in scapy on TLV based protocols rather than  
> static
> header types?

Here is my attempt to make TLV more generic in scapy using mechanisms  
found in actual DNS* objects.

It is fairly basic:
- build your TLV from Packet

class TLVPacket(Packet):
  name = 'TLV'
  fields_desc = [ ByteField('type', 0),
                  ByteField('len', None),
                  StrField('value', None)
                ]

- build your TLVCountField from the new (Short|Byte)CountField

class TLVCountField(ShortCountField):
  def __init__(self, name, default, field):
    ShortCountField.__init__(self, name, default, field, TLVPacket)

- build your TLVField from MainCountField and implement dissectme()

class TLVField(MainCountField):
  def __init__(self, name, countfld):
    MainCountField.__init__(self, name, countfld)
  # Note: each instance of MainCountField should re-implement  
dissectme()
  def dissectme(self, s, p):
    t = s[p:p+2]
    type,l = struct.unpack('BB', t)
    tlv = TLVPacket(s[p:p+2+l])
    p = p+l+2
    return tlv,p

- use them in a Packet

class Header(Packet):
  name = 'TLV based header'
  fields_desc = [
                  TLVCountField('num', None, 'tlv'),
                  TLVField('tlv', 'num')
                 ]

- use it
 tlv=Header(num=2, tlv=TLVPacket(type=1, len=4, value='toto')/ 
TLVPacket(type=2, len=5, value='pouet'))

I think it is better to make DHCPOptionsField more generic. The  
payload operator / is somwhow confusing and the tlv field in the  
packet should be a list.

Guillaume

tlv.py
Description: Text Data

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