/* Show how to get the remote and local IPs from a UDP socket connection */

/* For sockets */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>

/* For INET sockets */
#include <netinet/in.h>
#include <arpa/inet.h>

/* Printing info about connections */
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/param.h>

#define TEST_UDP_PORT   6667


int main(void) {
	int LISTENSOCKET;
	struct sockaddr_in bindsockaddr;
	const long true = 1L;

	LISTENSOCKET = socket(AF_INET,SOCK_DGRAM,0);

	/* Get information about each incoming packet */
	setsockopt(LISTENSOCKET, IPPROTO_IP, IP_PKTINFO, &true, sizeof(1L));

	bindsockaddr.sin_family = AF_INET;
	bindsockaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	bindsockaddr.sin_port = htons(TEST_UDP_PORT);

	bind(LISTENSOCKET,(struct sockaddr *)&bindsockaddr,sizeof(bindsockaddr));

	fprintf(stderr,"Now listening on udp port %d\n",TEST_UDP_PORT);

	while (1) {
		struct sockaddr_in cliAddress;
		int templen = sizeof(struct sockaddr_in);
		struct msghdr msg;
		char buf[512];
		union {
			struct cmsghdr cm;
			u_char data[ sizeof(struct cmsghdr) + sizeof(int) + sizeof(struct in_addr) ];
		} ip_msg;
		struct in_addr interface;

		/* Zero out the structures before we use them */
		/* This sets several key values to NULL */
		bzero(&msg,sizeof(msg));
		bzero(&ip_msg,sizeof(ip_msg));

		/* Initialize the message structure */
		msg.msg_control = ip_msg.data;
		msg.msg_controllen = sizeof(ip_msg);

		/* Get info about the incoming packet */
		recvmsg(LISTENSOCKET,&msg,MSG_PEEK);

		/* Receive the incoming packet */
		recvfrom(LISTENSOCKET,buf,sizeof(buf),0,(struct sockaddr *)&cliAddress, &templen);

		bcopy(ip_msg.data + sizeof(struct cmsghdr) + sizeof(int),&interface,sizeof(struct in_addr)); /* */

		fprintf(stderr,"Client: %s, port %d\r\n",inet_ntoa(cliAddress.sin_addr),ntohs(cliAddress.sin_port));
		fprintf(stderr,"Server: %s, port %d\r\n", inet_ntoa(interface),TEST_UDP_PORT);

		/* If this were a real application, we'd probably want to do something intelligent with buf here */
	}
}