udpserver.c

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

#define BUFF_SIZE 255

void error (char *err_msg) {
    perror(err_msg);
    exit(1);
}


int main (int argc, char **argv) {

    struct sockaddr_in my_addr;
    struct sockaddr_in their_addr;
    struct addrinfo hints, *res;
    char rcv_buf[BUFF_SIZE], send_buf[BUFF_SIZE], addrstr[BUFF_SIZE];
    int sockfd, ch, Pflag = 0, port = 1234;
    socklen_t addr_len = sizeof(struct sockaddr);
    int rcv_len;
    int IPv4flag, IPv6flag;
    int i = 0;
    unsigned int *paddr;

    if (argc != 1 && argc != 3)
        error("Usage: ./udpserver [-p port]");

    while ((ch = getopt(argc, argv, "p")) != -1){
        switch(ch){
            case 'p':
                Pflag = 1;
                break;
            default:
                error("Usage: ./udpserver [-p port]");
                break;
        }
    }

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0)
        error("Problem s otvaranjem socketa");

    memset(&my_addr, 0, sizeof(my_addr));
    my_addr.sin_family = AF_INET;
    my_addr.sin_addr.s_addr = INADDR_ANY;

    if (Pflag) {
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = AF_INET;
        hints.ai_socktype = SOCK_DGRAM;
        hints.ai_flags = AI_PASSIVE;
        if (getaddrinfo(NULL, argv[2], &hints, &res) < 0)
            error("Problem s getaddrinfo()");
        my_addr.sin_port = ((struct sockaddr_in *)res->ai_addr)->sin_port;
    }
    else {
        my_addr.sin_port = htons(port);
    }

    if (bind(sockfd, (struct sockaddr *) &my_addr, sizeof(my_addr)) < 0)
        error("Problem s bindanjem socketa");

    while (1) {

        IPv4flag = IPv6flag = 0;

        if ((rcv_len = recvfrom (sockfd, rcv_buf, BUFF_SIZE, 0,
                       (struct sockaddr *)&their_addr, &addr_len)) < 0)
            error("Problem s primanjem datagrama");

        if (rcv_len == 0) {
            return 0;
        } else {


            printf("%s\n", rcv_buf);

            // Brojac za duljinu adrese
            int rcv_buf_addr_len = 0;

            for (i = 2; i < rcv_len; i++) {

                    if(rcv_buf[i] == '\n') break;
                    rcv_buf_addr_len++;
            }

            char address[rcv_buf_addr_len];

            for(i = 0; i < rcv_buf_addr_len; i++) {
                    address[i] = rcv_buf[i+2];
            }

            if (rcv_buf[1] == '4') IPv4flag = 1;
            if (rcv_buf[1] == '6') IPv6flag = 1;

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

            if (IPv4flag) {
                hints.ai_family = AF_INET;
            }
            if (IPv6flag) {
                hints.ai_family = AF_INET6;
            }
            hints.ai_flags |= AI_CANONNAME;


            if (getaddrinfo(address, NULL, &hints, &res) < 0)
                error("Problem s getaddrinfo()");;

            memset(send_buf, 0, BUFF_SIZE);
            memset(addrstr, 0, BUFF_SIZE);

            if (rcv_buf[0] == 'S') {

                if (IPv4flag)
                    inet_ntop(res->ai_family, &((struct sockaddr_in *)res->ai_addr)->sin_addr,
                              addrstr, BUFF_SIZE);
                if (IPv6flag)
                    inet_ntop(res->ai_family, &((struct sockaddr_in6 *)res->ai_addr)->sin6_addr,
                              addrstr, BUFF_SIZE);

                strncpy(send_buf, "\x02", 1);
                strncpy(send_buf + 1, addrstr, sizeof(addrstr));

            }

            if (rcv_buf[0] == 'N') {

                strncpy(send_buf, "\x01", 1);

                if (IPv4flag) {

                    struct sockaddr_in *p = (struct sockaddr_in *)
                                            (res->ai_addr);
                    paddr = &(p->sin_addr.s_addr);
                    memcpy(addrstr, paddr, 4);
                    strncpy(send_buf + 1, addrstr, sizeof(addrstr));
                }

                if (IPv6flag) {

                    struct sockaddr_in6 *p = (struct sockaddr_in6 *)
                                             (res->ai_addr);

                    sprintf(addrstr, "%s", p->sin6_addr.s6_addr);

                    strncpy(send_buf + 1, addrstr, sizeof(addrstr));

                }

            }

            if (sendto(sockfd, send_buf, strlen(send_buf) + 1, 0,
                      (struct sockaddr *)&their_addr, addr_len) < 0)
                error("Problem s slanjem datagrama");

        }

    }

    freeaddrinfo(res);
    close(sockfd);
    return 0;
}