bridge.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007 - 2009, Digium, Inc.
 *
 * Joshua Colp <jcolp@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief Bridging API
 *
 * \author Joshua Colp <jcolp@digium.com>
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

/*** DOCUMENTATION
   <manager name="BridgeTechnologyList" language="en_US">
      <synopsis>
         List available bridging technologies and their statuses.
      </synopsis>
      <syntax>
         <xi:include xpointer="xpointer(/docs/manager[@name='Login']/syntax/parameter[@name='ActionID'])" />
      </syntax>
      <description>
         <para>Returns detailed information about the available bridging technologies.</para>
      </description>
      <see-also>
         <ref type="manager">BridgeTechnologySuspend</ref>
         <ref type="manager">BridgeTechnologyUnsuspend</ref>
      </see-also>
   </manager>
   <manager name="BridgeTechnologySuspend" language="en_US">
      <synopsis>
         Suspend a bridging technology.
      </synopsis>
      <syntax>
         <xi:include xpointer="xpointer(/docs/manager[@name='Login']/syntax/parameter[@name='ActionID'])" />
         <parameter name="BridgeTechnology" required="true">
            <para>The name of the bridging technology to suspend.</para>
         </parameter>
      </syntax>
      <description>
         <para>Marks a bridging technology as suspended, which prevents subsequently created bridges from using it.</para>
      </description>
      <see-also>
         <ref type="manager">BridgeTechnologySuspend</ref>
         <ref type="manager">BridgeTechnologyUnsuspend</ref>
      </see-also>
   </manager>
   <manager name="BridgeTechnologyUnsuspend" language="en_US">
      <synopsis>
         Unsuspend a bridging technology.
      </synopsis>
      <syntax>
         <xi:include xpointer="xpointer(/docs/manager[@name='Login']/syntax/parameter[@name='ActionID'])" />
         <parameter name="BridgeTechnology" required="true">
            <para>The name of the bridging technology to unsuspend.</para>
         </parameter>
      </syntax>
      <description>
         <para>Clears a previously suspended bridging technology, which allows subsequently created bridges to use it.</para>
      </description>
      <see-also>
         <ref type="manager">BridgeTechnologyList</ref>
         <ref type="manager">BridgeTechnologySuspend</ref>
      </see-also>
   </manager>
***/

#include "asterisk.h"

#include "asterisk/logger.h"
#include "asterisk/channel.h"
#include "asterisk/options.h"
#include "asterisk/utils.h"
#include "asterisk/lock.h"
#include "asterisk/linkedlists.h"
#include "asterisk/bridge.h"
#include "asterisk/bridge_internal.h"
#include "asterisk/bridge_channel_internal.h"
#include "asterisk/bridge_features.h"
#include "asterisk/bridge_basic.h"
#include "asterisk/bridge_technology.h"
#include "asterisk/bridge_channel.h"
#include "asterisk/bridge_after.h"
#include "asterisk/stasis_bridges.h"
#include "asterisk/stasis_channels.h"
#include "asterisk/stasis_cache_pattern.h"
#include "asterisk/app.h"
#include "asterisk/file.h"
#include "asterisk/module.h"
#include "asterisk/astobj2.h"
#include "asterisk/pbx.h"
#include "asterisk/test.h"
#include "asterisk/_private.h"
#include "asterisk/heap.h"
#include "asterisk/say.h"
#include "asterisk/timing.h"
#include "asterisk/stringfields.h"
#include "asterisk/musiconhold.h"
#include "asterisk/features.h"
#include "asterisk/cli.h"
#include "asterisk/parking.h"
#include "asterisk/core_local.h"
#include "asterisk/core_unreal.h"
#include "asterisk/causes.h"

/*! All bridges container. */
static struct ao2_container *bridges;

static AST_RWLIST_HEAD_STATIC(bridge_technologies, ast_bridge_technology);

static unsigned int optimization_id;

/* Initial starting point for the bridge array of channels */
#define BRIDGE_ARRAY_START 128

/* Grow rate of bridge array of channels */
#define BRIDGE_ARRAY_GROW 32

/* Variable name - stores peer information about the most recent blind transfer */
#define BLINDTRANSFER "BLINDTRANSFER"

/* Variable name - stores peer information about the most recent attended transfer */
#define ATTENDEDTRANSFER "ATTENDEDTRANSFER"

static void cleanup_video_mode(struct ast_bridge *bridge);

/*! Default DTMF keys for built in features */
static char builtin_features_dtmf[AST_BRIDGE_BUILTIN_END][MAXIMUM_DTMF_FEATURE_STRING];

/*! Function handlers for the built in features */
static ast_bridge_hook_callback builtin_features_handlers[AST_BRIDGE_BUILTIN_END];

/*! Function handlers for built in interval features */
static ast_bridge_builtin_set_limits_fn builtin_interval_handlers[AST_BRIDGE_BUILTIN_INTERVAL_END];

/*! Bridge manager service request */
struct bridge_manager_request {
   /*! List of bridge service requests. */
   AST_LIST_ENTRY(bridge_manager_request) node;
   /*! Refed bridge requesting service. */
   struct ast_bridge *bridge;
};

struct bridge_manager_controller {
   /*! Condition, used to wake up the bridge manager thread. */
   ast_cond_t cond;
   /*! Queue of bridge service requests. */
   AST_LIST_HEAD_NOLOCK(, bridge_manager_request) service_requests;
   /*! Manager thread */
   pthread_t thread;
   /*! TRUE if the manager needs to stop. */
   unsigned int stop:1;
};

/*! Bridge manager controller. */
static struct bridge_manager_controller *bridge_manager;

struct ao2_container *ast_bridges(void)
{
   return ao2_bump(bridges);
}

/*!
 * \internal
 * \brief Request service for a bridge from the bridge manager.
 * \since 12.0.0
 *
 * \param bridge Requesting service.
 *
 * \return Nothing
 */
static void bridge_manager_service_req(struct ast_bridge *bridge)
{
   struct bridge_manager_request *request;

   ao2_lock(bridge_manager);
   if (bridge_manager->stop) {
      ao2_unlock(bridge_manager);
      return;
   }

   /* Create the service request. */
   request = ast_calloc(1, sizeof(*request));
   if (!request) {
      /* Well. This isn't good. */
      ao2_unlock(bridge_manager);
      return;
   }
   ao2_ref(bridge, +1);
   request->bridge = bridge;

   /* Put request into the queue and wake the bridge manager. */
   AST_LIST_INSERT_TAIL(&bridge_manager->service_requests, request, node);
   ast_cond_signal(&bridge_manager->cond);
   ao2_unlock(bridge_manager);
}

int __ast_bridge_technology_register(struct ast_bridge_technology *technology, struct ast_module *module)
{
   struct ast_bridge_technology *current;

   /* Perform a sanity check to make sure the bridge technology conforms to our needed requirements */
   if (ast_strlen_zero(technology->name)
      || !technology->capabilities
      || !technology->write) {
      ast_log(LOG_WARNING, "Bridge technology %s failed registration sanity check.\n",
         technology->name);
      return -1;
   }

   AST_RWLIST_WRLOCK(&bridge_technologies);

   /* Look for duplicate bridge technology already using this name, or already registered */
   AST_RWLIST_TRAVERSE(&bridge_technologies, current, entry) {
      if ((!strcasecmp(current->name, technology->name)) || (current == technology)) {
         ast_log(LOG_WARNING, "A bridge technology of %s already claims to exist in our world.\n",
            technology->name);
         AST_RWLIST_UNLOCK(&bridge_technologies);
         return -1;
      }
   }

   /* Copy module pointer so reference counting can keep the module from unloading */
   technology->mod = module;

   /* Find the correct position to insert the technology. */
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&bridge_technologies, current, entry) {
      /* Put the highest preference tech's first in the list. */
      if (technology->preference >= current->preference) {
         AST_RWLIST_INSERT_BEFORE_CURRENT(technology, entry);

         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;

   if (!current) {
      /* Insert our new bridge technology to the end of the list. */
      AST_RWLIST_INSERT_TAIL(&bridge_technologies, technology, entry);
   }

   AST_RWLIST_UNLOCK(&bridge_technologies);

   ast_verb(2, "Registered bridge technology %s\n", technology->name);

   return 0;
}

int ast_bridge_technology_unregister(struct ast_bridge_technology *technology)
{
   struct ast_bridge_technology *current;

   AST_RWLIST_WRLOCK(&bridge_technologies);

   /* Ensure the bridge technology is registered before removing it */
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&bridge_technologies, current, entry) {
      if (current == technology) {
         AST_RWLIST_REMOVE_CURRENT(entry);
         ast_verb(2, "Unregistered bridge technology %s\n", technology->name);
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;

   AST_RWLIST_UNLOCK(&bridge_technologies);

   return current ? 0 : -1;
}

/*!
 * \internal
 * \brief Put an action onto the specified bridge. Don't dup the action frame.
 * \since 12.0.0
 *
 * \param bridge What to queue the action on.
 * \param action What to do.
 *
 * \return Nothing
 */
static void bridge_queue_action_nodup(struct ast_bridge *bridge, struct ast_frame *action)
{
   ast_debug(1, "Bridge %s: queueing action type:%u sub:%d\n",
      bridge->uniqueid, action->frametype, action->subclass.integer);

   ast_bridge_lock(bridge);
   AST_LIST_INSERT_TAIL(&bridge->action_queue, action, frame_list);
   ast_bridge_unlock(bridge);
   bridge_manager_service_req(bridge);
}

int ast_bridge_queue_action(struct ast_bridge *bridge, struct ast_frame *action)
{
   struct ast_frame *dup;

   dup = ast_frdup(action);
   if (!dup) {
      return -1;
   }
   bridge_queue_action_nodup(bridge, dup);
   return 0;
}

void bridge_dissolve(struct ast_bridge *bridge, int cause)
{
   struct ast_bridge_channel *bridge_channel;
   struct ast_frame action = {
      .frametype = AST_FRAME_BRIDGE_ACTION,
      .subclass.integer = BRIDGE_CHANNEL_ACTION_DEFERRED_DISSOLVING,
   };

   if (bridge->dissolved) {
      return;
   }
   bridge->dissolved = 1;

   if (cause <= 0) {
      cause = AST_CAUSE_NORMAL_CLEARING;
   }
   bridge->cause = cause;

   ast_debug(1, "Bridge %s: dissolving bridge with cause %d(%s)\n",
      bridge->uniqueid, cause, ast_cause2str(cause));

   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      ast_bridge_channel_leave_bridge(bridge_channel,
         BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, cause);
   }

   /* Must defer dissolving bridge because it is already locked. */
   ast_bridge_queue_action(bridge, &action);
}

/*!
 * \internal
 * \brief Check if a bridge should dissolve because of a stolen channel and do it.
 * \since 12.0.0
 *
 * \param bridge Bridge to check.
 * \param bridge_channel Stolen channel causing the check.  It is not in the bridge to check and may be in another bridge.
 *
 * \note On entry, bridge and bridge_channel->bridge are already locked.
 *
 * \return Nothing
 */
static void bridge_dissolve_check_stolen(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
   if (bridge->dissolved) {
      return;
   }

   if (bridge_channel->features->usable
      && ast_test_flag(&bridge_channel->features->feature_flags,
         AST_BRIDGE_CHANNEL_FLAG_DISSOLVE_HANGUP)) {
      /* The stolen channel controlled the bridge it was stolen from. */
      bridge_dissolve(bridge, 0);
      return;
   }
   if (bridge->num_channels < 2
      && ast_test_flag(&bridge->feature_flags, AST_BRIDGE_FLAG_DISSOLVE_HANGUP)) {
      /*
       * The stolen channel has not left enough channels to keep the
       * bridge alive.  Assume the stolen channel hung up.
       */
      bridge_dissolve(bridge, 0);
      return;
   }
}

/*!
 * \internal
 * \brief Update connected line information after a bridge has been reconfigured.
 *
 * \param bridge The bridge itself.
 *
 * \return Nothing
 */
static void bridge_reconfigured_connected_line_update(struct ast_bridge *bridge)
{
   struct ast_party_connected_line connected;
   struct ast_bridge_channel *bridge_channel = AST_LIST_FIRST(&bridge->channels), *peer;
   unsigned char data[1024];
   size_t datalen;

   if (!bridge_channel ||
      !(bridge->technology->capabilities & (AST_BRIDGE_CAPABILITY_1TO1MIX | AST_BRIDGE_CAPABILITY_NATIVE)) ||
      !(peer = ast_bridge_channel_peer(bridge_channel)) ||
      ast_test_flag(ast_channel_flags(bridge_channel->chan), AST_FLAG_ZOMBIE) ||
      ast_test_flag(ast_channel_flags(peer->chan), AST_FLAG_ZOMBIE) ||
      ast_check_hangup_locked(bridge_channel->chan) ||
      ast_check_hangup_locked(peer->chan)) {
      return;
   }

   ast_party_connected_line_init(&connected);

   ast_channel_lock(bridge_channel->chan);
   ast_connected_line_copy_from_caller(&connected, ast_channel_caller(bridge_channel->chan));
   ast_channel_unlock(bridge_channel->chan);

   if ((datalen = ast_connected_line_build_data(data, sizeof(data), &connected, NULL)) != (size_t) -1) {
      ast_bridge_channel_queue_control_data(peer, AST_CONTROL_CONNECTED_LINE, data, datalen);
   }

   ast_channel_lock(peer->chan);
   ast_connected_line_copy_from_caller(&connected, ast_channel_caller(peer->chan));
   ast_channel_unlock(peer->chan);

   if ((datalen = ast_connected_line_build_data(data, sizeof(data), &connected, NULL)) != (size_t) -1) {
      ast_bridge_channel_queue_control_data(bridge_channel, AST_CONTROL_CONNECTED_LINE, data, datalen);
   }

   ast_party_connected_line_free(&connected);
}

/*!
 * \internal
 * \brief Complete joining a channel to the bridge.
 * \since 12.0.0
 *
 * \param bridge What to operate upon.
 * \param bridge_channel What is joining the bridge technology.
 *
 * \note On entry, bridge is already locked.
 *
 * \return Nothing
 */
static void bridge_channel_complete_join(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
   /* Tell the bridge technology we are joining so they set us up */
   ast_debug(1, "Bridge %s: %p(%s) is joining %s technology\n",
      bridge->uniqueid, bridge_channel, ast_channel_name(bridge_channel->chan),
      bridge->technology->name);
   if (bridge->technology->join
      && bridge->technology->join(bridge, bridge_channel)) {
      /* We cannot leave the channel partially in the bridge so we must kick it out */
      ast_debug(1, "Bridge %s: %p(%s) failed to join %s technology (Kicking it out)\n",
         bridge->uniqueid, bridge_channel, ast_channel_name(bridge_channel->chan),
         bridge->technology->name);
      bridge_channel->just_joined = 1;
      ast_bridge_channel_leave_bridge(bridge_channel, BRIDGE_CHANNEL_STATE_END, 0);
      return;
   }

   bridge_channel->just_joined = 0;

   /*
    * When a channel joins the bridge its streams need to be mapped to the bridge's
    * media types vector. This way all streams map to the same media type index for
    * a given channel.
    */
   if (bridge_channel->bridge->technology->stream_topology_changed) {
      bridge_channel->bridge->technology->stream_topology_changed(
         bridge_channel->bridge, bridge_channel);
   } else {
      ast_bridge_channel_stream_map(bridge_channel);
   }
}

/*!
 * \internal
 * \brief Complete joining new channels to the bridge.
 * \since 12.0.0
 *
 * \param bridge Check for new channels on this bridge.
 *
 * \note On entry, bridge is already locked.
 *
 * \return Nothing
 */
static void bridge_complete_join(struct ast_bridge *bridge)
{
   struct ast_bridge_channel *bridge_channel;

   if (bridge->dissolved) {
      /*
       * No sense in completing the join on channels for a dissolved
       * bridge.  They are just going to be removed soon anyway.
       * However, we do have reason to abort here because the bridge
       * technology may not be able to handle the number of channels
       * still in the bridge.
       */
      return;
   }

   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      bridge_channel_queue_deferred_frames(bridge_channel);
      if (!bridge_channel->just_joined) {
         continue;
      }
      bridge_channel_complete_join(bridge, bridge_channel);
   }
}

/*! \brief Helper function used to find the "best" bridge technology given specified capabilities */
static struct ast_bridge_technology *find_best_technology(uint32_t capabilities, struct ast_bridge *bridge)
{
   struct ast_bridge_technology *current;
   struct ast_bridge_technology *best = NULL;

   AST_RWLIST_RDLOCK(&bridge_technologies);
   AST_RWLIST_TRAVERSE(&bridge_technologies, current, entry) {
      if (current->suspended) {
         ast_debug(1, "Bridge technology %s is suspended. Skipping.\n",
            current->name);
         continue;
      }
      if (!(current->capabilities & capabilities)) {
         ast_debug(1, "Bridge technology %s does not have any capabilities we want.\n",
            current->name);
         continue;
      }
      if (best && current->preference <= best->preference) {
         ast_debug(1, "Bridge technology %s has less preference than %s (%u <= %u). Skipping.\n",
            current->name, best->name, current->preference, best->preference);
         continue;
      }
      if (current->compatible && !current->compatible(bridge)) {
         ast_debug(1, "Bridge technology %s is not compatible with properties of existing bridge.\n",
            current->name);
         continue;
      }
      if (!ast_module_running_ref(current->mod)) {
         ast_debug(1, "Bridge technology %s is not running, skipping.\n", current->name);
         continue;
      }
      if (best) {
         ast_module_unref(best->mod);
      }
      best = current;
   }

   if (best) {
      ast_debug(1, "Chose bridge technology %s\n", best->name);
   }

   AST_RWLIST_UNLOCK(&bridge_technologies);

   return best;
}

struct tech_deferred_destroy {
   struct ast_bridge_technology *tech;
   void *tech_pvt;
};

/*!
 * \internal
 * \brief Deferred destruction of bridge tech private structure.
 * \since 12.0.0
 *
 * \param bridge What to execute the action on.
 * \param action Deferred bridge tech destruction.
 *
 * \note On entry, bridge must not be locked.
 *
 * \return Nothing
 */
static void bridge_tech_deferred_destroy(struct ast_bridge *bridge, struct ast_frame *action)
{
   struct tech_deferred_destroy *deferred = action->data.ptr;
   struct ast_bridge dummy_bridge = {
      .technology = deferred->tech,
      .tech_pvt = deferred->tech_pvt,
      .creator = bridge->creator,
      .name = bridge->name,
      .uniqueid = bridge->uniqueid,
      };

   ast_debug(1, "Bridge %s: calling %s technology destructor (deferred, dummy)\n",
      dummy_bridge.uniqueid, dummy_bridge.technology->name);
   dummy_bridge.technology->destroy(&dummy_bridge);
   ast_module_unref(dummy_bridge.technology->mod);
}

/*!
 * \internal
 * \brief Handle bridge action frame.
 * \since 12.0.0
 *
 * \param bridge What to execute the action on.
 * \param action What to do.
 *
 * \note On entry, bridge is already locked.
 * \note Can be called by the bridge destructor.
 *
 * \return Nothing
 */
static void bridge_action_bridge(struct ast_bridge *bridge, struct ast_frame *action)
{
#if 0 /* In case we need to know when the destructor is calling us. */
   int in_destructor = !ao2_ref(bridge, 0);
#endif

   switch (action->subclass.integer) {
   case BRIDGE_CHANNEL_ACTION_DEFERRED_TECH_DESTROY:
      ast_bridge_unlock(bridge);
      bridge_tech_deferred_destroy(bridge, action);
      ast_bridge_lock(bridge);
      break;
   case BRIDGE_CHANNEL_ACTION_DEFERRED_DISSOLVING:
      ast_bridge_unlock(bridge);
      bridge->v_table->dissolving(bridge);
      ast_bridge_lock(bridge);
      break;
   default:
      /* Unexpected deferred action type.  Should never happen. */
      ast_assert(0);
      break;
   }
}

/*!
 * \internal
 * \brief Do any pending bridge actions.
 * \since 12.0.0
 *
 * \param bridge What to do actions on.
 *
 * \note On entry, bridge is already locked.
 * \note Can be called by the bridge destructor.
 *
 * \return Nothing
 */
static void bridge_handle_actions(struct ast_bridge *bridge)
{
   struct ast_frame *action;

   while ((action = AST_LIST_REMOVE_HEAD(&bridge->action_queue, frame_list))) {
      switch (action->frametype) {
      case AST_FRAME_BRIDGE_ACTION:
         bridge_action_bridge(bridge, action);
         break;
      default:
         /* Unexpected deferred frame type.  Should never happen. */
         ast_assert(0);
         break;
      }
      ast_frfree(action);
   }
}

static void destroy_bridge(void *obj)
{
   struct ast_bridge *bridge = obj;

   ast_debug(1, "Bridge %s: actually destroying %s bridge, nobody wants it anymore\n",
      bridge->uniqueid, bridge->v_table->name);

   if (bridge->construction_completed) {
      bridge_topics_destroy(bridge);
   }

   /* Do any pending actions in the context of destruction. */
   ast_bridge_lock(bridge);
   bridge_handle_actions(bridge);
   ast_bridge_unlock(bridge);

   /* There should not be any channels left in the bridge. */
   ast_assert(AST_LIST_EMPTY(&bridge->channels));

   ast_debug(1, "Bridge %s: calling %s bridge destructor\n",
      bridge->uniqueid, bridge->v_table->name);
   bridge->v_table->destroy(bridge);

   /* Pass off the bridge to the technology to destroy if needed */
   if (bridge->technology) {
      ast_debug(1, "Bridge %s: calling %s technology stop\n",
         bridge->uniqueid, bridge->technology->name);
      if (bridge->technology->stop) {
         ast_bridge_lock(bridge);
         bridge->technology->stop(bridge);
         ast_bridge_unlock(bridge);
      }
      ast_debug(1, "Bridge %s: calling %s technology destructor\n",
         bridge->uniqueid, bridge->technology->name);
      if (bridge->technology->destroy) {
         bridge->technology->destroy(bridge);
      }
      ast_module_unref(bridge->technology->mod);
      bridge->technology = NULL;
   }

   AST_VECTOR_FREE(&bridge->media_types);

   bridge->callid = 0;

   cleanup_video_mode(bridge);

   ast_string_field_free_memory(bridge);
   ao2_cleanup(bridge->current_snapshot);
}

struct ast_bridge *bridge_register(struct ast_bridge *bridge)
{
   if (bridge) {
      bridge->construction_completed = 1;
      ast_bridge_lock(bridge);
      ast_bridge_publish_state(bridge);
      ast_bridge_unlock(bridge);
      if (!ao2_link(bridges, bridge)) {
         ast_bridge_destroy(bridge, 0);
         bridge = NULL;
      }
   }
   return bridge;
}

struct ast_bridge *bridge_alloc(size_t size, const struct ast_bridge_methods *v_table)
{
   struct ast_bridge *bridge;

   /* Check v_table that all methods are present. */
   if (!v_table
      || !v_table->name
      || !v_table->destroy
      || !v_table->dissolving
      || !v_table->push
      || !v_table->pull
      || !v_table->notify_masquerade
      || !v_table->get_merge_priority) {
      ast_log(LOG_ERROR, "Virtual method table for bridge class %s not complete.\n",
         v_table && v_table->name ? v_table->name : "<unknown>");
      ast_assert(0);
      return NULL;
   }

   bridge = ao2_alloc(size, destroy_bridge);
   if (!bridge) {
      return NULL;
   }

   if (ast_string_field_init(bridge, 80)) {
      ao2_cleanup(bridge);
      return NULL;
   }

   bridge->v_table = v_table;

   AST_VECTOR_INIT(&bridge->media_types, AST_MEDIA_TYPE_END);

   return bridge;
}

struct ast_bridge *bridge_base_init(struct ast_bridge *self, uint32_t capabilities, unsigned int flags, const char *creator, const char *name, const char *id)
{
   char uuid_hold[AST_UUID_STR_LEN];

   if (!self) {
      return NULL;
   }

   if (!ast_strlen_zero(id)) {
      ast_string_field_set(self, uniqueid, id);
   } else {
      ast_uuid_generate_str(uuid_hold, AST_UUID_STR_LEN);
      ast_string_field_set(self, uniqueid, uuid_hold);
   }
   ast_string_field_set(self, creator, creator);
   if (!ast_strlen_zero(creator)) {
      ast_string_field_set(self, name, name);
   }

   ast_set_flag(&self->feature_flags, flags);
   self->allowed_capabilities = capabilities;

   if (!(flags & AST_BRIDGE_FLAG_INVISIBLE)) {
      if (bridge_topics_init(self) != 0) {
         ast_log(LOG_WARNING, "Bridge %s: Could not initialize topics\n",
            self->uniqueid);
         ao2_ref(self, -1);
         return NULL;
      }
   }

   /* Use our helper function to find the "best" bridge technology. */
   self->technology = find_best_technology(capabilities, self);
   if (!self->technology) {
      ast_log(LOG_WARNING, "Bridge %s: Could not create class %s.  No technology to support it.\n",
         self->uniqueid, self->v_table->name);
      ao2_ref(self, -1);
      return NULL;
   }

   /* Pass off the bridge to the technology to manipulate if needed */
   ast_debug(1, "Bridge %s: calling %s technology constructor\n",
      self->uniqueid, self->technology->name);
   if (self->technology->create && self->technology->create(self)) {
      ast_log(LOG_WARNING, "Bridge %s: failed to setup bridge technology %s\n",
         self->uniqueid, self->technology->name);
      ao2_ref(self, -1);
      return NULL;
   }
   ast_debug(1, "Bridge %s: calling %s technology start\n",
      self->uniqueid, self->technology->name);
   if (self->technology->start && self->technology->start(self)) {
      ast_log(LOG_WARNING, "Bridge %s: failed to start bridge technology %s\n",
         self->uniqueid, self->technology->name);
      ao2_ref(self, -1);
      return NULL;
   }

   if (!(flags & AST_BRIDGE_FLAG_INVISIBLE)) {
      if (!ast_bridge_topic(self)) {
         ao2_ref(self, -1);
         return NULL;
      }
   }

   self->creationtime = ast_tvnow();

   return self;
}

/*!
 * \internal
 * \brief ast_bridge base class destructor.
 * \since 12.0.0
 *
 * \param self Bridge to operate upon.
 *
 * \note Stub because of nothing to do.
 *
 * \return Nothing
 */
static void bridge_base_destroy(struct ast_bridge *self)
{
}

/*!
 * \internal
 * \brief The bridge is being dissolved.
 * \since 12.0.0
 *
 * \param self Bridge to operate upon.
 *
 * \return Nothing
 */
static void bridge_base_dissolving(struct ast_bridge *self)
{
   ao2_unlink(bridges, self);
}

/*!
 * \internal
 * \brief ast_bridge base push method.
 * \since 12.0.0
 *
 * \param self Bridge to operate upon.
 * \param bridge_channel Bridge channel to push.
 * \param swap Bridge channel to swap places with if not NULL.
 *
 * \note On entry, self is already locked.
 * \note Stub because of nothing to do.
 *
 * \retval 0 on success
 * \retval -1 on failure
 */
static int bridge_base_push(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel, struct ast_bridge_channel *swap)
{
   return 0;
}

/*!
 * \internal
 * \brief ast_bridge base pull method.
 * \since 12.0.0
 *
 * \param self Bridge to operate upon.
 * \param bridge_channel Bridge channel to pull.
 *
 * \note On entry, self is already locked.
 *
 * \return Nothing
 */
static void bridge_base_pull(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel)
{
   ast_bridge_features_remove(bridge_channel->features, AST_BRIDGE_HOOK_REMOVE_ON_PULL);
}

/*!
 * \internal
 * \brief ast_bridge base notify_masquerade method.
 * \since 12.0.0
 *
 * \param self Bridge to operate upon.
 * \param bridge_channel Bridge channel that was masqueraded.
 *
 * \note On entry, self is already locked.
 *
 * \return Nothing
 */
static void bridge_base_notify_masquerade(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel)
{
   self->reconfigured = 1;
}

/*!
 * \internal
 * \brief Get the merge priority of this bridge.
 * \since 12.0.0
 *
 * \param self Bridge to operate upon.
 *
 * \note On entry, self is already locked.
 *
 * \return Merge priority
 */
static int bridge_base_get_merge_priority(struct ast_bridge *self)
{
   return 0;
}

/*!
 * \internal
 * \brief ast_bridge base push_peek method.
 * \since 13.2.0
 *
 * \param self Bridge to operate upon.
 * \param bridge_channel Bridge channel to push.
 * \param swap Bridge channel to swap places with if not NULL.
 *
 * \note On entry, self is already locked.
 * \note Stub because of nothing to do.
 *
 * \retval 0 on success
 * \retval -1 on failure
 */
static int bridge_base_push_peek(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel, struct ast_bridge_channel *swap)
{
   return 0;
}

struct ast_bridge_methods ast_bridge_base_v_table = {
   .name = "base",
   .destroy = bridge_base_destroy,
   .dissolving = bridge_base_dissolving,
   .push = bridge_base_push,
   .pull = bridge_base_pull,
   .notify_masquerade = bridge_base_notify_masquerade,
   .get_merge_priority = bridge_base_get_merge_priority,
   .push_peek = bridge_base_push_peek,
};

struct ast_bridge *ast_bridge_base_new(uint32_t capabilities, unsigned int flags, const char *creator, const char *name, const char *id)
{
   void *bridge;

   bridge = bridge_alloc(sizeof(struct ast_bridge), &ast_bridge_base_v_table);
   bridge = bridge_base_init(bridge, capabilities, flags, creator, name, id);
   bridge = bridge_register(bridge);
   return bridge;
}

int ast_bridge_destroy(struct ast_bridge *bridge, int cause)
{
   ast_debug(1, "Bridge %s: telling all channels to leave the party\n", bridge->uniqueid);
   ast_bridge_lock(bridge);
   bridge_dissolve(bridge, cause);
   ast_bridge_unlock(bridge);

   ao2_ref(bridge, -1);

   return 0;
}

/*!
 * \internal
 * \brief Perform the smart bridge operation.
 * \since 12.0.0
 *
 * \param bridge Work on this bridge.
 *
 * \details
 * Basically see if a new bridge technology should be used instead
 * of the current one.
 *
 * \note On entry, bridge is already locked.
 *
 * \retval 0 on success.
 * \retval -1 on error.
 */
static int smart_bridge_operation(struct ast_bridge *bridge)
{
   uint32_t new_capabilities;
   struct ast_bridge_technology *new_technology;
   struct ast_bridge_technology *old_technology = bridge->technology;
   struct ast_bridge_channel *bridge_channel;
   struct ast_frame *deferred_action;
   struct ast_bridge dummy_bridge = {
      .technology = bridge->technology,
      .tech_pvt = bridge->tech_pvt,
      .creator = bridge->creator,
      .name = bridge->name,
      .uniqueid = bridge->uniqueid,
   };

   if (bridge->dissolved) {
      ast_debug(1, "Bridge %s is dissolved, not performing smart bridge operation.\n",
         bridge->uniqueid);
      return 0;
   }

   /* Determine new bridge technology capabilities needed. */
   if (2 < bridge->num_channels) {
      new_capabilities = AST_BRIDGE_CAPABILITY_MULTIMIX;
      new_capabilities &= bridge->allowed_capabilities;
   } else {
      new_capabilities = AST_BRIDGE_CAPABILITY_NATIVE | AST_BRIDGE_CAPABILITY_1TO1MIX;
      new_capabilities &= bridge->allowed_capabilities;
      if (!new_capabilities
         && (bridge->allowed_capabilities & AST_BRIDGE_CAPABILITY_MULTIMIX)) {
         /* Allow switching between different multimix bridge technologies. */
         new_capabilities = AST_BRIDGE_CAPABILITY_MULTIMIX;
      }
   }

   /* Find a bridge technology to satisfy the new capabilities. */
   new_technology = find_best_technology(new_capabilities, bridge);
   if (!new_technology) {
      int is_compatible = 0;

      if (old_technology->compatible) {
         is_compatible = old_technology->compatible(bridge);
      } else if (old_technology->capabilities & AST_BRIDGE_CAPABILITY_MULTIMIX) {
         is_compatible = 1;
      } else if (bridge->num_channels <= 2
         && (old_technology->capabilities & AST_BRIDGE_CAPABILITY_1TO1MIX)) {
         is_compatible = 1;
      }

      if (is_compatible) {
         ast_debug(1, "Bridge %s could not get a new technology, staying with old technology.\n",
            bridge->uniqueid);
         return 0;
      }
      ast_log(LOG_WARNING, "Bridge %s has no technology available to support it.\n",
         bridge->uniqueid);
      return -1;
   }
   if (new_technology == old_technology) {
      ast_debug(1, "Bridge %s is already using the new technology.\n",
         bridge->uniqueid);
      ast_module_unref(old_technology->mod);
      return 0;
   }

   if (old_technology->destroy) {
      struct tech_deferred_destroy deferred_tech_destroy = {
         .tech = dummy_bridge.technology,
         .tech_pvt = dummy_bridge.tech_pvt,
      };
      struct ast_frame action = {
         .frametype = AST_FRAME_BRIDGE_ACTION,
         .subclass.integer = BRIDGE_CHANNEL_ACTION_DEFERRED_TECH_DESTROY,
         .data.ptr = &deferred_tech_destroy,
         .datalen = sizeof(deferred_tech_destroy),
      };

      /*
       * We need to defer the bridge technology destroy callback
       * because we have the bridge locked.
       */
      deferred_action = ast_frdup(&action);
      if (!deferred_action) {
         ast_module_unref(new_technology->mod);
         return -1;
      }
   } else {
      deferred_action = NULL;
   }

   /*
    * We are now committed to changing the bridge technology.  We
    * must not release the bridge lock until we have installed the
    * new bridge technology.
    */
   ast_verb(4, "Bridge %s: switching from %s technology to %s\n",
      bridge->uniqueid, old_technology->name, new_technology->name);

   /*
    * Since we are soon going to pass this bridge to a new
    * technology we need to NULL out the tech_pvt pointer but
    * don't worry as it still exists in dummy_bridge, ditto for the
    * old technology.
    */
   bridge->tech_pvt = NULL;
   bridge->technology = new_technology;

   /* Setup the new bridge technology. */
   ast_debug(1, "Bridge %s: calling %s technology constructor\n",
      bridge->uniqueid, new_technology->name);
   if (new_technology->create && new_technology->create(bridge)) {
      ast_log(LOG_WARNING, "Bridge %s: failed to setup bridge technology %s\n",
         bridge->uniqueid, new_technology->name);
      bridge->tech_pvt = dummy_bridge.tech_pvt;
      bridge->technology = dummy_bridge.technology;
      ast_module_unref(new_technology->mod);
      return -1;
   }

   /* To ensure that things are sane for the old technology move the channels it
    * expects to the dummy bridge
    */
   AST_LIST_TRAVERSE_SAFE_BEGIN(&bridge->channels, bridge_channel, entry) {
      if (bridge_channel->just_joined) {
         continue;
      }
      ast_debug(1, "Bridge %s: moving %p(%s) to dummy bridge temporarily\n",
         bridge->uniqueid, bridge_channel, ast_channel_name(bridge_channel->chan));
      AST_LIST_REMOVE_CURRENT(entry);
      AST_LIST_INSERT_TAIL(&dummy_bridge.channels, bridge_channel, entry);
      dummy_bridge.num_channels++;
      if (ast_test_flag(&bridge_channel->features->feature_flags, AST_BRIDGE_CHANNEL_FLAG_LONELY)) {
         dummy_bridge.num_lonely++;
      }
      if (!bridge_channel->suspended) {
         dummy_bridge.num_active++;
      }
   }
   AST_LIST_TRAVERSE_SAFE_END;

   /* Take all the channels out of the old technology */
   AST_LIST_TRAVERSE_SAFE_BEGIN(&dummy_bridge.channels, bridge_channel, entry) {
      ast_debug(1, "Bridge %s: %p(%s) is leaving %s technology (dummy)\n",
         dummy_bridge.uniqueid, bridge_channel, ast_channel_name(bridge_channel->chan),
         old_technology->name);
      if (old_technology->leave) {
         old_technology->leave(&dummy_bridge, bridge_channel);
      }
      AST_LIST_REMOVE_CURRENT(entry);
      AST_LIST_INSERT_TAIL(&bridge->channels, bridge_channel, entry);
      dummy_bridge.num_channels--;
      if (ast_test_flag(&bridge_channel->features->feature_flags, AST_BRIDGE_CHANNEL_FLAG_LONELY)) {
         dummy_bridge.num_lonely--;
      }
      if (!bridge_channel->suspended) {
         dummy_bridge.num_active--;
      }
   }
   AST_LIST_TRAVERSE_SAFE_END;

   ast_debug(1, "Bridge %s: calling %s technology stop\n",
      dummy_bridge.uniqueid, old_technology->name);
   if (old_technology->stop) {
      old_technology->stop(&dummy_bridge);
   }

   /* Add any new channels or re-add existing channels to the bridge. */
   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      bridge_channel_complete_join(bridge, bridge_channel);
   }

   ast_debug(1, "Bridge %s: calling %s technology start\n",
      bridge->uniqueid, new_technology->name);
   if (new_technology->start && new_technology->start(bridge)) {
      ast_log(LOG_WARNING, "Bridge %s: failed to start bridge technology %s\n",
         bridge->uniqueid, new_technology->name);
   }

   /*
    * Now that all the channels have been moved over we need to get
    * rid of all the information the old technology may have left
    * around.
    */
   if (old_technology->destroy) {
      ast_debug(1, "Bridge %s: deferring %s technology destructor\n",
         dummy_bridge.uniqueid, old_technology->name);
      bridge_queue_action_nodup(bridge, deferred_action);
   } else {
      ast_debug(1, "Bridge %s: calling %s technology destructor\n",
         dummy_bridge.uniqueid, old_technology->name);
      ast_module_unref(old_technology->mod);
   }

   return 0;
}

/*!
 * \internal
 * \brief Bridge channel to check if a BRIDGE_PLAY_SOUND needs to be played.
 * \since 12.0.0
 *
 * \param bridge_channel What to check.
 *
 * \return Nothing
 */
static void check_bridge_play_sound(struct ast_bridge_channel *bridge_channel)
{
   const char *play_file;

   ast_channel_lock(bridge_channel->chan);
   play_file = pbx_builtin_getvar_helper(bridge_channel->chan, "BRIDGE_PLAY_SOUND");
   if (!ast_strlen_zero(play_file)) {
      play_file = ast_strdupa(play_file);
      pbx_builtin_setvar_helper(bridge_channel->chan, "BRIDGE_PLAY_SOUND", NULL);
   } else {
      play_file = NULL;
   }
   ast_channel_unlock(bridge_channel->chan);

   if (play_file) {
      ast_bridge_channel_queue_playfile(bridge_channel, NULL, play_file, NULL);
   }
}

/*!
 * \internal
 * \brief Check for any BRIDGE_PLAY_SOUND channel variables in the bridge.
 * \since 12.0.0
 *
 * \param bridge What to operate on.
 *
 * \note On entry, the bridge is already locked.
 *
 * \return Nothing
 */
static void check_bridge_play_sounds(struct ast_bridge *bridge)
{
   struct ast_bridge_channel *bridge_channel;

   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      check_bridge_play_sound(bridge_channel);
   }
}

void ast_bridge_vars_set(struct ast_channel *chan, const char *name, const char *pvtid)
{
   ast_channel_stage_snapshot(chan);
   pbx_builtin_setvar_helper(chan, "BRIDGEPEER", name);
   pbx_builtin_setvar_helper(chan, "BRIDGEPVTCALLID", pvtid);
   ast_channel_stage_snapshot_done(chan);
}

/*!
 * \internal
 * \brief Set BRIDGEPEER and BRIDGEPVTCALLID channel variables in a 2 party bridge.
 * \since 12.0.0
 *
 * \param c0 Party of the first part.
 * \param c1 Party of the second part.
 *
 * \note On entry, the bridge is already locked.
 * \note The bridge is expected to have exactly two parties.
 *
 * \return Nothing
 */
static void set_bridge_peer_vars_2party(struct ast_channel *c0, struct ast_channel *c1)
{
   const char *c0_name;
   const char *c1_name;
   const char *c0_pvtid = NULL;
   const char *c1_pvtid = NULL;
#define UPDATE_BRIDGE_VARS_GET(chan, name, pvtid)                          \
   do {                                                        \
      name = ast_strdupa(ast_channel_name(chan));                          \
      if (ast_channel_tech(chan)->get_pvt_uniqueid) {                      \
         pvtid = ast_strdupa(ast_channel_tech(chan)->get_pvt_uniqueid(chan)); \
      }                                                        \
   } while (0)

   ast_channel_lock(c1);
   UPDATE_BRIDGE_VARS_GET(c1, c1_name, c1_pvtid);
   ast_channel_unlock(c1);

   ast_channel_lock(c0);
   ast_bridge_vars_set(c0, c1_name, c1_pvtid);
   UPDATE_BRIDGE_VARS_GET(c0, c0_name, c0_pvtid);
   ast_channel_unlock(c0);

   ast_channel_lock(c1);
   ast_bridge_vars_set(c1, c0_name, c0_pvtid);
   ast_channel_unlock(c1);
}

/*!
 * \internal
 * \brief Fill the BRIDGEPEER value buffer with a comma separated list of channel names.
 * \since 12.0.0
 *
 * \param buf Buffer to fill.  The caller must guarantee the buffer is large enough.
 * \param cur_idx Which index into names[] to skip.
 * \param names Channel names to put in the buffer.
 * \param num_names Number of names in the array.
 *
 * \return Nothing
 */
static void fill_bridgepeer_buf(char *buf, unsigned int cur_idx, const char *names[], unsigned int num_names)
{
   int need_separator = 0;
   unsigned int idx;
   const char *src;
   char *pos;

   pos = buf;
   for (idx = 0; idx < num_names; ++idx) {
      if (idx == cur_idx) {
         continue;
      }

      if (need_separator) {
         *pos++ = ',';
      }
      need_separator = 1;

      /* Copy name into buffer. */
      src = names[idx];
      while (*src) {
         *pos++ = *src++;
      }
   }
   *pos = '\0';
}

/*!
 * \internal
 * \brief Set BRIDGEPEER and BRIDGEPVTCALLID channel variables in a multi-party bridge.
 * \since 12.0.0
 *
 * \param bridge What to operate on.
 *
 * \note On entry, the bridge is already locked.
 * \note The bridge is expected to have more than two parties.
 *
 * \return Nothing
 */
static void set_bridge_peer_vars_multiparty(struct ast_bridge *bridge)
{
/*
 * Set a maximum number of channel names for the BRIDGEPEER
 * list.  The plus one is for the current channel which is not
 * put in the list.
 */
#define MAX_BRIDGEPEER_CHANS  (10 + 1)

   unsigned int idx;
   unsigned int num_names;
   unsigned int len;
   const char **names;
   char *buf;
   struct ast_bridge_channel *bridge_channel;

   /* Get first MAX_BRIDGEPEER_CHANS channel names. */
   num_names = MIN(bridge->num_channels, MAX_BRIDGEPEER_CHANS);
   names = ast_alloca(num_names * sizeof(*names));
   idx = 0;
   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      if (num_names <= idx) {
         break;
      }
      ast_channel_lock(bridge_channel->chan);
      names[idx++] = ast_strdupa(ast_channel_name(bridge_channel->chan));
      ast_channel_unlock(bridge_channel->chan);
   }

   /* Determine maximum buf size needed. */
   len = num_names;
   for (idx = 0; idx < num_names; ++idx) {
      len += strlen(names[idx]);
   }
   buf = ast_alloca(len);

   /* Set the bridge channel variables. */
   idx = 0;
   buf[0] = '\0';
   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      if (idx < num_names) {
         fill_bridgepeer_buf(buf, idx, names, num_names);
      }
      ++idx;

      ast_channel_lock(bridge_channel->chan);
      ast_bridge_vars_set(bridge_channel->chan, buf, NULL);
      ast_channel_unlock(bridge_channel->chan);
   }
}

/*!
 * \internal
 * \brief Set BRIDGEPEER and BRIDGEPVTCALLID channel variables in a holding bridge.
 * \since 12.0.0
 *
 * \param bridge What to operate on.
 *
 * \note On entry, the bridge is already locked.
 *
 * \return Nothing
 */
static void set_bridge_peer_vars_holding(struct ast_bridge *bridge)
{
   struct ast_bridge_channel *bridge_channel;

   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      ast_channel_lock(bridge_channel->chan);
      ast_bridge_vars_set(bridge_channel->chan, NULL, NULL);
      ast_channel_unlock(bridge_channel->chan);
   }
}

/*!
 * \internal
 * \brief Set BRIDGEPEER and BRIDGEPVTCALLID channel variables in the bridge.
 * \since 12.0.0
 *
 * \param bridge What to operate on.
 *
 * \note On entry, the bridge is already locked.
 *
 * \return Nothing
 */
static void set_bridge_peer_vars(struct ast_bridge *bridge)
{
   if (bridge->technology->capabilities & AST_BRIDGE_CAPABILITY_HOLDING) {
      set_bridge_peer_vars_holding(bridge);
      return;
   }
   if (bridge->num_channels < 2) {
      return;
   }
   if (bridge->num_channels == 2) {
      set_bridge_peer_vars_2party(AST_LIST_FIRST(&bridge->channels)->chan,
         AST_LIST_LAST(&bridge->channels)->chan);
   } else {
      set_bridge_peer_vars_multiparty(bridge);
   }
}

void bridge_reconfigured(struct ast_bridge *bridge, unsigned int colp_update)
{
   if (!bridge->reconfigured) {
      return;
   }
   bridge->reconfigured = 0;
   if (ast_test_flag(&bridge->feature_flags, AST_BRIDGE_FLAG_SMART)
      && smart_bridge_operation(bridge)) {
      /* Smart bridge failed. */
      bridge_dissolve(bridge, 0);
      return;
   }
   bridge_complete_join(bridge);

   if (bridge->dissolved) {
      return;
   }
   check_bridge_play_sounds(bridge);
   set_bridge_peer_vars(bridge);
   ast_bridge_publish_state(bridge);

   if (colp_update) {
      bridge_reconfigured_connected_line_update(bridge);
   }
}

struct ast_bridge_channel *bridge_find_channel(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;

   AST_LIST_TRAVERSE(&bridge->channels, bridge_channel, entry) {
      if (bridge_channel->chan == chan) {
         break;
      }
   }

   return bridge_channel;
}

void ast_bridge_notify_masquerade(struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;
   struct ast_bridge *bridge;

   /* Safely get the bridge_channel pointer for the chan. */
   ast_channel_lock(chan);
   bridge_channel = ast_channel_get_bridge_channel(chan);
   ast_channel_unlock(chan);
   if (!bridge_channel) {
      /* Not in a bridge */
      return;
   }

   ast_bridge_channel_lock_bridge(bridge_channel);
   bridge = bridge_channel->bridge;
   if (bridge_channel == bridge_find_channel(bridge, chan)) {
/*
 * XXX ASTERISK-22366 this needs more work.  The channels need
 * to be made compatible again if the formats change. The
 * bridge_channel thread needs to monitor for this case.
 */
      /* The channel we want to notify is still in a bridge. */
      bridge->v_table->notify_masquerade(bridge, bridge_channel);
      bridge_reconfigured(bridge, 1);
   }
   ast_bridge_unlock(bridge);
   ao2_ref(bridge_channel, -1);
}

/*!
 * \brief Internal bridge impart wait condition and associated conditional.
 */
struct bridge_channel_impart_cond {
   AST_LIST_ENTRY(bridge_channel_impart_cond) node;
   /*! Lock for the data structure */
   ast_mutex_t lock;
   /*! Wait condition */
   ast_cond_t cond;
   /*! Wait until done */
   int done;
};

AST_LIST_HEAD_NOLOCK(bridge_channel_impart_ds_head, bridge_channel_impart_cond);

/*!
 * \internal
 * \brief Signal imparting threads to wake up.
 * \since 13.9.0
 *
 * \param ds_head List of imparting threads to wake up.
 *
 * \return Nothing
 */
static void bridge_channel_impart_ds_head_signal(struct bridge_channel_impart_ds_head *ds_head)
{
   if (ds_head) {
      struct bridge_channel_impart_cond *cond;

      while ((cond = AST_LIST_REMOVE_HEAD(ds_head, node))) {
         ast_mutex_lock(&cond->lock);
         cond->done = 1;
         ast_cond_signal(&cond->cond);
         ast_mutex_unlock(&cond->lock);
      }
   }
}

static void bridge_channel_impart_ds_head_dtor(void *doomed)
{
   bridge_channel_impart_ds_head_signal(doomed);
   ast_free(doomed);
}

/*!
 * \internal
 * \brief Fixup the bridge impart datastore.
 * \since 13.9.0
 *
 * \param data Bridge impart datastore data to fixup from old_chan.
 * \param old_chan The datastore is moving from this channel.
 * \param new_chan The datastore is moving to this channel.
 *
 * \return Nothing
 */
static void bridge_channel_impart_ds_head_fixup(void *data, struct ast_channel *old_chan, struct ast_channel *new_chan)
{
   /*
    * Signal any waiting impart threads.  The masquerade is going to kill
    * old_chan and we don't need to be waiting on new_chan.
    */
   bridge_channel_impart_ds_head_signal(data);
}

static const struct ast_datastore_info bridge_channel_impart_ds_info = {
   .type = "bridge-impart-ds",
   .destroy = bridge_channel_impart_ds_head_dtor,
   .chan_fixup = bridge_channel_impart_ds_head_fixup,
};

/*!
 * \internal
 * \brief Add impart wait datastore conditional to channel.
 * \since 13.9.0
 *
 * \param chan Channel to add the impart wait conditional.
 * \param cond Imparting conditional to add.
 *
 * \retval 0 on success.
 * \retval -1 on error.
 */
static int bridge_channel_impart_add(struct ast_channel *chan, struct bridge_channel_impart_cond *cond)
{
   struct ast_datastore *datastore;
   struct bridge_channel_impart_ds_head *ds_head;

   ast_channel_lock(chan);

   datastore = ast_channel_datastore_find(chan, &bridge_channel_impart_ds_info, NULL);
   if (!datastore) {
      datastore = ast_datastore_alloc(&bridge_channel_impart_ds_info, NULL);
      if (!datastore) {
         ast_channel_unlock(chan);
         return -1;
      }
      ds_head = ast_calloc(1, sizeof(*ds_head));
      if (!ds_head) {
         ast_channel_unlock(chan);
         ast_datastore_free(datastore);
         return -1;
      }
      datastore->data = ds_head;
      ast_channel_datastore_add(chan, datastore);
   } else {
      ds_head = datastore->data;
      ast_assert(ds_head != NULL);
   }

   AST_LIST_INSERT_TAIL(ds_head, cond, node);

   ast_channel_unlock(chan);
   return 0;
}

void bridge_channel_impart_signal(struct ast_channel *chan)
{
   struct ast_datastore *datastore;

   ast_channel_lock(chan);
   datastore = ast_channel_datastore_find(chan, &bridge_channel_impart_ds_info, NULL);
   if (datastore) {
      bridge_channel_impart_ds_head_signal(datastore->data);
   }
   ast_channel_unlock(chan);
}

/*!
 * \internal
 * \brief Block imparting channel thread until signaled.
 * \since 13.9.0
 *
 * \param cond Imparting conditional to wait for.
 *
 * \return Nothing
 */
static void bridge_channel_impart_wait(struct bridge_channel_impart_cond *cond)
{
   ast_mutex_lock(&cond->lock);
   while (!cond->done) {
      ast_cond_wait(&cond->cond, &cond->lock);
   }
   ast_mutex_unlock(&cond->lock);
}

/*
 * XXX ASTERISK-21271 make ast_bridge_join() require features to be allocated just like ast_bridge_impart() and not expect the struct back.
 *
 * This change is really going to break ConfBridge.  All other
 * users are easily changed.  However, it is needed so the
 * bridging code can manipulate features on all channels
 * consistently no matter how they joined.
 *
 * Need to update the features parameter doxygen when this
 * change is made to be like ast_bridge_impart().
 */
int ast_bridge_join(struct ast_bridge *bridge,
   struct ast_channel *chan,
   struct ast_channel *swap,
   struct ast_bridge_features *features,
   struct ast_bridge_tech_optimizations *tech_args,
   enum ast_bridge_join_flags flags)
{
   struct ast_bridge_channel *bridge_channel;
   int res = 0;
   SCOPE_TRACE(1, "%s Bridge: %s\n", ast_channel_name(chan), bridge->uniqueid);

   bridge_channel = bridge_channel_internal_alloc(bridge);
   if (flags & AST_BRIDGE_JOIN_PASS_REFERENCE) {
      ao2_ref(bridge, -1);
   }
   if (!bridge_channel) {
      ao2_t_cleanup(swap, "Error exit: bridge_channel alloc failed");
      res = -1;
      goto join_exit;
   }
/* XXX ASTERISK-21271 features cannot be NULL when passed in. When it is changed to allocated we can do like ast_bridge_impart() and allocate one. */
   ast_assert(features != NULL);
   if (!features) {
      ao2_ref(bridge_channel, -1);
      ao2_t_cleanup(swap, "Error exit: features is NULL");
      res = -1;
      goto join_exit;
   }
   if (tech_args) {
      bridge_channel->tech_args = *tech_args;
   }

   ast_channel_lock(chan);
   if (ast_test_flag(ast_channel_flags(chan), AST_FLAG_ZOMBIE)) {
      res = -1;
   } else {
      ast_channel_internal_bridge_channel_set(chan, bridge_channel);
   }
   ast_channel_unlock(chan);
   bridge_channel->thread = pthread_self();
   bridge_channel->chan = chan;
   bridge_channel->swap = swap;
   bridge_channel->features = features;
   bridge_channel->inhibit_colp = !!(flags & AST_BRIDGE_JOIN_INHIBIT_JOIN_COLP);

   /* allow subclass to peek at upcoming push operation */
   if (bridge->v_table->push_peek && !res) {
      struct ast_bridge_channel *bcswap = NULL;

      ast_bridge_lock(bridge);
      if (bridge_channel->swap) {
         bcswap = bridge_find_channel(bridge, bridge_channel->swap);
      }
      res = bridge->v_table->push_peek(bridge, bridge_channel, bcswap);
      ast_bridge_unlock(bridge);
   }

   if (!res) {
      res = bridge_channel_internal_join(bridge_channel);
   }

   /* Cleanup all the data in the bridge channel after it leaves the bridge. */
   ast_channel_lock(chan);
   ast_channel_internal_bridge_channel_set(chan, NULL);
   ast_channel_unlock(chan);
   /* Due to a race condition, we lock the bridge channel here for ast_bridge_channel_get_chan */
   ao2_lock(bridge_channel);
   bridge_channel->chan = NULL;
   ao2_unlock(bridge_channel);
   /* If bridge_channel->swap is not NULL then the join failed. */
   ao2_t_cleanup(bridge_channel->swap, "Bridge complete: join failed");
   bridge_channel->swap = NULL;
   bridge_channel->features = NULL;

   ao2_ref(bridge_channel, -1);

join_exit:
   ast_bridge_run_after_callback(chan);
   bridge_channel_impart_signal(chan);
   if (!(ast_channel_softhangup_internal_flag(chan) & AST_SOFTHANGUP_ASYNCGOTO)
      && !ast_bridge_setup_after_goto(chan)) {
      /* Claim the after bridge goto is an async goto destination. */
      ast_channel_lock(chan);
      ast_softhangup_nolock(chan, AST_SOFTHANGUP_ASYNCGOTO);
      ast_channel_unlock(chan);
   }
   return res;
}

/*! \brief Thread responsible for imparted bridged channels to be departed */
static void *bridge_channel_depart_thread(void *data)
{
   struct ast_bridge_channel *bridge_channel = data;
   int res = 0;

   if (bridge_channel->callid) {
      ast_callid_threadassoc_add(bridge_channel->callid);
   }

   res = bridge_channel_internal_join(bridge_channel);

   /*
    * cleanup
    *
    * If bridge_channel->swap is not NULL then the join failed.
    */
   ao2_t_cleanup(bridge_channel->swap, "Bridge complete: Departable impart join failed");
   bridge_channel->swap = NULL;
   ast_bridge_features_destroy(bridge_channel->features);
   bridge_channel->features = NULL;

   ast_bridge_discard_after_callback(bridge_channel->chan,
      res ? AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED : AST_BRIDGE_AFTER_CB_REASON_DEPART);
   /* If join failed there will be impart threads waiting. */
   bridge_channel_impart_signal(bridge_channel->chan);
   ast_bridge_discard_after_goto(bridge_channel->chan);

   return NULL;
}

/*! \brief Thread responsible for independent imparted bridged channels */
static void *bridge_channel_ind_thread(void *data)
{
   struct ast_bridge_channel *bridge_channel = data;
   struct ast_channel *chan;

   if (bridge_channel->callid) {
      ast_callid_threadassoc_add(bridge_channel->callid);
   }

   bridge_channel_internal_join(bridge_channel);
   chan = bridge_channel->chan;

   /* cleanup */
   ast_channel_lock(chan);
   ast_channel_internal_bridge_channel_set(chan, NULL);
   ast_channel_unlock(chan);
   /* Lock here for ast_bridge_channel_get_chan */
   ao2_lock(bridge_channel);
   bridge_channel->chan = NULL;
   ao2_unlock(bridge_channel);
   /* If bridge_channel->swap is not NULL then the join failed. */
   ao2_t_cleanup(bridge_channel->swap, "Bridge complete: Independent impart join failed");
   bridge_channel->swap = NULL;
   ast_bridge_features_destroy(bridge_channel->features);
   bridge_channel->features = NULL;

   ao2_ref(bridge_channel, -1);

   ast_bridge_run_after_callback(chan);
   /* If join failed there will be impart threads waiting. */
   bridge_channel_impart_signal(chan);
   ast_bridge_run_after_goto(chan);
   return NULL;
}

static int bridge_impart_internal(struct ast_bridge *bridge,
   struct ast_channel *chan,
   struct ast_channel *swap,
   struct ast_bridge_features *features,
   enum ast_bridge_impart_flags flags,
   struct bridge_channel_impart_cond *cond)
{
   int res = 0;
   struct ast_bridge_channel *bridge_channel;

   /* Imparted channels cannot have a PBX. */
   if (ast_channel_pbx(chan)) {
      ast_log(AST_LOG_WARNING, "Channel %s has a PBX thread and cannot be imparted into bridge %s\n",
         ast_channel_name(chan), bridge->uniqueid);
      ast_bridge_features_destroy(features);
      return -1;
   }

   /* Supply an empty features structure if the caller did not. */
   if (!features) {
      features = ast_bridge_features_new();
      if (!features) {
         return -1;
      }
   }

   /* Try to allocate a structure for the bridge channel */
   bridge_channel = bridge_channel_internal_alloc(bridge);
   if (!bridge_channel) {
      ast_bridge_features_destroy(features);
      return -1;
   }

   ast_channel_lock(chan);
   if (ast_test_flag(ast_channel_flags(chan), AST_FLAG_ZOMBIE)) {
      ast_log(AST_LOG_NOTICE, "Channel %s is a zombie and cannot be imparted into bridge %s\n",
         ast_channel_name(chan), bridge->uniqueid);
      res = -1;
   } else {
      ast_channel_internal_bridge_channel_set(chan, bridge_channel);
   }
   ast_channel_unlock(chan);
   bridge_channel->chan = chan;
   bridge_channel->swap = ao2_t_bump(swap, "Setting up bridge impart");
   bridge_channel->features = features;
   bridge_channel->inhibit_colp = !!(flags & AST_BRIDGE_IMPART_INHIBIT_JOIN_COLP);
   bridge_channel->depart_wait =
      (flags & AST_BRIDGE_IMPART_CHAN_MASK) == AST_BRIDGE_IMPART_CHAN_DEPARTABLE;
   bridge_channel->callid = ast_read_threadstorage_callid();

   /* allow subclass to peek at swap channel before it can hangup */
   if (bridge->v_table->push_peek && !res) {
      struct ast_bridge_channel *bcswap = NULL;

      ast_bridge_lock(bridge);
      if (bridge_channel->swap) {
         bcswap = bridge_find_channel(bridge, bridge_channel->swap);
      }
      res = bridge->v_table->push_peek(bridge, bridge_channel, bcswap);
      ast_bridge_unlock(bridge);
   }

   /* Actually create the thread that will handle the channel */
   if (!res) {
      res = bridge_channel_impart_add(chan, cond);
   }
   if (!res) {
      if ((flags & AST_BRIDGE_IMPART_CHAN_MASK) == AST_BRIDGE_IMPART_CHAN_INDEPENDENT) {
         res = ast_pthread_create_detached(&bridge_channel->thread, NULL,
            bridge_channel_ind_thread, bridge_channel);
      } else {
         res = ast_pthread_create(&bridge_channel->thread, NULL,
            bridge_channel_depart_thread, bridge_channel);
      }

      if (!res) {
         bridge_channel_impart_wait(cond);
      }
   }

   if (res) {
      /* cleanup */
      ast_channel_lock(chan);
      ast_channel_internal_bridge_channel_set(chan, NULL);
      ast_channel_unlock(chan);
      /* Lock here for ast_bridge_channel_get_chan */
      ao2_lock(bridge_channel);
      bridge_channel->chan = NULL;
      ao2_unlock(bridge_channel);
      ao2_t_cleanup(bridge_channel->swap, "Bridge complete: Impart failed");
      bridge_channel->swap = NULL;
      ast_bridge_features_destroy(bridge_channel->features);
      bridge_channel->features = NULL;

      ao2_ref(bridge_channel, -1);
      return -1;
   }

   return 0;
}

int ast_bridge_impart(struct ast_bridge *bridge,
   struct ast_channel *chan,
   struct ast_channel *swap,
   struct ast_bridge_features *features,
   enum ast_bridge_impart_flags flags)
{
   struct bridge_channel_impart_cond cond = {
      .done = 0,
   };
   int res;
   SCOPE_TRACE(1, "%s Bridge: %s\n", ast_channel_name(chan), bridge->uniqueid);

   ast_mutex_init(&cond.lock);
   ast_cond_init(&cond.cond, NULL);

   res = bridge_impart_internal(bridge, chan, swap, features, flags, &cond);
   if (res) {
      /* Impart failed.  Signal any other waiting impart threads */
      ast_bridge_discard_after_callback(chan, AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED);
      bridge_channel_impart_signal(chan);
   }

   ast_cond_destroy(&cond.cond);
   ast_mutex_destroy(&cond.lock);

   return res;
}

int ast_bridge_depart(struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;
   int departable;
   SCOPE_TRACE(1, "%s\n", ast_channel_name(chan));

   ast_channel_lock(chan);
   bridge_channel = ast_channel_internal_bridge_channel(chan);
   departable = bridge_channel && bridge_channel->depart_wait;
   ast_channel_unlock(chan);
   if (!departable) {
      ast_log(LOG_ERROR, "Channel %s cannot be departed.\n",
         ast_channel_name(chan));
      /*
       * Should never happen.  It likely means that
       * ast_bridge_depart() is called by two threads for the same
       * channel, the channel was never imparted to be departed, or it
       * has already been departed.
       */
      ast_assert(0);
      return -1;
   }

   /*
    * We are claiming the bridge_channel reference held by
    * bridge_channel_depart_thread().
    */

   ast_bridge_channel_leave_bridge(bridge_channel,
      BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, AST_CAUSE_NORMAL_CLEARING);

   /* Wait for the depart thread to die */
   ast_debug(1, "Waiting for %p(%s) bridge thread to die.\n",
      bridge_channel, ast_channel_name(bridge_channel->chan));
   pthread_join(bridge_channel->thread, NULL);

   ast_channel_lock(chan);
   ast_channel_internal_bridge_channel_set(chan, NULL);
   ast_channel_unlock(chan);

   /* We can get rid of the bridge_channel after the depart thread has died. */
   ao2_ref(bridge_channel, -1);
   return 0;
}

int ast_bridge_remove(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;

   ast_debug(1, "Removing channel %s from bridge %s\n",
      ast_channel_name(chan), bridge->uniqueid);

   ast_bridge_lock(bridge);

   /* Try to find the channel that we want to remove */
   if (!(bridge_channel = bridge_find_channel(bridge, chan))) {
      ast_bridge_unlock(bridge);
      return -1;
   }

   ast_bridge_channel_leave_bridge(bridge_channel,
      BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, AST_CAUSE_NORMAL_CLEARING);

   ast_bridge_unlock(bridge);

   return 0;
}

static void kick_it(struct ast_bridge_channel *bridge_channel, const void *payload, size_t payload_size)
{
   ast_bridge_channel_kick(bridge_channel, AST_CAUSE_NORMAL_CLEARING);
}

int ast_bridge_kick(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;
   int res;

   ast_bridge_lock(bridge);

   /* Try to find the channel that we want to kick. */
   if (!(bridge_channel = bridge_find_channel(bridge, chan))) {
      ast_bridge_unlock(bridge);
      return -1;
   }

   res = ast_bridge_channel_queue_callback(bridge_channel, 0, kick_it, NULL, 0);

   ast_bridge_unlock(bridge);

   return res;
}

/*!
 * \internal
 * \brief Point the bridge_channel to a new bridge.
 * \since 12.0.0
 *
 * \param bridge_channel What is to point to a new bridge.
 * \param new_bridge Where the bridge channel should point.
 *
 * \return Nothing
 */
static void bridge_channel_change_bridge(struct ast_bridge_channel *bridge_channel, struct ast_bridge *new_bridge)
{
   struct ast_bridge *old_bridge;

   ao2_ref(new_bridge, +1);
   ast_bridge_channel_lock(bridge_channel);
   ast_channel_lock(bridge_channel->chan);
   old_bridge = bridge_channel->bridge;
   bridge_channel->bridge = new_bridge;
   ast_channel_internal_bridge_set(bridge_channel->chan, new_bridge);
   ast_channel_unlock(bridge_channel->chan);
   ast_bridge_channel_unlock(bridge_channel);
   ao2_ref(old_bridge, -1);
}

static void bridge_channel_moving(struct ast_bridge_channel *bridge_channel, struct ast_bridge *src, struct ast_bridge *dst)
{
   struct ast_bridge_features *features = bridge_channel->features;
   struct ast_bridge_hook *hook;
   struct ao2_iterator iter;

   /* Run any moving hooks. */
   iter = ao2_iterator_init(features->other_hooks, 0);
   for (; (hook = ao2_iterator_next(&iter)); ao2_ref(hook, -1)) {
      int remove_me;
      ast_bridge_move_indicate_callback move_cb;

      if (hook->type != AST_BRIDGE_HOOK_TYPE_MOVE) {
         continue;
      }
      move_cb = (ast_bridge_move_indicate_callback) hook->callback;
      remove_me = move_cb(bridge_channel, hook->hook_pvt, src, dst);
      if (remove_me) {
         ast_debug(1, "Move detection hook %p is being removed from %p(%s)\n",
            hook, bridge_channel, ast_channel_name(bridge_channel->chan));
         ao2_unlink(features->other_hooks, hook);
      }
   }
   ao2_iterator_destroy(&iter);
}

void bridge_do_merge(struct ast_bridge *dst_bridge, struct ast_bridge *src_bridge, struct ast_bridge_channel **kick_me, unsigned int num_kick,
   unsigned int optimized)
{
   struct ast_bridge_channel *bridge_channel;
   unsigned int idx;

   ast_debug(1, "Merging bridge %s into bridge %s\n",
      src_bridge->uniqueid, dst_bridge->uniqueid);

   ast_bridge_publish_merge(dst_bridge, src_bridge);

   /*
    * Move channels from src_bridge over to dst_bridge.
    *
    * We must use AST_LIST_TRAVERSE_SAFE_BEGIN() because
    * bridge_channel_internal_pull() alters the list we are traversing.
    */
   AST_LIST_TRAVERSE_SAFE_BEGIN(&src_bridge->channels, bridge_channel, entry) {
      if (bridge_channel->state != BRIDGE_CHANNEL_STATE_WAIT) {
         /*
          * The channel is already leaving let it leave normally because
          * pulling it may delete hooks that should run for this channel.
          */
         continue;
      }
      if (ast_test_flag(&bridge_channel->features->feature_flags,
         AST_BRIDGE_CHANNEL_FLAG_IMMOVABLE)) {
         continue;
      }

      if (kick_me) {
         for (idx = 0; idx < num_kick; ++idx) {
            if (bridge_channel == kick_me[idx]) {
               ast_bridge_channel_leave_bridge(bridge_channel,
                  BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, AST_CAUSE_NORMAL_CLEARING);
               break;
            }
         }
      }
      bridge_channel_internal_pull(bridge_channel);
      if (bridge_channel->state != BRIDGE_CHANNEL_STATE_WAIT) {
         /*
          * The channel died as a result of being pulled or it was
          * kicked.  Leave it pointing to the original bridge.
          */
         continue;
      }

      bridge_channel_moving(bridge_channel, bridge_channel->bridge, dst_bridge);

      /* Point to new bridge.*/
      bridge_channel_change_bridge(bridge_channel, dst_bridge);

      if (bridge_channel_internal_push(bridge_channel)) {
         ast_bridge_features_remove(bridge_channel->features,
            AST_BRIDGE_HOOK_REMOVE_ON_PULL);
         ast_bridge_channel_leave_bridge(bridge_channel,
            BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, bridge_channel->bridge->cause);
      }
   }
   AST_LIST_TRAVERSE_SAFE_END;

   if (kick_me) {
      /*
       * Now we can kick any channels in the dst_bridge without
       * potentially dissolving the bridge.
       */
      for (idx = 0; idx < num_kick; ++idx) {
         bridge_channel = kick_me[idx];
         ast_bridge_channel_lock(bridge_channel);
         if (bridge_channel->state == BRIDGE_CHANNEL_STATE_WAIT) {
            ast_bridge_channel_leave_bridge_nolock(bridge_channel,
               BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, AST_CAUSE_NORMAL_CLEARING);
            bridge_channel_internal_pull(bridge_channel);
         }
         ast_bridge_channel_unlock(bridge_channel);
      }
   }

   bridge_reconfigured(dst_bridge, !optimized);
   bridge_reconfigured(src_bridge, !optimized);

   ast_debug(1, "Merged bridge %s into bridge %s\n",
      src_bridge->uniqueid, dst_bridge->uniqueid);
}

struct merge_direction {
   /*! Destination merge bridge. */
   struct ast_bridge *dest;
   /*! Source merge bridge. */
   struct ast_bridge *src;
};

/*!
 * \internal
 * \brief Determine which bridge should merge into the other.
 * \since 12.0.0
 *
 * \param bridge1 A bridge for merging
 * \param bridge2 A bridge for merging
 *
 * \note The two bridges are assumed already locked.
 *
 * \return Which bridge merges into which or NULL bridges if cannot merge.
 */
static struct merge_direction bridge_merge_determine_direction(struct ast_bridge *bridge1, struct ast_bridge *bridge2)
{
   struct merge_direction merge = { NULL, NULL };
   int bridge1_priority;
   int bridge2_priority;

   if (!ast_test_flag(&bridge1->feature_flags,
         AST_BRIDGE_FLAG_MERGE_INHIBIT_TO | AST_BRIDGE_FLAG_MERGE_INHIBIT_FROM)
      && !ast_test_flag(&bridge2->feature_flags,
         AST_BRIDGE_FLAG_MERGE_INHIBIT_TO | AST_BRIDGE_FLAG_MERGE_INHIBIT_FROM)) {
      /*
       * Can merge either way.  Merge to the higher priority merge
       * bridge.  Otherwise merge to the larger bridge.
       */
      bridge1_priority = bridge1->v_table->get_merge_priority(bridge1);
      bridge2_priority = bridge2->v_table->get_merge_priority(bridge2);
      if (bridge2_priority < bridge1_priority) {
         merge.dest = bridge1;
         merge.src = bridge2;
      } else if (bridge1_priority < bridge2_priority) {
         merge.dest = bridge2;
         merge.src = bridge1;
      } else {
         /* Merge to the larger bridge. */
         if (bridge2->num_channels <= bridge1->num_channels) {
            merge.dest = bridge1;
            merge.src = bridge2;
         } else {
            merge.dest = bridge2;
            merge.src = bridge1;
         }
      }
   } else if (!ast_test_flag(&bridge1->feature_flags, AST_BRIDGE_FLAG_MERGE_INHIBIT_TO)
      && !ast_test_flag(&bridge2->feature_flags, AST_BRIDGE_FLAG_MERGE_INHIBIT_FROM)) {
      /* Can merge only one way. */
      merge.dest = bridge1;
      merge.src = bridge2;
   } else if (!ast_test_flag(&bridge2->feature_flags, AST_BRIDGE_FLAG_MERGE_INHIBIT_TO)
      && !ast_test_flag(&bridge1->feature_flags, AST_BRIDGE_FLAG_MERGE_INHIBIT_FROM)) {
      /* Can merge only one way. */
      merge.dest = bridge2;
      merge.src = bridge1;
   }

   return merge;
}

/*!
 * \internal
 * \brief Merge two bridges together
 * \since 12.0.0
 *
 * \param dst_bridge Destination bridge of merge.
 * \param src_bridge Source bridge of merge.
 * \param merge_best_direction TRUE if don't care about which bridge merges into the other.
 * \param kick_me Array of channels to kick from the bridges.
 * \param num_kick Number of channels in the kick_me array.
 *
 * \note The dst_bridge and src_bridge are assumed already locked.
 *
 * \retval 0 on success
 * \retval -1 on failure
 */
static int bridge_merge_locked(struct ast_bridge *dst_bridge, struct ast_bridge *src_bridge, int merge_best_direction, struct ast_channel **kick_me, unsigned int num_kick)
{
   struct merge_direction merge;
   struct ast_bridge_channel **kick_them = NULL;

   /* Sanity check. */
   ast_assert(dst_bridge && src_bridge && dst_bridge != src_bridge && (!num_kick || kick_me));

   if (dst_bridge->dissolved || src_bridge->dissolved) {
      ast_debug(1, "Can't merge bridges %s and %s, at least one bridge is dissolved.\n",
         src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (ast_test_flag(&dst_bridge->feature_flags, AST_BRIDGE_FLAG_MASQUERADE_ONLY)
      || ast_test_flag(&src_bridge->feature_flags, AST_BRIDGE_FLAG_MASQUERADE_ONLY)) {
      ast_debug(1, "Can't merge bridges %s and %s, masquerade only.\n",
         src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (dst_bridge->inhibit_merge || src_bridge->inhibit_merge) {
      ast_debug(1, "Can't merge bridges %s and %s, merging temporarily inhibited.\n",
         src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }

   if (merge_best_direction) {
      merge = bridge_merge_determine_direction(dst_bridge, src_bridge);
   } else {
      merge.dest = dst_bridge;
      merge.src = src_bridge;
   }

   if (!merge.dest
      || ast_test_flag(&merge.dest->feature_flags, AST_BRIDGE_FLAG_MERGE_INHIBIT_TO)
      || ast_test_flag(&merge.src->feature_flags, AST_BRIDGE_FLAG_MERGE_INHIBIT_FROM)) {
      ast_debug(1, "Can't merge bridges %s and %s, merging inhibited.\n",
         src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (merge.src->num_channels < 2) {
      /*
       * For a two party bridge, a channel may be temporarily removed
       * from the source bridge or the initial bridge members have not
       * joined yet.
       */
      ast_debug(1, "Can't merge bridge %s into bridge %s, not enough channels in source bridge.\n",
         merge.src->uniqueid, merge.dest->uniqueid);
      return -1;
   }
   if (2 + num_kick < merge.dest->num_channels + merge.src->num_channels
      && !(merge.dest->technology->capabilities & AST_BRIDGE_CAPABILITY_MULTIMIX)
      && (!ast_test_flag(&merge.dest->feature_flags, AST_BRIDGE_FLAG_SMART)
         || !(merge.dest->allowed_capabilities & AST_BRIDGE_CAPABILITY_MULTIMIX))) {
      ast_debug(1, "Can't merge bridge %s into bridge %s, multimix is needed and it cannot be acquired.\n",
         merge.src->uniqueid, merge.dest->uniqueid);
      return -1;
   }

   if (num_kick) {
      unsigned int num_to_kick = 0;
      unsigned int idx;

      kick_them = ast_alloca(num_kick * sizeof(*kick_them));
      for (idx = 0; idx < num_kick; ++idx) {
         kick_them[num_to_kick] = bridge_find_channel(merge.src, kick_me[idx]);
         if (!kick_them[num_to_kick]) {
            kick_them[num_to_kick] = bridge_find_channel(merge.dest, kick_me[idx]);
         }
         if (kick_them[num_to_kick]) {
            ++num_to_kick;
         }
      }

      if (num_to_kick != num_kick) {
         ast_debug(1, "Can't merge bridge %s into bridge %s, at least one kicked channel is not in either bridge.\n",
            merge.src->uniqueid, merge.dest->uniqueid);
         return -1;
      }
   }

   bridge_do_merge(merge.dest, merge.src, kick_them, num_kick, 0);
   return 0;
}

int ast_bridge_merge(struct ast_bridge *dst_bridge, struct ast_bridge *src_bridge, int merge_best_direction, struct ast_channel **kick_me, unsigned int num_kick)
{
   int res;

   /* Sanity check. */
   ast_assert(dst_bridge && src_bridge);

   ast_bridge_lock_both(dst_bridge, src_bridge);
   res = bridge_merge_locked(dst_bridge, src_bridge, merge_best_direction, kick_me, num_kick);
   ast_bridge_unlock(src_bridge);
   ast_bridge_unlock(dst_bridge);
   return res;
}

int bridge_do_move(struct ast_bridge *dst_bridge, struct ast_bridge_channel *bridge_channel, int attempt_recovery,
   unsigned int optimized)
{
   struct ast_bridge *orig_bridge;
   int was_in_bridge;
   int res = 0;

   if (bridge_channel->swap) {
      ast_debug(1, "Moving %p(%s) into bridge %s swapping with %s\n",
         bridge_channel, ast_channel_name(bridge_channel->chan), dst_bridge->uniqueid,
         ast_channel_name(bridge_channel->swap));
   } else {
      ast_debug(1, "Moving %p(%s) into bridge %s\n",
         bridge_channel, ast_channel_name(bridge_channel->chan), dst_bridge->uniqueid);
   }

   orig_bridge = bridge_channel->bridge;
   was_in_bridge = bridge_channel->in_bridge;

   bridge_channel_internal_pull(bridge_channel);
   if (bridge_channel->state != BRIDGE_CHANNEL_STATE_WAIT) {
      /*
       * The channel died as a result of being pulled.  Leave it
       * pointing to the original bridge.
       *
       * Clear out the swap channel pointer.  A ref is not held
       * by bridge_channel->swap at this point.
       */
      bridge_channel->swap = NULL;
      bridge_reconfigured(orig_bridge, 0);
      return -1;
   }

   /* Point to new bridge.*/
   ao2_ref(orig_bridge, +1);/* Keep a ref in case the push fails. */
   bridge_channel_change_bridge(bridge_channel, dst_bridge);

   bridge_channel_moving(bridge_channel, orig_bridge, dst_bridge);

   if (bridge_channel_internal_push_full(bridge_channel, optimized)) {
      /* Try to put the channel back into the original bridge. */
      ast_bridge_features_remove(bridge_channel->features,
         AST_BRIDGE_HOOK_REMOVE_ON_PULL);
      if (attempt_recovery && was_in_bridge) {
         /* Point back to original bridge. */
         bridge_channel_change_bridge(bridge_channel, orig_bridge);

         if (bridge_channel_internal_push(bridge_channel)) {
            ast_bridge_features_remove(bridge_channel->features,
               AST_BRIDGE_HOOK_REMOVE_ON_PULL);
            ast_bridge_channel_leave_bridge(bridge_channel,
               BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, bridge_channel->bridge->cause);
         }
      } else {
         ast_bridge_channel_leave_bridge(bridge_channel,
            BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, bridge_channel->bridge->cause);
         bridge_channel_settle_owed_events(orig_bridge, bridge_channel);
      }
      res = -1;
   } else if (!optimized) {
      bridge_channel_settle_owed_events(orig_bridge, bridge_channel);
   }

   bridge_reconfigured(dst_bridge, !optimized);
   bridge_reconfigured(orig_bridge, !optimized);
   ao2_ref(orig_bridge, -1);
   return res;
}

/*!
 * \internal
 * \brief Move a channel from one bridge to another.
 * \since 12.0.0
 *
 * \param dst_bridge Destination bridge of bridge channel move.
 * \param src_bridge Source bridge of bridge channel move.
 * \param chan Channel to move.
 * \param swap Channel to replace in dst_bridge.
 * \param attempt_recovery TRUE if failure attempts to push channel back into original bridge.
 *
 * \note The dst_bridge and src_bridge are assumed already locked.
 *
 * \retval 0 on success.
 * \retval -1 on failure.
 */
static int bridge_move_locked(struct ast_bridge *dst_bridge, struct ast_bridge *src_bridge, struct ast_channel *chan, struct ast_channel *swap, int attempt_recovery)
{
   struct ast_bridge_channel *bridge_channel;

   if (dst_bridge->dissolved || src_bridge->dissolved) {
      ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, at least one bridge is dissolved.\n",
         ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (ast_test_flag(&dst_bridge->feature_flags, AST_BRIDGE_FLAG_MASQUERADE_ONLY)
      || ast_test_flag(&src_bridge->feature_flags, AST_BRIDGE_FLAG_MASQUERADE_ONLY)) {
      ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, masquerade only.\n",
         ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (dst_bridge->inhibit_merge || src_bridge->inhibit_merge) {
      ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, temporarily inhibited.\n",
         ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }

   bridge_channel = bridge_find_channel(src_bridge, chan);
   if (!bridge_channel) {
      ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, channel not in bridge.\n",
         ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (bridge_channel->state != BRIDGE_CHANNEL_STATE_WAIT) {
      ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, channel leaving bridge.\n",
         ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }
   if (ast_test_flag(&bridge_channel->features->feature_flags,
      AST_BRIDGE_CHANNEL_FLAG_IMMOVABLE)) {
      ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, channel immovable.\n",
         ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid);
      return -1;
   }

   if (swap) {
      struct ast_bridge_channel *bridge_channel_swap;

      bridge_channel_swap = bridge_find_channel(dst_bridge, swap);
      if (!bridge_channel_swap) {
         ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, swap channel %s not in bridge.\n",
            ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid,
            ast_channel_name(swap));
         return -1;
      }
      if (bridge_channel_swap->state != BRIDGE_CHANNEL_STATE_WAIT) {
         ast_debug(1, "Can't move channel %s from bridge %s into bridge %s, swap channel %s leaving bridge.\n",
            ast_channel_name(chan), src_bridge->uniqueid, dst_bridge->uniqueid,
            ast_channel_name(swap));
         return -1;
      }
   }

   bridge_channel->swap = swap;
   return bridge_do_move(dst_bridge, bridge_channel, attempt_recovery, 0);
}

int ast_bridge_move(struct ast_bridge *dst_bridge, struct ast_bridge *src_bridge, struct ast_channel *chan, struct ast_channel *swap, int attempt_recovery)
{
   int res;

   ast_bridge_lock_both(dst_bridge, src_bridge);
   res = bridge_move_locked(dst_bridge, src_bridge, chan, swap, attempt_recovery);
   ast_bridge_unlock(src_bridge);
   ast_bridge_unlock(dst_bridge);
   return res;
}

int ast_bridge_add_channel(struct ast_bridge *bridge, struct ast_channel *chan,
   struct ast_bridge_features *features, int play_tone, const char *xfersound)
{
   RAII_VAR(struct ast_bridge *, chan_bridge, NULL, ao2_cleanup);
   RAII_VAR(struct ast_channel *, yanked_chan, NULL, ao2_cleanup);

   ast_moh_stop(chan);

   ast_channel_lock(chan);
   chan_bridge = ast_channel_get_bridge(chan);
   ast_channel_unlock(chan);

   if (chan_bridge) {
      struct ast_bridge_channel *bridge_channel;

      /* The channel is in a bridge so it is not getting any new features. */
      ast_bridge_features_destroy(features);

      ast_bridge_lock_both(bridge, chan_bridge);
      bridge_channel = bridge_find_channel(chan_bridge, chan);

      if (bridge_move_locked(bridge, chan_bridge, chan, NULL, 1)) {
         ast_bridge_unlock(chan_bridge);
         ast_bridge_unlock(bridge);
         return -1;
      }

      /*
       * bridge_move_locked() will implicitly ensure that
       * bridge_channel is not NULL.
       */
      ast_assert(bridge_channel != NULL);

      /*
       * Additional checks if the channel we just stole dissolves the
       * original bridge.
       */
      bridge_dissolve_check_stolen(chan_bridge, bridge_channel);
      ast_bridge_unlock(chan_bridge);
      ast_bridge_unlock(bridge);
   } else {
      /* Slightly less easy case. We need to yank channel A from
       * where he currently is and impart him into our bridge.
       */
      yanked_chan = ast_channel_yank(chan);
      if (!yanked_chan) {
         ast_log(LOG_WARNING, "Could not gain control of channel %s\n", ast_channel_name(chan));
         ast_bridge_features_destroy(features);
         return -1;
      }
      if (ast_channel_state(yanked_chan) != AST_STATE_UP) {
         ast_answer(yanked_chan);
      }
      ast_channel_ref(yanked_chan);
      if (ast_bridge_impart(bridge, yanked_chan, NULL, features,
         AST_BRIDGE_IMPART_CHAN_INDEPENDENT)) {
         /* It is possible for us to yank a channel and have some other
          * thread start a PBX on the channl after we yanked it. In particular,
          * this can theoretically happen on the ;2 of a Local channel if we
          * yank it prior to the ;1 being answered. Make sure that it isn't
          * executing a PBX before hanging it up.
          */
         if (ast_channel_pbx(yanked_chan)) {
            ast_channel_unref(yanked_chan);
         } else {
            ast_hangup(yanked_chan);
         }
         return -1;
      }
   }

   if (play_tone && !ast_strlen_zero(xfersound)) {
      struct ast_channel *play_chan = yanked_chan ?: chan;
      RAII_VAR(struct ast_bridge_channel *, play_bridge_channel, NULL, ao2_cleanup);

      ast_channel_lock(play_chan);
      play_bridge_channel = ast_channel_get_bridge_channel(play_chan);
      ast_channel_unlock(play_chan);

      if (!play_bridge_channel) {
         ast_log(LOG_WARNING, "Unable to play tone for channel %s. No longer in a bridge.\n",
            ast_channel_name(play_chan));
      } else {
         ast_bridge_channel_queue_playfile(play_bridge_channel, NULL, xfersound, NULL);
      }
   }
   return 0;
}

static int bridge_allows_optimization(struct ast_bridge *bridge)
{
   return !(bridge->inhibit_merge
      || bridge->dissolved
      || ast_test_flag(&bridge->feature_flags, AST_BRIDGE_FLAG_MASQUERADE_ONLY));
}

/*!
 * \internal
 * \brief Lock the unreal channel stack for chan and prequalify it.
 * \since 12.0.0
 *
 * \param chan Unreal channel writing a frame into the channel driver.
 *
 * \note It is assumed that chan is already locked.
 *
 * \retval bridge on success with bridge and bridge_channel locked.
 * \retval NULL if cannot do optimization now.
 */
static struct ast_bridge *optimize_lock_chan_stack(struct ast_channel *chan)
{
   struct ast_bridge *bridge;
   struct ast_bridge_channel *bridge_channel;

   if (!AST_LIST_EMPTY(ast_channel_readq(chan))) {
      return NULL;
   }
   if (ast_test_flag(ast_channel_flags(chan), AST_FLAG_EMULATE_DTMF)) {
      return NULL;
   }
   if (ast_channel_has_audio_frame_or_monitor(chan)) {
      /* Channel has an active monitor, audiohook, or framehook. */
      return NULL;
   }
   bridge_channel = ast_channel_internal_bridge_channel(chan);
   if (!bridge_channel || ast_bridge_channel_trylock(bridge_channel)) {
      return NULL;
   }
   bridge = bridge_channel->bridge;
   if (bridge_channel->activity != BRIDGE_CHANNEL_THREAD_SIMPLE
      || bridge_channel->state != BRIDGE_CHANNEL_STATE_WAIT
      || ast_bridge_trylock(bridge)) {
      ast_bridge_channel_unlock(bridge_channel);
      return NULL;
   }
   if (!bridge_channel_internal_allows_optimization(bridge_channel) ||
         !bridge_allows_optimization(bridge)) {
      ast_bridge_unlock(bridge);
      ast_bridge_channel_unlock(bridge_channel);
      return NULL;
   }
   return bridge;
}

/*!
 * \internal
 * \brief Lock the unreal channel stack for peer and prequalify it.
 * \since 12.0.0
 *
 * \param peer Other unreal channel in the pair.
 *
 * \retval bridge on success with bridge, bridge_channel, and peer locked.
 * \retval NULL if cannot do optimization now.
 */
static struct ast_bridge *optimize_lock_peer_stack(struct ast_channel *peer)
{
   struct ast_bridge *bridge;
   struct ast_bridge_channel *bridge_channel;

   if (ast_channel_trylock(peer)) {
      return NULL;
   }
   if (!AST_LIST_EMPTY(ast_channel_readq(peer))) {
      ast_channel_unlock(peer);
      return NULL;
   }
   if (ast_test_flag(ast_channel_flags(peer), AST_FLAG_EMULATE_DTMF)) {
      ast_channel_unlock(peer);
      return NULL;
   }
   if (ast_channel_has_audio_frame_or_monitor(peer)) {
      /* Peer has an active monitor, audiohook, or framehook. */
      ast_channel_unlock(peer);
      return NULL;
   }
   bridge_channel = ast_channel_internal_bridge_channel(peer);
   if (!bridge_channel || ast_bridge_channel_trylock(bridge_channel)) {
      ast_channel_unlock(peer);
      return NULL;
   }
   bridge = bridge_channel->bridge;
   if (bridge_channel->activity != BRIDGE_CHANNEL_THREAD_IDLE
      || bridge_channel->state != BRIDGE_CHANNEL_STATE_WAIT
      || ast_bridge_trylock(bridge)) {
      ast_bridge_channel_unlock(bridge_channel);
      ast_channel_unlock(peer);
      return NULL;
   }
   if (!bridge_allows_optimization(bridge) ||
         !bridge_channel_internal_allows_optimization(bridge_channel)) {
      ast_bridge_unlock(bridge);
      ast_bridge_channel_unlock(bridge_channel);
      ast_channel_unlock(peer);
      return NULL;
   }
   return bridge;
}

/*!
 * \internal
 * \brief Indicates allowability of a swap optimization
 */
enum bridge_allow_swap {
   /*! Bridges cannot allow for a swap optimization to occur */
   SWAP_PROHIBITED,
   /*! Bridge swap optimization can occur into the chan_bridge */
   SWAP_TO_CHAN_BRIDGE,
   /*! Bridge swap optimization can occur into the peer_bridge */
   SWAP_TO_PEER_BRIDGE,
};

/*!
 * \internal
 * \brief Determine if two bridges allow for swap optimization to occur
 *
 * \param chan_bridge First bridge being tested
 * \param peer_bridge Second bridge being tested
 * \return Allowability of swap optimization
 */
static enum bridge_allow_swap bridges_allow_swap_optimization(struct ast_bridge *chan_bridge,
      struct ast_bridge *peer_bridge)
{
   int chan_priority;
   int peer_priority;

   if (!ast_test_flag(&chan_bridge->feature_flags,
         AST_BRIDGE_FLAG_SWAP_INHIBIT_TO | AST_BRIDGE_FLAG_SWAP_INHIBIT_FROM |
         AST_BRIDGE_FLAG_TRANSFER_BRIDGE_ONLY)
      && !ast_test_flag(&peer_bridge->feature_flags,
         AST_BRIDGE_FLAG_SWAP_INHIBIT_TO | AST_BRIDGE_FLAG_SWAP_INHIBIT_FROM |
         AST_BRIDGE_FLAG_TRANSFER_BRIDGE_ONLY)) {
      /*
       * Can swap either way.  Swap to the higher priority merge
       * bridge.
       */
      chan_priority = chan_bridge->v_table->get_merge_priority(chan_bridge);
      peer_priority = peer_bridge->v_table->get_merge_priority(peer_bridge);
      if (chan_bridge->num_channels == 2
         && chan_priority <= peer_priority) {
         return SWAP_TO_PEER_BRIDGE;
      } else if (peer_bridge->num_channels == 2
         && peer_priority <= chan_priority) {
         return SWAP_TO_CHAN_BRIDGE;
      }
   } else if (chan_bridge->num_channels == 2
      && !ast_test_flag(&chan_bridge->feature_flags, AST_BRIDGE_FLAG_SWAP_INHIBIT_FROM | AST_BRIDGE_FLAG_TRANSFER_BRIDGE_ONLY)
      && !ast_test_flag(&peer_bridge->feature_flags, AST_BRIDGE_FLAG_SWAP_INHIBIT_TO)) {
      /* Can swap optimize only one way. */
      return SWAP_TO_PEER_BRIDGE;
   } else if (peer_bridge->num_channels == 2
      && !ast_test_flag(&peer_bridge->feature_flags, AST_BRIDGE_FLAG_SWAP_INHIBIT_FROM | AST_BRIDGE_FLAG_TRANSFER_BRIDGE_ONLY)
      && !ast_test_flag(&chan_bridge->feature_flags, AST_BRIDGE_FLAG_SWAP_INHIBIT_TO)) {
      /* Can swap optimize only one way. */
      return SWAP_TO_CHAN_BRIDGE;
   }

   return SWAP_PROHIBITED;
}

/*!
 * \internal
 * \brief Check and attempt to swap optimize out the unreal channels.
 * \since 12.0.0
 *
 * \param chan_bridge
 * \param chan_bridge_channel
 * \param peer_bridge
 * \param peer_bridge_channel
 * \param pvt Unreal data containing callbacks to call if the optimization actually
 * happens
 *
 * \retval 1 if unreal channels failed to optimize out.
 * \retval 0 if unreal channels were not optimized out.
 * \retval -1 if unreal channels were optimized out.
 */
static int try_swap_optimize_out(struct ast_bridge *chan_bridge,
   struct ast_bridge_channel *chan_bridge_channel, struct ast_bridge *peer_bridge,
   struct ast_bridge_channel *peer_bridge_channel,
   struct ast_unreal_pvt *pvt)
{
   struct ast_bridge *dst_bridge;
   struct ast_bridge_channel *dst_bridge_channel;
   struct ast_bridge_channel *src_bridge_channel;
   struct ast_bridge_channel *other;
   int res = 1;

   switch (bridges_allow_swap_optimization(chan_bridge, peer_bridge)) {
   case SWAP_TO_CHAN_BRIDGE:
      dst_bridge = chan_bridge;
      dst_bridge_channel = chan_bridge_channel;
      src_bridge_channel = peer_bridge_channel;
      break;
   case SWAP_TO_PEER_BRIDGE:
      dst_bridge = peer_bridge;
      dst_bridge_channel = peer_bridge_channel;
      src_bridge_channel = chan_bridge_channel;
      break;
   case SWAP_PROHIBITED:
   default:
      return 0;
   }

   other = ast_bridge_channel_peer(src_bridge_channel);
   if (other && other->state == BRIDGE_CHANNEL_STATE_WAIT) {
      unsigned int id;

      if (ast_channel_trylock(other->chan)) {
         return 1;
      }

      id = ast_atomic_fetchadd_int((int *) &optimization_id, +1);

      ast_verb(4, "Move-swap optimizing %s <-- %s.\n",
         ast_channel_name(dst_bridge_channel->chan),
         ast_channel_name(other->chan));

      if (pvt && !ast_test_flag(pvt, AST_UNREAL_OPTIMIZE_BEGUN) && pvt->callbacks
            && pvt->callbacks->optimization_started) {
         pvt->callbacks->optimization_started(pvt, other->chan,
               dst_bridge_channel->chan == pvt->owner ? AST_UNREAL_OWNER : AST_UNREAL_CHAN,
               id);
         ast_set_flag(pvt, AST_UNREAL_OPTIMIZE_BEGUN);
      }
      other->swap = dst_bridge_channel->chan;
      if (!bridge_do_move(dst_bridge, other, 1, 1)) {
         ast_bridge_channel_leave_bridge(src_bridge_channel,
            BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, AST_CAUSE_NORMAL_CLEARING);
         res = -1;
      }
      if (pvt && pvt->callbacks && pvt->callbacks->optimization_finished) {
         pvt->callbacks->optimization_finished(pvt, res == 1, id);
      }
      ast_channel_unlock(other->chan);
   }
   return res;
}

/*!
 * \internal
 * \brief Indicates allowability of a merge optimization
 */
enum bridge_allow_merge {
   /*! Bridge properties prohibit merge optimization */
   MERGE_PROHIBITED,
   /*! Merge optimization cannot occur because the source bridge has too few channels */
   MERGE_NOT_ENOUGH_CHANNELS,
   /*! Merge optimization cannot occur because multimix capability could not be requested */
   MERGE_NO_MULTIMIX,
   /*! Merge optimization allowed between bridges */
   MERGE_ALLOWED,
};

/*!
 * \internal
 * \brief Determines allowability of a merge optimization
 *
 * \note The merge output parameter is undefined if MERGE_PROHIBITED is returned. For success
 * and other failure returns, a merge direction was determined, and the parameter is safe to
 * access.
 *
 * \param chan_bridge First bridge being tested
 * \param peer_bridge Second bridge being tested
 * \param num_kick_channels The number of channels to remove from the bridges during merging
 * \param[out] merge Indicates the recommended direction for the bridge merge
 */
static enum bridge_allow_merge bridges_allow_merge_optimization(struct ast_bridge *chan_bridge,
      struct ast_bridge *peer_bridge, int num_kick_channels, struct merge_direction *merge)
{
   *merge = bridge_merge_determine_direction(chan_bridge, peer_bridge);
   if (!merge->dest) {
      return MERGE_PROHIBITED;
   }
   if (merge->src->num_channels < 2) {
      return MERGE_NOT_ENOUGH_CHANNELS;
   } else if ((2 + num_kick_channels) < merge->dest->num_channels + merge->src->num_channels
      && !(merge->dest->technology->capabilities & AST_BRIDGE_CAPABILITY_MULTIMIX)
      && (!ast_test_flag(&merge->dest->feature_flags, AST_BRIDGE_FLAG_SMART)
         || !(merge->dest->allowed_capabilities & AST_BRIDGE_CAPABILITY_MULTIMIX))) {
      return MERGE_NO_MULTIMIX;
   }

   return MERGE_ALLOWED;
}

/*!
 * \internal
 * \brief Check and attempt to merge optimize out the unreal channels.
 * \since 12.0.0
 *
 * \param chan_bridge
 * \param chan_bridge_channel
 * \param peer_bridge
 * \param peer_bridge_channel
 * \param pvt Unreal data containing callbacks to call if the optimization actually
 * happens
 *
 * \retval 0 if unreal channels were not optimized out.
 * \retval -1 if unreal channels were optimized out.
 */
static int try_merge_optimize_out(struct ast_bridge *chan_bridge,
   struct ast_bridge_channel *chan_bridge_channel, struct ast_bridge *peer_bridge,
   struct ast_bridge_channel *peer_bridge_channel,
   struct ast_unreal_pvt *pvt)
{
   struct merge_direction merge;
   struct ast_bridge_channel *kick_me[] = {
      chan_bridge_channel,
      peer_bridge_channel,
   };
   unsigned int id;

   switch (bridges_allow_merge_optimization(chan_bridge, peer_bridge, ARRAY_LEN(kick_me), &merge)) {
   case MERGE_ALLOWED:
      break;
   case MERGE_PROHIBITED:
      return 0;
   case MERGE_NOT_ENOUGH_CHANNELS:
      ast_debug(4, "Can't optimize %s -- %s out, not enough channels in bridge %s.\n",
         ast_channel_name(chan_bridge_channel->chan),
         ast_channel_name(peer_bridge_channel->chan),
         merge.src->uniqueid);
      return 0;
   case MERGE_NO_MULTIMIX:
      ast_debug(4, "Can't optimize %s -- %s out, multimix is needed and it cannot be acquired.\n",
         ast_channel_name(chan_bridge_channel->chan),
         ast_channel_name(peer_bridge_channel->chan));
      return 0;
   }

   ast_verb(4, "Merge optimizing %s -- %s out.\n",
      ast_channel_name(chan_bridge_channel->chan),
      ast_channel_name(peer_bridge_channel->chan));

   id = ast_atomic_fetchadd_int((int *) &optimization_id, +1);

   if (pvt && !ast_test_flag(pvt, AST_UNREAL_OPTIMIZE_BEGUN) && pvt->callbacks
         && pvt->callbacks->optimization_started) {
      pvt->callbacks->optimization_started(pvt, NULL,
            merge.dest == ast_channel_internal_bridge(pvt->owner) ? AST_UNREAL_OWNER : AST_UNREAL_CHAN,
            id);
      ast_set_flag(pvt, AST_UNREAL_OPTIMIZE_BEGUN);
   }
   bridge_do_merge(merge.dest, merge.src, kick_me, ARRAY_LEN(kick_me), 1);
   if (pvt && pvt->callbacks && pvt->callbacks->optimization_finished) {
      pvt->callbacks->optimization_finished(pvt, 1, id);
   }

   return -1;
}

int ast_bridge_unreal_optimize_out(struct ast_channel *chan, struct ast_channel *peer, struct ast_unreal_pvt *pvt)
{
   struct ast_bridge *chan_bridge;
   struct ast_bridge *peer_bridge;
   struct ast_bridge_channel *chan_bridge_channel;
   struct ast_bridge_channel *peer_bridge_channel;
   int res = 0;

   chan_bridge = optimize_lock_chan_stack(chan);
   if (!chan_bridge) {
      return res;
   }
   chan_bridge_channel = ast_channel_internal_bridge_channel(chan);

   peer_bridge = optimize_lock_peer_stack(peer);
   if (peer_bridge) {
      peer_bridge_channel = ast_channel_internal_bridge_channel(peer);

      res = try_swap_optimize_out(chan_bridge, chan_bridge_channel,
         peer_bridge, peer_bridge_channel, pvt);
      if (!res) {
         res = try_merge_optimize_out(chan_bridge, chan_bridge_channel,
            peer_bridge, peer_bridge_channel, pvt);
      } else if (0 < res) {
         res = 0;
      }

      /* Release peer locks. */
      ast_bridge_unlock(peer_bridge);
      ast_bridge_channel_unlock(peer_bridge_channel);
      ast_channel_unlock(peer);
   }

   /* Release chan locks. */
   ast_bridge_unlock(chan_bridge);
   ast_bridge_channel_unlock(chan_bridge_channel);

   return res;
}

enum ast_bridge_optimization ast_bridges_allow_optimization(struct ast_bridge *chan_bridge,
      struct ast_bridge *peer_bridge)
{
   struct merge_direction merge;

   if (!bridge_allows_optimization(chan_bridge) || !bridge_allows_optimization(peer_bridge)) {
      return AST_BRIDGE_OPTIMIZE_PROHIBITED;
   }

   switch (bridges_allow_swap_optimization(chan_bridge, peer_bridge)) {
   case SWAP_TO_CHAN_BRIDGE:
      return AST_BRIDGE_OPTIMIZE_SWAP_TO_CHAN_BRIDGE;
   case SWAP_TO_PEER_BRIDGE:
      return AST_BRIDGE_OPTIMIZE_SWAP_TO_PEER_BRIDGE;
   case SWAP_PROHIBITED:
   default:
      break;
   }

   /* Two channels will be kicked from the bridges, the unreal;1 and unreal;2 channels */
   if (bridges_allow_merge_optimization(chan_bridge, peer_bridge, 2, &merge) != MERGE_ALLOWED) {
      return AST_BRIDGE_OPTIMIZE_PROHIBITED;
   }

   if (merge.dest == chan_bridge) {
      return AST_BRIDGE_OPTIMIZE_MERGE_TO_CHAN_BRIDGE;
   } else {
      return AST_BRIDGE_OPTIMIZE_MERGE_TO_PEER_BRIDGE;
   }
}

/*!
 * \internal
 * \brief Adjust the bridge merge inhibit request count.
 * \since 12.0.0
 *
 * \param bridge What to operate on.
 * \param request Inhibit request increment.
 *     (Positive to add requests.  Negative to remove requests.)
 *
 * \note This function assumes bridge is locked.
 *
 * \return Nothing
 */
void bridge_merge_inhibit_nolock(struct ast_bridge *bridge, int request)
{
   int new_request;

   new_request = bridge->inhibit_merge + request;
   ast_assert(0 <= new_request);
   bridge->inhibit_merge = new_request;
}

void ast_bridge_merge_inhibit(struct ast_bridge *bridge, int request)
{
   ast_bridge_lock(bridge);
   bridge_merge_inhibit_nolock(bridge, request);
   ast_bridge_unlock(bridge);
}

int ast_bridge_suspend(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;
/* XXX ASTERISK-21271 the case of a disolved bridge while channel is suspended is not handled. */
/* XXX ASTERISK-21271 suspend/unsuspend needs to be rethought. The caller must block until it has successfully suspended the channel for temporary control. */
/* XXX ASTERISK-21271 external suspend/unsuspend needs to be eliminated. The channel may be playing a file at the time and stealing it then is not good. */

   ast_bridge_lock(bridge);

   if (!(bridge_channel = bridge_find_channel(bridge, chan))) {
      ast_bridge_unlock(bridge);
      return -1;
   }

   bridge_channel_internal_suspend_nolock(bridge_channel);

   ast_bridge_unlock(bridge);

   return 0;
}

int ast_bridge_unsuspend(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_bridge_channel *bridge_channel;
/* XXX ASTERISK-21271 the case of a disolved bridge while channel is suspended is not handled. */

   ast_bridge_lock(bridge);

   if (!(bridge_channel = bridge_find_channel(bridge, chan))) {
      ast_bridge_unlock(bridge);
      return -1;
   }

   bridge_channel_internal_unsuspend_nolock(bridge_channel);

   ast_bridge_unlock(bridge);

   return 0;
}

void ast_bridge_technology_suspend(struct ast_bridge_technology *technology)
{
   technology->suspended = 1;
}

void ast_bridge_technology_unsuspend(struct ast_bridge_technology *technology)
{
   /*
    * XXX We may want the act of unsuspending a bridge technology
    * to prod all existing bridges to see if they should start
    * using it.
    */
   technology->suspended = 0;
}

int ast_bridge_features_register(enum ast_bridge_builtin_feature feature, ast_bridge_hook_callback callback, const char *dtmf)
{
   if (ARRAY_LEN(builtin_features_handlers) <= feature
      || builtin_features_handlers[feature]) {
      return -1;
   }

   if (!ast_strlen_zero(dtmf)) {
      ast_copy_string(builtin_features_dtmf[feature], dtmf, sizeof(builtin_features_dtmf[feature]));
   }

   builtin_features_handlers[feature] = callback;

   return 0;
}

int ast_bridge_features_unregister(enum ast_bridge_builtin_feature feature)
{
   if (ARRAY_LEN(builtin_features_handlers) <= feature
      || !builtin_features_handlers[feature]) {
      return -1;
   }

   builtin_features_handlers[feature] = NULL;

   return 0;
}

int ast_bridge_features_do(enum ast_bridge_builtin_feature feature, struct ast_bridge_channel *bridge_channel, void *hook_pvt)
{
   ast_bridge_hook_callback callback;

   if (ARRAY_LEN(builtin_features_handlers) <= feature) {
      return -1;
   }

   callback = builtin_features_handlers[feature];
   if (!callback) {
      return -1;
   }
   callback(bridge_channel, hook_pvt);

   return 0;
}

int ast_bridge_interval_register(enum ast_bridge_builtin_interval interval, ast_bridge_builtin_set_limits_fn callback)
{
   if (ARRAY_LEN(builtin_interval_handlers) <= interval
      || builtin_interval_handlers[interval]) {
      return -1;
   }

   builtin_interval_handlers[interval] = callback;

   return 0;
}

int ast_bridge_interval_unregister(enum ast_bridge_builtin_interval interval)
{
   if (ARRAY_LEN(builtin_interval_handlers) <= interval
      || !builtin_interval_handlers[interval]) {
      return -1;
   }

   builtin_interval_handlers[interval] = NULL;

   return 0;

}

/*!
 * \internal
 * \brief Bridge hook destructor.
 * \since 12.0.0
 *
 * \param vhook Object to destroy.
 *
 * \return Nothing
 */
static void bridge_hook_destroy(void *vhook)
{
   struct ast_bridge_hook *hook = vhook;

   if (hook->destructor) {
      hook->destructor(hook->hook_pvt);
   }
}

/*!
 * \internal
 * \brief Allocate and setup a generic bridge hook.
 * \since 12.0.0
 *
 * \param size How big an object to allocate.
 * \param callback Function to execute upon activation
 * \param hook_pvt Unique data
 * \param destructor Optional destructor callback for hook_pvt data
 * \param remove_flags Dictates what situations the hook should be removed.
 *
 * \retval hook on success.
 * \retval NULL on error.
 */
static struct ast_bridge_hook *bridge_hook_generic(size_t size,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   struct ast_bridge_hook *hook;

   /* Allocate new hook and setup it's basic variables */
   hook = ao2_alloc_options(size, bridge_hook_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
   if (hook) {
      hook->callback = callback;
      hook->destructor = destructor;
      hook->hook_pvt = hook_pvt;
      ast_set_flag(&hook->remove_flags, remove_flags);
   }

   return hook;
}

int ast_bridge_dtmf_hook(struct ast_bridge_features *features,
   const char *dtmf,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   struct ast_bridge_hook_dtmf *hook;
   int res;

   /* Allocate new hook and setup it's various variables */
   hook = (struct ast_bridge_hook_dtmf *) bridge_hook_generic(sizeof(*hook), callback,
      hook_pvt, destructor, remove_flags);
   if (!hook) {
      return -1;
   }
   hook->generic.type = AST_BRIDGE_HOOK_TYPE_DTMF;
   ast_copy_string(hook->dtmf.code, dtmf, sizeof(hook->dtmf.code));

   /* Once done we put it in the container. */
   res = ao2_link(features->dtmf_hooks, hook) ? 0 : -1;
   if (res) {
      /*
       * Could not link the hook into the container.
       *
       * Remove the hook_pvt destructor call from the hook since we
       * are returning failure to install the hook.
       */
      hook->generic.destructor = NULL;
   }
   ao2_ref(hook, -1);

   return res;
}

/*!
 * \internal
 * \brief Attach an other hook to a bridge features structure
 *
 * \param features Bridge features structure
 * \param callback Function to execute upon activation
 * \param hook_pvt Unique data
 * \param destructor Optional destructor callback for hook_pvt data
 * \param remove_flags Dictates what situations the hook should be removed.
 * \param type What type of hook is being attached.
 *
 * \retval 0 on success
 * \retval -1 on failure (The caller must cleanup any hook_pvt resources.)
 */
static int bridge_other_hook(struct ast_bridge_features *features,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags,
   enum ast_bridge_hook_type type)
{
   struct ast_bridge_hook *hook;
   int res;

   /* Allocate new hook and setup it's various variables */
   hook = bridge_hook_generic(sizeof(*hook), callback, hook_pvt, destructor,
      remove_flags);
   if (!hook) {
      return -1;
   }
   hook->type = type;

   /* Once done we put it in the container. */
   res = ao2_link(features->other_hooks, hook) ? 0 : -1;
   if (res) {
      /*
       * Could not link the hook into the container.
       *
       * Remove the hook_pvt destructor call from the hook since we
       * are returning failure to install the hook.
       */
      hook->destructor = NULL;
   }
   ao2_ref(hook, -1);

   return res;
}

int ast_bridge_hangup_hook(struct ast_bridge_features *features,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   return bridge_other_hook(features, callback, hook_pvt, destructor, remove_flags,
      AST_BRIDGE_HOOK_TYPE_HANGUP);
}

int ast_bridge_join_hook(struct ast_bridge_features *features,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   return bridge_other_hook(features, callback, hook_pvt, destructor, remove_flags,
      AST_BRIDGE_HOOK_TYPE_JOIN);
}

int ast_bridge_leave_hook(struct ast_bridge_features *features,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   return bridge_other_hook(features, callback, hook_pvt, destructor, remove_flags,
      AST_BRIDGE_HOOK_TYPE_LEAVE);
}

int ast_bridge_talk_detector_hook(struct ast_bridge_features *features,
   ast_bridge_talking_indicate_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   ast_bridge_hook_callback hook_cb = (ast_bridge_hook_callback) callback;

   return bridge_other_hook(features, hook_cb, hook_pvt, destructor, remove_flags,
      AST_BRIDGE_HOOK_TYPE_TALK);
}

int ast_bridge_move_hook(struct ast_bridge_features *features,
   ast_bridge_move_indicate_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   ast_bridge_hook_callback hook_cb = (ast_bridge_hook_callback) callback;

   return bridge_other_hook(features, hook_cb, hook_pvt, destructor, remove_flags,
      AST_BRIDGE_HOOK_TYPE_MOVE);
}

int ast_bridge_interval_hook(struct ast_bridge_features *features,
   enum ast_bridge_hook_timer_option flags,
   unsigned int interval,
   ast_bridge_hook_callback callback,
   void *hook_pvt,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   struct ast_bridge_hook_timer *hook;
   int res;

   if (!features ||!interval || !callback) {
      return -1;
   }

   /* Allocate new hook and setup it's various variables */
   hook = (struct ast_bridge_hook_timer *) bridge_hook_generic(sizeof(*hook), callback,
      hook_pvt, destructor, remove_flags);
   if (!hook) {
      return -1;
   }
   hook->generic.type = AST_BRIDGE_HOOK_TYPE_TIMER;
   hook->timer.interval = interval;
   hook->timer.trip_time = ast_tvadd(ast_tvnow(), ast_samp2tv(interval, 1000));
   hook->timer.seqno = ast_atomic_fetchadd_int((int *) &features->interval_sequence, +1);
   hook->timer.flags = flags;

   ast_debug(1, "Putting interval hook %p with interval %u in the heap on features %p\n",
      hook, hook->timer.interval, features);
   ast_heap_wrlock(features->interval_hooks);
   res = ast_heap_push(features->interval_hooks, hook);
   ast_heap_unlock(features->interval_hooks);
   if (res) {
      /*
       * Could not push the hook into the heap
       *
       * Remove the hook_pvt destructor call from the hook since we
       * are returning failure to install the hook.
       */
      hook->generic.destructor = NULL;
      ao2_ref(hook, -1);
   }

   return res ? -1 : 0;
}

int ast_bridge_features_enable(struct ast_bridge_features *features,
   enum ast_bridge_builtin_feature feature,
   const char *dtmf,
   void *config,
   ast_bridge_hook_pvt_destructor destructor,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   if (ARRAY_LEN(builtin_features_handlers) <= feature
      || !builtin_features_handlers[feature]) {
      return -1;
   }

   /* If no alternate DTMF stream was provided use the default one */
   if (ast_strlen_zero(dtmf)) {
      dtmf = builtin_features_dtmf[feature];
      /* If no DTMF is still available (ie: it has been disabled) then error out now */
      if (ast_strlen_zero(dtmf)) {
         ast_debug(1, "Failed to enable built in feature %u on %p, no DTMF string is available for it.\n",
            feature, features);
         return -1;
      }
   }

   /*
    * The rest is basically pretty easy.  We create another hook
    * using the built in feature's DTMF callback.  Easy as pie.
    */
   return ast_bridge_dtmf_hook(features, dtmf, builtin_features_handlers[feature],
      config, destructor, remove_flags);
}

int ast_bridge_features_limits_construct(struct ast_bridge_features_limits *limits)
{
   memset(limits, 0, sizeof(*limits));

   if (ast_string_field_init(limits, 256)) {
      return -1;
   }

   return 0;
}

void ast_bridge_features_limits_destroy(struct ast_bridge_features_limits *limits)
{
   ast_string_field_free_memory(limits);
}

int ast_bridge_features_set_limits(struct ast_bridge_features *features,
   struct ast_bridge_features_limits *limits,
   enum ast_bridge_hook_remove_flags remove_flags)
{
   if (builtin_interval_handlers[AST_BRIDGE_BUILTIN_INTERVAL_LIMITS]) {
      ast_bridge_builtin_set_limits_fn callback;

      callback = builtin_interval_handlers[AST_BRIDGE_BUILTIN_INTERVAL_LIMITS];
      return callback(features, limits, remove_flags);
   }

   ast_log(LOG_ERROR, "Attempted to set limits without an AST_BRIDGE_BUILTIN_INTERVAL_LIMITS callback registered.\n");
   return -1;
}

void ast_bridge_features_set_flag(struct ast_bridge_features *features, unsigned int flag)
{
   ast_set_flag(&features->feature_flags, flag);
   features->usable = 1;
}

/*!
 * \internal
 * \brief ao2 object match hooks with appropriate remove_flags.
 * \since 12.0.0
 *
 * \param obj Feature hook object.
 * \param arg Removal flags
 * \param flags Not used
 *
 * \retval CMP_MATCH if hook's remove_flags match the removal flags set.
 * \retval 0 if not match.
 */
static int hook_remove_match(void *obj, void *arg, int flags)
{
   struct ast_bridge_hook *hook = obj;
   enum ast_bridge_hook_remove_flags *remove_flags = arg;

   if (ast_test_flag(&hook->remove_flags, *remove_flags)) {
      return CMP_MATCH;
   } else {
      return 0;
   }
}

/*!
 * \internal
 * \brief Remove all hooks with appropriate remove_flags in the container.
 * \since 12.0.0
 *
 * \param hooks Hooks container to work on.
 * \param remove_flags Determinator for whether hook is removed
 *
 * \return Nothing
 */
static void hooks_remove_container(struct ao2_container *hooks, enum ast_bridge_hook_remove_flags remove_flags)
{
   ao2_callback(hooks, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE,
      hook_remove_match, &remove_flags);
}

/*!
 * \internal
 * \brief Remove all hooks in the heap with appropriate remove_flags set.
 * \since 12.0.0
 *
 * \param hooks Hooks heap to work on.
 * \param remove_flags Determinator for whether hook is removed
 *
 * \return Nothing
 */
static void hooks_remove_heap(struct ast_heap *hooks, enum ast_bridge_hook_remove_flags remove_flags)
{
   struct ast_bridge_hook *hook;
   int changed;

   ast_heap_wrlock(hooks);
   do {
      int idx;

      changed = 0;
      for (idx = ast_heap_size(hooks); idx; --idx) {
         hook = ast_heap_peek(hooks, idx);
         if (ast_test_flag(&hook->remove_flags, remove_flags)) {
            ast_heap_remove(hooks, hook);
            ao2_ref(hook, -1);
            changed = 1;
         }
      }
   } while (changed);
   ast_heap_unlock(hooks);
}

void ast_bridge_features_remove(struct ast_bridge_features *features, enum ast_bridge_hook_remove_flags remove_flags)
{
   hooks_remove_container(features->dtmf_hooks, remove_flags);
   hooks_remove_container(features->other_hooks, remove_flags);
   hooks_remove_heap(features->interval_hooks, remove_flags);
}

static int interval_hook_time_cmp(void *a, void *b)
{
   struct ast_bridge_hook_timer *hook_a = a;
   struct ast_bridge_hook_timer *hook_b = b;
   int cmp;

   cmp = ast_tvcmp(hook_b->timer.trip_time, hook_a->timer.trip_time);
   if (cmp) {
      return cmp;
   }

   cmp = hook_b->timer.seqno - hook_a->timer.seqno;
   return cmp;
}

/*!
 * \internal
 * \brief DTMF hook container sort comparison function.
 * \since 12.0.0
 *
 * \param obj_left pointer to the (user-defined part) of an object.
 * \param obj_right pointer to the (user-defined part) of an object.
 * \param flags flags from ao2_callback()
 *   OBJ_POINTER - if set, 'obj_right', is an object.
 *   OBJ_KEY - if set, 'obj_right', is a search key item that is not an object.
 *   OBJ_PARTIAL_KEY - if set, 'obj_right', is a partial search key item that is not an object.
 *
 * \retval <0 if obj_left < obj_right
 * \retval =0 if obj_left == obj_right
 * \retval >0 if obj_left > obj_right
 */
static int bridge_dtmf_hook_sort(const void *obj_left, const void *obj_right, int flags)
{
   const struct ast_bridge_hook_dtmf *hook_left = obj_left;
   const struct ast_bridge_hook_dtmf *hook_right = obj_right;
   const char *right_key = obj_right;
   int cmp;

   switch (flags & (OBJ_POINTER | OBJ_KEY | OBJ_PARTIAL_KEY)) {
   default:
   case OBJ_POINTER:
      right_key = hook_right->dtmf.code;
      /* Fall through */
   case OBJ_KEY:
      cmp = strcasecmp(hook_left->dtmf.code, right_key);
      break;
   case OBJ_PARTIAL_KEY:
      cmp = strncasecmp(hook_left->dtmf.code, right_key, strlen(right_key));
      break;
   }
   return cmp;
}

/*! \brief Callback for merging hook ao2_containers */
static int merge_container_cb(void *obj, void *data, int flags)
{
   ao2_link(data, obj);
   return 0;
}

/*! \brief Wrapper for interval hooks that calls into the wrapped hook */
static int interval_wrapper_cb(struct ast_bridge_channel *bridge_channel, void *obj)
{
   struct ast_bridge_hook_timer *hook = obj;

   return hook->generic.callback(bridge_channel, hook->generic.hook_pvt);
}

/*! \brief Destructor for the hook wrapper */
static void interval_wrapper_pvt_dtor(void *obj)
{
   ao2_cleanup(obj);
}

/*! \brief Wrap the provided interval hook and add it to features */
static void wrap_hook(struct ast_bridge_features *features, struct ast_bridge_hook_timer *hook)
{
   /* Break out of the current wrapper if it exists to avoid multiple layers */
   if (hook->generic.callback == interval_wrapper_cb) {
      hook = hook->generic.hook_pvt;
   }

   ast_bridge_interval_hook(features, hook->timer.flags, hook->timer.interval,
      interval_wrapper_cb, ao2_bump(hook), interval_wrapper_pvt_dtor,
      hook->generic.remove_flags.flags);
}

void ast_bridge_features_merge(struct ast_bridge_features *into, const struct ast_bridge_features *from)
{
   struct ast_bridge_hook_timer *hook;
   int idx;

   /* Merge hook containers */
   ao2_callback(from->dtmf_hooks, 0, merge_container_cb, into->dtmf_hooks);
   ao2_callback(from->other_hooks, 0, merge_container_cb, into->other_hooks);

   /* Merge hook heaps */
   ast_heap_wrlock(from->interval_hooks);
   for (idx = 1; (hook = ast_heap_peek(from->interval_hooks, idx)); idx++) {
      wrap_hook(into, hook);
   }
   ast_heap_unlock(from->interval_hooks);

   /* Merge feature flags */
   into->feature_flags.flags |= from->feature_flags.flags;
   into->usable |= from->usable;

   into->mute |= from->mute;
   into->dtmf_passthrough |= from->dtmf_passthrough;
}

/* XXX ASTERISK-21271 make ast_bridge_features_init() static when make ast_bridge_join() requires features to be allocated. */
int ast_bridge_features_init(struct ast_bridge_features *features)
{
   /* Zero out the structure */
   memset(features, 0, sizeof(*features));

   /* Initialize the DTMF hooks container */
   features->dtmf_hooks = ao2_container_alloc_list(AO2_ALLOC_OPT_LOCK_MUTEX,
      AO2_CONTAINER_ALLOC_OPT_DUPS_REPLACE, bridge_dtmf_hook_sort, NULL);
   if (!features->dtmf_hooks) {
      return -1;
   }

   /* Initialize the miscellaneous other hooks container */
   features->other_hooks = ao2_container_alloc_list(AO2_ALLOC_OPT_LOCK_MUTEX, 0, NULL,
      NULL);
   if (!features->other_hooks) {
      return -1;
   }

   /* Initialize the interval hooks heap */
   features->interval_hooks = ast_heap_create(8, interval_hook_time_cmp,
      offsetof(struct ast_bridge_hook_timer, timer.heap_index));
   if (!features->interval_hooks) {
      return -1;
   }

   features->dtmf_passthrough = 1;
   features->text_messaging = 1;

   return 0;
}

/* XXX ASTERISK-21271 make ast_bridge_features_cleanup() static when make ast_bridge_join() requires features to be allocated. */
void ast_bridge_features_cleanup(struct ast_bridge_features *features)
{
   struct ast_bridge_hook_timer *hook;

   /* Destroy the interval hooks heap. */
   if (features->interval_hooks) {
      while ((hook = ast_heap_pop(features->interval_hooks))) {
         ao2_ref(hook, -1);
      }
      features->interval_hooks = ast_heap_destroy(features->interval_hooks);
   }

   /* Destroy the miscellaneous other hooks container. */
   ao2_cleanup(features->other_hooks);
   features->other_hooks = NULL;

   /* Destroy the DTMF hooks container. */
   ao2_cleanup(features->dtmf_hooks);
   features->dtmf_hooks = NULL;
}

void ast_bridge_features_destroy(struct ast_bridge_features *features)
{
   if (!features) {
      return;
   }
   ast_bridge_features_cleanup(features);
   ast_free(features);
}

struct ast_bridge_features *ast_bridge_features_new(void)
{
   struct ast_bridge_features *features;

   features = ast_malloc(sizeof(*features));
   if (features) {
      if (ast_bridge_features_init(features)) {
         ast_bridge_features_destroy(features);
         features = NULL;
      }
   }

   return features;
}

void ast_bridge_set_mixing_interval(struct ast_bridge *bridge, unsigned int mixing_interval)
{
   ast_bridge_lock(bridge);
   bridge->softmix.internal_mixing_interval = mixing_interval;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_binaural_active(struct ast_bridge *bridge, unsigned int binaural_active)
{
   ast_bridge_lock(bridge);
   bridge->softmix.binaural_active = binaural_active;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_internal_sample_rate(struct ast_bridge *bridge, unsigned int sample_rate)
{
   ast_bridge_lock(bridge);
   bridge->softmix.internal_sample_rate = sample_rate;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_maximum_sample_rate(struct ast_bridge *bridge, unsigned int sample_rate)
{
   ast_bridge_lock(bridge);
   bridge->softmix.maximum_sample_rate = sample_rate;
   ast_bridge_unlock(bridge);
}

static void cleanup_video_mode(struct ast_bridge *bridge)
{
   switch (bridge->softmix.video_mode.mode) {
   case AST_BRIDGE_VIDEO_MODE_NONE:
      break;
   case AST_BRIDGE_VIDEO_MODE_SINGLE_SRC:
      if (bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc) {
         ast_channel_unref(bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc);
      }
      break;
   case AST_BRIDGE_VIDEO_MODE_TALKER_SRC:
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc) {
         ast_channel_unref(bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc);
      }
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc) {
         ast_channel_unref(bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc);
      }
   case AST_BRIDGE_VIDEO_MODE_SFU:
      break;
   }
   memset(&bridge->softmix.video_mode, 0, sizeof(bridge->softmix.video_mode));
}

void ast_bridge_set_single_src_video_mode(struct ast_bridge *bridge, struct ast_channel *video_src_chan)
{
   ast_bridge_lock(bridge);
   cleanup_video_mode(bridge);
   bridge->softmix.video_mode.mode = AST_BRIDGE_VIDEO_MODE_SINGLE_SRC;
   if (video_src_chan) {
      bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc = ast_channel_ref(video_src_chan);
      ast_verb(5, "Video source in bridge '%s' (%s) is now '%s' (%s)\n",
         bridge->name, bridge->uniqueid,
         ast_channel_name(video_src_chan),
         ast_channel_uniqueid(video_src_chan));
      ast_indicate(video_src_chan, AST_CONTROL_VIDUPDATE);
   }
   ast_bridge_publish_state(bridge);
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_talker_src_video_mode(struct ast_bridge *bridge)
{
   ast_bridge_lock(bridge);
   cleanup_video_mode(bridge);
   bridge->softmix.video_mode.mode = AST_BRIDGE_VIDEO_MODE_TALKER_SRC;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_sfu_video_mode(struct ast_bridge *bridge)
{
   ast_bridge_lock(bridge);
   cleanup_video_mode(bridge);
   bridge->softmix.video_mode.mode = AST_BRIDGE_VIDEO_MODE_SFU;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_video_update_discard(struct ast_bridge *bridge, unsigned int video_update_discard)
{
   ast_bridge_lock(bridge);
   bridge->softmix.video_mode.video_update_discard = video_update_discard;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_remb_send_interval(struct ast_bridge *bridge, unsigned int remb_send_interval)
{
   ast_assert(bridge->softmix.video_mode.mode == AST_BRIDGE_VIDEO_MODE_SFU);

   ast_bridge_lock(bridge);
   bridge->softmix.video_mode.mode_data.sfu_data.remb_send_interval = remb_send_interval;
   ast_bridge_unlock(bridge);
}

void ast_brige_set_remb_behavior(struct ast_bridge *bridge, enum ast_bridge_video_sfu_remb_behavior behavior)
{
   ast_assert(bridge->softmix.video_mode.mode == AST_BRIDGE_VIDEO_MODE_SFU);

   ast_bridge_lock(bridge);
   bridge->softmix.video_mode.mode_data.sfu_data.remb_behavior = behavior;
   ast_bridge_unlock(bridge);
}

void ast_bridge_set_remb_estimated_bitrate(struct ast_bridge *bridge, float estimated_bitrate)
{
   ast_assert(bridge->softmix.video_mode.mode == AST_BRIDGE_VIDEO_MODE_SFU);

   ast_bridge_lock(bridge);
   bridge->softmix.video_mode.mode_data.sfu_data.estimated_bitrate = estimated_bitrate;
   ast_bridge_unlock(bridge);
}

void ast_bridge_update_talker_src_video_mode(struct ast_bridge *bridge, struct ast_channel *chan, int talker_energy, int is_keyframe)
{
   struct ast_bridge_video_talker_src_data *data;

   /* If the channel doesn't support video, we don't care about it */
   if (!ast_format_cap_has_type(ast_channel_nativeformats(chan), AST_MEDIA_TYPE_VIDEO)) {
      return;
   }

   ast_bridge_lock(bridge);
   data = &bridge->softmix.video_mode.mode_data.talker_src_data;

   if (data->chan_vsrc == chan) {
      data->average_talking_energy = talker_energy;
   } else if ((data->average_talking_energy < talker_energy) && is_keyframe) {
      if (data->chan_old_vsrc) {
         data->chan_old_vsrc = ast_channel_unref(data->chan_old_vsrc);
      }
      if (data->chan_vsrc) {
         data->chan_old_vsrc = data->chan_vsrc;
         ast_indicate(data->chan_old_vsrc, AST_CONTROL_VIDUPDATE);
      }
      data->chan_vsrc = ast_channel_ref(chan);
      data->average_talking_energy = talker_energy;
      ast_verb(5, "Video source in bridge '%s' (%s) is now '%s' (%s)\n",
         bridge->name, bridge->uniqueid,
         ast_channel_name(data->chan_vsrc),
         ast_channel_uniqueid(data->chan_vsrc));
      ast_bridge_publish_state(bridge);
      ast_indicate(data->chan_vsrc, AST_CONTROL_VIDUPDATE);
   } else if ((data->average_talking_energy < talker_energy) && !is_keyframe) {
      ast_indicate(chan, AST_CONTROL_VIDUPDATE);
   } else if (!data->chan_vsrc && is_keyframe) {
      data->chan_vsrc = ast_channel_ref(chan);
      data->average_talking_energy = talker_energy;
      ast_verb(5, "Video source in bridge '%s' (%s) is now '%s' (%s)\n",
         bridge->name, bridge->uniqueid,
         ast_channel_name(data->chan_vsrc),
         ast_channel_uniqueid(data->chan_vsrc));
      ast_bridge_publish_state(bridge);
      ast_indicate(chan, AST_CONTROL_VIDUPDATE);
   } else if (!data->chan_old_vsrc && is_keyframe) {
      data->chan_old_vsrc = ast_channel_ref(chan);
      ast_indicate(chan, AST_CONTROL_VIDUPDATE);
   }
   ast_bridge_unlock(bridge);
}

int ast_bridge_number_video_src(struct ast_bridge *bridge)
{
   int res = 0;

   ast_bridge_lock(bridge);
   switch (bridge->softmix.video_mode.mode) {
   case AST_BRIDGE_VIDEO_MODE_NONE:
      break;
   case AST_BRIDGE_VIDEO_MODE_SINGLE_SRC:
      if (bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc) {
         res = 1;
      }
      break;
   case AST_BRIDGE_VIDEO_MODE_TALKER_SRC:
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc) {
         res++;
      }
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc) {
         res++;
      }
   case AST_BRIDGE_VIDEO_MODE_SFU:
      break;
   }
   ast_bridge_unlock(bridge);
   return res;
}

int ast_bridge_is_video_src(struct ast_bridge *bridge, struct ast_channel *chan)
{
   int res = 0;

   ast_bridge_lock(bridge);
   switch (bridge->softmix.video_mode.mode) {
   case AST_BRIDGE_VIDEO_MODE_NONE:
      break;
   case AST_BRIDGE_VIDEO_MODE_SINGLE_SRC:
      if (bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc == chan) {
         res = 1;
      }
      break;
   case AST_BRIDGE_VIDEO_MODE_TALKER_SRC:
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc == chan) {
         res = 1;
      } else if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc == chan) {
         res = 2;
      }
   case AST_BRIDGE_VIDEO_MODE_SFU:
      break;
   }
   ast_bridge_unlock(bridge);
   return res;
}

void ast_bridge_remove_video_src(struct ast_bridge *bridge, struct ast_channel *chan)
{
   ast_bridge_lock(bridge);
   switch (bridge->softmix.video_mode.mode) {
   case AST_BRIDGE_VIDEO_MODE_NONE:
      break;
   case AST_BRIDGE_VIDEO_MODE_SINGLE_SRC:
      if (bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc == chan) {
         if (bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc) {
            ast_channel_unref(bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc);
         }
         bridge->softmix.video_mode.mode_data.single_src_data.chan_vsrc = NULL;
      }
      break;
   case AST_BRIDGE_VIDEO_MODE_TALKER_SRC:
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc == chan) {
         if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc) {
            ast_channel_unref(bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc);
         }
         bridge->softmix.video_mode.mode_data.talker_src_data.chan_vsrc = NULL;
         bridge->softmix.video_mode.mode_data.talker_src_data.average_talking_energy = 0;
      }
      if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc == chan) {
         if (bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc) {
            ast_channel_unref(bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc);
         }
         bridge->softmix.video_mode.mode_data.talker_src_data.chan_old_vsrc = NULL;
      }
   case AST_BRIDGE_VIDEO_MODE_SFU:
      break;
   }
   ast_bridge_unlock(bridge);
}

const char *ast_bridge_video_mode_to_string(enum ast_bridge_video_mode_type video_mode)
{
   switch (video_mode) {
   case AST_BRIDGE_VIDEO_MODE_TALKER_SRC:
      return "talker";
   case AST_BRIDGE_VIDEO_MODE_SINGLE_SRC:
      return "single";
   case AST_BRIDGE_VIDEO_MODE_SFU:
      return "sfu";
   case AST_BRIDGE_VIDEO_MODE_NONE:
   default:
      return "none";
   }
}

void ast_bridge_set_send_sdp_label(struct ast_bridge *bridge, unsigned int send_sdp_label)
{
   ast_bridge_lock(bridge);
   bridge->softmix.send_sdp_label = send_sdp_label;
   ast_bridge_unlock(bridge);
}

static int channel_hash(const void *obj, int flags)
{
   const struct ast_channel *chan = obj;
   const char *name = obj;
   int hash;

   switch (flags & (OBJ_POINTER | OBJ_KEY | OBJ_PARTIAL_KEY)) {
   default:
   case OBJ_POINTER:
      name = ast_channel_name(chan);
      /* Fall through */
   case OBJ_KEY:
      hash = ast_str_hash(name);
      break;
   case OBJ_PARTIAL_KEY:
      /* Should never happen in hash callback. */
      ast_assert(0);
      hash = 0;
      break;
   }
   return hash;
}

static int channel_cmp(void *obj, void *arg, int flags)
{
   const struct ast_channel *left = obj;
   const struct ast_channel *right = arg;
   const char *right_name = arg;
   int cmp;

   switch (flags & (OBJ_POINTER | OBJ_KEY | OBJ_PARTIAL_KEY)) {
   default:
   case OBJ_POINTER:
      right_name = ast_channel_name(right);
      /* Fall through */
   case OBJ_KEY:
      cmp = strcmp(ast_channel_name(left), right_name);
      break;
   case OBJ_PARTIAL_KEY:
      cmp = strncmp(ast_channel_name(left), right_name, strlen(right_name));
      break;
   }
   return cmp ? 0 : CMP_MATCH;
}

struct ao2_container *ast_bridge_peers_nolock(struct ast_bridge *bridge)
{
   struct ao2_container *channels;
   struct ast_bridge_channel *iter;

   channels = ao2_container_alloc_hash(AO2_ALLOC_OPT_LOCK_NOLOCK, 0,
      13, channel_hash, NULL, channel_cmp);
   if (!channels) {
      return NULL;
   }

   AST_LIST_TRAVERSE(&bridge->channels, iter, entry) {
      ao2_link(channels, iter->chan);
   }

   return channels;
}

struct ao2_container *ast_bridge_peers(struct ast_bridge *bridge)
{
   struct ao2_container *channels;

   ast_bridge_lock(bridge);
   channels = ast_bridge_peers_nolock(bridge);
   ast_bridge_unlock(bridge);

   return channels;
}

struct ast_channel *ast_bridge_peer_nolock(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_channel *peer = NULL;
   struct ast_bridge_channel *iter;

   /* Asking for the peer channel only makes sense on a two-party bridge. */
   if (bridge->num_channels == 2
      && bridge->technology->capabilities
         & (AST_BRIDGE_CAPABILITY_NATIVE | AST_BRIDGE_CAPABILITY_1TO1MIX)) {
      int in_bridge = 0;

      AST_LIST_TRAVERSE(&bridge->channels, iter, entry) {
         if (iter->chan != chan) {
            peer = iter->chan;
         } else {
            in_bridge = 1;
         }
      }
      if (in_bridge && peer) {
         ast_channel_ref(peer);
      } else {
         peer = NULL;
      }
   }

   return peer;
}

struct ast_channel *ast_bridge_peer(struct ast_bridge *bridge, struct ast_channel *chan)
{
   struct ast_channel *peer;

   ast_bridge_lock(bridge);
   peer = ast_bridge_peer_nolock(bridge, chan);
   ast_bridge_unlock(bridge);

   return peer;
}

/*!
 * \internal
 * \brief Transfer an entire bridge to a specific destination.
 *
 * This creates a local channel to dial out and swaps the called local channel
 * with the transferer channel. By doing so, all participants in the bridge are
 * connected to the specified destination.
 *
 * While this means of transferring would work for both two-party and multi-party
 * bridges, this method is only used for multi-party bridges since this method would
 * be less efficient for two-party bridges.
 *
 * \param is_external Whether the transfer is externally initiated
 * \param transferer The channel performing a transfer
 * \param bridge The bridge where the transfer is being performed
 * \param exten The destination extension for the blind transfer
 * \param context The destination context for the blind transfer
 * \param transferee The party being transferred if there is only one
 * \param new_channel_cb Callback to call on channel that is created to
 *        facilitate the blind transfer.
 * \param user_data_wrapper User-provided data needed in new_channel_cb
 * \param transfer_message The Stasis publication for this transfer.
 *
 * \return The success or failure of the operation
 */
static enum ast_transfer_result blind_transfer_bridge(int is_external,
      struct ast_channel *transferer, struct ast_bridge *bridge,
      const char *exten, const char *context, struct ast_channel *transferee,
      transfer_channel_cb new_channel_cb,
      struct transfer_channel_data *user_data_wrapper,
      struct ast_blind_transfer_message *transfer_message)
{
   struct ast_channel *local;
   char chan_name[AST_MAX_EXTENSION + AST_MAX_CONTEXT + 2];
   int cause;

   snprintf(chan_name, sizeof(chan_name), "%s@%s", exten, context);
   local = ast_request("Local", ast_channel_nativeformats(transferer), NULL, transferer,
         chan_name, &cause);
   if (!local) {
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   ast_channel_lock_both(local, transferer);
   ast_channel_req_accountcodes(local, transferer, AST_CHANNEL_REQUESTOR_REPLACEMENT);

   transfer_message->replace_channel = ast_channel_snapshot_get_latest(ast_channel_uniqueid(local));
   if (!transfer_message->replace_channel) {
      ast_hangup(local);
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   pbx_builtin_setvar_helper(local, BLINDTRANSFER, ast_channel_name(transferer));
   ast_channel_unlock(local);
   ast_channel_unlock(transferer);

   if (new_channel_cb) {
      new_channel_cb(local, user_data_wrapper, AST_BRIDGE_TRANSFER_MULTI_PARTY);
   }

   if (ast_call(local, chan_name, 0)) {
      ast_hangup(local);
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   if (ast_bridge_impart(bridge, local, transferer, NULL,
      AST_BRIDGE_IMPART_CHAN_INDEPENDENT)) {
      ast_hangup(local);
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   return AST_BRIDGE_TRANSFER_SUCCESS;
}

/*!
 * \internal
 * \brief Get the transferee channel
 *
 * This is only applicable to cases where a transfer is occurring on a
 * two-party bridge. The channels container passed in is expected to only
 * contain two channels, the transferer and the transferee. The transferer
 * channel is passed in as a parameter to ensure we don't return it as
 * the transferee channel.
 *
 * \param channels A two-channel container containing the transferer and transferee
 * \param transferer The party that is transfering the call
 * \return The party that is being transferred
 */
static struct ast_channel *get_transferee(struct ao2_container *channels, struct ast_channel *transferer)
{
   struct ao2_iterator channel_iter;
   struct ast_channel *transferee;

   for (channel_iter = ao2_iterator_init(channels, 0);
         (transferee = ao2_iterator_next(&channel_iter));
         ao2_cleanup(transferee)) {
      if (transferee != transferer) {
         break;
      }
   }

   ao2_iterator_destroy(&channel_iter);
   return transferee;
}

/*!
 * \brief Perform an attended transfer of a bridge
 *
 * This performs an attended transfer of an entire bridge to a target.
 * The target varies, depending on what bridges exist during the transfer
 * attempt.
 *
 * If two bridges exist, then a local channel is created to link the two
 * bridges together.
 *
 * If only one bridge exists, then a local channel is created with one end
 * placed into the existing bridge and the other end masquerading into
 * the unbridged channel.
 *
 * \param chan1 Transferer channel. Guaranteed to be bridged.
 * \param chan2 Other transferer channel. May or may not be bridged.
 * \param bridge1 Bridge that chan1 is in. Guaranteed to be non-NULL.
 * \param bridge2 Bridge that chan2 is in. If NULL, then chan2 is not bridged.
 * \param publication Data to publish for a stasis attended transfer message.
 * \retval AST_BRIDGE_TRANSFER_FAIL Internal error occurred
 * \retval AST_BRIDGE_TRANSFER_SUCCESS Succesfully transferred the bridge
 */
static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *chan1,
      struct ast_channel *chan2, struct ast_bridge *bridge1, struct ast_bridge *bridge2,
      struct ast_attended_transfer_message *transfer_msg)
{
#define BRIDGE_LOCK_ONE_OR_BOTH(b1, b2) \
   do { \
      if (b2) { \
         ast_bridge_lock_both(b1, b2); \
      } else { \
         ast_bridge_lock(b1); \
      } \
   } while (0)

   static const char *dest = "_attended@transfer/m";
   struct ast_channel *local_chan;
   int cause;
   int res;
   const char *app = NULL;

   local_chan = ast_request("Local", ast_channel_nativeformats(chan1), NULL, chan1,
         dest, &cause);
   if (!local_chan) {
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   ast_channel_lock_both(local_chan, chan1);
   ast_channel_req_accountcodes(local_chan, chan1, AST_CHANNEL_REQUESTOR_REPLACEMENT);
   pbx_builtin_setvar_helper(local_chan, ATTENDEDTRANSFER, ast_channel_name(chan1));
   ast_channel_unlock(local_chan);
   ast_channel_unlock(chan1);

   if (bridge2) {
      res = ast_local_setup_bridge(local_chan, bridge2, chan2, NULL);
   } else {
      app = ast_strdupa(ast_channel_appl(chan2));
      res = ast_local_setup_masquerade(local_chan, chan2);
   }

   if (res) {
      ast_hangup(local_chan);
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   /*
    * Since bridges need to be unlocked before entering ast_bridge_impart and
    * core_local may call into it then the bridges need to be unlocked here.
    */
   ast_bridge_unlock(bridge1);
   if (bridge2) {
      ast_bridge_unlock(bridge2);
   }

   if (ast_call(local_chan, dest, 0)) {
      ast_hangup(local_chan);
      BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   /* Get a ref for use later since this one is being stolen */
   ao2_ref(local_chan, +1);
   if (ast_bridge_impart(bridge1, local_chan, chan1, NULL,
      AST_BRIDGE_IMPART_CHAN_INDEPENDENT)) {
      ast_hangup(local_chan);
      ao2_cleanup(local_chan);
      BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);
      return AST_BRIDGE_TRANSFER_FAIL;
   }
   BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);

   if (bridge2) {
      void *tech;
      struct ast_channel *locals[2];

      /* Have to lock everything just in case a hangup comes in early */
      ast_local_lock_all(local_chan, &tech, &locals[0], &locals[1]);
      if (!locals[0] || !locals[1]) {
         ast_log(LOG_ERROR, "Transfer failed probably due to an early hangup - "
            "missing other half of '%s'\n", ast_channel_name(local_chan));
         ast_local_unlock_all(tech, locals[0], locals[1]);
         ao2_cleanup(local_chan);
         return AST_BRIDGE_TRANSFER_FAIL;
      }

      /* Make sure the peer is properly set */
      if (local_chan != locals[0]) {
         SWAP(locals[0], locals[1]);
      }

      ast_attended_transfer_message_add_link(transfer_msg, locals);
      ast_local_unlock_all(tech, locals[0], locals[1]);
   } else {
      ast_attended_transfer_message_add_app(transfer_msg, app, local_chan);
   }

   ao2_cleanup(local_chan);
   return AST_BRIDGE_TRANSFER_SUCCESS;
}

static enum ast_transfer_result try_parking(struct ast_channel *transferer,
   const char *context, const char *exten, transfer_channel_cb new_channel_cb,
   struct transfer_channel_data *user_data_wrapper)
{
   RAII_VAR(struct ast_bridge_channel *, transferer_bridge_channel, NULL, ao2_cleanup);

   if (!ast_parking_provider_registered()) {
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   ast_channel_lock(transferer);
   transferer_bridge_channel = ast_channel_get_bridge_channel(transferer);
   ast_channel_unlock(transferer);

   if (!transferer_bridge_channel) {
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   if (ast_parking_blind_transfer_park(transferer_bridge_channel,
      context, exten, new_channel_cb, user_data_wrapper)) {
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   return AST_BRIDGE_TRANSFER_SUCCESS;
}

void ast_bridge_set_transfer_variables(struct ast_channel *chan, const char *value, int attended)
{
   char *writevar;
   char *erasevar;

   if (attended) {
      writevar = ATTENDEDTRANSFER;
      erasevar = BLINDTRANSFER;
   } else {
      writevar = BLINDTRANSFER;
      erasevar = ATTENDEDTRANSFER;
   }

   pbx_builtin_setvar_helper(chan, writevar, value);
   pbx_builtin_setvar_helper(chan, erasevar, NULL);
}

/*!
 * \internal
 * \brief Set the transfer variable as appropriate on channels involved in the transfer
 *
 * The transferer channel will have its variable set the same as its BRIDGEPEER
 * variable. This will account for all channels that it is bridged to. The other channels
 * involved in the transfer will have their variable set to the transferer
 * channel's name.
 *
 * \param transferer The channel performing the transfer
 * \param channels The channels belonging to the bridge
 * \param is_attended false  set BLINDTRANSFER and unset ATTENDEDTRANSFER
 *                    true   set ATTENDEDTRANSFER and unset BLINDTRANSFER
 */
static void set_transfer_variables_all(struct ast_channel *transferer, struct ao2_container *channels, int is_attended)
{
   struct ao2_iterator iter;
   struct ast_channel *chan;
   const char *transferer_name;
   const char *transferer_bridgepeer;

   ast_channel_lock(transferer);
   transferer_name = ast_strdupa(ast_channel_name(transferer));
   transferer_bridgepeer = ast_strdupa(S_OR(pbx_builtin_getvar_helper(transferer, "BRIDGEPEER"), ""));
   ast_channel_unlock(transferer);

   for (iter = ao2_iterator_init(channels, 0);
         (chan = ao2_iterator_next(&iter));
         ao2_cleanup(chan)) {
      if (chan == transferer) {
         ast_bridge_set_transfer_variables(chan, transferer_bridgepeer, is_attended);
      } else {
         ast_bridge_set_transfer_variables(chan, transferer_name, is_attended);
      }
   }

   ao2_iterator_destroy(&iter);
}

struct ast_bridge *ast_bridge_transfer_acquire_bridge(struct ast_channel *chan)
{
   struct ast_bridge *bridge;

   ast_channel_lock(chan);
   bridge = ast_channel_get_bridge(chan);
   ast_channel_unlock(chan);

   if (bridge && ast_test_flag(&bridge->feature_flags,
         (AST_BRIDGE_FLAG_MASQUERADE_ONLY | AST_BRIDGE_FLAG_INVISIBLE))) {
      ao2_ref(bridge, -1);
      bridge = NULL;
   }

   return bridge;
}

enum ast_transfer_result ast_bridge_transfer_blind(int is_external,
      struct ast_channel *transferer, const char *exten, const char *context,
      transfer_channel_cb new_channel_cb, void *user_data)
{
   RAII_VAR(struct ast_bridge *, bridge, NULL, ao2_cleanup);
   RAII_VAR(struct ast_bridge_channel *, bridge_channel, NULL, ao2_cleanup);
   RAII_VAR(struct ao2_container *, channels, NULL, ao2_cleanup);
   RAII_VAR(struct ast_channel *, transferee, NULL, ast_channel_cleanup);
   RAII_VAR(struct transfer_channel_data *, user_data_wrapper, NULL, ao2_cleanup);
   RAII_VAR(struct ast_blind_transfer_message *, transfer_message, NULL, ao2_cleanup);
   int do_bridge_transfer;
   int transfer_prohibited;
   enum ast_transfer_result transfer_result;

   transfer_message = ast_blind_transfer_message_create(is_external, transferer, exten, context);
   if (!transfer_message) {
      /* Out of memory. Not even possible to publish a Stasis message about the
       * failure
       */
      ast_log(LOG_ERROR, "Unable to allocate memory for blind transfer publication from %s\n",
            ast_channel_name(transferer));
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   bridge = ast_bridge_transfer_acquire_bridge(transferer);
   if (!bridge) {
      transfer_result = AST_BRIDGE_TRANSFER_INVALID;
      goto publish;
   }

   ast_bridge_lock(bridge);
   transfer_message->bridge = ast_bridge_snapshot_create(bridge);
   ast_bridge_unlock(bridge);
   if (!transfer_message->bridge) {
      transfer_result = AST_BRIDGE_TRANSFER_FAIL;
      goto publish;
   }

   transferee = ast_bridge_peer(bridge, transferer);
   if (transferee) {
      transfer_message->transferee = ast_channel_snapshot_get_latest(ast_channel_uniqueid(transferee));
      if (!transfer_message->transferee) {
         transfer_result = AST_BRIDGE_TRANSFER_FAIL;
         goto publish;
      }
   }

   ast_channel_lock(transferer);
   bridge_channel = ast_channel_get_bridge_channel(transferer);
   ast_channel_unlock(transferer);
   if (!bridge_channel) {
      transfer_result = AST_BRIDGE_TRANSFER_INVALID;
      goto publish;
   }

   user_data_wrapper = ao2_alloc(sizeof(*user_data_wrapper), NULL);
   if (!user_data_wrapper) {
      transfer_result = AST_BRIDGE_TRANSFER_FAIL;
      goto publish;
   }

   user_data_wrapper->data = user_data;

   /* Take off hold if they are on hold. */
   ast_bridge_channel_write_unhold(bridge_channel);

   transfer_result = try_parking(transferer, context, exten, new_channel_cb, user_data_wrapper);
   if (transfer_result == AST_BRIDGE_TRANSFER_SUCCESS) {
      goto publish;
   }

   /* Since parking didn't take control of the user_data_wrapper, we are just going to raise the completed flag now. */
   user_data_wrapper->completed = 1;

   {
      SCOPED_LOCK(lock, bridge, ast_bridge_lock, ast_bridge_unlock);

      channels = ast_bridge_peers_nolock(bridge);
      if (!channels) {
         transfer_result = AST_BRIDGE_TRANSFER_FAIL;
         goto publish;
      }
      if (ao2_container_count(channels) <= 1) {
         transfer_result = AST_BRIDGE_TRANSFER_INVALID;
         goto publish;
      }
      transfer_prohibited = ast_test_flag(&bridge->feature_flags,
            AST_BRIDGE_FLAG_TRANSFER_PROHIBITED);
      do_bridge_transfer = ast_test_flag(&bridge->feature_flags,
            AST_BRIDGE_FLAG_TRANSFER_BRIDGE_ONLY) ||
            ao2_container_count(channels) > 2;
   }

   if (transfer_prohibited) {
      transfer_result = AST_BRIDGE_TRANSFER_NOT_PERMITTED;
      goto publish;
   }

   set_transfer_variables_all(transferer, channels, 0);

   if (do_bridge_transfer) {
      transfer_result = blind_transfer_bridge(is_external, transferer, bridge,
         exten, context, transferee, new_channel_cb, user_data_wrapper, transfer_message);
      goto publish;
   }

   /* Reaching this portion means that we're dealing with a two-party bridge */

   if (!transferee) {
      transfer_result = AST_BRIDGE_TRANSFER_FAIL;
      goto publish;
   }

   if (bridge_channel_internal_queue_blind_transfer(transferee, exten, context,
            new_channel_cb, user_data_wrapper)) {
      transfer_result = AST_BRIDGE_TRANSFER_FAIL;
      goto publish;
   }

   ast_bridge_remove(bridge, transferer);
   transfer_result = AST_BRIDGE_TRANSFER_SUCCESS;

publish:
   transfer_message->result = transfer_result;
   ast_bridge_publish_blind_transfer(transfer_message);
   return transfer_result;
}

/*!
 * \internal
 * \brief Performs an attended transfer by moving a channel from one bridge to another
 *
 * The channel that is bridged to the source_channel is moved into the dest_bridge from
 * the source_bridge_channel's bridge. The swap_channel is swapped out of the dest_bridge and placed in
 * the source_bridge_channel's bridge.
 *
 * \note dest_bridge and source_bridge_channel's bridge MUST be locked before calling this function.
 *
 * \param dest_bridge The final bridge for the attended transfer
 * \param source_channel Channel who is bridged to the channel that will move
 * \param swap_channel Channel to be swapped out of the dest_bridge
 * \return The success or failure of the swap attempt
 */
static enum ast_transfer_result bridge_swap_attended_transfer(struct ast_bridge *dest_bridge,
      struct ast_bridge_channel *source_bridge_channel, struct ast_channel *swap_channel)
{
   struct ast_bridge_channel *bridged_to_source;

   bridged_to_source = ast_bridge_channel_peer(source_bridge_channel);
   if (bridged_to_source
      && bridged_to_source->state == BRIDGE_CHANNEL_STATE_WAIT
      && !ast_test_flag(&bridged_to_source->features->feature_flags,
         AST_BRIDGE_CHANNEL_FLAG_IMMOVABLE)) {
      bridged_to_source->swap = swap_channel;
      if (bridge_do_move(dest_bridge, bridged_to_source, 1, 0)) {
         return AST_BRIDGE_TRANSFER_FAIL;
      }
      /* Must kick the source channel out of its bridge. */
      ast_bridge_channel_leave_bridge(source_bridge_channel,
         BRIDGE_CHANNEL_STATE_END_NO_DISSOLVE, AST_CAUSE_NORMAL_CLEARING);
      return AST_BRIDGE_TRANSFER_SUCCESS;
   } else {
      return AST_BRIDGE_TRANSFER_INVALID;
   }
}

/*!
 * \internal
 * \brief Function that performs an attended transfer when both transferer channels are bridged
 *
 * The method by which the transfer is performed is dependent on whether the bridges allow for
 * optimization to occur between them. If no optimization is permitted, then an unreal channel
 * is placed as a link between the two bridges. If optimization is permitted, then that means
 * we are free to perform move or merge operations in order to perform the transfer.
 *
 * \note to_transferee_bridge and to_target_bridge MUST be locked before calling this function
 *
 * \param to_transferee The channel that is bridged to the transferee
 * \param to_transferee_bridge_channel to_transferee's bridge_channel
 * \param to_transfer_target The channel that is bridged to the transfer target
 * \param to_target_bridge_channel to_transfer_target's bridge_channel
 * \param to_transferee_bridge The bridge between to_transferee and the transferee
 * \param to_target_bridge The bridge between to_transfer_target and the transfer_target
 * \param publication Data to publish for a stasis attended transfer message
 * \return The success or failure of the attended transfer
 */
static enum ast_transfer_result two_bridge_attended_transfer(struct ast_channel *to_transferee,
      struct ast_bridge_channel *to_transferee_bridge_channel,
      struct ast_channel *to_transfer_target,
      struct ast_bridge_channel *to_target_bridge_channel,
      struct ast_bridge *to_transferee_bridge, struct ast_bridge *to_target_bridge,
      struct ast_attended_transfer_message *transfer_msg)
{
   struct ast_bridge_channel *kick_me[] = {
         to_transferee_bridge_channel,
         to_target_bridge_channel,
   };
   enum ast_transfer_result res;
   struct ast_bridge *final_bridge = NULL;
   RAII_VAR(struct ao2_container *, channels, NULL, ao2_cleanup);

   channels = ast_bridge_peers_nolock(to_transferee_bridge);

   if (!channels) {
      res = AST_BRIDGE_TRANSFER_FAIL;
      goto end;
   }

   set_transfer_variables_all(to_transferee, channels, 1);

   switch (ast_bridges_allow_optimization(to_transferee_bridge, to_target_bridge)) {
   case AST_BRIDGE_OPTIMIZE_SWAP_TO_CHAN_BRIDGE:
      final_bridge = to_transferee_bridge;
      res = bridge_swap_attended_transfer(to_transferee_bridge, to_target_bridge_channel, to_transferee);
      goto end;
   case AST_BRIDGE_OPTIMIZE_SWAP_TO_PEER_BRIDGE:
      final_bridge = to_target_bridge;
      res = bridge_swap_attended_transfer(to_target_bridge, to_transferee_bridge_channel, to_transfer_target);
      goto end;
   case AST_BRIDGE_OPTIMIZE_MERGE_TO_CHAN_BRIDGE:
      final_bridge = to_transferee_bridge;
      bridge_do_merge(to_transferee_bridge, to_target_bridge, kick_me, ARRAY_LEN(kick_me), 0);
      res = AST_BRIDGE_TRANSFER_SUCCESS;
      goto end;
   case AST_BRIDGE_OPTIMIZE_MERGE_TO_PEER_BRIDGE:
      final_bridge = to_target_bridge;
      bridge_do_merge(to_target_bridge, to_transferee_bridge, kick_me, ARRAY_LEN(kick_me), 0);
      res = AST_BRIDGE_TRANSFER_SUCCESS;
      goto end;
   case AST_BRIDGE_OPTIMIZE_PROHIBITED:
   default:
      /* Just because optimization wasn't doable doesn't necessarily mean
       * that we can actually perform the transfer. Some reasons for non-optimization
       * indicate bridge invalidity, so let's check those before proceeding.
       */
      if (to_transferee_bridge->inhibit_merge || to_transferee_bridge->dissolved ||
            to_target_bridge->inhibit_merge || to_target_bridge->dissolved) {
         return AST_BRIDGE_TRANSFER_INVALID;
      }

      return attended_transfer_bridge(to_transferee, to_transfer_target,
         to_transferee_bridge, to_target_bridge, transfer_msg);
   }

end:
   if (res == AST_BRIDGE_TRANSFER_SUCCESS) {
      ast_attended_transfer_message_add_merge(transfer_msg, final_bridge);
   }

   return res;
}

enum ast_transfer_result ast_bridge_transfer_attended(struct ast_channel *to_transferee,
      struct ast_channel *to_transfer_target)
{
   RAII_VAR(struct ast_bridge *, to_transferee_bridge, NULL, ao2_cleanup);
   RAII_VAR(struct ast_bridge *, to_target_bridge, NULL, ao2_cleanup);
   RAII_VAR(struct ast_bridge_channel *, to_transferee_bridge_channel, NULL, ao2_cleanup);
   RAII_VAR(struct ast_bridge_channel *, to_target_bridge_channel, NULL, ao2_cleanup);
   RAII_VAR(struct ao2_container *, channels, NULL, ao2_cleanup);
   RAII_VAR(struct ast_channel *, transferee, NULL, ao2_cleanup);
   RAII_VAR(struct ast_attended_transfer_message *, transfer_msg, NULL, ao2_cleanup);
   struct ast_bridge *the_bridge = NULL;
   struct ast_channel *chan_bridged;
   struct ast_channel *chan_unbridged;
   int transfer_prohibited;
   int do_bridge_transfer;
   enum ast_transfer_result res;
   const char *app = NULL;
   int hangup_target = 0;

   to_transferee_bridge = ast_bridge_transfer_acquire_bridge(to_transferee);
   to_target_bridge = ast_bridge_transfer_acquire_bridge(to_transfer_target);

   transfer_msg = ast_attended_transfer_message_create(1, to_transferee, to_transferee_bridge,
         to_transfer_target, to_target_bridge, NULL, NULL);
   if (!transfer_msg) {
      ast_log(LOG_ERROR, "Unable to create Stasis publication for attended transfer from %s\n",
            ast_channel_name(to_transferee));
      return AST_BRIDGE_TRANSFER_FAIL;
   }

   /* They can't both be unbridged, you silly goose! */
   if (!to_transferee_bridge && !to_target_bridge) {
      res = AST_BRIDGE_TRANSFER_INVALID;
      goto end;
   }

   ast_channel_lock(to_transferee);
   to_transferee_bridge_channel = ast_channel_get_bridge_channel(to_transferee);
   ast_channel_unlock(to_transferee);

   ast_channel_lock(to_transfer_target);
   to_target_bridge_channel = ast_channel_get_bridge_channel(to_transfer_target);
   ast_channel_unlock(to_transfer_target);

   if (to_transferee_bridge_channel) {
      /* Take off hold if they are on hold. */
      if (ast_bridge_channel_write_unhold(to_transferee_bridge_channel)) {
         ast_log(LOG_ERROR, "Transferee channel disappeared during transfer!\n");
         res = AST_BRIDGE_TRANSFER_FAIL;
         goto end;
      }
   }

   if (to_target_bridge_channel) {
      const char *target_complete_sound;

      /* Take off hold if they are on hold. */
      if (ast_bridge_channel_write_unhold(to_target_bridge_channel)) {
         ast_log(LOG_ERROR, "Target channel disappeared during transfer!\n");
         res = AST_BRIDGE_TRANSFER_FAIL;
         goto end;
      }

      /* Is there a courtesy sound to play to the target? */
      ast_channel_lock(to_transfer_target);
      target_complete_sound = pbx_builtin_getvar_helper(to_transfer_target,
         "ATTENDED_TRANSFER_COMPLETE_SOUND");
      if (!ast_strlen_zero(target_complete_sound)) {
         target_complete_sound = ast_strdupa(target_complete_sound);
      } else {
         target_complete_sound = NULL;
      }
      ast_channel_unlock(to_transfer_target);
      if (!target_complete_sound) {
         ast_channel_lock(to_transferee);
         target_complete_sound = pbx_builtin_getvar_helper(to_transferee,
            "ATTENDED_TRANSFER_COMPLETE_SOUND");
         if (!ast_strlen_zero(target_complete_sound)) {
            target_complete_sound = ast_strdupa(target_complete_sound);
         } else {
            target_complete_sound = NULL;
         }
         ast_channel_unlock(to_transferee);
      }
      if (target_complete_sound) {
         ast_bridge_channel_write_playfile(to_target_bridge_channel, NULL,
            target_complete_sound, NULL);
      }
   }

   /* Let's get the easy one out of the way first */
   if (to_transferee_bridge && to_target_bridge) {

      if (!to_transferee_bridge_channel || !to_target_bridge_channel) {
         res = AST_BRIDGE_TRANSFER_INVALID;
         goto end;
      }

      ast_bridge_lock_both(to_transferee_bridge, to_target_bridge);
      res = two_bridge_attended_transfer(to_transferee, to_transferee_bridge_channel,
            to_transfer_target, to_target_bridge_channel,
            to_transferee_bridge, to_target_bridge, transfer_msg);
      ast_bridge_unlock(to_transferee_bridge);
      ast_bridge_unlock(to_target_bridge);

      hangup_target = 1;
      goto end;
   }

   the_bridge = to_transferee_bridge ?: to_target_bridge;
   chan_bridged = to_transferee_bridge ? to_transferee : to_transfer_target;
   chan_unbridged = to_transferee_bridge ? to_transfer_target : to_transferee;

   /*
    * Race condition makes it possible for app to be NULL, so get the app prior to
    * transferring with a fallback of "unknown".
    */
   app = ast_strdupa(ast_channel_appl(chan_unbridged) ?: "unknown");

   {
      int chan_count;
      SCOPED_LOCK(lock, the_bridge, ast_bridge_lock, ast_bridge_unlock);

      channels = ast_bridge_peers_nolock(the_bridge);
      if (!channels) {
         res = AST_BRIDGE_TRANSFER_FAIL;
         goto end;
      }
      chan_count = ao2_container_count(channels);
      if (chan_count <= 1) {
         res = AST_BRIDGE_TRANSFER_INVALID;
         goto end;
      }
      transfer_prohibited = ast_test_flag(&the_bridge->feature_flags,
            AST_BRIDGE_FLAG_TRANSFER_PROHIBITED);
      do_bridge_transfer = ast_test_flag(&the_bridge->feature_flags,
            AST_BRIDGE_FLAG_TRANSFER_BRIDGE_ONLY) ||
            chan_count > 2;
   }

   if (transfer_prohibited) {
      res = AST_BRIDGE_TRANSFER_NOT_PERMITTED;
      goto end;
   }

   set_transfer_variables_all(to_transferee, channels, 1);

   if (do_bridge_transfer) {
      /*
       * Hang up the target if it was bridged. Note, if it is not bridged
       * it is hung up during the masquerade.
       */
      hangup_target = chan_bridged == to_transfer_target;
      ast_bridge_lock(the_bridge);
      res = attended_transfer_bridge(chan_bridged, chan_unbridged, the_bridge, NULL, transfer_msg);
      ast_bridge_unlock(the_bridge);
      goto end;
   }

   transferee = get_transferee(channels, chan_bridged);
   if (!transferee) {
      res = AST_BRIDGE_TRANSFER_FAIL;
      goto end;
   }

   if (bridge_channel_internal_queue_attended_transfer(transferee, chan_unbridged)) {
      res = AST_BRIDGE_TRANSFER_FAIL;
      goto end;
   }

   ast_bridge_remove(the_bridge, chan_bridged);

   ast_attended_transfer_message_add_app(transfer_msg, app, NULL);
   res = AST_BRIDGE_TRANSFER_SUCCESS;

end:
   if ((res == AST_BRIDGE_TRANSFER_SUCCESS && hangup_target) || res == AST_BRIDGE_TRANSFER_FAIL) {
      ast_softhangup(to_transfer_target, AST_SOFTHANGUP_DEV);
   }

   transfer_msg->result = res;
   ast_bridge_publish_attended_transfer(transfer_msg);
   return res;
}

/*!
 * \internal
 * \brief Service the bridge manager request.
 * \since 12.0.0
 *
 * \param bridge requesting service.
 *
 * \return Nothing
 */
static void bridge_manager_service(struct ast_bridge *bridge)
{
   ast_bridge_lock(bridge);
   if (bridge->callid) {
      ast_callid_threadassoc_change(bridge->callid);
   }

   /* Do any pending bridge actions. */
   bridge_handle_actions(bridge);
   ast_bridge_unlock(bridge);
}

/*!
 * \internal
 * \brief Bridge manager service thread.
 * \since 12.0.0
 *
 * \return Nothing
 */
static void *bridge_manager_thread(void *data)
{
   struct bridge_manager_controller *manager = data;
   struct bridge_manager_request *request;

   ao2_lock(manager);
   while (!manager->stop) {
      request = AST_LIST_REMOVE_HEAD(&manager->service_requests, node);
      if (!request) {
         ast_cond_wait(&manager->cond, ao2_object_get_lockaddr(manager));
         continue;
      }
      ao2_unlock(manager);

      /* Service the bridge. */
      bridge_manager_service(request->bridge);
      ao2_ref(request->bridge, -1);
      ast_free(request);

      ao2_lock(manager);
   }
   ao2_unlock(manager);

   return NULL;
}

/*!
 * \internal
 * \brief Destroy the bridge manager controller.
 * \since 12.0.0
 *
 * \param obj Bridge manager to destroy.
 *
 * \return Nothing
 */
static void bridge_manager_destroy(void *obj)
{
   struct bridge_manager_controller *manager = obj;
   struct bridge_manager_request *request;

   if (manager->thread != AST_PTHREADT_NULL) {
      /* Stop the manager thread. */
      ao2_lock(manager);
      manager->stop = 1;
      ast_cond_signal(&manager->cond);
      ao2_unlock(manager);
      ast_debug(1, "Waiting for bridge manager thread to die.\n");
      pthread_join(manager->thread, NULL);
   }

   /* Destroy the service request queue. */
   while ((request = AST_LIST_REMOVE_HEAD(&manager->service_requests, node))) {
      ao2_ref(request->bridge, -1);
      ast_free(request);
   }

   ast_cond_destroy(&manager->cond);
}

/*!
 * \internal
 * \brief Create the bridge manager controller.
 * \since 12.0.0
 *
 * \retval manager on success.
 * \retval NULL on error.
 */
static struct bridge_manager_controller *bridge_manager_create(void)
{
   struct bridge_manager_controller *manager;

   manager = ao2_alloc(sizeof(*manager), bridge_manager_destroy);
   if (!manager) {
      /* Well. This isn't good. */
      return NULL;
   }
   ast_cond_init(&manager->cond, NULL);
   AST_LIST_HEAD_INIT_NOLOCK(&manager->service_requests);

   /* Create the bridge manager thread. */
   if (ast_pthread_create(&manager->thread, NULL, bridge_manager_thread, manager)) {
      /* Well. This isn't good either. */
      manager->thread = AST_PTHREADT_NULL;
      ao2_ref(manager, -1);
      manager = NULL;
   }

   return manager;
}

/*!
 * \internal
 * \brief Bridge ao2 container sort function.
 * \since 12.0.0
 *
 * \param obj_left pointer to the (user-defined part) of an object.
 * \param obj_right pointer to the (user-defined part) of an object.
 * \param flags flags from ao2_callback()
 *   OBJ_POINTER - if set, 'obj_right', is an object.
 *   OBJ_KEY - if set, 'obj_right', is a search key item that is not an object.
 *   OBJ_PARTIAL_KEY - if set, 'obj_right', is a partial search key item that is not an object.
 *
 * \retval <0 if obj_left < obj_right
 * \retval =0 if obj_left == obj_right
 * \retval >0 if obj_left > obj_right
 */
static int bridge_sort_cmp(const void *obj_left, const void *obj_right, int flags)
{
   const struct ast_bridge *bridge_left = obj_left;
   const struct ast_bridge *bridge_right = obj_right;
   const char *right_key = obj_right;
   int cmp;

   switch (flags & (OBJ_POINTER | OBJ_KEY | OBJ_PARTIAL_KEY)) {
   default:
   case OBJ_POINTER:
      right_key = bridge_right->uniqueid;
      /* Fall through */
   case OBJ_KEY:
      cmp = strcmp(bridge_left->uniqueid, right_key);
      break;
   case OBJ_PARTIAL_KEY:
      cmp = strncmp(bridge_left->uniqueid, right_key, strlen(right_key));
      break;
   }
   return cmp;
}

struct ast_bridge *ast_bridge_find_by_id(const char *bridge_id)
{
   return ao2_find(bridges, bridge_id, OBJ_SEARCH_KEY);
}

static int complete_bridge_live_search(void *obj, void *arg, int flags)
{
   struct ast_bridge *bridge = obj;

   if (ast_cli_completion_add(ast_strdup(bridge->uniqueid))) {
      return CMP_STOP;
   }

   return 0;
}

static char *complete_bridge_live(const char *word)
{
   ao2_callback(bridges, ast_strlen_zero(word) ? 0 : OBJ_PARTIAL_KEY,
      complete_bridge_live_search, (char *) word);

   return NULL;
}

static char *handle_bridge_show_all(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
#define FORMAT_HDR "%-36s %5s %-15s %-15s %s\n"
#define FORMAT_ROW "%-36s %5u %-15s %-15s %s\n"

   struct ao2_iterator iter;
   struct ast_bridge *bridge;

   switch (cmd) {
   case CLI_INIT:
      e->