import socket
import sys
import time
import struct

HOST, PORT = "10.60.66.66", 10086

def make_forward_iphdr(source_ip = '1.0.0.1', dest_ip = '2.0.0.2', proto = socket.IPPROTO_UDP) :
    # ip header fields
    ip_ihl = 5
    ip_ver = 4
    ip_tos = 0
    ip_tot_len = 0  # kernel will fill the correct total length
    ip_id = 54321   #Id of this packet
    ip_frag_off = 0
    ip_ttl = 255
    ip_proto = proto
    ip_check = 0    # kernel will fill the correct checksum
    ip_saddr = socket.inet_aton ( source_ip )   #Spoof the source ip address if you want to
    ip_daddr = socket.inet_aton ( dest_ip )

    ip_ihl_ver = (ip_ver << 4) + ip_ihl

    # the ! in the pack format string means network order
    ip_header = struct.pack('!BBHHHBBH4s4s', ip_ihl_ver, ip_tos, ip_tot_len, ip_id, ip_frag_off, ip_ttl, ip_proto, ip_check, ip_saddr, ip_daddr)
    return ip_header

def make_forward_udphdr(src_port = 1024, dst_port = 10086) :
    udp_header = struct.pack('!HHHH', src_port, dst_port, 0, 0)
    return udp_header
    
# checksum functions needed for calculation checksum
def checksum(msg):
    s = 0

    # loop taking 2 characters at a time
    for i in range(0, len(msg), 2):
        w = ord(msg[i]) + (ord(msg[i+1]) << 8 )
        s = s + w

    s = (s>>16) + (s & 0xffff);
    s = s + (s >> 16);

    #complement and mask to 4 byte short
    s = ~s & 0xffff

    return s
    
def make_tcp_data(ip_header, src_port = 1024, dst_port = 10086, source_ip='1.0.0.1', dest_ip='2.0.0.2', user_data = 'test') :
    tcp_source = src_port    # source port
    tcp_dest = dst_port   # destination port
    tcp_seq = 454
    tcp_ack_seq = 0
    tcp_doff = 5    #4 bit field, size of tcp header, 5 * 4 = 20 bytes
    #tcp flags
    tcp_fin = 0
    tcp_syn = 1
    tcp_rst = 0
    tcp_psh = 0
    tcp_ack = 0
    tcp_urg = 0
    tcp_window = socket.htons (5840)    #   maximum allowed window size
    tcp_check = 0
    tcp_urg_ptr = 0

    tcp_offset_res = (tcp_doff << 4) + 0
    tcp_flags = tcp_fin + (tcp_syn << 1) + (tcp_rst << 2) + (tcp_psh <<3) + (tcp_ack << 4) + (tcp_urg << 5)

    # the ! in the pack format string means network order
    tcp_header = struct.pack('!HHLLBBHHH' , tcp_source, tcp_dest, tcp_seq, tcp_ack_seq, tcp_offset_res, tcp_flags,  tcp_window, tcp_check, tcp_urg_ptr)
    
    source_address = socket.inet_aton(source_ip)
    dest_address = socket.inet_aton(dest_ip)
    placeholder = 0
    protocol = socket.IPPROTO_TCP
    tcp_length = len(tcp_header) + len(user_data)

    psh = struct.pack('!4s4sBBH' , source_address , dest_address , placeholder , protocol , tcp_length);
    psh = psh + tcp_header + user_data;

    tcp_check = checksum(psh)
    #print tcp_checksum

    # make the tcp header again and fill the correct checksum - remember checksum is NOT in network byte order
    tcp_header = struct.pack('!HHLLBBH' , tcp_source, tcp_dest, tcp_seq, tcp_ack_seq, tcp_offset_res, tcp_flags,  tcp_window) + struct.pack('H' , tcp_check) + struct.pack('!H' ,tcp_urg_ptr)

    # final full packet - syn packets dont have any data
    packet = ip_header + tcp_header + user_data
    return packet