inet.py 文件源码

def post_build(self, p, pay):
        p += pay
        dataofs = self.dataofs
        if dataofs is None:
            dataofs = 5+((len(self.get_field("options").i2m(self,self.options))+3)/4)
            p = p[:12]+chr((dataofs << 4) | ord(p[12])&0x0f)+p[13:]
        if self.chksum is None:
            if isinstance(self.underlayer, IP):
                if self.underlayer.len is not None:
                    ln = self.underlayer.len-20
                else:
                    ln = len(p)
                psdhdr = struct.pack("!4s4sHH",
                                     inet_aton(self.underlayer.src),
                                     inet_aton(self.underlayer.dst),
                                     self.underlayer.proto,
                                     ln)
                ck=checksum(psdhdr+p)
                p = p[:16]+struct.pack("!H", ck)+p[18:]
            elif conf.ipv6_enabled and isinstance(self.underlayer, scapy.layers.inet6.IPv6) or isinstance(self.underlayer, scapy.layers.inet6._IPv6ExtHdr):
                ck = scapy.layers.inet6.in6_chksum(socket.IPPROTO_TCP, self.underlayer, p)
                p = p[:16]+struct.pack("!H", ck)+p[18:]
            else:
                warning("No IP underlayer to compute checksum. Leaving null.")
        return p