#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <strings.h>
#include <netdb.h>
#include <stdio.h>

void error(char *msg)
{
	perror(msg);
	exit(0);
}
		
int main(int argc, char *argv[])
{
	int sock, length, fromlen, n;
	struct sockaddr_in server;
	struct sockaddr_in from;
	char buf[1024];
	
	if (argc < 2) 
	{
		fprintf(stderr, "ERROR, no port provided\n");
		exit(0);
	}
	
	sock = socket(AF_INET, SOCK_DGRAM, 0);
	if (sock < 0) error("Opening socket");

	length = sizeof(server);
	bzero(&server,length);
	
	server.sin_family = AF_INET;
	server.sin_addr.s_addr = INADDR_ANY;
	server.sin_port = htons(atoi(argv[1]));
	
	if ( bind(sock,(struct sockaddr *) &server,length) < 0 ) 
		error("binding");

	fromlen = sizeof(struct sockaddr_in);
	printf("Waiting to recv.\n"); fflush(stdout);

	while (1) 
        {
		n = recvfrom(sock, buf, 1024, 0, (struct sockaddr *) &from, &fromlen);
		if (n < 0) error("recvfrom");
			
		printf("Received a datagram.\n"); fflush(stdout);
		printf("%s\n", buf); fflush(stdout);

		n = sendto(sock, "Got your message\n", 17, 0, (struct sockaddr *) &from, fromlen);
		if (n  < 0) error("sendto");
	} // while

	return(1);
 } // main

void error(char *msg)
{
	perror(msg);
	exit(0);
} // error

int main(int argc, char *argv[])
{
	int sock, length, n;
	struct sockaddr_in server, from;
	struct hostent *hp;
	char buffer[256];
	
	if (argc != 3) 
	{ 
		printf("Usage: client <server IP> <port>\n");
		exit(1);
	}

	sock = socket(AF_INET, SOCK_DGRAM, 0);
	if (sock < 0) 
		error("socket");
	
	///////////////////////////////////////
	/* Specify Socket Info */
	server.sin_family = AF_INET;			
	server.sin_port = htons(atoi(argv[2]));		// port
	server.sin_addr.s_addr = inet_addr(argv[1]);	// ip
	///////////////////////////////////////
	
	length = sizeof(struct sockaddr_in);

	printf("Please enter the message: ");
	bzero(buffer, 256);
	fgets(buffer, 255, stdin);

	n = sendto(sock, buffer, strlen(buffer), 0, &server, length);
	if (n < 0) 
		error("Sendto");

	printf("\nSent the message, waiting for response.\n"); fflush(stdout); 

	n = recvfrom(sock, buffer, 256, 0, &from, &length);
	if (n < 0) 
		error("recvfrom");

	printf("Got an ACK: %s", buffer); fflush(stdout); 
} // main

         n = recvfrom(sock, buf, 1024, 0, (struct sockaddr *) &from, &fromlen);
         if (n < 0) error("recvfrom");
 
         printf("Received a datagram.\n"); fflush(stdout);
         printf("%s\n", buf); fflush(stdout);

n = recvfrom(sock, buf, SIZE_OF_BUFFER - 1, 0, .....);
// check n for errors
buf[n] = 0; // null terminate that buffer.
printf("%s\n", buf);

     printf("Please enter the message: ");
     bzero(buffer, 256);
     fgets(buffer, 255, stdin);

No.    Time      Source         Destination      Protocol      Info
1     0.000      10.0.0.X        10.0.0.X          UDP         Source port: 33267 Destination port: search-agent
#      1947.3    10.0.0.X        10.0.0.X         ICMP         Echo (ping) reply