/*
 * Listing 4:
 * Example UDP (connectionless) server
 * Ivan Griffin (ivan.griffin@ul.ie)
 */

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

#define MAX_MESG_SIZE 4096
char mesg[MAX_MESG_SIZE] = "";

int main(int argc, char *argv[])
{
    int udpSocket = 0,
        myPort = 0,
        status = 0,
        size = 0,
        clientLength = 0;
    struct sockaddr_in serverName = { 0 },
        clientName = { 0 };

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

    myPort = atoi(argv[1]);

    udpSocket = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (-1 == udpSocket)
    {
        perror("socket()");
        exit(1);
    }

    memset(&serverName, 0, sizeof(serverName));
    memset(&clientName, 0, sizeof(clientName));

    serverName.sin_family = AF_INET;
    serverName.sin_addr.s_addr = htonl(INADDR_ANY);
    serverName.sin_port = htons(myPort);

    status = bind(udpSocket, (struct sockaddr *) &serverName,
        sizeof(serverName));
    if (-1 == status)
    {
        perror("bind()");
        exit(1);
    }

    for (;;)
    {
        size = recvfrom(udpSocket, mesg, MAX_MESG_SIZE, 0,
            (struct sockaddr *) &clientName, &clientLength);
        if (size == -1)
        {
            perror("recvfrom()");
            exit(1);
        }

        status = sendto(udpSocket, mesg, size, 0,
            (struct sockaddr *) &clientName, clientLength);
        if (status != size)
        {
            fprintf(stderr, "sendto(): short write.\n");
            exit(1);
        }
    }

    /* never reached */
    return 0;
}

Listing 4. Example UDP server.