bridge_simple.c

Go to the documentation of this file.

/*
 * 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");