#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>

#define PORT_NO 3221
#define BUFLEN 512

int main(void) {
    int s;
    struct sockaddr_in sa;
    char buf[BUFLEN];
    int addrlen;
    int pktlen;

    if((s = socket(PF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("socket");
        return(-1);
    }

    memset(&sa, 0, sizeof(sa));

    sa.sin_family = AF_INET;
    sa.sin_addr.s_addr = INADDR_ANY;
    sa.sin_port = htons(PORT_NO);

    if((bind(s, (struct sockaddr *) &sa, sizeof(sa))) < 0) {
        perror("bind");
        close(s);
        return(-1);
    }

    while((pktlen = recvfrom(s, buf, sizeof(buf), 0, &sa, &addrlen)) > 0) {
        sendto(s, buf, pktlen, 0, &sa, addrlen);
        printf("Packet received!\n");
    }
}