bridge_simple.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007, Digium, Inc.
 *
 * Joshua Colp <[email protected]>
 *
 * 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 Simple two channel bridging module
 *
 * \author Joshua Colp <[email protected]>
 *
 * \ingroup bridges
 */

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

#include "asterisk.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "asterisk/module.h"
#include "asterisk/channel.h"
#include "asterisk/bridge.h"
#include "asterisk/bridge_technology.h"
#include "asterisk/frame.h"
#include "asterisk/stream.h"

static void simple_bridge_stream_topology_changed(struct ast_bridge *bridge,
      struct ast_bridge_channel *bridge_channel);
static int simple_bridge_join(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel);
static int simple_bridge_write(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel, struct ast_frame *frame);

static struct ast_bridge_technology simple_bridge = {
   .name = "simple_bridge",
   .capabilities = AST_BRIDGE_CAPABILITY_1TO1MIX,
   .preference = AST_BRIDGE_PREFERENCE_BASE_1TO1MIX,
   .join = simple_bridge_join,
   .write = simple_bridge_write,
   .stream_topology_changed = simple_bridge_stream_topology_changed,
};

static struct ast_stream_topology *simple_bridge_request_stream_topology_update(
   struct ast_stream_topology *existing_topology,
   struct ast_stream_topology *requested_topology)
{
   struct ast_stream *stream;
   const struct ast_format_cap *audio_formats = NULL;
   struct ast_stream_topology *new_topology;
   int i;

   new_topology = ast_stream_topology_clone(requested_topology);
   if (!new_topology) {
      return NULL;
   }

   /* We find an existing stream with negotiated audio formats that we can place into
    * any audio streams in the new topology to ensure that negotiation succeeds. Some
    * endpoints incorrectly terminate the call if SDP negotiation fails.
    */
   for (i = 0; i < ast_stream_topology_get_count(existing_topology); ++i) {
      stream = ast_stream_topology_get_stream(existing_topology, i);

      if (ast_stream_get_type(stream) != AST_MEDIA_TYPE_AUDIO ||
         ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
         continue;
      }

      audio_formats = ast_stream_get_formats(stream);
      break;
   }

   if (audio_formats) {
      for (i = 0; i < ast_stream_topology_get_count(new_topology); ++i) {
         stream = ast_stream_topology_get_stream(new_topology, i);

         if (ast_stream_get_type(stream) != AST_MEDIA_TYPE_AUDIO ||
            ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
            continue;
         }

         /* We haven't actually modified audio_formats so this is safe */
         ast_stream_set_formats(stream, (struct ast_format_cap *)audio_formats);
      }
   }

   for (i = 0; i < ast_stream_topology_get_count(new_topology); ++i) {
      stream = ast_stream_topology_get_stream(new_topology, i);

      /* For both recvonly and sendonly the stream state reflects our state, that is we
       * are receiving only and we are sending only. Since we are renegotiating a remote
       * party we need to swap this to reflect what we will be doing. That is, if we are
       * receiving from Alice then we want to be sending to Bob, so swap recvonly to
       * sendonly.
       */
      if (ast_stream_get_state(stream) == AST_STREAM_STATE_RECVONLY) {
         ast_stream_set_state(stream, AST_STREAM_STATE_SENDONLY);
      } else if (ast_stream_get_state(stream) == AST_STREAM_STATE_SENDONLY) {
         ast_stream_set_state(stream, AST_STREAM_STATE_RECVONLY);
      }
   }

   return new_topology;
}

static int simple_bridge_join(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
   struct ast_stream_topology *req_top;
   struct ast_stream_topology *existing_top;
   struct ast_stream_topology *new_top;
   struct ast_channel *c0 = AST_LIST_FIRST(&bridge->channels)->chan;
   struct ast_channel *c1 = AST_LIST_LAST(&bridge->channels)->chan;

   /*
    * If this is the first channel we can't make it compatible...
    * unless we make it compatible with itself.  O.o
    */
   if (c0 == c1) {
      return 0;
   }

   if (ast_channel_make_compatible(c0, c1)) {
      return -1;
   }

   /* When both channels are joined we want to try to improve the experience by
    * raising the number of streams so they match.
    */
   ast_channel_lock_both(c0, c1);
   req_top = ast_channel_get_stream_topology(c0);
   existing_top = ast_channel_get_stream_topology(c1);
   if (ast_stream_topology_get_count(req_top) < ast_stream_topology_get_count(existing_top)) {
      SWAP(req_top, existing_top);
      SWAP(c0, c1);
   }
   new_top = simple_bridge_request_stream_topology_update(existing_top, req_top);
   ast_channel_unlock(c0);
   ast_channel_unlock(c1);

   if (!new_top) {
      /* Failure.  We'll just have to live with the current topology. */
      return 0;
   }

   ast_channel_request_stream_topology_change(c1, new_top, &simple_bridge);
   ast_stream_topology_free(new_top);

   return 0;
}

static int simple_bridge_write(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel, struct ast_frame *frame)
{
   const struct ast_control_t38_parameters *t38_parameters;
   int defer = 0;

   if (!ast_bridge_queue_everyone_else(bridge, bridge_channel, frame)) {
      /* This frame was successfully queued so no need to defer */
      return 0;
   }

   /* Depending on the frame defer it so when the next channel joins it receives it */
   switch (frame->frametype) {
   case AST_FRAME_CONTROL:
      switch (frame->subclass.integer) {
      case AST_CONTROL_T38_PARAMETERS:
         t38_parameters = frame->data.ptr;
         switch (t38_parameters->request_response) {
         case AST_T38_REQUEST_NEGOTIATE:
            defer = -1;
            break;
         default:
            break;
         }
         break;
      default:
         break;
      }
      break;
   default:
      break;
   }

   return defer;
}

static void simple_bridge_stream_topology_changed(struct ast_bridge *bridge,
      struct ast_bridge_channel *bridge_channel)
{
   struct ast_channel *c0 = bridge_channel->chan;
   struct ast_channel *c1 = AST_LIST_FIRST(&bridge->channels)->chan;
   struct ast_stream_topology *req_top;
   struct ast_stream_topology *existing_top;
   struct ast_stream_topology *new_top;

   ast_bridge_channel_stream_map(bridge_channel);

   if (ast_channel_get_stream_topology_change_source(bridge_channel->chan)
      == &simple_bridge) {
      return;
   }

   if (c0 == c1) {
      c1 = AST_LIST_LAST(&bridge->channels)->chan;
   }

   if (c0 == c1) {
      return;
   }

   /* If a party renegotiates we want to renegotiate their counterpart to a matching
    * topology.
    */
   ast_channel_lock_both(c0, c1);
   req_top = ast_channel_get_stream_topology(c0);
   existing_top = ast_channel_get_stream_topology(c1);
   new_top = simple_bridge_request_stream_topology_update(existing_top, req_top);
   ast_channel_unlock(c0);
   ast_channel_unlock(c1);

   if (!new_top) {
      /* Failure.  We'll just have to live with the current topology. */
      return;
   }

   ast_channel_request_stream_topology_change(c1, new_top, &simple_bridge);
   ast_stream_topology_free(new_top);
}

static int unload_module(void)
{
   ast_bridge_technology_unregister(&simple_bridge);
   return 0;
}

static int load_module(void)
{
   if (ast_bridge_technology_register(&simple_bridge)) {
      unload_module();
      return AST_MODULE_LOAD_DECLINE;
   }
   return AST_MODULE_LOAD_SUCCESS;
}

AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Simple two channel bridging module");