udpclient.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) {

    int sockfd, port = 1234, Pflag = 0, ch;
    int status;
    int rcv_len;
    char rcv_buf[BUFF_SIZE], send_buf[BUFF_SIZE];
    struct sockaddr_in servaddr;
    struct addrinfo hints, *res;
    socklen_t serv_len;
    char *host;
    int i;

    if (argc < 2) {
        error("Usage: ./udpklijent [-p port] server_IP");
    }

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

    host = argv[argc - 1];

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

    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    inet_pton(AF_INET, host , &servaddr.sin_addr);

    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()");
        servaddr.sin_port = ((struct sockaddr_in *)res->ai_addr)->sin_port;
    }
    else {
        servaddr.sin_port = htons(port);
    }

    serv_len = sizeof(struct sockaddr);

    while (1) {

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

        // Citaj s standardnog ulaza
        status = scanf("%s", send_buf);

        // Ako je duljina buffera 0, posalji serveru prazan datagram
        if (status == EOF) {
            if( sendto(sockfd, 0, 0, 0, (struct sockaddr *) &servaddr, serv_len) < 0)
                error("Problem s slanjem praznog datagrama");
            return 0;
        } else {

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


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

            if (rcv_buf[0] == 0x00)
                printf("posluzitelj nije pronasao odgovor\n");

            if (rcv_buf[0] == 0x01) {

                for (i=1; i<rcv_len - 1; i++) {

                    printf("%X ", rcv_buf[i]);

                }

                printf("\n");

            }

            if (rcv_buf[0] == 0x02) {

                memmove(rcv_buf, rcv_buf + 1, rcv_len - 1);
                printf("%s\n", rcv_buf);
            }
        }


    }

    freeaddrinfo(res);
    close(sockfd);

    return 0;

}