func_frame_drop.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 Function that drops specified frames from channels
 *
 * \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"

/*** DOCUMENTATION
   <function name="FRAME_DROP" language="en_US">
      <synopsis>
         Drops specific frame types in the TX or RX direction on a channel.
      </synopsis>
      <syntax>
         <parameter name="direction" required="true">
            <para>List of frame types to be dropped for the specified direction. Direction can be <literal>TX</literal> or <literal>RX</literal>. The <literal>TX</literal> direction will prevent Asterisk from sending frames to a channel, and the <literal>RX</literal> direction will prevent Asterisk from receiving frames from a channel.</para>
            <para>Subsequent calls to this function will replace previous settings, allowing certain frames to be dropped only temporarily, for instance.</para>
            <para>Below are the different types of frames that can be dropped. Other actions may need to be taken in conjunction with use of this function:
            for instance, if you drop ANSWER control frames, you should explicitly use <literal>Progress()</literal> for your call or undesired behavior
            may occur.</para>
            <enumlist>
               <enum name = "DTMF_BEGIN" />
               <enum name = "DTMF_END" />
               <enum name = "VOICE" />
               <enum name = "VIDEO" />
               <enum name = "CONTROL" />
               <enum name = "NULL" />
               <enum name = "IAX" />
               <enum name = "TEXT" />
               <enum name = "TEXT_DATA" />
               <enum name = "IMAGE" />
               <enum name = "HTML" />
               <enum name = "CNG" />
               <enum name = "MODEM" />
            </enumlist>
            <para>The following CONTROL frames can also be dropped:</para>
            <enumlist>
               <enum name = "RING" />
               <enum name = "RINGING" />
               <enum name = "ANSWER" />
               <enum name = "BUSY" />
               <enum name = "TAKEOFFHOOK" />
               <enum name = "OFFHOOK" />
               <enum name = "CONGESTION" />
               <enum name = "FLASH" />
               <enum name = "WINK" />
               <enum name = "PROGRESS" />
               <enum name = "PROCEEDING" />
               <enum name = "HOLD" />
               <enum name = "UNHOLD" />
               <enum name = "VIDUPDATE" />
               <enum name = "CONNECTED_LINE" />
               <enum name = "REDIRECTING" />
            </enumlist>
         </parameter>
      </syntax>
      <description>
         <para>Examples:</para>
         <para>exten => 1,1,Set(FRAME_DROP(TX)=DTMF_BEGIN,DTMF_END); drop only DTMF frames towards this channel.</para>
         <para>exten => 1,1,Set(FRAME_DROP(TX)=ANSWER); drop only ANSWER CONTROL frames towards this channel.</para>
         <para>exten => 1,1,Set(FRAME_DROP(RX)=DTMF_BEGIN,DTMF_END); drop only DTMF frames received on this channel.</para>
      </description>
   </function>
 ***/

static struct {
   enum ast_frame_type type;
   const char *str;
} frametype2str[] = {
   { AST_FRAME_DTMF_BEGIN,   ",DTMF_BEGIN," },
   { AST_FRAME_DTMF_END,   ",DTMF_END," },
   { AST_FRAME_VOICE,   ",VOICE," },
   { AST_FRAME_VIDEO,   ",VIDEO," },
   { AST_FRAME_CONTROL,   ",CONTROL," },
   { AST_FRAME_NULL,   ",NULL," },
   { AST_FRAME_IAX,   ",IAX," },
   { AST_FRAME_TEXT,   ",TEXT," },
   { AST_FRAME_TEXT_DATA,   ",TEXT_DATA," },
   { AST_FRAME_IMAGE,   ",IMAGE," },
   { AST_FRAME_HTML,   ",HTML," },
   { AST_FRAME_CNG,   ",CNG," },
   { AST_FRAME_MODEM,   ",MODEM," },
};

static struct {
   int type;
   const char *str;
} controlframetype2str[] = {
   { AST_CONTROL_RING,   ",RING," },
   { AST_CONTROL_RINGING,   ",RINGING," },
   { AST_CONTROL_ANSWER,   ",ANSWER," },
   { AST_CONTROL_BUSY,   ",BUSY," },
   { AST_CONTROL_TAKEOFFHOOK,   ",TAKEOFFHOOK," },
   { AST_CONTROL_OFFHOOK,   ",OFFHOOK," },
   { AST_CONTROL_CONGESTION,   ",CONGESTION," },
   { AST_CONTROL_FLASH,   ",FLASH," },
   { AST_CONTROL_WINK,   ",WINK," },
   { AST_CONTROL_PROGRESS,   ",PROGRESS," },
   { AST_CONTROL_PROCEEDING,   ",PROCEEDING," },
   { AST_CONTROL_HOLD,   ",HOLD," },
   { AST_CONTROL_UNHOLD,   ",UNHOLD," },
   { AST_CONTROL_VIDUPDATE,   ",VIDUPDATE," },
   { AST_CONTROL_CONNECTED_LINE,   ",CONNECTED_LINE," },
   { AST_CONTROL_REDIRECTING,   ",REDIRECTING," },
};

enum direction {
    TX = 0,
    RX,
};

struct frame_drop_data {
   enum direction list_type;
   int values[ARRAY_LEN(frametype2str)];
   int controlvalues[ARRAY_LEN(controlframetype2str)];
};

static void datastore_destroy_cb(void *data) {
   ast_free(data);
}

static const struct ast_datastore_info frame_drop_datastore = {
   .type = "framedrop",
   .destroy = datastore_destroy_cb
};

static void hook_destroy_cb(void *framedata)
{
   ast_free(framedata);
}

static struct ast_frame *hook_event_cb(struct ast_channel *chan, struct ast_frame *frame, enum ast_framehook_event event, void *data)
{
   int i;
   int drop_frame = 0;
   struct frame_drop_data *framedata = data;
   if (!frame) {
      return frame;
   }

   if (!((event == AST_FRAMEHOOK_EVENT_WRITE && framedata->list_type == TX) ||
      (event == AST_FRAMEHOOK_EVENT_READ && framedata->list_type == RX))) {
      return frame;
   }

   if (frame->frametype == AST_FRAME_CONTROL) {
      for (i = 0; i < ARRAY_LEN(controlframetype2str); i++) {
         if (frame->subclass.integer == controlframetype2str[i].type) {
            if (framedata->controlvalues[i]) {
               drop_frame = 1;
            }
            break;
         }
      }
   } else {
      for (i = 0; i < ARRAY_LEN(frametype2str); i++) {
         if (frame->frametype == frametype2str[i].type) {
            if (framedata->values[i]) {
               drop_frame = 1;
            }
            break;
         }
      }
   }

   if (drop_frame) {
      ast_frfree(frame);
      frame = &ast_null_frame;
   }
   return frame;
}

static int frame_drop_helper(struct ast_channel *chan, const char *cmd, char *data, const char *value)
{
   char *buffer;
   struct frame_drop_data *framedata;
   struct ast_datastore *datastore = NULL;
   struct ast_framehook_interface interface = {
      .version = AST_FRAMEHOOK_INTERFACE_VERSION,
      .event_cb = hook_event_cb,
      .destroy_cb = hook_destroy_cb,
   };
   int i = 0;

   if (!(framedata = ast_calloc(1, sizeof(*framedata)))) {
      return 0;
   }

   interface.data = framedata;

   if (!strcasecmp(data, "RX")) {
      framedata->list_type = RX;
   } else {
      framedata->list_type = TX;
   }

   buffer = ast_malloc(sizeof(value) + 3); /* leading and trailing comma and null terminator */
   snprintf(buffer, sizeof(value) + 2, ",%s,", value);
   for (i = 0; i < ARRAY_LEN(frametype2str); i++) {
      if (strcasestr(value, frametype2str[i].str)) {
         framedata->values[i] = 1;
      }
   }

   for (i = 0; i < ARRAY_LEN(controlframetype2str); i++) {
      if (strcasestr(value, controlframetype2str[i].str)) {
         framedata->controlvalues[i] = 1;
      }
   }
   ast_free(buffer);

   ast_channel_lock(chan);
   i = ast_framehook_attach(chan, &interface);
   if (i >= 0) {
      int *id;
      if ((datastore = ast_channel_datastore_find(chan, &frame_drop_datastore, NULL))) {
         id = datastore->data;
         ast_framehook_detach(chan, *id);
         ast_channel_datastore_remove(chan, datastore);
         ast_datastore_free(datastore);
      }

      if (!(datastore = ast_datastore_alloc(&frame_drop_datastore, NULL))) {
         ast_framehook_detach(chan, i);
         ast_channel_unlock(chan);
         return 0;
      }

      if (!(id = ast_calloc(1, sizeof(int)))) {
         ast_datastore_free(datastore);
         ast_framehook_detach(chan, i);
         ast_channel_unlock(chan);
         return 0;
      }

      *id = i; /* Store off the id. The channel is still locked so it is safe to access this ptr. */
      datastore->data = id;
      ast_channel_datastore_add(chan, datastore);
   }
   ast_channel_unlock(chan);

   return 0;
}

static struct ast_custom_function frame_drop_function = {
   .name = "FRAME_DROP",
   .write = frame_drop_helper,
};

static int unload_module(void)
{
   return ast_custom_function_unregister(&frame_drop_function);
}

static int load_module(void)
{
   int res = ast_custom_function_register(&frame_drop_function);
   return res ? AST_MODULE_LOAD_DECLINE : AST_MODULE_LOAD_SUCCESS;
}

AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "Function to drop frames on a channel.");