#include<stdio.h>	//printf
#include<string.h> //memset
#include<stdlib.h> //exit(0);
#include<arpa/inet.h>
#include<sys/socket.h>
#include<unistd.h>

#define BUFLEN 1500	//Max length of buffer
#define PORT 8888	//The port on which to listen for incoming data


//Hi Alex,
//These are the two lines that allow you to switch between the three socket options outlined in my patch
//The socket options tell the kernel to add a control message (cmsg), allowing the program
//to recieve the data it is requesting. The three options are: IP_RECVTOS for the type of service byte,
//IP_RECVORIGDSTADDR for the orignial dst address, and IP_PKTINFO for some random packet info.
#define SOCKOPT IP_RECVORIGDSTADDR
//This field is synonymous with the above one. Valid options are: IP_TOS, IP_ORIGDSTADDR, and IP_PKTINFO
#define RECIVEOPTION IP_ORIGDSTADDR

void die(char *s)
{
	perror(s);
	exit(1);
}

int main(void)
{
	struct sockaddr_in si_me, si_other;
	
	int s, i, slen = sizeof(si_other) , recv_len;
	char buf[BUFLEN];
	
	if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
	{
		die("socket");
	}
	
	memset((char *) &si_me, 0, sizeof(si_me));
	
	si_me.sin_family = AF_INET;
	si_me.sin_port = htons(PORT);
	si_me.sin_addr.s_addr = htonl(INADDR_ANY);
	
	if( bind(s , (struct sockaddr*)&si_me, sizeof(si_me) ) == -1)
	{
		die("bind");
	}
	int yes = 1;
	if(setsockopt(s, IPPROTO_IP, SOCKOPT, &yes, sizeof(yes)) != 0){
		die("setsockopt");
	}
	while(1)
	{
		struct msghdr mhdr;
		struct iovec iov[1];
		struct cmsghdr *cmhdr;
		char control[1000];
		char databuf[1500];
		unsigned char tos = 0;
		
		mhdr.msg_name = &si_me;
		mhdr.msg_namelen = sizeof(si_me);
		mhdr.msg_iov = iov;
		mhdr.msg_iovlen = 1;
		mhdr.msg_control = &control;
		mhdr.msg_controllen = sizeof(control);
		iov[0].iov_base = databuf;
		iov[0].iov_len = sizeof(databuf);
		memset(databuf, 0, sizeof(databuf));	
		fflush(stdout);
		
		//this is blocking
		if ((recv_len = recvmsg(s, &mhdr, 0)) == -1)
		{
			die("recvfrom()");
		}
		cmhdr = CMSG_FIRSTHDR(&mhdr);
		while (cmhdr) {
			printf("cmsg recieved\n");
    		    if (cmhdr->cmsg_level == IPPROTO_IP && cmhdr->cmsg_type == RECIVEOPTION) {
    		        //read the byte recieved
			    tos = ((unsigned char *)CMSG_DATA(cmhdr))[0];
    		    }
    		    cmhdr = CMSG_NXTHDR(&mhdr, cmhdr);
    		}
		//print out the data recieved as a hex byte
    		printf("data read: %sbyte = %02X\n", databuf, tos); 	
		
	}

	close(s);
	return 0;
}