asterisk/bridges/bridge_simple.c

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007, 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 Simple two channel bridging module
 *
 * \author Joshua Colp <jcolp@digium.com>
 *
 * \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");