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

#define BUFLEN sizeof(struct timeval)
#define PORT 9876

void diep(char * s)
{
    perror(s);
    exit(1);
}

int main(void)
{
    struct sockaddr_in si_me, si_other;
    int s, slen = sizeof(si_other);
    struct timeval buf;

    if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
        diep("socket");

    memset((char *) &si_me, 0, sizeof(si_me));
    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(PORT);
    si_me.sin_addr.s_addr = htonl(INADDR_ANY);
    if (bind(s, (struct sockaddr *) &si_me, sizeof(si_me)) == -1)
        diep("bind");

    for (;;)
    {
        if (recvfrom(s, &buf, BUFLEN, 0,
                    (struct sockaddr *) &si_other, &slen) == -1)
            diep("recvfrom()");
        if (sendto(s, &buf, BUFLEN, 0,
                    (struct sockaddr *) &si_other, slen) == -1)
            diep("sendto()");
    }

    close(s);
    return 0;
}