def validatePacket(packet):
if not IP.validateChecksumZero(packet[0:20]):
return False, "IP"
else:
print "IP VALIDATION: SUCCESS"
ip_header = IP.unpackHeader(packet[0:20])
#Get Length of IP header
ip_ver = ip_header[0] >> 4
ip_header_length = ip_header[0] & 0xF
ip_length = ip_header_length * 4
tcp_packet = packet[ip_length:]
pseudo = pack('!4s4sBBH', ip_header[8], ip_header[9], 0, socket.IPPROTO_TCP, len(tcp_packet))
if not TCP.validateChecksumZero(pseudo + tcp_packet):
return False, "TCP"
else:
print "TCP VALIDATION: SUCCESS"
return True, ""
sender_socket.sendto(syn_packet, (DESTINATION_IP, DESTINATION_PORT))
#Time when the packet was sent
packet_sent_time = time.time()
#WAIT FOR A SYN_ACK
while True:
try:
packet = receiver_socket.recvfrom(65565)
packet = packet[0]
#print packet
validation_status, faulty_packet = validatePacket(packet)
if validation_status:
#IP header bytes
ip_header = IP.unpackHeader(packet[0:20])
if socket.inet_ntoa(ip_header[8]) == DESTINATION_IP and socket.inet_ntoa(ip_header[9]) == SOURCE_IP:
#Get Length of IP header
ip_ver = ip_header[0] >> 4
ip_header_length = ip_header[0] & 0xF
ip_length = ip_header_length * 4
tcp_header = TCP.unpackHeader(packet[ip_length: ip_length + 20])
ack = (tcp_header[5] & 0x10) >> 4
syn = (tcp_header[5] & 0x02) >> 1
if ack == 1 and syn == 1 and tcp_header[0] == DESTINATION_PORT and tcp_header[1] == SOURCE_PORT and tcp_header[3] == (ACK_NUM + 1):
#SYN-ACK received
SEQ_NUM = tcp_header[2] + 1
SEQ_START = tcp_header[2]
ACK_NUM = tcp_header[3]
