Adds a function to scramble audio on a channel using whole spectrum frequency inversion. This can be used as a privacy enhancement with applications like ChanSpy or other potentially sensitive audio. ASTERISK-29542 Change-Id: I01020769d91060a1f56a708eb405f87648d1a67eremotes/origin/18.7
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Subject: func_scramble
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Adds an audio scrambler function that may be used to
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distort voice audio on a channel as a privacy
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enhancement.
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/*
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* Asterisk -- An open source telephony toolkit.
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*
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* Copyright (C) 2021, Naveen Albert
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*
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* Naveen Albert <asterisk@phreaknet.org>
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*
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* See http://www.asterisk.org for more information about
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* the Asterisk project. Please do not directly contact
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* any of the maintainers of this project for assistance;
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* the project provides a web site, mailing lists and IRC
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* channels for your use.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License Version 2. See the LICENSE file
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* at the top of the source tree.
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*/
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/*! \file
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*
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* \brief Frequency inverter
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*
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* \author Naveen Albert <asterisk@phreaknet.org>
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*
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* \ingroup functions
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*
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*/
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/*** MODULEINFO
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<support_level>extended</support_level>
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***/
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/*** DOCUMENTATION
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<function name="SCRAMBLE" language="en_US">
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<synopsis>
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Scrambles audio on a channel.
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</synopsis>
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<syntax>
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<parameter name="direction" required="false">
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<para>Must be <literal>TX</literal> or <literal>RX</literal>
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to limit to a specific direction, or <literal>both</literal>
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for both directions. <literal>remove</literal>
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will remove an existing scrambler.</para>
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</parameter>
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</syntax>
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<description>
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<para>Scrambles audio on a channel using whole spectrum inversion.
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This is not intended to be used for securely scrambling
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audio. It merely renders obfuscates audio on a channel
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to render it unintelligible, as a privacy enhancement.</para>
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</description>
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<see-also>
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<ref type="application">ChanSpy</ref>
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</see-also>
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</function>
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***/
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#include "asterisk.h"
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#include "asterisk/module.h"
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#include "asterisk/channel.h"
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#include "asterisk/pbx.h"
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#include "asterisk/utils.h"
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#include "asterisk/audiohook.h"
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#include "asterisk/app.h"
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#include <stdio.h>
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#include <string.h>
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struct scramble_information {
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struct ast_audiohook audiohook;
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unsigned short int tx;
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unsigned short int rx;
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unsigned short int state;
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};
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static void destroy_callback(void *data)
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{
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struct scramble_information *ni = data;
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/* Destroy the audiohook, and destroy ourselves */
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ast_audiohook_lock(&ni->audiohook);
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ast_audiohook_detach(&ni->audiohook);
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ast_audiohook_unlock(&ni->audiohook);
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ast_audiohook_destroy(&ni->audiohook);
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ast_free(ni);
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return;
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}
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/*! \brief Static structure for datastore information */
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static const struct ast_datastore_info scramble_datastore = {
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.type = "scramble",
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.destroy = destroy_callback
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};
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/* modifies buffer pointed to by 'amp' with inverted values */
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static inline void freq_invert(short *amp, int samples)
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{
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int i;
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/* invert every other sample by 1 */
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for (i = 0; i < samples; i += 2) {
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amp[i] = -amp[i];
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}
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}
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static int scramble_callback(struct ast_audiohook *audiohook, struct ast_channel *chan, struct ast_frame *frame, enum ast_audiohook_direction direction)
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{
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struct ast_datastore *datastore = NULL;
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struct scramble_information *ni = NULL;
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/* If the audiohook is stopping it means the channel is shutting down.... but we let the datastore destroy take care of it */
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if (audiohook->status == AST_AUDIOHOOK_STATUS_DONE) {
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return 0;
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}
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/* Grab datastore which contains our gain information */
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if (!(datastore = ast_channel_datastore_find(chan, &scramble_datastore, NULL))) {
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return 0;
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}
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if (frame->frametype == AST_FRAME_VOICE) { /* only invert voice frequencies */
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/* Based on direction of frame, and confirm it is applicable */
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if (!(direction == AST_AUDIOHOOK_DIRECTION_READ ? &ni->rx : &ni->tx)) {
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return 0;
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}
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/* Scramble the sample now */
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freq_invert(frame->data.ptr, frame->samples);
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}
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return 0;
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}
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/*! \internal \brief Disable scrambling on the channel */
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static int remove_scrambler(struct ast_channel *chan)
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{
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struct ast_datastore *datastore = NULL;
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struct scramble_information *data;
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SCOPED_CHANNELLOCK(chan_lock, chan);
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datastore = ast_channel_datastore_find(chan, &scramble_datastore, NULL);
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if (!datastore) {
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ast_log(AST_LOG_WARNING, "Cannot remove SCRAMBLE from %s: SCRAMBLE not currently enabled\n",
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ast_channel_name(chan));
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return -1;
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}
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data = datastore->data;
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if (ast_audiohook_remove(chan, &data->audiohook)) {
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ast_log(AST_LOG_WARNING, "Failed to remove SCRAMBLE audiohook from channel %s\n", ast_channel_name(chan));
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return -1;
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}
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if (ast_channel_datastore_remove(chan, datastore)) {
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ast_log(AST_LOG_WARNING, "Failed to remove SCRAMBLE datastore from channel %s\n",
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ast_channel_name(chan));
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return -1;
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}
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ast_datastore_free(datastore);
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return 0;
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}
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static int scramble_write(struct ast_channel *chan, const char *cmd, char *data, const char *value)
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{
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char *parse;
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struct ast_datastore *datastore = NULL;
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struct scramble_information *ni = NULL;
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int tx = 1, rx = 1;
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AST_DECLARE_APP_ARGS(args,
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AST_APP_ARG(direction);
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);
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if (!chan) {
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ast_log(LOG_WARNING, "No channel was provided to %s function.\n", cmd);
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return -1;
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}
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parse = ast_strdupa(value);
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AST_STANDARD_APP_ARGS(args, parse);
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if (!strcasecmp(args.direction, "remove")) {
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return remove_scrambler(chan);
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}
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if (!strcasecmp(args.direction, "tx")) {
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tx = 1;
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rx = 0;
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} else if (!strcasecmp(args.direction, "rx")) {
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rx = 0;
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tx = 1;
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} else if (strcasecmp(args.direction, "both")) {
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ast_log(LOG_ERROR, "Direction must be either RX, TX, both, or remove\n");
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return -1;
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}
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ast_channel_lock(chan);
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if (!(datastore = ast_channel_datastore_find(chan, &scramble_datastore, NULL))) {
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/* Allocate a new datastore to hold the reference to this audiohook information */
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if (!(datastore = ast_datastore_alloc(&scramble_datastore, NULL))) {
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return 0;
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}
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if (!(ni = ast_calloc(1, sizeof(*ni)))) {
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ast_datastore_free(datastore);
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return 0;
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}
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ast_audiohook_init(&ni->audiohook, AST_AUDIOHOOK_TYPE_MANIPULATE, "Voice scrambler", AST_AUDIOHOOK_MANIPULATE_ALL_RATES);
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ni->audiohook.manipulate_callback = scramble_callback;
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datastore->data = ni;
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ast_channel_datastore_add(chan, datastore);
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ast_audiohook_attach(chan, &ni->audiohook);
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} else {
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ni = datastore->data;
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}
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ni->tx = tx;
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ni->rx = rx;
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ast_channel_unlock(chan);
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return 0;
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}
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static struct ast_custom_function scramble_function = {
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.name = "SCRAMBLE",
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.write = scramble_write,
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};
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static int unload_module(void)
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{
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return ast_custom_function_unregister(&scramble_function);
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}
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static int load_module(void)
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{
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return ast_custom_function_register(&scramble_function);
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}
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AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Frequency inverting voice scrambler");
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