#!/usr/bin/python

from socket import *
from dpkt.dns import *
import dpkt.ethernet, struct, time, sys

EtherType_IPv6 = 0x86DD

Protocol_TCP       =  6
Protocol_UDP       = 17
Protocol_IPv6_Frag = 44
Protocol_ICMPv6    = 58

ICMPv6Type_PTB = 2

DNSFlags_TC = 2

try:
	d = socket(AF_INET6, SOCK_DGRAM)		# To prevent ICMPv6
	d.bind(('', 53))				# dst port unreachable
except:
	pass

s = socket(AF_PACKET, SOCK_RAW, EtherType_IPv6)		# Open raw IPv6 socket
s.bind(( 'eth0' if len(sys.argv) == 1 else sys.argv[1]	# On eth0 or the given
       , EtherType_IPv6))				# interface.

frag_id = int(time.time())				# Fragment id

while True:
	frame = s.recv(1500 + 14)			# max packet size +
							# ethernet header size

	eth = dpkt.ethernet.Ethernet(frame)		# We asked for IPv6!
	assert eth.type == EtherType_IPv6, "Non IPv6!"	# Expect IPv6!

	ipv6 = eth.data
	if ipv6.nxt != Protocol_UDP:	continue	# Skip when not UDP

	udp = ipv6.data
	if udp.dport != 53:		continue	# Skip when not DNS
	
	dns = DNS(udp.data)
	if dns.qr != DNS_Q		\
	or dns.opcode != DNS_QUERY 	\
	or len(dns.qd) != 1:		continue	# Skip when not a query

	dns.op |= DNS_AA				# Turn query packet
	dns.rcode = DNS_RCODE_NOERR			# into a response
	dns.qr  = DNS_R					# packet.
	dns.op &= ~(DNS_AD|DNS_CD)
	dns.ar  = list()				# No OPT leftovers...

	qname   = dns.qd[0].name
	qname_l = qname.lower().split('.')
	qcls    = dns.qd[0].cls
	qtype   = dns.qd[0].type
	pkt_sz  = [int(l[1:]) for l in qname_l
	           if len(l) > 1 and l[0] == 'p' and l[1:].isdigit()]
	pkt_sz  = pkt_sz[0] if pkt_sz else None
	frag_sz = [int(l[1:]) for l in qname_l
	           if len(l) > 1 and l[0] == 'f' and l[1:].isdigit()]
	frag_sz = frag_sz[0] if frag_sz else None

	if qtype == DNS_AAAA:
		dns.an.append(DNS.RR( cls = qcls, type = qtype, name = qname
		                    , ip6 = ipv6.dst if qname_l[0] == 'ns'
				                     else ipv6.src
		                    , ttl = 30
				    ))


	elif qtype == DNS_NS:
		dns.an.append(DNS.RR( cls = qcls, type = qtype, name = qname
		                    , nsname = 'ns.' + qname
		                    , ttl = 30
				    ))
		dns.ar.append(DNS.RR( cls = qcls, type = DNS_AAAA
				    , name = 'ns.' + qname, ip6 = ipv6.dst
		                    , ttl = 30
				    ))

	elif qtype == DNS_SOA:
		dns.an.append(DNS.RR( cls = qcls, type = qtype, name = qname
		                    , mname   = 'ns.' + qname
			            , rname   = 'willem.nlnetlabs.nl'
			            , serial  = int(time.time())
			            , refresh =  40
			            , retry   =  10
			            , expire  = 100
			            , minimum =   5
		                    , ttl = 30
			            ))
	elif qtype == DNS_TXT:
		dns.an.append(DNS.RR( cls = qcls, type = qtype, name = qname
		                    , text = [ ( 'received at %s from [%s].%d'
		                               + ' for [%s].%d' )
		                    % ( time.strftime('%Y-%m-%d %H:%M:%S.') +
		                        ('%.2f' % time.time())[-2:] +
					time.strftime(' %Z')
		                      , inet_ntop(AF_INET6, ipv6.src)
				      , udp.sport
		                      , inet_ntop(AF_INET6, ipv6.dst)
				      , udp.dport
				      )]
		                    , ttl = 30
				    ))
		for once in (1,):
			if pkt_sz is None: break
			if pkt_sz <= 0 or pkt_sz > 65535: break
			cur_sz = len(str(dns)) + 48
			while cur_sz < pkt_sz:
				if pkt_sz - cur_sz <= 41:
					txt = [ 'padding.....................'[
						:(pkt_sz - cur_sz - 13)]]
				else:
					txt = [ '%5d more bytes'
					      % (pkt_sz - cur_sz) ]
				dns.an.append(DNS.RR( cls = qcls, type = qtype
				                    , name = qname
						    , text = txt
						    , ttl = 30
						    ))
				cur_sz = len(str(dns)) + 48

	elif qname_l[0] == 'ns':
		dns.ns.append(DNS.RR( cls = qcls, type = DNS_SOA, name = qname[3:]
		                    , mname   = qname
			            , rname   = 'willem.nlnetlabs.nl'
			            , serial  = int(time.time())
			            , refresh =  40
			            , retry   =  10
			            , expire  = 100
			            , minimum =   5
		                    , ttl = 30
			            ))

		

	## --------------------------------------------------------------------

	log_xtra = ''
	eth.src, eth.dst = eth.dst, eth.src

	udp.data = str(dns)
	udp.ulen = len(udp.data) + 8			# Including header size
	udp.sport, udp.dport = udp.dport, udp.sport	# Swap ports
	udp.sum  = 0					# Reset to recalculate

	ipv6.data = udp
	ipv6.nxt = Protocol_UDP
	ipv6.plen = len(ipv6.data)			# Reuse header
	ipv6.src, ipv6.dst = ipv6.dst, ipv6.src		# swap addresses

	str(ipv6)					# Set UDP checksum
	udpdata = str(ipv6.data)			# UDP data + checksum

	for once in (1,):
		if frag_sz is not None:
			if frag_sz >= 56 and frag_sz <= 1496 \
			                 and frag_sz % 8 == 0:
				frag_sz -= 48
				break

		if '2frags' in qname_l:
			frag_sz = (len(udpdata) + 15) / 16 * 8
			if frag_sz >= 8 and frag_sz <= 1448:
				break

		if len(udpdata) > 1460:
			frag_sz = 1448
		elif '1frag' in qname_l and len(udpdata) <= 1452:
			frag_sz = len(udpdata)
		else:
			frag_sz = 0
	
	if frag_sz:
		offset = 0
		while True:
			more = int(offset + frag_sz < len(udpdata))
			frag  = chr(Protocol_UDP)		\
			      + '\x00'				\
			      + struct.pack('!H', offset + more)\
			      + struct.pack('I', frag_id)[:4]

			ipv6.data = frag + udpdata[offset:offset+frag_sz]
			ipv6.plen = len(ipv6.data)
			ipv6.nxt  = Protocol_IPv6_Frag

			log_xtra += ' (%d..%d)' % ( offset
			                          , offset + ipv6.plen - 8)

			if not more: break

			eth.data = ipv6
			s.send(str(eth))
			offset += frag_sz

		frag_id += 1
		frag_id %= 1 << 32

	eth.data = ipv6
	s.send(str(eth))
	dns = DNS(udp.data)
	print "%s Sent %s. TYPE%.3d to %s%s" % (
		time.strftime('%Y-%m-%d %H:%M:%S.')+
			('%.2f' % time.time())[-2:],
		qname, qtype, inet_ntop(AF_INET6, ipv6.dst), log_xtra
	)