Проблемы с исходным кодом

Question

В главе 60 список исходных кодов

id_echo.h

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2018.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* Listing 60-1 */

/* id_echo.h

   Header file for id_echo_sv.c and id_echo_cl.c.
*/
#include "inet_sockets.h"       /* Declares our socket functions */
#include "tlpi_hdr.h"

#define SERVICE "echo"          /* Name of UDP service */

#define BUF_SIZE 500            /* Maximum size of datagrams that can
                                   be read by client and server */

id_echo_sv.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2018.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* Listing 60-2 */

/* id_echo_sv.c

   This program implements a daemon that provides the UDP "echo" service. It
   reads datagrams and then sends copies back to the originating address.

   NOTE: this program must be run under a root login, in order to allow the
   "echo" port (7) to be bound. Alternatively, for test purposes, you can edit
   id_echo.h and replace the SERVICE name with a suitable unreserved port
   number (e.g., "51000"), and make a corresponding change in the client.

   See also id_echo_cl.c.
*/
#include <syslog.h>
#include "id_echo.h"
#include "become_daemon.h"

int
main(int argc, char *argv[])
{
    int sfd;
    ssize_t numRead;
    socklen_t len;
    struct sockaddr_storage claddr;
    char buf[BUF_SIZE];
    char addrStr[IS_ADDR_STR_LEN];

    if (becomeDaemon(0) == -1)
        errExit("becomeDaemon");

    sfd = inetBind(SERVICE, SOCK_DGRAM, NULL);
    if (sfd == -1) {
        syslog(LOG_ERR, "Could not create server socket (%s)", strerror(errno));
        exit(EXIT_FAILURE);
    }

    /* Receive datagrams and return copies to senders */

    for (;;) {
        len = sizeof(struct sockaddr_storage);
        numRead = recvfrom(sfd, buf, BUF_SIZE, 0,
                           (struct sockaddr *) &claddr, &len);
        if (numRead == -1)
            errExit("recvfrom");

        if (sendto(sfd, buf, numRead, 0, (struct sockaddr *) &claddr, len)
                        != numRead)
            syslog(LOG_WARNING, "Error echoing response to %s (%s)",
                    inetAddressStr((struct sockaddr *) &claddr, len,
                                   addrStr, IS_ADDR_STR_LEN),
                    strerror(errno));
    }
}

id_echo_cl.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2018.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* Listing 60-3 */

/* id_echo_cl.c

   A client for the UDP "echo" service. This program sends each of its
   command-line arguments as a datagram to the server and echoes the
   contents of the datagrams that the server sends in response.

   See also id_echo_sv.c.
*/
#include "id_echo.h"

int
main(int argc, char *argv[])
{
    int sfd, j;
    size_t len;
    ssize_t numRead;
    char buf[BUF_SIZE];

    if (argc < 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s host msg...\n", argv[0]);

    /* Construct server address from first command-line argument */

    sfd = inetConnect(argv[1], SERVICE, SOCK_DGRAM);
    if (sfd == -1)
        fatal("Could not connect to server socket");

    /* Send remaining command-line arguments to server as separate datagrams */

    for (j = 2; j < argc; j++) {
        len = strlen(argv[j]);
        if (write(sfd, argv[j], len) != len)
            fatal("partial/failed write");

        numRead = read(sfd, buf, BUF_SIZE);
        if (numRead == -1)
            errExit("read");

        printf("[%ld bytes] %.*s\n", (long) numRead, (int) numRead, buf);
    }

    exit(EXIT_SUCCESS);
}

мой вопрос:*

Если я изменю localhost на 127.0.0.1, все идет хорошо.В третьей строке 1988 / id_echo_sv работает хорошо, я не понимаю, почему это происходит, при использовании функции чтения localhost не удалось в клиентском коде.

[root@centos7-10 sockets]# netstat -nupl | grep 7
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           874/avahi-daemon: r 
udp        0      0 127.0.0.1:323           0.0.0.0:*                           884/chronyd         
udp        0      0 0.0.0.0:7               0.0.0.0:*                           1988/id_echo_sv     
udp        0      0 0.0.0.0:35873           0.0.0.0:*                           874/avahi-daemon: r 
udp        0      0 192.168.122.1:53        0.0.0.0:*                           1782/dnsmasq        
udp        0      0 0.0.0.0:67              0.0.0.0:*                           1782/dnsmasq 

из-за функции inetBind () и т. Д. Используйте авторверсия, поэтому, если вы хотите запустить, необходимо загрузить исходный код в tlpi

Если у вас есть идеи, пожалуйста, дайте мне знать, спасибо заранее.