func_channel.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2006, Digium, Inc.
 *
 * 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 Channel info dialplan functions
 *
 * \author Kevin P. Fleming <kpfleming@digium.com>
 * \author Ben Winslow
 * 
 * \ingroup functions
 */

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

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 361476 $")

#include <regex.h>
#include <ctype.h>

#include "asterisk/module.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/utils.h"
#include "asterisk/app.h"
#include "asterisk/indications.h"
#include "asterisk/stringfields.h"
#include "asterisk/global_datastores.h"

/*** DOCUMENTATION
   <function name="CHANNELS" language="en_US">
      <synopsis>
         Gets the list of channels, optionally filtering by a regular expression.
      </synopsis>
      <syntax>
         <parameter name="regular_expression" />
      </syntax>
      <description>
         <para>Gets the list of channels, optionally filtering by a <replaceable>regular_expression</replaceable>. If
         no argument is provided, all known channels are returned. The
         <replaceable>regular_expression</replaceable> must correspond to
         the POSIX.2 specification, as shown in <emphasis>regex(7)</emphasis>. The list returned
         will be space-delimited.</para>
      </description>
   </function>
   <function name="MASTER_CHANNEL" language="en_US">
      <synopsis>
         Gets or sets variables on the master channel
      </synopsis>
      <description>
         <para>Allows access to the channel which created the current channel, if any.  If the channel is already
         a master channel, then accesses local channel variables.</para>
      </description>
   </function>
   <function name="CHANNEL" language="en_US">
      <synopsis>
         Gets/sets various pieces of information about the channel.
      </synopsis>
      <syntax>
         <parameter name="item" required="true">
            <para>Standard items (provided by all channel technologies) are:</para>
            <enumlist>
               <enum name="audioreadformat">
                  <para>R/O format currently being read.</para>
               </enum>
               <enum name="audionativeformat">
                  <para>R/O format used natively for audio.</para>
               </enum>
               <enum name="audiowriteformat">
                  <para>R/O format currently being written.</para>
               </enum>
               <enum name="callgroup">
                  <para>R/W call groups for call pickup.</para>
               </enum>
               <enum name="pickupgroup">
                  <para>R/W call groups for call pickup.</para>
               </enum>
               <enum name="channeltype">
                  <para>R/O technology used for channel.</para>
               </enum>
               <enum name="checkhangup">
                  <para>R/O Whether the channel is hanging up (1/0)</para>
               </enum>
               <enum name="language">
                  <para>R/W language for sounds played.</para>
               </enum>
               <enum name="musicclass">
                  <para>R/W class (from musiconhold.conf) for hold music.</para>
               </enum>
               <enum name="name">
                  <para>The name of the channel</para>
               </enum>
               <enum name="parkinglot">
                  <para>R/W parkinglot for parking.</para>
               </enum>
               <enum name="rxgain">
                  <para>R/W set rxgain level on channel drivers that support it.</para>
               </enum>
               <enum name="secure_bridge_signaling">
                  <para>Whether or not channels bridged to this channel require secure signaling</para>
               </enum>
               <enum name="secure_bridge_media">
                  <para>Whether or not channels bridged to this channel require secure media</para>
               </enum>
               <enum name="state">
                  <para>R/O state for channel</para>
               </enum>
               <enum name="tonezone">
                  <para>R/W zone for indications played</para>
               </enum>
               <enum name="transfercapability">
                  <para>R/W ISDN Transfer Capability, one of:</para>
                  <enumlist>
                     <enum name="SPEECH" />
                     <enum name="DIGITAL" />
                     <enum name="RESTRICTED_DIGITAL" />
                     <enum name="3K1AUDIO" />
                     <enum name="DIGITAL_W_TONES" />
                     <enum name="VIDEO" />
                  </enumlist>
               </enum>
               <enum name="txgain">
                  <para>R/W set txgain level on channel drivers that support it.</para>
               </enum>
               <enum name="videonativeformat">
                  <para>R/O format used natively for video</para>
               </enum>
               <enum name="trace">
                  <para>R/W whether or not context tracing is enabled, only available
                  <emphasis>if CHANNEL_TRACE is defined</emphasis>.</para>
               </enum>
            </enumlist>
            <para><emphasis>chan_sip</emphasis> provides the following additional options:</para>
            <enumlist>
               <enum name="peerip">
                  <para>R/O Get the IP address of the peer.</para>
               </enum>
               <enum name="recvip">
                  <para>R/O Get the source IP address of the peer.</para>
               </enum>
               <enum name="from">
                  <para>R/O Get the URI from the From: header.</para>
               </enum>
               <enum name="uri">
                  <para>R/O Get the URI from the Contact: header.</para>
               </enum>
               <enum name="useragent">
                  <para>R/O Get the useragent.</para>
               </enum>
               <enum name="peername">
                  <para>R/O Get the name of the peer.</para>
               </enum>
               <enum name="t38passthrough">
                  <para>R/O <literal>1</literal> if T38 is offered or enabled in this channel,
                  otherwise <literal>0</literal></para>
               </enum>
               <enum name="rtpqos">
                  <para>R/O Get QOS information about the RTP stream</para>
                  <para>    This option takes two additional arguments:</para>
                  <para>    Argument 1:</para>
                  <para>     <literal>audio</literal>             Get data about the audio stream</para>
                  <para>     <literal>video</literal>             Get data about the video stream</para>
                  <para>     <literal>text</literal>              Get data about the text stream</para>
                  <para>    Argument 2:</para>
                  <para>     <literal>local_ssrc</literal>        Local SSRC (stream ID)</para>
                  <para>     <literal>local_lostpackets</literal> Local lost packets</para>
                  <para>     <literal>local_jitter</literal>      Local calculated jitter</para>
                  <para>     <literal>local_maxjitter</literal>   Local calculated jitter (maximum)</para>
                  <para>     <literal>local_minjitter</literal>   Local calculated jitter (minimum)</para>
                  <para>     <literal>local_normdevjitter</literal>Local calculated jitter (normal deviation)</para>
                  <para>     <literal>local_stdevjitter</literal> Local calculated jitter (standard deviation)</para>
                  <para>     <literal>local_count</literal>       Number of received packets</para>
                  <para>     <literal>remote_ssrc</literal>       Remote SSRC (stream ID)</para>
                  <para>     <literal>remote_lostpackets</literal>Remote lost packets</para>
                  <para>     <literal>remote_jitter</literal>     Remote reported jitter</para>
                  <para>     <literal>remote_maxjitter</literal>  Remote calculated jitter (maximum)</para>
                  <para>     <literal>remote_minjitter</literal>  Remote calculated jitter (minimum)</para>
                  <para>     <literal>remote_normdevjitter</literal>Remote calculated jitter (normal deviation)</para>
                  <para>     <literal>remote_stdevjitter</literal>Remote calculated jitter (standard deviation)</para>
                  <para>     <literal>remote_count</literal>      Number of transmitted packets</para>
                  <para>     <literal>rtt</literal>               Round trip time</para>
                  <para>     <literal>maxrtt</literal>            Round trip time (maximum)</para>
                  <para>     <literal>minrtt</literal>            Round trip time (minimum)</para>
                  <para>     <literal>normdevrtt</literal>        Round trip time (normal deviation)</para>
                  <para>     <literal>stdevrtt</literal>          Round trip time (standard deviation)</para>
                  <para>     <literal>all</literal>               All statistics (in a form suited to logging,
                  but not for parsing)</para>
               </enum>
               <enum name="rtpdest">
                  <para>R/O Get remote RTP destination information.</para>
                  <para>   This option takes one additional argument:</para>
                  <para>    Argument 1:</para>
                  <para>     <literal>audio</literal>             Get audio destination</para>
                  <para>     <literal>video</literal>             Get video destination</para>
                  <para>     <literal>text</literal>              Get text destination</para>
               </enum>
            </enumlist>
            <para><emphasis>chan_iax2</emphasis> provides the following additional options:</para>
            <enumlist>
               <enum name="peerip">
                  <para>R/O Get the peer's ip address.</para>
               </enum>
               <enum name="peername">
                  <para>R/O Get the peer's username.</para>
               </enum>
            </enumlist>
            <para><emphasis>chan_dahdi</emphasis> provides the following additional options:</para>
            <enumlist>
               <enum name="dahdi_channel">
                  <para>R/O DAHDI channel related to this channel.</para>
               </enum>
               <enum name="dahdi_span">
                  <para>R/O DAHDI span related to this channel.</para>
               </enum>
               <enum name="dahdi_type">
                  <para>R/O DAHDI channel type, one of:</para>
                  <enumlist>
                     <enum name="analog" />
                     <enum name="mfc/r2" />
                     <enum name="pri" />
                     <enum name="pseudo" />
                     <enum name="ss7" />
                  </enumlist>
               </enum>
               <enum name="keypad_digits">
                  <para>R/O PRI Keypad digits that came in with the SETUP message.</para>
               </enum>
               <enum name="reversecharge">
                  <para>R/O PRI Reverse Charging Indication, one of:</para>
                  <enumlist>
                     <enum name="-1"> <para>None</para></enum>
                     <enum name=" 1"> <para>Reverse Charging Requested</para></enum>
                  </enumlist>
               </enum>
               <enum name="no_media_path">
                  <para>R/O PRI Nonzero if the channel has no B channel.
                  The channel is either on hold or a call waiting call.</para>
               </enum>
            </enumlist>
            <para><emphasis>chan_ooh323</emphasis> provides the following additional options:</para>
            <enumlist>
               <enum name="faxdetect">
                  <para>Fax Detect [R/W]</para>
                  <para>Returns 0 or 1</para>
                  <para>Write yes or no</para>
               </enum>
               <enum name="t38support">
                  <para>t38support [R/W]</para>
                  <para>Returns 0 or 1</para>
                  <para>Write yes or no</para>
               </enum>
               <enum name="h323id">
                  <para>Returns h323id [R]</para>
               </enum>
            </enumlist>
         </parameter>
      </syntax>
      <description>
         <para>Gets/sets various pieces of information about the channel, additional <replaceable>item</replaceable> may
         be available from the channel driver; see its documentation for details. Any <replaceable>item</replaceable>
         requested that is not available on the current channel will return an empty string.</para>
      </description>
   </function>
 ***/

#define locked_copy_string(chan, dest, source, len) \
   do { \
      ast_channel_lock(chan); \
      ast_copy_string(dest, source, len); \
      ast_channel_unlock(chan); \
   } while (0)
#define locked_string_field_set(chan, field, source) \
   do { \
      ast_channel_lock(chan); \
      ast_channel_##field##_set(chan, source); \
      ast_channel_unlock(chan); \
   } while (0)

static const char * const transfercapability_table[0x20] = {
   "SPEECH", "UNK", "UNK", "UNK", "UNK", "UNK", "UNK", "UNK",
   "DIGITAL", "RESTRICTED_DIGITAL", "UNK", "UNK", "UNK", "UNK", "UNK", "UNK",
   "3K1AUDIO", "DIGITAL_W_TONES", "UNK", "UNK", "UNK", "UNK", "UNK", "UNK",
   "VIDEO", "UNK", "UNK", "UNK", "UNK", "UNK", "UNK", "UNK", };

static int func_channel_read(struct ast_channel *chan, const char *function,
              char *data, char *buf, size_t len)
{
   int ret = 0;
   char tmp[512];
   struct ast_format_cap *tmpcap;

   if (!strcasecmp(data, "audionativeformat")) {
      if ((tmpcap = ast_format_cap_get_type(ast_channel_nativeformats(chan), AST_FORMAT_TYPE_AUDIO))) {
         ast_copy_string(buf, ast_getformatname_multiple(tmp, sizeof(tmp), tmpcap), len);
         tmpcap = ast_format_cap_destroy(tmpcap);
      }
   } else if (!strcasecmp(data, "videonativeformat")) {
      if ((tmpcap = ast_format_cap_get_type(ast_channel_nativeformats(chan), AST_FORMAT_TYPE_VIDEO))) {
         ast_copy_string(buf, ast_getformatname_multiple(tmp, sizeof(tmp), tmpcap), len);
         tmpcap = ast_format_cap_destroy(tmpcap);
      }
   } else if (!strcasecmp(data, "audioreadformat")) {
      ast_copy_string(buf, ast_getformatname(ast_channel_readformat(chan)), len);
   } else if (!strcasecmp(data, "audiowriteformat")) {
      ast_copy_string(buf, ast_getformatname(ast_channel_writeformat(chan)), len);
#ifdef CHANNEL_TRACE
   } else if (!strcasecmp(data, "trace")) {
      ast_channel_lock(chan);
      ast_copy_string(buf, ast_channel_trace_is_enabled(chan) ? "1" : "0", len);
      ast_channel_unlock(chan);
#endif
   } else if (!strcasecmp(data, "tonezone") && ast_channel_zone(chan))
      locked_copy_string(chan, buf, ast_channel_zone(chan)->country, len);
   else if (!strcasecmp(data, "language"))
      locked_copy_string(chan, buf, ast_channel_language(chan), len);
   else if (!strcasecmp(data, "musicclass"))
      locked_copy_string(chan, buf, ast_channel_musicclass(chan), len);
   else if (!strcasecmp(data, "name")) {
      locked_copy_string(chan, buf, ast_channel_name(chan), len);
   } else if (!strcasecmp(data, "parkinglot"))
      locked_copy_string(chan, buf, ast_channel_parkinglot(chan), len);
   else if (!strcasecmp(data, "state"))
      locked_copy_string(chan, buf, ast_state2str(ast_channel_state(chan)), len);
   else if (!strcasecmp(data, "channeltype"))
      locked_copy_string(chan, buf, ast_channel_tech(chan)->type, len);
   else if (!strcasecmp(data, "accountcode"))
      locked_copy_string(chan, buf, ast_channel_accountcode(chan), len);
   else if (!strcasecmp(data, "checkhangup")) {
      ast_channel_lock(chan);
      ast_copy_string(buf, ast_check_hangup(chan) ? "1" : "0", len);
      ast_channel_unlock(chan);
   } else if (!strcasecmp(data, "peeraccount"))
      locked_copy_string(chan, buf, ast_channel_peeraccount(chan), len);
   else if (!strcasecmp(data, "hangupsource"))
      locked_copy_string(chan, buf, ast_channel_hangupsource(chan), len);
   else if (!strcasecmp(data, "appname") && ast_channel_appl(chan))
      locked_copy_string(chan, buf, ast_channel_appl(chan), len);
   else if (!strcasecmp(data, "appdata") && ast_channel_data(chan))
      locked_copy_string(chan, buf, ast_channel_data(chan), len);
   else if (!strcasecmp(data, "exten") && ast_channel_data(chan))
      locked_copy_string(chan, buf, ast_channel_exten(chan), len);
   else if (!strcasecmp(data, "context") && ast_channel_data(chan))
      locked_copy_string(chan, buf, ast_channel_context(chan), len);
   else if (!strcasecmp(data, "userfield") && ast_channel_data(chan))
      locked_copy_string(chan, buf, ast_channel_userfield(chan), len);
   else if (!strcasecmp(data, "channame") && ast_channel_data(chan))
      locked_copy_string(chan, buf, ast_channel_name(chan), len);
   else if (!strcasecmp(data, "linkedid")) {
      ast_channel_lock(chan);
      if (ast_strlen_zero(ast_channel_linkedid(chan))) {
         /* fall back on the channel's uniqueid if linkedid is unset */
         ast_copy_string(buf, ast_channel_uniqueid(chan), len);
      }
      else {
         ast_copy_string(buf, ast_channel_linkedid(chan), len);
      }
      ast_channel_unlock(chan);
   } else if (!strcasecmp(data, "peer")) {
      struct ast_channel *p;
      ast_channel_lock(chan);
      p = ast_bridged_channel(chan);
      if (p || ast_channel_tech(chan) || ast_channel_cdr(chan)) /* dummy channel? if so, we hid the peer name in the language */
         ast_copy_string(buf, (p ? ast_channel_name(p) : ""), len);
      else {
         /* a dummy channel can still pass along bridged peer info via
                           the BRIDGEPEER variable */
         const char *pname = pbx_builtin_getvar_helper(chan, "BRIDGEPEER");
         if (!ast_strlen_zero(pname))
            ast_copy_string(buf, pname, len); /* a horrible kludge, but... how else? */
         else
            buf[0] = 0;
      }
      ast_channel_unlock(chan);
   } else if (!strcasecmp(data, "uniqueid")) {
      locked_copy_string(chan, buf, ast_channel_uniqueid(chan), len);
   } else if (!strcasecmp(data, "transfercapability")) {
      locked_copy_string(chan, buf, transfercapability_table[ast_channel_transfercapability(chan) & 0x1f], len);
   } else if (!strcasecmp(data, "callgroup")) {
      char groupbuf[256];
      locked_copy_string(chan, buf,  ast_print_group(groupbuf, sizeof(groupbuf), ast_channel_callgroup(chan)), len);
   } else if (!strcasecmp(data, "pickupgroup")) {
      char groupbuf[256];
      locked_copy_string(chan, buf,  ast_print_group(groupbuf, sizeof(groupbuf), ast_channel_pickupgroup(chan)), len);
   } else if (!strcasecmp(data, "amaflags")) {
      char amabuf[256];
      snprintf(amabuf,sizeof(amabuf), "%d", ast_channel_amaflags(chan));
      locked_copy_string(chan, buf, amabuf, len);
   } else if (!strncasecmp(data, "secure_bridge_", 14)) {
      struct ast_datastore *ds;
      ast_channel_lock(chan);
      if ((ds = ast_channel_datastore_find(chan, &secure_call_info, NULL))) {
         struct ast_secure_call_store *encrypt = ds->data;
         if (!strcasecmp(data, "secure_bridge_signaling")) {
            snprintf(buf, len, "%s", encrypt->signaling ? "1" : "");
         } else if (!strcasecmp(data, "secure_bridge_media")) {
            snprintf(buf, len, "%s", encrypt->media ? "1" : "");
         }
      }
      ast_channel_unlock(chan);
   } else if (!ast_channel_tech(chan) || !ast_channel_tech(chan)->func_channel_read || ast_channel_tech(chan)->func_channel_read(chan, function, data, buf, len)) {
      ast_log(LOG_WARNING, "Unknown or unavailable item requested: '%s'\n", data);
      ret = -1;
   }

   return ret;
}

static int func_channel_write_real(struct ast_channel *chan, const char *function,
               char *data, const char *value)
{
   int ret = 0;
   signed char gainset;

   if (!strcasecmp(data, "language"))
      locked_string_field_set(chan, language, value);
   else if (!strcasecmp(data, "parkinglot"))
      locked_string_field_set(chan, parkinglot, value);
   else if (!strcasecmp(data, "musicclass"))
      locked_string_field_set(chan, musicclass, value);
   else if (!strcasecmp(data, "accountcode"))
      locked_string_field_set(chan, accountcode, value);
   else if (!strcasecmp(data, "userfield"))
      locked_string_field_set(chan, userfield, value);
   else if (!strcasecmp(data, "amaflags")) {
      ast_channel_lock(chan);
      if(isdigit(*value)) {
         int amaflags;
         sscanf(value, "%30d", &amaflags);
         ast_channel_amaflags_set(chan, amaflags);
      } else if (!strcasecmp(value,"OMIT")){
         ast_channel_amaflags_set(chan, 1);
      } else if (!strcasecmp(value,"BILLING")){
         ast_channel_amaflags_set(chan, 2);
      } else if (!strcasecmp(value,"DOCUMENTATION")){
         ast_channel_amaflags_set(chan, 3);
      }
      ast_channel_unlock(chan);
   } else if (!strcasecmp(data, "peeraccount"))
      locked_string_field_set(chan, peeraccount, value);
   else if (!strcasecmp(data, "hangupsource"))
      /* XXX - should we be forcing this here? */
      ast_set_hangupsource(chan, value, 0);
#ifdef CHANNEL_TRACE
   else if (!strcasecmp(data, "trace")) {
      ast_channel_lock(chan);
      if (ast_true(value)) 
         ret = ast_channel_trace_enable(chan);
      else if (ast_false(value))
         ret = ast_channel_trace_disable(chan);
      else {
         ret = -1;
         ast_log(LOG_WARNING, "Invalid value for CHANNEL(trace).\n");
      }
      ast_channel_unlock(chan);
   }
#endif
   else if (!strcasecmp(data, "tonezone")) {
      struct ast_tone_zone *new_zone;
      if (!(new_zone = ast_get_indication_zone(value))) {
         ast_log(LOG_ERROR, "Unknown country code '%s' for tonezone. Check indications.conf for available country codes.\n", value);
         ret = -1;   
      } else {
         ast_channel_lock(chan);
         if (ast_channel_zone(chan)) {
            ast_channel_zone_set(chan, ast_tone_zone_unref(ast_channel_zone(chan)));
         }
         ast_channel_zone_set(chan, ast_tone_zone_ref(new_zone));
         ast_channel_unlock(chan);
         new_zone = ast_tone_zone_unref(new_zone);
      }
   } else if (!strcasecmp(data, "callgroup")) {
      ast_channel_callgroup_set(chan, ast_get_group(value));
   } else if (!strcasecmp(data, "pickupgroup")) {
      ast_channel_pickupgroup_set(chan, ast_get_group(value));
   } else if (!strcasecmp(data, "txgain")) {
      sscanf(value, "%4hhd", &gainset);
      ast_channel_setoption(chan, AST_OPTION_TXGAIN, &gainset, sizeof(gainset), 0);
   } else if (!strcasecmp(data, "rxgain")) {
      sscanf(value, "%4hhd", &gainset);
      ast_channel_setoption(chan, AST_OPTION_RXGAIN, &gainset, sizeof(gainset), 0);
   } else if (!strcasecmp(data, "transfercapability")) {
      unsigned short i;
      for (i = 0; i < 0x20; i++) {
         if (!strcasecmp(transfercapability_table[i], value) && strcmp(value, "UNK")) {
            ast_channel_transfercapability_set(chan, i);
            break;
         }
      }
   } else if (!strncasecmp(data, "secure_bridge_", 14)) {
      struct ast_datastore *ds;
      struct ast_secure_call_store *store;

      if (!chan || !value) {
         return -1;
      }

      ast_channel_lock(chan);
      if (!(ds = ast_channel_datastore_find(chan, &secure_call_info, NULL))) {
         if (!(ds = ast_datastore_alloc(&secure_call_info, NULL))) {
            ast_channel_unlock(chan);
            return -1;
         }
         if (!(store = ast_calloc(1, sizeof(*store)))) {
            ast_channel_unlock(chan);
            ast_free(ds);
            return -1;
         }
         ds->data = store;
         ast_channel_datastore_add(chan, ds);
      } else {
         store = ds->data;
      }
      ast_channel_unlock(chan);

      if (!strcasecmp(data, "secure_bridge_signaling")) {
         store->signaling = ast_true(value) ? 1 : 0;
      } else if (!strcasecmp(data, "secure_bridge_media")) {
         store->media = ast_true(value) ? 1 : 0;
      }
   } else if (!ast_channel_tech(chan)->func_channel_write
       || ast_channel_tech(chan)->func_channel_write(chan, function, data, value)) {
      ast_log(LOG_WARNING, "Unknown or unavailable item requested: '%s'\n",
            data);
      ret = -1;
   }

   return ret;
}

static int func_channel_write(struct ast_channel *chan, const char *function, char *data, const char *value)
{
   int res;
   ast_chan_write_info_t write_info = {
      .version = AST_CHAN_WRITE_INFO_T_VERSION,
      .write_fn = func_channel_write_real,
      .chan = chan,
      .function = function,
      .data = data,
      .value = value,
   };

   res = func_channel_write_real(chan, function, data, value);
   ast_channel_setoption(chan, AST_OPTION_CHANNEL_WRITE, &write_info, sizeof(write_info), 0);

   return res;
}

static struct ast_custom_function channel_function = {
   .name = "CHANNEL",
   .read = func_channel_read,
   .write = func_channel_write,
};

static int func_channels_read(struct ast_channel *chan, const char *function, char *data, char *buf, size_t maxlen)
{
   struct ast_channel *c = NULL;
   regex_t re;
   int res;
   size_t buflen = 0;
   struct ast_channel_iterator *iter;

   buf[0] = '\0';

   if (!ast_strlen_zero(data)) {
      if ((res = regcomp(&re, data, REG_EXTENDED | REG_ICASE | REG_NOSUB))) {
         regerror(res, &re, buf, maxlen);
         ast_log(LOG_WARNING, "Error compiling regular expression for %s(%s): %s\n", function, data, buf);
         return -1;
      }
   }

   if (!(iter = ast_channel_iterator_all_new())) {
      if (!ast_strlen_zero(data)) {
         regfree(&re);
      }
      return -1;
   }

   while ((c = ast_channel_iterator_next(iter))) {
      ast_channel_lock(c);
      if (ast_strlen_zero(data) || regexec(&re, ast_channel_name(c), 0, NULL, 0) == 0) {
         size_t namelen = strlen(ast_channel_name(c));
         if (buflen + namelen + (ast_strlen_zero(buf) ? 0 : 1) + 1 < maxlen) {
            if (!ast_strlen_zero(buf)) {
               strcat(buf, " ");
               buflen++;
            }
            strcat(buf, ast_channel_name(c));
            buflen += namelen;
         } else {
            ast_log(LOG_WARNING, "Number of channels exceeds the available buffer space.  Output will be truncated!\n");
         }
      }
      ast_channel_unlock(c);
      c = ast_channel_unref(c);
   }

   ast_channel_iterator_destroy(iter);

   if (!ast_strlen_zero(data)) {
      regfree(&re);
   }

   return 0;
}

static struct ast_custom_function channels_function = {
   .name = "CHANNELS",
   .read = func_channels_read,
};

static int func_mchan_read(struct ast_channel *chan, const char *function,
              char *data, struct ast_str **buf, ssize_t len)
{
   struct ast_channel *mchan = ast_channel_get_by_name(ast_channel_linkedid(chan));
   char *template = alloca(4 + strlen(data));
   sprintf(template, "${%s}", data); /* SAFE */
   ast_str_substitute_variables(buf, len, mchan ? mchan : chan, template);
   if (mchan) {
      ast_channel_unref(mchan);
   }
   return 0;
}

static int func_mchan_write(struct ast_channel *chan, const char *function,
               char *data, const char *value)
{
   struct ast_channel *mchan = ast_channel_get_by_name(ast_channel_linkedid(chan));
   pbx_builtin_setvar_helper(mchan ? mchan : chan, data, value);
   if (mchan) {
      ast_channel_unref(mchan);
   }
   return 0;
}

static struct ast_custom_function mchan_function = {
   .name = "MASTER_CHANNEL",
   .read2 = func_mchan_read,
   .write = func_mchan_write,
};

static int unload_module(void)
{
   int res = 0;

   res |= ast_custom_function_unregister(&channel_function);
   res |= ast_custom_function_unregister(&channels_function);
   res |= ast_custom_function_unregister(&mchan_function);

   return res;
}

static int load_module(void)
{
   int res = 0;

   res |= ast_custom_function_register(&channel_function);
   res |= ast_custom_function_register(&channels_function);
   res |= ast_custom_function_register(&mchan_function);

   return res;
}

AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Channel information dialplan functions");