/*client_udp.c*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define MAXLINE 4096
#define SERV_PORT 9877

void process(FILE *fp, int sockfd, const struct sockaddr *pservaddr,
        socklen_t servlen)
{
    int n;
    char send[MAXLINE], recv[MAXLINE];

    while (fgets(send, MAXLINE, fp) != NULL) {
        sendto(sockfd, send, strlen(send), , pservaddr, servlen);
        n = recvfrom(sockfd, recv, MAXLINE, , NULL, NULL);
        recv[n] = ;
        fputs(recv, stdout);
    }
}

int main(int argc, char *argv[])
{
    int sockfd;
    struct sockaddr_in servaddr;

    ) {
        fprintf(stderr, "usage: client_udp <IP>\n");
        exit();
    }

    memset(&servaddr, , sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(SERV_PORT);
    inet_pton(AF_INET, argv[], &servaddr.sin_addr);

    sockfd = socket(AF_INET, SOCK_DGRAM, );

    process(stdin, sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

    exit();
}

/*server_udp.c*/
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define MAXLINE 4096
#define    SERV_PORT 9877

void process(int sockfd, struct sockaddr *pcliaddr, socklen_t clilen)
{
    int n;
    socklen_t len;
    char mesg[MAXLINE];

    ) {
        len = clilen;
        n = recvfrom(sockfd, mesg, MAXLINE, , pcliaddr, &len);
        sendto(sockfd, mesg, n, , pcliaddr, len);
    }
}

int main(int argc, char *argv[])
{
    int sockfd;
    struct sockaddr_in servaddr, cliaddr;

    sockfd = socket(AF_INET, SOCK_DGRAM, );

    memset(&servaddr, , sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);

    bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

    process(sockfd, (struct sockaddr *)&cliaddr, sizeof(cliaddr));
}