icmp.py

来自「Network Administration Visualized 网络管理可」· Python 代码 · 共 125 行

"""ICMP packets.
"""

# Copyright 1997, Corporation for National Research Initiatives
# written by Jeremy Hylton, [e-mail]

import inet
import array
import struct

ICMP_MINLEN = 8
ICMP_MASKLEN = 12
ICMP_ECHOREPLY = 0
ICMP_UNREACH = 3
ICMP_UNREACH_NET = 0
ICMP_UNREACH_HOST = 1
ICMP_UNREACH_PROTOCOL = 2
ICMP_UNREACH_PORT = 3
ICMP_UNREACH_NEEDFRAG = 4
ICMP_UNREACH_SRCFAIL = 5
ICMP_SOURCEQUENCH = 4
ICMP_REDIRECT = 5
ICMP_REDIRECT_NET = 0
ICMP_REDIRECT_HOST = 1
ICMP_REDIRECT_TOSNET = 2
ICMP_REDIRECT_TOSHOST = 3
ICMP_ECHO = 8
ICMP_TIMXCEED = 11
ICMP_TIMXCEED_INTRANS = 0
ICMP_TIMXCEED_REASS = 1
ICMP_PARAMPROB = 12
ICMP_TSTAMP = 13
ICMP_TSTAMPREPLY = 14
ICMP_IREQ = 15
ICMP_IREQREPLY = 16
ICMP_MASKREQ = 17
ICMP_MASKREPLY = 18

class Packet:
    """Basic ICMP packet definition.

    Equivalent to ICMP_ECHO_REQUEST and ICMP_REPLY packets.
    Other packets are defined as subclasses probably.
    """

    def __init__(self, packet=None, cksum=1):
	if packet:
	    self.__disassemble(packet, cksum)
	else:
	    self.type = 0
	    self.code = 0
	    self.cksum = 0
	    self.id = 0
	    self.seq = 0
	    self.data = ''

    def __repr__(self):
	return "<ICMP packet %d %d %d %d>" % (self.type, self.code,
					      self.id, self.seq)

    def assemble(self, cksum=1):
	idseq = struct.pack('HH', self.id, self.seq)
	packet = chr(self.type) + chr(self.code) + '\000\000' + idseq \
		 + self.data
	if cksum:
	    self.cksum = inet.cksum(packet)
	    packet = chr(self.type) + chr(self.code) \
		     + struct.pack('H', self.cksum) + idseq + self.data
	# Don't need to do any byte-swapping, because idseq is
	# appplication defined and others are single byte values.
	self.__packet = packet
	return self.__packet

    def __disassemble(self, packet, cksum=1):
	if cksum:
	    our_cksum = inet.cksum(packet)
	    if our_cksum != 0:
		raise ValueError, packet

	self.type = ord(packet[0])
	self.code = ord(packet[1])
	elts = struct.unpack('HHH', packet[2:8])
	[self.cksum, self.id, self.seq] = map(lambda x:x & 0xffff, elts)
	self.data = packet[8:]

    def __compute_cksum(self):
	"Use inet.cksum instead"
	packet = self.packet
	if len(packet) & 1:
	    packet = packet + '\0'
	words = array.array('H', packet)
	sum = 0
	for word in words:
	    sum = sum + (word & 0xffff)
	hi = sum >> 16
	lo = sum & 0xffff
	sum = hi + lo
	sum = sum + (sum >> 16)
	return (~sum) & 0xffff
	

class TimeExceeded(Packet):
    
    def __init__(self, packet=None, cksum=1):
	Packet.__init__(self, packet, cksum)
	if packet:
	    if self.type != ICMP_TIMXCEED:
		raise ValueError, "supplied packet of wrong type"
	else:
	    self.type = ICMP_TIMXCEED
	    self.id = self.seq = 0

class Unreachable(Packet):
    
    def __init__(self, packet=None, cksum=1):
	Packet.__init__(self, packet, cksum)
	if packet:
	    if self.type != ICMP_UNREACH:
		raise ValueError, "supplied packet of wrong type"
	else:
	    self.type = ICMP_UNREACH
	    self.id = self.seq = 0