udp.c

	
/* 
 * name: udp.c
 * this file is part of the "Net-Injector" project. It defines the write_udp() function
 * Copyright (C) 2002 by Jean Philippe GUILLEMIN <jp.guillemin@free.fr>
 * license: This software is under GPL license
 * date: 04 17 2003
 * rev: 0.8

			 0      7 8     15 16    23 24    31  
			+--------+--------+--------+--------+ 
			|     Source      |   Destination   | 
			|      Port       |      Port       | 
			+--------+--------+--------+--------+ 
			|                 |                 | 
			|     Length      |    Checksum     | 
			+--------+--------+--------+--------+ 
			|                                     
			|          data octets ...            
			+---------------- ...                 
*/

#include "neti.h"

/* function that create the UDP header and data field 
the result is a pointer (*udp_packet) to the begining of UDP header
*/


int write_udp(char *udp_packet, int size, u_int32_t ip_saddr, u_int32_t ip_daddr){
	
	struct udphdr *udph;
	struct pseudohdr *pseudoh;
		
	
	pseudoh = (struct pseudohdr*) udp_packet;		/* address of pseudo-header */
	udph =  (struct udphdr*) (udp_packet+PSEUDOHDR_SIZE);    /* address of udp-header */
	data = (char*) (udp_packet+PSEUDOHDR_SIZE+UDPHDR_SIZE);	/* address of begining of payload */
	
	memset(data, 0, myhdr->data_size);
	memset(udp_packet, 0, PSEUDOHDR_SIZE+size);
	
	memcpy (data, payload, myhdr->data_size);

	/*filling UDP header */
	udph->source = myhdr->inet_src_port;	
	udph->dest = myhdr->inet_dst_port;
	udph->len = UDPHDR_SIZE + myhdr->data_size; /* size of UDP packet */
	udph->check = 0;  /* checksum will be set later */
	
	/*filling PSEUDO header */	
	memcpy(&pseudoh->saddr, &ip_saddr, 4);
	memcpy(&pseudoh->daddr, &ip_daddr, 4);
	pseudoh->protocol	= 17; /* layer 4 protocole */
	pseudoh->lenght = htons(size);
	
	udph->check = sum((u_int16_t *) udp_packet, PSEUDOHDR_SIZE + size);

	return EXIT_SUCCESS;
}