/*	UDP Example code by Kien Pham (Heavily documented to help others understand.)
	This code is now in Public Domain.
	Look ma, I did this all by myself.	*/

#include<sys/socket.h>	// Include these for socket(), bind(), etc.
#include<sys/types.h>
#include<netdb.h>	// Include this for getprotobyname()
#include<string.h>	// Include this for memset()
#include<netinet/in.h>	// Include this for htonl(), htons(), etc.
#include<unistd.h>
#include<errno.h>	// Include this for errno.
#include<sys/wait.h>	// Include this for wait()

#define	PORT1	2000
#define	PORT2	2001

int	create_UDP_socket(int	port)
	{
	 int	file_descriptor;
	 struct	sockaddr_in	host_address;
	 file_descriptor=socket(AF_INET,	SOCK_DGRAM,	IPPROTO_UDP);	// Only thing different from the TCP example is the IPPROTO_??? constant.
	 if	(file_descriptor<0)
		{
		 perror("socket()");
		 return	-1;
		}
	 memset((void*)&host_address,	0,	sizeof(host_address));
	 host_address.sin_family=AF_INET;
	 host_address.sin_addr.s_addr=INADDR_ANY;
	 host_address.sin_port=htons(port);
	 if	(bind(file_descriptor, (struct sockaddr*)&host_address, sizeof(host_address))<0)
		{
		 perror("bind()");
		 return	-1;
		}
	 return	file_descriptor;
	}

void	entity(int	file_descriptor,	int	port)
	{
	 struct	sockaddr_in	host_address;
	 int	host_address_size;
	 unsigned	char	*address_holder;
	 char	message[]="Testing, testing, 1, 2, 3.";
	 char	buffer[256];

	 memset((void*)&host_address,	0,	sizeof(host_address));
	 host_address.sin_family=AF_INET;
	 host_address.sin_port=htons(port);
	 address_holder=(unsigned char*)&host_address.sin_addr.s_addr;
	 address_holder[0]=127;
	 address_holder[1]=0;
	 address_holder[2]=0;
	 address_holder[3]=1;
	 if	(sendto(file_descriptor,	message,	sizeof(message),	0,	(struct	sockaddr*)&host_address,	sizeof(host_address))<0)	// Must use sendto() unless other care is taken. Must explicitly tell where to send each packet of data. Beyond our scope for now. (Hint: Use connect())
		{
		 perror("sendto()");
		 return;
		}
       memset((void*)&host_address,   0,      sizeof(host_address));
       host_address.sin_family=AF_INET;
	 host_address_size=sizeof(host_address);
	 if	(recvfrom(file_descriptor,	buffer,	255,	0,	(struct	sockaddr*)&host_address,	&host_address_size)<0)	// Read and put where we got the data from in host_address.
		{
		 printf("%d", errno);
		 perror("recvfrom()");
		 return;
		}
	printf("Port %d obtained message '%s' from host %d.%d.%d.%d.\n",	port,	buffer,	address_holder[0],	address_holder[1],	address_holder[2],	address_holder[3]);
	}

int	main(int number_of_arguments, char *arguments[])
	{
	 int	process_id;
	 int	sock1, sock2, status;

       printf("\nUDP Networking Example\n");
       printf("Written by Kien Pham\n");
       printf("For the Networking mini-Tutorial (http://www.tripod.com/~Xengren)\n");
	 sock1=create_UDP_socket(PORT1);
	 sock2=create_UDP_socket(PORT2);
	 if	((sock1<0)||(sock2<0))
		{
                 perror("create_UDP_socket()");
                 return 1;
		}
	 process_id=fork();
	 if	(process_id<0)
		{
		 perror("fork()");
		 return 1;
		}
	 if	(process_id!=0)
		{
		 entity(sock1,	PORT2);
		 wait(&status);	// This is where all the IRC ppl. helped me. So much wasted time for something so simple. Ugh. It just makes sure the other process is finished with its read before exitting and destroying its resources.
		 if	(WIFEXITED(status)==0)
			{
			 printf("Child did not exit normally.\n");
			 return	1;
			}
		 close(sock1);
		}
	 else
		{
		 entity(sock2,	PORT1);
		 close(sock2);
		}
	}