/*
 ** udp_listener.c -- listens for udp packets
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define MYPORT 4950    // the port i listen on
#define MAXBUFLEN 256  // define the length of the receive buffer

int main(void)
{
	int sockfd;
	struct sockaddr_in my_addr;    // my address information
	struct sockaddr_in their_addr; // connector's address information
	socklen_t addr_len;
	
	int numbytes;
	char buf[MAXBUFLEN];
	
	// create a socket
	if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
		perror("socket");
		exit(1);
	}

	my_addr.sin_family = AF_INET;         // host byte order
	my_addr.sin_port = htons(MYPORT);     // short, network byte order
	my_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
	memset(my_addr.sin_zero, '\0', sizeof my_addr.sin_zero);
	
	// bind the socket to the port
	if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof my_addr) == -1) {
		perror("bind");
		exit(1);
	}

	addr_len = sizeof their_addr;

	// recvfrom waits for a packet and returns the number of bytes read ...
	// typically this will be in a while loop to ensure that the whole message
	// is read
	if ((numbytes = recvfrom(sockfd, &buf, MAXBUFLEN-1 , 0,
					(struct sockaddr *)&their_addr, &addr_len)) == -1) {
		perror("recvfrom");
		exit(1);
	}

	printf("got packet from %s\n",inet_ntoa(their_addr.sin_addr));
	printf("packet is %d bytes long\n",numbytes);
	// terminate the received 'string'
	buf[numbytes] = '\0';
	printf("packet contains \"%s\"\n", buf);
	close(sockfd);

	return 0;
}