udpd.c

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

#define IPv4(a, b, c, d) ((uint32_t)(((a) & 0xff) << 24) |		\
	(((b) & 0xff) << 16) |						\
	(((c) & 0xff) << 8) |						\
	((d) & 0xff))

#define ERR_EXIT(m) \
do { \
	perror(m); \
	exit(EXIT_FAILURE); \
} while (0)

#define BIND_ADDR INADDR_ANY
//#define BIND_ADDR IPv4(0,0,0,0)

int main(int argc, char *argv[])
{
	int sock, port, n;
	struct sockaddr_in servaddr, peeraddr;
	char recvbuf[1024] = {0};
	socklen_t peerlen;
	//int on;


	if (!(argc == 2 && (port = atoi(argv[1])))) {
		fprintf(stderr, "Usage\n\t%s <port> \n",
				argv[0]);
		exit(EXIT_FAILURE);
	}

	if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
		ERR_EXIT("socket error");

	//on = 1;
	//setsockopt( sock, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on) );
	//
	
	printf("port %d\n", port);

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(port);
	servaddr.sin_addr.s_addr = htonl(BIND_ADDR);

	printf("serv %s:%d \n", inet_ntoa(servaddr.sin_addr),
			ntohs(servaddr.sin_port));

	if (bind(sock, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
		ERR_EXIT("bind error");

	while (1){
		peerlen = sizeof(peeraddr);
		memset(recvbuf, 0, sizeof(recvbuf));
		n = recvfrom(sock, recvbuf, sizeof(recvbuf), 0,
				(struct sockaddr *)&peeraddr, &peerlen);
		if(n == -1) {
			if (errno == EINTR)
				continue;
			ERR_EXIT("recvfrom error");
		}else if(n > 0) {
			printf("recv(%d) peer from %s:%d\n",
					n, inet_ntoa(peeraddr.sin_addr),
					ntohs(peeraddr.sin_port));
			sendto(sock, recvbuf, n, 0,
					(struct sockaddr*)&peeraddr,
					sizeof(peeraddr));
			fputs(recvbuf, stdout);
		}
	}
	close(sock);

	return 0;
}