/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */

/* GIO - GLib Input, Output and Streaming Library

 *

 * Copyright (C) 2008 Red Hat, Inc.

 *

 * SPDX-License-Identifier: LGPL-2.1-or-later

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * This library 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

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General

 * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.

 */

#include "config.h"

#include <glib.h>

#include "glibintl.h"

#include "gsrvtarget.h"

#include <stdlib.h>

#include <string.h>

/**

 * SECTION:gsrvtarget

 * @short_description: DNS SRV record target

 * @include: gio/gio.h

 *

 * SRV (service) records are used by some network protocols to provide

 * service-specific aliasing and load-balancing. For example, XMPP

 * (Jabber) uses SRV records to locate the XMPP server for a domain;

 * rather than connecting directly to "example.com" or assuming a

 * specific server hostname like "xmpp.example.com", an XMPP client

 * would look up the "xmpp-client" SRV record for "example.com", and

 * then connect to whatever host was pointed to by that record.

 *

 * You can use g_resolver_lookup_service() or

 * g_resolver_lookup_service_async() to find the #GSrvTargets

 * for a given service. However, if you are simply planning to connect

 * to the remote service, you can use #GNetworkService's

 * #GSocketConnectable interface and not need to worry about

 * #GSrvTarget at all.

 */

struct _GSrvTarget {

  gchar   *hostname;

  guint16  port;

  guint16  priority;

  guint16  weight;

};

/**

 * GSrvTarget:

 *

 * A single target host/port that a network service is running on.

 */

G_DEFINE_BOXED_TYPE (GSrvTarget, g_srv_target,

                     g_srv_target_copy, g_srv_target_free)

/**

 * g_srv_target_new:

 * @hostname: the host that the service is running on

 * @port: the port that the service is running on

 * @priority: the target's priority

 * @weight: the target's weight

 *

 * Creates a new #GSrvTarget with the given parameters.

 *

 * You should not need to use this; normally #GSrvTargets are

 * created by #GResolver.

 *

 * Returns: a new #GSrvTarget.

 *

 * Since: 2.22

 */

GSrvTarget *

g_srv_target_new (const gchar *hostname,

                  guint16      port,

                  guint16      priority,

                  guint16      weight)

{

  GSrvTarget *target = g_slice_new0 (GSrvTarget);

  target->hostname = g_strdup (hostname);

  target->port = port;

  target->priority = priority;

  target->weight = weight;

  return target;

}

/**

 * g_srv_target_copy:

 * @target: a #GSrvTarget

 *

 * Copies @target

 *

 * Returns: a copy of @target

 *

 * Since: 2.22

 */

GSrvTarget *

g_srv_target_copy (GSrvTarget *target)

{

  return g_srv_target_new (target->hostname, target->port,

                           target->priority, target->weight);

}

/**

 * g_srv_target_free:

 * @target: a #GSrvTarget

 *

 * Frees @target

 *

 * Since: 2.22

 */

void

g_srv_target_free (GSrvTarget *target)

{

  g_free (target->hostname);

  g_slice_free (GSrvTarget, target);

}

/**

 * g_srv_target_get_hostname:

 * @target: a #GSrvTarget

 *

 * Gets @target's hostname (in ASCII form; if you are going to present

 * this to the user, you should use g_hostname_is_ascii_encoded() to

 * check if it contains encoded Unicode segments, and use

 * g_hostname_to_unicode() to convert it if it does.)

 *

 * Returns: @target's hostname

 *

 * Since: 2.22

 */

const gchar *

g_srv_target_get_hostname (GSrvTarget *target)

{

  return target->hostname;

}

/**

 * g_srv_target_get_port:

 * @target: a #GSrvTarget

 *

 * Gets @target's port

 *

 * Returns: @target's port

 *

 * Since: 2.22

 */

guint16

g_srv_target_get_port (GSrvTarget *target)

{

  return target->port;

}

/**

 * g_srv_target_get_priority:

 * @target: a #GSrvTarget

 *

 * Gets @target's priority. You should not need to look at this;

 * #GResolver already sorts the targets according to the algorithm in

 * RFC 2782.

 *

 * Returns: @target's priority

 *

 * Since: 2.22

 */

guint16

g_srv_target_get_priority (GSrvTarget *target)

{

  return target->priority;

}

/**

 * g_srv_target_get_weight:

 * @target: a #GSrvTarget

 *

 * Gets @target's weight. You should not need to look at this;

 * #GResolver already sorts the targets according to the algorithm in

 * RFC 2782.

 *

 * Returns: @target's weight

 *

 * Since: 2.22

 */

guint16

g_srv_target_get_weight (GSrvTarget *target)

{

  return target->weight;

}

static gint

compare_target (gconstpointer a, gconstpointer b)

{

  GSrvTarget *ta = (GSrvTarget *)a;

  GSrvTarget *tb = (GSrvTarget *)b;

  if (ta->priority == tb->priority)

    {

      /* Arrange targets of the same priority "in any order, except

       * that all those with weight 0 are placed at the beginning of

       * the list"

       */

      return ta->weight - tb->weight;

    }

  else

    return ta->priority - tb->priority;

}

/**

 * g_srv_target_list_sort: (skip)

 * @targets: a #GList of #GSrvTarget

 *

 * Sorts @targets in place according to the algorithm in RFC 2782.

 *

 * Returns: (transfer full): the head of the sorted list.

 *

 * Since: 2.22

 */

GList *

g_srv_target_list_sort (GList *targets)

{

  gint sum, num, val, priority, weight;

  GList *t, *out, *tail;

  GSrvTarget *target;

  if (!targets)

    return NULL;

  if (!targets->next)

    {

      target = targets->data;

      if (!strcmp (target->hostname, "."))

        {

          /* 'A Target of "." means that the service is decidedly not

           * available at this domain.'

           */

          g_srv_target_free (target);

          g_list_free (targets);

          return NULL;

        }

    }

  /* Sort input list by priority, and put the 0-weight targets first

   * in each priority group. Initialize output list to %NULL.

   */

  targets = g_list_sort (targets, compare_target);

  out = tail = NULL;

  /* For each group of targets with the same priority, remove them

   * from @targets and append them to @out in a valid order.

   */

  while (targets)

    {

      priority = ((GSrvTarget *)targets->data)->priority;

      /* Count the number of targets at this priority level, and

       * compute the sum of their weights.

       */

      sum = num = 0;

      for (t = targets; t; t = t->next)

        {

          target = (GSrvTarget *)t->data;

          if (target->priority != priority)

            break;

          sum += target->weight;

          num++;

        }

      /* While there are still targets at this priority level... */

      while (num)

        {

          /* Randomly select from the targets at this priority level,

           * giving precedence to the ones with higher weight,

           * according to the rules from RFC 2782.

           */

          val = g_random_int_range (0, sum + 1);

          for (t = targets; ; t = t->next)

            {

              weight = ((GSrvTarget *)t->data)->weight;

              if (weight >= val)

                break;

              val -= weight;

            }

          targets = g_list_remove_link (targets, t);

          if (!out)

            out = t;

          else

            tail->next = t;

          tail = t;

          sum -= weight;

          num--;

        }

    }

  return out;

}