Thu Apr 28 2011 17:13:29

Asterisk developer's documentation


chan_bridge.c

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 1999 - 2008, Digium, Inc.
00005  *
00006  * Joshua Colp <jcolp@digium.com>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  */
00018 
00019 /*! \file
00020  *
00021  * \author Joshua Colp <jcolp@digium.com>
00022  *
00023  * \brief Bridge Interaction Channel
00024  *
00025  * \ingroup channel_drivers
00026  */
00027 
00028 #include "asterisk.h"
00029 
00030 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 180369 $")
00031 
00032 #include <fcntl.h>
00033 #include <sys/signal.h>
00034 
00035 #include "asterisk/lock.h"
00036 #include "asterisk/channel.h"
00037 #include "asterisk/config.h"
00038 #include "asterisk/module.h"
00039 #include "asterisk/pbx.h"
00040 #include "asterisk/sched.h"
00041 #include "asterisk/io.h"
00042 #include "asterisk/rtp.h"
00043 #include "asterisk/acl.h"
00044 #include "asterisk/callerid.h"
00045 #include "asterisk/file.h"
00046 #include "asterisk/cli.h"
00047 #include "asterisk/app.h"
00048 #include "asterisk/bridging.h"
00049 
00050 static struct ast_channel *bridge_request(const char *type, int format, void *data, int *cause);
00051 static int bridge_call(struct ast_channel *ast, char *dest, int timeout);
00052 static int bridge_hangup(struct ast_channel *ast);
00053 static struct ast_frame *bridge_read(struct ast_channel *ast);
00054 static int bridge_write(struct ast_channel *ast, struct ast_frame *f);
00055 static struct ast_channel *bridge_bridgedchannel(struct ast_channel *chan, struct ast_channel *bridge);
00056 
00057 static const struct ast_channel_tech bridge_tech = {
00058    .type = "Bridge",
00059    .description = "Bridge Interaction Channel",
00060    .capabilities = -1,
00061    .requester = bridge_request,
00062    .call = bridge_call,
00063    .hangup = bridge_hangup,
00064    .read = bridge_read,
00065    .write = bridge_write,
00066    .write_video = bridge_write,
00067    .exception = bridge_read,
00068    .bridged_channel = bridge_bridgedchannel,
00069 };
00070 
00071 struct bridge_pvt {
00072    ast_mutex_t lock;           /*!< Lock that protects this structure */
00073    struct ast_channel *input;  /*!< Input channel - talking to source */
00074    struct ast_channel *output; /*!< Output channel - talking to bridge */
00075 };
00076 
00077 /*! \brief Called when the user of this channel wants to get the actual channel in the bridge */
00078 static struct ast_channel *bridge_bridgedchannel(struct ast_channel *chan, struct ast_channel *bridge)
00079 {
00080    struct bridge_pvt *p = chan->tech_pvt;
00081    return (chan == p->input) ? p->output : bridge;
00082 }
00083 
00084 /*! \brief Called when a frame should be read from the channel */
00085 static struct ast_frame  *bridge_read(struct ast_channel *ast)
00086 {
00087    return &ast_null_frame;
00088 }
00089 
00090 /*! \brief Called when a frame should be written out to a channel */
00091 static int bridge_write(struct ast_channel *ast, struct ast_frame *f)
00092 {
00093    struct bridge_pvt *p = ast->tech_pvt;
00094    struct ast_channel *other;
00095 
00096    ast_mutex_lock(&p->lock);
00097 
00098    other = (p->input == ast ? p->output : p->input);
00099 
00100    while (other && ast_channel_trylock(other)) {
00101       ast_mutex_unlock(&p->lock);
00102       do {
00103          CHANNEL_DEADLOCK_AVOIDANCE(ast);
00104       } while (ast_mutex_trylock(&p->lock));
00105       other = (p->input == ast ? p->output : p->input);
00106    }
00107 
00108    /* We basically queue the frame up on the other channel if present */
00109    if (other) {
00110       ast_queue_frame(other, f);
00111       ast_channel_unlock(other);
00112    }
00113 
00114    ast_mutex_unlock(&p->lock);
00115 
00116    return 0;
00117 }
00118 
00119 /*! \brief Called when the channel should actually be dialed */
00120 static int bridge_call(struct ast_channel *ast, char *dest, int timeout)
00121 {
00122    struct bridge_pvt *p = ast->tech_pvt;
00123 
00124    /* If no bridge has been provided on the input channel, bail out */
00125    if (!ast->bridge) {
00126       return -1;
00127    }
00128 
00129    /* Impart the output channel upon the given bridge of the input channel */
00130    ast_bridge_impart(p->input->bridge, p->output, NULL, NULL);
00131 
00132    return 0;
00133 }
00134 
00135 /*! \brief Helper function to not deadlock when queueing the hangup frame */
00136 static void bridge_queue_hangup(struct bridge_pvt *p, struct ast_channel *us)
00137 {
00138    struct ast_channel *other = (p->input == us ? p->output : p->input);
00139 
00140    while (other && ast_channel_trylock(other)) {
00141       ast_mutex_unlock(&p->lock);
00142       do {
00143          CHANNEL_DEADLOCK_AVOIDANCE(us);
00144       } while (ast_mutex_trylock(&p->lock));
00145       other = (p->input == us ? p->output : p->input);
00146    }
00147 
00148    /* We basically queue the frame up on the other channel if present */
00149    if (other) {
00150       ast_queue_hangup(other);
00151       ast_channel_unlock(other);
00152    }
00153 
00154    return;
00155 }
00156 
00157 /*! \brief Called when a channel should be hung up */
00158 static int bridge_hangup(struct ast_channel *ast)
00159 {
00160    struct bridge_pvt *p = ast->tech_pvt;
00161 
00162    ast_mutex_lock(&p->lock);
00163 
00164    /* Figure out which channel this is... and set it to NULL as it has gone, but also queue up a hangup frame. */
00165    if (p->input == ast) {
00166       if (p->output) {
00167          bridge_queue_hangup(p, ast);
00168       }
00169       p->input = NULL;
00170    } else if (p->output == ast) {
00171       if (p->input) {
00172          bridge_queue_hangup(p, ast);
00173       }
00174       p->output = NULL;
00175    }
00176 
00177    /* Deal with the Asterisk portion of it */
00178    ast->tech_pvt = NULL;
00179 
00180    /* If both sides have been terminated free the structure and be done with things */
00181    if (!p->input && !p->output) {
00182       ast_mutex_unlock(&p->lock);
00183       ast_mutex_destroy(&p->lock);
00184       ast_free(p);
00185    } else {
00186       ast_mutex_unlock(&p->lock);
00187    }
00188 
00189    return 0;
00190 }
00191 
00192 /*! \brief Called when we want to place a call somewhere, but not actually call it... yet */
00193 static struct ast_channel *bridge_request(const char *type, int format, void *data, int *cause)
00194 {
00195    struct bridge_pvt *p = NULL;
00196 
00197    /* Try to allocate memory for our very minimal pvt structure */
00198    if (!(p = ast_calloc(1, sizeof(*p)))) {
00199       return NULL;
00200    }
00201 
00202    /* Try to grab two Asterisk channels to use as input and output channels */
00203    if (!(p->input = ast_channel_alloc(1, AST_STATE_UP, 0, 0, "", "", "", 0, "Bridge/%p-input", p))) {
00204       ast_free(p);
00205       return NULL;
00206    }
00207    if (!(p->output = ast_channel_alloc(1, AST_STATE_UP, 0, 0, "", "", "", 0, "Bridge/%p-output", p))) {
00208       ast_channel_free(p->input);
00209       ast_free(p);
00210       return NULL;
00211    }
00212 
00213    /* Setup the lock on the pvt structure, we will need that */
00214    ast_mutex_init(&p->lock);
00215 
00216    /* Setup parameters on both new channels */
00217    p->input->tech = p->output->tech = &bridge_tech;
00218    p->input->tech_pvt = p->output->tech_pvt = p;
00219    p->input->nativeformats = p->output->nativeformats = AST_FORMAT_SLINEAR;
00220    p->input->readformat = p->output->readformat = AST_FORMAT_SLINEAR;
00221    p->input->rawreadformat = p->output->rawreadformat = AST_FORMAT_SLINEAR;
00222    p->input->writeformat = p->output->writeformat = AST_FORMAT_SLINEAR;
00223    p->input->rawwriteformat = p->output->rawwriteformat = AST_FORMAT_SLINEAR;
00224 
00225    return p->input;
00226 }
00227 
00228 /*! \brief Load module into PBX, register channel */
00229 static int load_module(void)
00230 {
00231    /* Make sure we can register our channel type */
00232    if (ast_channel_register(&bridge_tech)) {
00233       ast_log(LOG_ERROR, "Unable to register channel class 'Bridge'\n");
00234       return AST_MODULE_LOAD_FAILURE;
00235    }
00236    return AST_MODULE_LOAD_SUCCESS;
00237 }
00238 
00239 /*! \brief Unload the bridge interaction channel from Asterisk */
00240 static int unload_module(void)
00241 {
00242    ast_channel_unregister(&bridge_tech);
00243    return 0;
00244 }
00245 
00246 AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Bridge Interaction Channel");