getout_ip.c

/* 
 * name: getout_ip.c
 * this file is part of the "Net-Injector" project. It defines the getout_ip() function
 * Adapted from R.Stevens
 * license: This software is under GPL license
 * date: 04 17 2003
 * rev: 0.8
*/

#include "neti.h"


/* Finds the IP address of the output interface from OS routing table */
 
int getout_ip(struct sockaddr_in *if_addr, struct sockaddr_in *dest){
	
	int sock_rt, len, one=1;
	struct sockaddr_in found_if_addr;
 
	memset(&found_if_addr, 0, sizeof(found_if_addr));
	sock_rt = socket(AF_INET, SOCK_DGRAM, 0 );

	dest->sin_port = htons(53);
	if (setsockopt(sock_rt, SOL_SOCKET, SO_BROADCAST, &one, sizeof(one))
            == -1) {
		fprintf(stderr, "Error : (getout_ip) in setsockopt !\n");
		close(sock_rt);
		return EXIT_FAILURE;
	}
  
	if (connect(sock_rt, (struct sockaddr*)dest, sizeof(struct sockaddr_in))
	    == -1 ) {
		fprintf(stderr, "Error : (getout_ip) bad IP address !\n");
		close(sock_rt);
		return EXIT_FAILURE;
	}

	len = sizeof(found_if_addr);
	if (getsockname(sock_rt, (struct sockaddr *)&found_if_addr, &len) == -1 ) {
		fprintf(stderr, "Error : (getout_ip) in getsockname !\n");
		close(sock_rt);
		return EXIT_FAILURE;
	}
	close(sock_rt);
	if (found_if_addr.sin_addr.s_addr == 0)
		return EXIT_FAILURE;
	memcpy(if_addr, &found_if_addr, sizeof(struct sockaddr_in));
        return EXIT_SUCCESS;
}