app_dtmfstore.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2021, Naveen Albert
 *
 * Naveen Albert <[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 Technology independent asynchronous DTMF collection
 *
 * \author Naveen Albert <[email protected]>
 *
 * \ingroup functions
 *
 */

/*** MODULEINFO
   <support_level>extended</support_level>
 ***/

#include "asterisk.h"

#include "asterisk/module.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/framehook.h"
#include "asterisk/app.h"
#include "asterisk/conversions.h"

/*** DOCUMENTATION
   <application name="StoreDTMF" language="en_US">
      <synopsis>
         Stores DTMF digits transmitted or received on a channel.
      </synopsis>
      <syntax>
         <parameter name="direction" required="true">
            <para>Must be <literal>TX</literal> or <literal>RX</literal>.</para>
         </parameter>
      </syntax>
      <description>
         <para>The StoreDTMF function can be used to obtain digits sent in the
         <literal>TX</literal> or <literal>RX</literal> direction of any channel.</para>
         <para>The arguments are:</para>
         <para><replaceable>var_name</replaceable>: Name of variable to which to append
         digits.</para>
         <para><replaceable>max_digits</replaceable>: The maximum number of digits to
         store in the variable. Defaults to 0 (no maximum). After reading <literal>
         maximum</literal> digits, no more digits will be stored.</para>
         <para>For example:</para>
         <para>StoreDTMF(TX,CDR(digits))</para>
         <para>StoreDTMF(RX,testvar,24)</para>
         <para>StoreDTMF(remove)</para>
      </description>
   </application>
 ***/

static char *app = "StoreDTMF";

/*! \brief Private data structure used with the function's datastore */
struct dtmf_store_data {
   int framehook_id;
   char *rx_var;
   char *tx_var;
   int maxdigits;
};

static void datastore_destroy_cb(void *data) {
   struct dtmf_store_data *d;
   d = data;
   if (d) {
      if (d->rx_var) {
         ast_free(d->rx_var);
      }
      if (d->tx_var) {
         ast_free(d->tx_var);
      }
      ast_free(data);
   }
}

/*! \brief The channel datastore the function uses to store state */
static const struct ast_datastore_info dtmf_store_datastore = {
   .type = "dtmf_store",
   .destroy = datastore_destroy_cb
};

/*! \internal \brief Store digits tx/rx on the channel */
static int remove_dtmf_store(struct ast_channel *chan)
{
   struct ast_datastore *datastore = NULL;
   struct dtmf_store_data *data;
   SCOPED_CHANNELLOCK(chan_lock, chan);

   datastore = ast_channel_datastore_find(chan, &dtmf_store_datastore, NULL);
   if (!datastore) {
      ast_log(AST_LOG_WARNING, "Cannot remove StoreDTMF from %s: StoreDTMF not currently enabled\n",
              ast_channel_name(chan));
      return -1;
   }
   data = datastore->data;

   if (ast_framehook_detach(chan, data->framehook_id)) {
      ast_log(AST_LOG_WARNING, "Failed to remove StoreDTMF framehook from channel %s\n",
              ast_channel_name(chan));
      return -1;
   }

   if (ast_channel_datastore_remove(chan, datastore)) {
      ast_log(AST_LOG_WARNING, "Failed to remove StoreDTMF datastore from channel %s\n",
              ast_channel_name(chan));
      return -1;
   }
   ast_datastore_free(datastore);

   return 0;
}

/*! \brief Frame hook that is called to intercept digit/undigit */
static struct ast_frame *dtmf_store_framehook(struct ast_channel *chan,
   struct ast_frame *f, enum ast_framehook_event event, void *data)
{
   char currentdata[512];
   char varnamesub[64];
   char *varname = NULL;
   struct dtmf_store_data *framedata = data;
   int len;

   if (!f || !framedata) {
      return f;
   }

   if ((event != AST_FRAMEHOOK_EVENT_WRITE) && (event != AST_FRAMEHOOK_EVENT_READ)) {
      return f;
   }

   if (f->frametype != AST_FRAME_DTMF_END) {
      return f;
   }

   /* If this is DTMF then store the digits */
   if (event == AST_FRAMEHOOK_EVENT_READ && framedata->rx_var) { /* coming from source */
      varname = framedata->rx_var;
   } else if (event == AST_FRAMEHOOK_EVENT_WRITE && framedata->tx_var) { /* going to source */
      varname = framedata->tx_var;
   }

   if (!varname) {
      return f;
   }

   sprintf(varnamesub, "${%s}", varname);
   pbx_substitute_variables_helper(chan, varnamesub, currentdata, 511);
   /* pbx_builtin_getvar_helper works for regular vars but not CDR vars */
   if (ast_strlen_zero(currentdata)) { /* var doesn't exist yet */
      ast_debug(3, "Creating new digit store: %s\n", varname);
   }
   len = strlen(currentdata);
   if (framedata->maxdigits > 0 && len >= framedata->maxdigits) {
      ast_debug(3, "Reached digit limit: %d\n", framedata->maxdigits);
      remove_dtmf_store(chan); /* reached max digit count, stop now */
      return f;
   } else {
      char newdata[len + 2]; /* one more char + terminator */
      if (len > 0) {
         ast_copy_string(newdata, currentdata, len + 2);
      }
      newdata[len] = (unsigned) f->subclass.integer;
      newdata[len + 1] = '\0';
      ast_debug(3, "Appending to digit store: now %s\n", newdata);
      pbx_builtin_setvar_helper(chan, varname, newdata);
   }
   return f;
}

/*! \internal \brief Enable digit interception on the channel */
static int dtmfstore_exec(struct ast_channel *chan, const char *appdata)
{
   struct ast_datastore *datastore;
   struct dtmf_store_data *data;
   static struct ast_framehook_interface digit_framehook_interface = {
      .version = AST_FRAMEHOOK_INTERFACE_VERSION,
      .event_cb = dtmf_store_framehook,
      .disable_inheritance = 1,
   };
   char *parse = ast_strdupa(appdata);
   AST_DECLARE_APP_ARGS(args,
      AST_APP_ARG(direction);
      AST_APP_ARG(varname);
      AST_APP_ARG(maxdigits);
   );
   SCOPED_CHANNELLOCK(chan_lock, chan);
   AST_STANDARD_APP_ARGS(args, parse);

   if (ast_strlen_zero(appdata)) {
      ast_log(AST_LOG_WARNING, "StoreDTMF requires an argument\n");
      return -1;
   }

   if (!strcasecmp(args.direction, "remove")) {
      return remove_dtmf_store(chan);
   }

   datastore = ast_channel_datastore_find(chan, &dtmf_store_datastore, NULL);
   if (datastore) {
      ast_log(AST_LOG_WARNING, "StoreDTMF already set on '%s'\n",
              ast_channel_name(chan));
      return 0;
   }

   datastore = ast_datastore_alloc(&dtmf_store_datastore, NULL);
   if (!datastore) {
      return -1;
   }

   data = ast_calloc(1, sizeof(*data));
   if (!data) {
      ast_datastore_free(datastore);
      return -1;
   }

   digit_framehook_interface.data = data;

   data->rx_var = NULL;
   data->tx_var = NULL;
   data->maxdigits = 0;

   if (!strcasecmp(args.direction, "tx")) {
      data->tx_var = ast_strdup(args.varname);
   } else if (!strcasecmp(args.direction, "rx")) {
      data->rx_var = ast_strdup(args.varname);
   } else {
      ast_log(LOG_ERROR, "Direction must be either RX or TX\n");
      return -1;
   }

   if (!ast_strlen_zero(args.maxdigits)) {
      if (ast_str_to_int(args.maxdigits,&(data->maxdigits))) {
         ast_log(LOG_ERROR, "Invalid integer: %s\n", args.maxdigits);
         return -1;
      }
      if (data->maxdigits < 0) {
         ast_log(LOG_ERROR, "Invalid natural number: %d\n", data->maxdigits);
         return -1;
      } else if (data->maxdigits == 0) {
         ast_log(LOG_WARNING, "No maximum digit count set\n");
      }
   }

   data->framehook_id = ast_framehook_attach(chan, &digit_framehook_interface);
   if (data->framehook_id < 0) {
      ast_log(AST_LOG_WARNING, "Failed to attach StoreDTMF framehook to '%s'\n",
              ast_channel_name(chan));
      ast_datastore_free(datastore);
      ast_free(data);
      return -1;
   }
   datastore->data = data;

   ast_channel_datastore_add(chan, datastore);

   return 0;
}

static int unload_module(void)
{
   return ast_unregister_application(app);
}

static int load_module(void)
{
   return ast_register_application_xml(app, dtmfstore_exec);
}

AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "Technology independent async DTMF storage");