bridge_simple.c

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/*
 * 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;
    int unhold_c0, unhold_c1;
 
    /*
     * 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);
 
    /* The ast_channel_hold_state() and ast_channel_name() accessors need to be
     * called with the associated channel lock held.
     */
    if ((unhold_c1 = ast_channel_hold_state(c1) == AST_CONTROL_HOLD)) {
        ast_debug(1, "Channel %s simulating UNHOLD for bridge simple join.\n", ast_channel_name(c1));
    }
 
    if ((unhold_c0 = ast_channel_hold_state(c0) == AST_CONTROL_HOLD)) {
        ast_debug(1, "Channel %s simulating UNHOLD for bridge simple join.\n", ast_channel_name(c0));
    }
 
    ast_channel_unlock(c0);
    ast_channel_unlock(c1);
 
    if (unhold_c1) {
        ast_indicate(c1, AST_CONTROL_UNHOLD);
    }
 
    if (unhold_c0) {
        ast_indicate(c0, AST_CONTROL_UNHOLD);
    }
 
    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");