func_frame_drop.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2021, Naveen Albert
 *
 * Naveen Albert <asterisk@phreaknet.org>
 *
 * 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 <asterisk@phreaknet.org>
 *
 * \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">
        <since>
            <version>16.21.0</version>
            <version>18.7.0</version>
            <version>19.0.0</version>
        </since>
        <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>
            <example title="Drop only DTMF frames towards this channel">
            exten => 1,1,Set(FRAME_DROP(TX)=DTMF_BEGIN,DTMF_END)
            </example>
            <example title="Drop only Answer control frames towards this channel">
            exten => 1,1,Set(FRAME_DROP(TX)=ANSWER)
            </example>
            <example title="Drop only DTMF frames received on this channel">
            exten => 1,1,Set(FRAME_DROP(RX)=DTMF_BEGIN,DTMF_END)
            </example>
        </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(buffer, frametype2str[i].str)) {
            framedata->values[i] = 1;
        }
    }
 
    for (i = 0; i < ARRAY_LEN(controlframetype2str); i++) {
        if (strcasestr(buffer, 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.");