/*	A simple UDP example - receiver(signal-driven I/O version)	*/

#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
#include <signal.h>
#include <fcntl.h>
#define MAX_MSG_SIZE	1000  

// SIGIO signal handler
void sig_io(int);

// socket descriptor is global(since the signal handler needs it) 
int sockfd;

int main(int argc, char* argv[])
{
	struct sockaddr_in recvAddr;
	int recvPort, flags;

	//	check the number of arguments
	if (argc != 2) {
		printf("Usage : %s port-number\n", argv[0]);
		exit(-1);
	}
	
	// 	parse arguments
	recvPort = atoi(argv[1]);

	//	fill out serverAddr
	memset(&recvAddr, 0, sizeof(recvAddr));
	recvAddr.sin_family = PF_INET;
	recvAddr.sin_addr.s_addr = htonl(INADDR_ANY);
	recvAddr.sin_port = htons(recvPort);
	
	// 	register the SIGIO signal handler
	signal(SIGIO, sig_io);
	
	//	socket
	if ((sockfd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
		perror("socket");
	
	// 	set the socket owner
	if (fcntl(sockfd, F_SETOWN, getpid()) < 0)
		perror("fcntl");

	// 	enable signal-driven I/O(set socket async)
	flags = fcntl(sockfd, F_GETFL);
	fcntl(sockfd, F_SETFL, O_ASYNC);

	//	bind
	if (bind(sockfd, (struct sockaddr*)&recvAddr, sizeof(recvAddr)) < 0)
		perror("bind");
	
	//	wait!
	while(1) ; 
	return 0;
}

void sig_io(int signo)
{
	struct sockaddr_in sendAddr;
	socklen_t len;
	char msg[MAX_MSG_SIZE];
	ssize_t r;

	r = recvfrom(sockfd, msg, sizeof(msg), 0, (struct sockaddr*) &sendAddr, &len);
	if (r < 1)
		perror("recvfrom");
	else
		printf("%s\n", (msg[r] = '\0',msg));
}