Home > Articles, Internet Applications > A useful function for getting the host name and service of a socket.

A useful function for getting the host name and service of a socket.

October 20, 2014 Leave a comment Go to comments

In this article I will present to you a useful function for getting the host name and service of a socket.

Below, is the header containing the interface of the function:

/*
 *  Copyright (C) 2014  Efstathios Chatzikyriakidis (contact@efxa.org).
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef _SOCKET_HELPER_UTILITIES_H_
#define _SOCKET_HELPER_UTILITIES_H_

#include <sys/socket.h>

#include "shared-types.h"

/*
 * function prototypes.
 */

bool_t get_host_and_service (const int socket_descriptor,
                             socklen_t address_length,
                             const string_t const host,
                             socklen_t host_length,
                             const string_t const service,
                             socklen_t service_length,
                             const unsigned int flags);

#endif // _SOCKET_HELPER_UTILITIES_H_

Next, follows the implementation of the function:

/*
 *  Copyright (C) 2014  Efstathios Chatzikyriakidis (contact@efxa.org).
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#include <netdb.h>
#include <stdlib.h>

#include "socket-helper-utilities.h"

/*
 * functions.
 */

bool_t
get_host_and_service (const int socket_descriptor,
                      socklen_t address_length,
                      const string_t const host,
                      socklen_t host_length,
                      const string_t const service,
                      socklen_t service_length,
                      const unsigned int flags)
{
  struct sockaddr * address = (struct sockaddr *) malloc (address_length);

  if (!address)
  {
    return false;
  }

  if (getsockname (socket_descriptor, address, &address_length) < 0)
  {
    free(address);

    return false;
  }

  const int return_value = getnameinfo (address,
                                        address_length,
                                        host,
                                        host_length,
                                        service,
                                        service_length,
                                        flags);

  free(address);

  if (return_value != 0)
  {
    return false;
  }

  return true;
}

Here is an example of using the function in a server application:

  ... code before

  socklen_t server_address_length;

  const int server_socket_descriptor =
    create_server_socket (options->server_address,
                          options->server_port,
                          AI_PASSIVE | AI_NUMERICSERV,
                          AF_UNSPEC,
                          IPPROTO_TCP,
                          SOCK_STREAM,
                          &server_address_length);

  if (server_socket_descriptor < 0)
  {
    log_error (_(failed_to_connect_server_socket_message));

    return false;
  }

  char host[NI_MAXHOST], service[NI_MAXSERV];

  if (!get_host_and_service (server_socket_descriptor,
                             server_address_length, 
                             host,
                             NI_MAXHOST,
                             service,
                             NI_MAXSERV,
                             NI_NUMERICHOST | NI_NUMERICSERV))
  {
    log_error (_(failed_to_get_server_host_name_and_service_message));

    return false;
  }

  log_info ("%s [%s - %s]", 
            _(server_listens_on_following_socket_message),
            host,
            service);

  ... code after

Happy Hacking!

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