app_stack.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (c) 2004-2006 Tilghman Lesher <app_stack_v003@the-tilghman.com>.
 *
 * This code is released by the author with no restrictions on usage.
 *
 * 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 Stack applications Gosub, Return, etc.
 *
 * \author Tilghman Lesher <app_stack_v003@the-tilghman.com>
 *
 * \ingroup applications
 */
 
/*** MODULEINFO
    <use type="module">res_agi</use>
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/pbx.h"
#include "asterisk/module.h"
#include "asterisk/app.h"
#include "asterisk/manager.h"
#include "asterisk/channel.h"
#include "asterisk/agi.h"
#include "asterisk/stasis_channels.h"
 
/*** DOCUMENTATION
    <application name="Gosub" language="en_US">
        <since>
            <version>1.2.0</version>
        </since>
        <synopsis>
            Jump to label, saving return address.
        </synopsis>
        <syntax>
            <parameter name="context" documentationtype="dialplan_context" />
            <parameter name="extension" documentationtype="dialplan_extension" />
            <parameter name="priority" documentationtype="dialplan_priority" required="true" hasparams="optional">
                <argument name="arg1" multiple="true" required="true" />
                <argument name="argN" />
            </parameter>
        </syntax>
        <description>
            <para>Jumps to the label specified, saving the return address.</para>
        </description>
        <see-also>
            <ref type="application">GosubIf</ref>
            <ref type="application">Goto</ref>
            <ref type="application">Return</ref>
            <ref type="application">StackPop</ref>
        </see-also>
    </application>
    <application name="GosubIf" language="en_US">
        <since>
            <version>1.2.0</version>
        </since>
        <synopsis>
            Conditionally jump to label, saving return address.
        </synopsis>
        <syntax argsep="?">
            <parameter name="condition" required="true" />
            <parameter name="destination" required="true" argsep=":">
                <argument name="labeliftrue" hasparams="optional">
                    <para>Continue at <replaceable>labeliftrue</replaceable> if the condition is true.
                    Takes the form similar to Goto() of [[context,]extension,]priority.</para>
                    <argument name="arg1" required="true" multiple="true" />
                    <argument name="argN" />
                </argument>
                <argument name="labeliffalse" hasparams="optional">
                    <para>Continue at <replaceable>labeliffalse</replaceable> if the condition is false.
                    Takes the form similar to Goto() of [[context,]extension,]priority.</para>
                    <argument name="arg1" required="true" multiple="true" />
                    <argument name="argN" />
                </argument>
            </parameter>
        </syntax>
        <description>
            <para>If the condition is true, then jump to labeliftrue.  If false, jumps to
            labeliffalse, if specified.  In either case, a jump saves the return point
            in the dialplan, to be returned to with a Return.</para>
        </description>
        <see-also>
            <ref type="application">Gosub</ref>
            <ref type="application">Return</ref>
            <ref type="function">IF</ref>
            <ref type="application">GotoIf</ref>
            <ref type="application">Goto</ref>
        </see-also>
    </application>
    <application name="Return" language="en_US">
        <since>
            <version>1.2.0</version>
        </since>
        <synopsis>
            Return from gosub routine.
        </synopsis>
        <syntax>
            <parameter name="value">
                <para>Return value.</para>
            </parameter>
        </syntax>
        <description>
            <para>Jumps to the last label on the stack, removing it. The return <replaceable>value</replaceable>, if
            any, is saved in the channel variable <variable>GOSUB_RETVAL</variable>.</para>
        </description>
        <see-also>
            <ref type="application">Gosub</ref>
            <ref type="application">StackPop</ref>
        </see-also>
    </application>
    <application name="StackPop" language="en_US">
        <since>
            <version>1.2.0</version>
        </since>
        <synopsis>
            Remove one address from gosub stack.
        </synopsis>
        <syntax />
        <description>
            <para>Removes last label on the stack, discarding it.</para>
        </description>
        <see-also>
            <ref type="application">Return</ref>
            <ref type="application">Gosub</ref>
        </see-also>
    </application>
    <function name="LOCAL" language="en_US">
        <since>
            <version>1.6.1.0</version>
        </since>
        <synopsis>
            Manage variables local to the gosub stack frame.
        </synopsis>
        <syntax>
            <parameter name="varname" required="true" />
        </syntax>
        <description>
            <para>Read and write a variable local to the gosub stack frame, once we Return() it will be lost
            (or it will go back to whatever value it had before the Gosub()).</para>
        </description>
        <see-also>
            <ref type="application">Gosub</ref>
            <ref type="application">GosubIf</ref>
            <ref type="application">Return</ref>
        </see-also>
    </function>
    <function name="LOCAL_PEEK" language="en_US">
        <since>
            <version>1.6.1.0</version>
        </since>
        <synopsis>
            Retrieve variables hidden by the local gosub stack frame.
        </synopsis>
        <syntax>
            <parameter name="n" required="true" />
            <parameter name="varname" required="true" />
        </syntax>
        <description>
            <para>Read a variable <replaceable>varname</replaceable> hidden by
            <replaceable>n</replaceable> levels of gosub stack frames.  Note that ${LOCAL_PEEK(0,foo)}
            is the same as <variable>foo</variable>, since the value of <replaceable>n</replaceable>
            peeks under 0 levels of stack frames; in other words, 0 is the current level.  If
            <replaceable>n</replaceable> exceeds the available number of stack frames, then an empty
            string is returned.</para>
        </description>
        <see-also>
            <ref type="application">Gosub</ref>
            <ref type="application">GosubIf</ref>
            <ref type="application">Return</ref>
        </see-also>
    </function>
    <function name="STACK_PEEK" language="en_US">
        <since>
            <version>1.8.11.0</version>
            <version>10.3.0</version>
        </since>
        <synopsis>
            View info about the location which called Gosub
        </synopsis>
        <syntax>
            <parameter name="n" required="true" />
            <parameter name="which" required="true" />
            <parameter name="suppress" required="false" />
        </syntax>
        <description>
            <para>Read the calling <literal>c</literal>ontext, <literal>e</literal>xtension,
            <literal>p</literal>riority, or <literal>l</literal>abel, as specified by
            <replaceable>which</replaceable>, by going up <replaceable>n</replaceable> frames
            in the Gosub stack.  If <replaceable>suppress</replaceable> is true, then if the
            number of available stack frames is exceeded, then no error message will be
            printed.</para>
        </description>
    </function>
    <agi name="gosub" language="en_US">
        <synopsis>
            Cause the channel to execute the specified dialplan subroutine.
        </synopsis>
        <syntax>
            <parameter name="context" required="true" />
            <parameter name="extension" required="true" />
            <parameter name="priority" required="true" />
            <parameter name="optional-argument" />
        </syntax>
        <description>
            <para>Cause the channel to execute the specified dialplan subroutine,
            returning to the dialplan with execution of a Return().</para>
        </description>
        <see-also>
            <ref type="application">Gosub</ref>
        </see-also>
    </agi>
    <managerEvent language="en_US" name="VarSet">
        <managerEventInstance class="EVENT_FLAG_DIALPLAN">
            <since>
                <version>12.0.0</version>
            </since>
            <synopsis>Raised when a variable local to the gosub stack frame is set due to a subroutine call.</synopsis>
            <syntax>
                <channel_snapshot/>
                <parameter name="Variable">
                    <para>The LOCAL variable being set.</para>
                    <note><para>The variable name will always be enclosed with
                    <literal>LOCAL()</literal></para></note>
                </parameter>
                <parameter name="Value">
                    <para>The new value of the variable.</para>
                </parameter>
            </syntax>
            <see-also>
                <ref type="application">Gosub</ref>
                <ref type="agi">gosub</ref>
                <ref type="function">LOCAL</ref>
                <ref type="function">LOCAL_PEEK</ref>
            </see-also>
        </managerEventInstance>
    </managerEvent>
 ***/
 
static const char app_gosub[] = "Gosub";
static const char app_gosubif[] = "GosubIf";
static const char app_return[] = "Return";
static const char app_pop[] = "StackPop";
 
static void gosub_free(void *data);
 
static const struct ast_datastore_info stack_info = {
    .type = "GOSUB",
    .destroy = gosub_free,
};
 
struct gosub_stack_frame {
    AST_LIST_ENTRY(gosub_stack_frame) entries;
    /* 100 arguments is all that we support anyway, but this will handle up to 255 */
    unsigned char arguments;
    struct varshead varshead;
    int priority;
    /*! TRUE if the return location marks the end of a special routine. */
    unsigned int is_special:1;
    /*! Whether or not we were in a subroutine when this one was created */
    unsigned int in_subroutine:1;
    char *context;
    char extension[0];
};
 
AST_LIST_HEAD(gosub_stack_list, gosub_stack_frame);
 
static int frame_set_var(struct ast_channel *chan, struct gosub_stack_frame *frame, const char *var, const char *value)
{
    struct ast_var_t *variables;
    int found = 0;
    int len;
    RAII_VAR(char *, local_buffer, NULL, ast_free);
 
    /* Does this variable already exist? */
    AST_LIST_TRAVERSE(&frame->varshead, variables, entries) {
        if (!strcmp(var, ast_var_name(variables))) {
            found = 1;
            break;
        }
    }
 
    if (!found) {
        if ((variables = ast_var_assign(var, ""))) {
            AST_LIST_INSERT_HEAD(&frame->varshead, variables, entries);
        }
        pbx_builtin_pushvar_helper(chan, var, value);
    } else {
        pbx_builtin_setvar_helper(chan, var, value);
    }
 
    len = 8 + strlen(var); /* LOCAL() + var */
    local_buffer = ast_malloc(len);
    if (!local_buffer) {
        return 0;
    }
    sprintf(local_buffer, "LOCAL(%s)", var);
    ast_channel_publish_varset(chan, local_buffer, value);
    return 0;
}
 
static void gosub_release_frame(struct ast_channel *chan, struct gosub_stack_frame *frame)
{
    struct ast_var_t *vardata;
 
    /* If chan is not defined, then we're calling it as part of gosub_free,
     * and the channel variables will be deallocated anyway.  Otherwise, we're
     * just releasing a single frame, so we need to clean up the arguments for
     * that frame, so that we re-expose the variables from the previous frame
     * that were hidden by this one.
     */
    while ((vardata = AST_LIST_REMOVE_HEAD(&frame->varshead, entries))) {
        if (chan)
            pbx_builtin_setvar_helper(chan, ast_var_name(vardata), NULL);
        ast_var_delete(vardata);
    }
 
    ast_free(frame);
}
 
static struct gosub_stack_frame *gosub_allocate_frame(const char *context, const char *extension, int priority, int in_subroutine, unsigned char arguments)
{
    struct gosub_stack_frame *new = NULL;
    int len_extension = strlen(extension) + 1;
    int len_context = strlen(context) + 1;
 
    if ((new = ast_calloc(1, sizeof(*new) + len_extension + len_context))) {
        AST_LIST_HEAD_INIT_NOLOCK(&new->varshead);
        ast_copy_string(new->extension, extension, len_extension);
        new->context = new->extension + len_extension;
        ast_copy_string(new->context, context, len_context);
        new->priority = priority;
        new->in_subroutine = in_subroutine ? 1 : 0;
        new->arguments = arguments;
    }
    return new;
}
 
static void gosub_free(void *data)
{
    struct gosub_stack_list *oldlist = data;
    struct gosub_stack_frame *oldframe;
 
    AST_LIST_LOCK(oldlist);
    while ((oldframe = AST_LIST_REMOVE_HEAD(oldlist, entries))) {
        gosub_release_frame(NULL, oldframe);
    }
    AST_LIST_UNLOCK(oldlist);
    AST_LIST_HEAD_DESTROY(oldlist);
    ast_free(oldlist);
}
 
static int pop_exec(struct ast_channel *chan, const char *data)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_frame *oldframe;
    struct gosub_stack_list *oldlist;
    int res = 0;
 
    ast_channel_lock(chan);
    if (!(stack_store = ast_channel_datastore_find(chan, &stack_info, NULL))) {
        ast_log(LOG_WARNING, "%s called with no gosub stack allocated.\n", app_pop);
        ast_channel_unlock(chan);
        return 0;
    }
 
    oldlist = stack_store->data;
    AST_LIST_LOCK(oldlist);
    oldframe = AST_LIST_FIRST(oldlist);
    if (oldframe) {
        if (oldframe->is_special) {
            ast_debug(1, "%s attempted to pop special return location.\n", app_pop);
 
            /* Abort the special routine dialplan execution.  Dialplan programming error. */
            res = -1;
        } else {
            AST_LIST_REMOVE_HEAD(oldlist, entries);
            gosub_release_frame(chan, oldframe);
        }
    } else {
        ast_debug(1, "%s called with an empty gosub stack\n", app_pop);
    }
    AST_LIST_UNLOCK(oldlist);
    ast_channel_unlock(chan);
    return res;
}
 
static int return_exec(struct ast_channel *chan, const char *data)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_frame *oldframe;
    struct gosub_stack_list *oldlist;
    const char *retval = data;
    int res = 0;
 
    ast_channel_lock(chan);
    if (!(stack_store = ast_channel_datastore_find(chan, &stack_info, NULL))) {
        ast_log(LOG_ERROR, "Return without Gosub: stack is unallocated\n");
        ast_channel_unlock(chan);
        return -1;
    }
 
    oldlist = stack_store->data;
    AST_LIST_LOCK(oldlist);
    oldframe = AST_LIST_REMOVE_HEAD(oldlist, entries);
    AST_LIST_UNLOCK(oldlist);
 
    if (!oldframe) {
        ast_log(LOG_ERROR, "Return without Gosub: stack is empty\n");
        ast_channel_unlock(chan);
        return -1;
    }
    if (oldframe->is_special) {
        /* Exit from special routine. */
        res = -1;
    }
 
    /*
     * We cannot use ast_explicit_goto() because we MUST restore
     * what was there before.  Channels that do not have a PBX may
     * not have the context or exten set.
     */
    ast_channel_context_set(chan, oldframe->context);
    ast_channel_exten_set(chan, oldframe->extension);
    if (ast_test_flag(ast_channel_flags(chan), AST_FLAG_IN_AUTOLOOP)) {
        --oldframe->priority;
    }
    ast_channel_priority_set(chan, oldframe->priority);
    ast_set2_flag(ast_channel_flags(chan), oldframe->in_subroutine, AST_FLAG_SUBROUTINE_EXEC);
 
    gosub_release_frame(chan, oldframe);
 
    /* Set a return value, if any */
    pbx_builtin_setvar_helper(chan, "GOSUB_RETVAL", S_OR(retval, ""));
    ast_channel_unlock(chan);
    return res;
}
 
/*!
 * \internal
 * \brief Add missing context and/or exten to Gosub application argument string.
 * \since 11.0
 *
 * \param chan Channel to obtain context/exten.
 * \param args Gosub application argument string.
 *
 * \details
 * Fills in the optional context and exten from the given channel.
 * Convert: [[context,]exten,]priority[(arg1[,...][,argN])]
 * To: context,exten,priority[(arg1[,...][,argN])]
 *
 * \retval expanded Gosub argument string on success.  Must be freed.
 * \retval NULL on error.
 *
 * \note The parsing needs to be kept in sync with the
 * gosub_exec() argument format.
 */
static const char *expand_gosub_args(struct ast_channel *chan, const char *args)
{
    int len;
    char *parse;
    char *label;
    char *new_args;
    const char *context;
    const char *exten;
    const char *pri;
 
    /* Separate the context,exten,pri from the optional routine arguments. */
    parse = ast_strdupa(args);
    label = strsep(&parse, "(");
    if (parse) {
        char *endparen;
 
        endparen = strrchr(parse, ')');
        if (endparen) {
            *endparen = '\0';
        } else {
            ast_log(LOG_WARNING, "Ouch.  No closing paren: '%s'?\n", args);
        }
    }
 
    /* Split context,exten,pri */
    context = strsep(&label, ",");
    exten = strsep(&label, ",");
    pri = strsep(&label, ",");
    if (!exten) {
        /* Only a priority in this one */
        pri = context;
        exten = NULL;
        context = NULL;
    } else if (!pri) {
        /* Only an extension and priority in this one */
        pri = exten;
        exten = context;
        context = NULL;
    }
 
    ast_channel_lock(chan);
    if (ast_strlen_zero(exten)) {
        exten = ast_channel_exten(chan);
    }
    if (ast_strlen_zero(context)) {
        context = ast_channel_context(chan);
    }
    len = strlen(context) + strlen(exten) + strlen(pri) + 3;
    if (!ast_strlen_zero(parse)) {
        len += 2 + strlen(parse);
    }
    new_args = ast_malloc(len);
    if (new_args) {
        if (ast_strlen_zero(parse)) {
            snprintf(new_args, len, "%s,%s,%s", context, exten, pri);
        } else {
            snprintf(new_args, len, "%s,%s,%s(%s)", context, exten, pri, parse);
        }
    }
    ast_channel_unlock(chan);
 
    ast_debug(4, "Gosub args:%s new_args:%s\n", args, new_args ? new_args : "");
 
    return new_args;
}
 
static int gosub_exec(struct ast_channel *chan, const char *data)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_list *oldlist;
    struct gosub_stack_frame *newframe;
    struct gosub_stack_frame *lastframe;
    char argname[15];
    char *parse;
    char *label;
    char *caller_id;
    char *orig_context;
    char *orig_exten;
    char *dest_context;
    char *dest_exten;
    int orig_in_subroutine;
    int orig_priority;
    int dest_priority;
    int i;
    int max_argc = 0;
    AST_DECLARE_APP_ARGS(args2,
        AST_APP_ARG(argval)[100];
    );
 
    if (ast_strlen_zero(data)) {
        ast_log(LOG_ERROR, "%s requires an argument: %s([[context,]exten,]priority[(arg1[,...][,argN])])\n", app_gosub, app_gosub);
        return -1;
    }
 
    /*
     * Separate the arguments from the label
     *
     * NOTE:  You cannot use ast_app_separate_args for this, because
     * '(' cannot be used as a delimiter.
     */
    parse = ast_strdupa(data);
    label = strsep(&parse, "(");
    if (parse) {
        char *endparen;
 
        endparen = strrchr(parse, ')');
        if (endparen) {
            *endparen = '\0';
        } else {
            ast_log(LOG_WARNING, "Ouch.  No closing paren: '%s'?\n", data);
        }
        AST_STANDARD_RAW_ARGS(args2, parse);
    } else {
        args2.argc = 0;
    }
 
    ast_channel_lock(chan);
    orig_context = ast_strdupa(ast_channel_context(chan));
    orig_exten = ast_strdupa(ast_channel_exten(chan));
    orig_priority = ast_channel_priority(chan);
    orig_in_subroutine = ast_test_flag(ast_channel_flags(chan), AST_FLAG_SUBROUTINE_EXEC);
    ast_channel_unlock(chan);
 
    if (ast_parseable_goto(chan, label)) {
        ast_log(LOG_ERROR, "%s address is invalid: '%s'\n", app_gosub, data);
        goto error_exit;
    }
 
    ast_channel_lock(chan);
    dest_context = ast_strdupa(ast_channel_context(chan));
    dest_exten = ast_strdupa(ast_channel_exten(chan));
    dest_priority = ast_channel_priority(chan);
    if (ast_test_flag(ast_channel_flags(chan), AST_FLAG_IN_AUTOLOOP)) {
        ++dest_priority;
    }
    caller_id = S_COR(ast_channel_caller(chan)->id.number.valid,
        ast_channel_caller(chan)->id.number.str, NULL);
    if (caller_id) {
        caller_id = ast_strdupa(caller_id);
    }
    ast_channel_unlock(chan);
 
    if (!ast_exists_extension(chan, dest_context, dest_exten, dest_priority, caller_id)) {
        ast_log(LOG_ERROR, "%s attempted to reach non-existent destination '%s,%s,%d' from '%s,%s,%d'",
            app_gosub, dest_context, dest_exten, dest_priority, orig_context, orig_exten, orig_priority);
        goto error_exit;
    }
 
    /* Now we know that we're going to a new location */
 
    ast_channel_lock(chan);
 
    /* Find stack datastore return list. */
    if (!(stack_store = ast_channel_datastore_find(chan, &stack_info, NULL))) {
        ast_debug(1, "Channel %s has no datastore, so we're allocating one.\n",
            ast_channel_name(chan));
        stack_store = ast_datastore_alloc(&stack_info, NULL);
        if (!stack_store) {
            ast_log(LOG_ERROR, "Unable to allocate new datastore.  %s failed.\n",
                app_gosub);
            goto error_exit_locked;
        }
 
        oldlist = ast_calloc(1, sizeof(*oldlist));
        if (!oldlist) {
            ast_log(LOG_ERROR, "Unable to allocate datastore list head.  %s failed.\n",
                app_gosub);
            ast_datastore_free(stack_store);
            goto error_exit_locked;
        }
        AST_LIST_HEAD_INIT(oldlist);
 
        stack_store->data = oldlist;
        ast_channel_datastore_add(chan, stack_store);
    } else {
        oldlist = stack_store->data;
    }
 
    if ((lastframe = AST_LIST_FIRST(oldlist))) {
        max_argc = lastframe->arguments;
    }
 
    /* Mask out previous Gosub arguments in this invocation */
    if (args2.argc > max_argc) {
        max_argc = args2.argc;
    }
 
    /* Create the return address */
    newframe = gosub_allocate_frame(orig_context, orig_exten, orig_priority + 1, orig_in_subroutine, max_argc);
    if (!newframe) {
        goto error_exit_locked;
    }
 
    /* Set our arguments */
    for (i = 0; i < max_argc; i++) {
        snprintf(argname, sizeof(argname), "ARG%d", i + 1);
        frame_set_var(chan, newframe, argname, i < args2.argc ? args2.argval[i] : "");
        ast_debug(1, "Setting '%s' to '%s'\n", argname, i < args2.argc ? args2.argval[i] : "");
    }
    snprintf(argname, sizeof(argname), "%u", args2.argc);
    frame_set_var(chan, newframe, "ARGC", argname);
 
    ast_set_flag(ast_channel_flags(chan), AST_FLAG_SUBROUTINE_EXEC);
 
    /* And finally, save our return address */
    AST_LIST_LOCK(oldlist);
    AST_LIST_INSERT_HEAD(oldlist, newframe, entries);
    AST_LIST_UNLOCK(oldlist);
    ast_channel_unlock(chan);
 
    return 0;
 
error_exit:
    ast_channel_lock(chan);
 
error_exit_locked:
    /* Restore the original dialplan location. */
    ast_channel_context_set(chan, orig_context);
    ast_channel_exten_set(chan, orig_exten);
    ast_channel_priority_set(chan, orig_priority);
    ast_channel_unlock(chan);
    return -1;
}
 
static int gosubif_exec(struct ast_channel *chan, const char *data)
{
    char *args;
    int res=0;
    AST_DECLARE_APP_ARGS(cond,
        AST_APP_ARG(ition);
        AST_APP_ARG(labels);
    );
    AST_DECLARE_APP_ARGS(label,
        AST_APP_ARG(iftrue);
        AST_APP_ARG(iffalse);
    );
 
    if (ast_strlen_zero(data)) {
        ast_log(LOG_WARNING, "GosubIf requires an argument: GosubIf(cond?label1(args):label2(args)\n");
        return 0;
    }
 
    args = ast_strdupa(data);
    AST_NONSTANDARD_RAW_ARGS(cond, args, '?');
    if (cond.argc != 2) {
        ast_log(LOG_WARNING, "GosubIf requires an argument: GosubIf(cond?label1(args):label2(args)\n");
        return 0;
    }
 
    AST_NONSTANDARD_RAW_ARGS(label, cond.labels, ':');
 
    if (pbx_checkcondition(cond.ition)) {
        if (!ast_strlen_zero(label.iftrue))
            res = gosub_exec(chan, label.iftrue);
    } else if (!ast_strlen_zero(label.iffalse)) {
        res = gosub_exec(chan, label.iffalse);
    }
 
    return res;
}
 
static int local_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_list *oldlist;
    struct gosub_stack_frame *frame;
    struct ast_var_t *variables;
 
    if (!chan) {
        ast_log(LOG_WARNING, "No channel was provided to %s function.\n", cmd);
        return -1;
    }
 
    ast_channel_lock(chan);
    if (!(stack_store = ast_channel_datastore_find(chan, &stack_info, NULL))) {
        ast_channel_unlock(chan);
        return -1;
    }
 
    oldlist = stack_store->data;
    AST_LIST_LOCK(oldlist);
    if (!(frame = AST_LIST_FIRST(oldlist))) {
        /* Not within a Gosub routine */
        AST_LIST_UNLOCK(oldlist);
        ast_channel_unlock(chan);
        return -1;
    }
 
    AST_LIST_TRAVERSE(&frame->varshead, variables, entries) {
        if (!strcmp(data, ast_var_name(variables))) {
            const char *tmp;
            tmp = pbx_builtin_getvar_helper(chan, data);
            ast_copy_string(buf, S_OR(tmp, ""), len);
            break;
        }
    }
    AST_LIST_UNLOCK(oldlist);
    ast_channel_unlock(chan);
    return 0;
}
 
static int local_write(struct ast_channel *chan, const char *cmd, char *var, const char *value)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_list *oldlist;
    struct gosub_stack_frame *frame;
 
    if (!chan) {
        ast_log(LOG_WARNING, "No channel was provided to %s function.\n", cmd);
        return -1;
    }
 
    ast_channel_lock(chan);
    if (!(stack_store = ast_channel_datastore_find(chan, &stack_info, NULL))) {
        ast_log(LOG_ERROR, "Tried to set LOCAL(%s), but we aren't within a Gosub routine\n", var);
        ast_channel_unlock(chan);
        return -1;
    }
 
    oldlist = stack_store->data;
    AST_LIST_LOCK(oldlist);
    frame = AST_LIST_FIRST(oldlist);
 
    if (frame) {
        frame_set_var(chan, frame, var, value);
    }
 
    AST_LIST_UNLOCK(oldlist);
    ast_channel_unlock(chan);
 
    return 0;
}
 
static struct ast_custom_function local_function = {
    .name = "LOCAL",
    .write = local_write,
    .read = local_read,
};
 
static int peek_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
{
    int found = 0, n;
    struct ast_var_t *variables;
    AST_DECLARE_APP_ARGS(args,
        AST_APP_ARG(n);
        AST_APP_ARG(name);
    );
 
    if (!chan) {
        ast_log(LOG_ERROR, "LOCAL_PEEK must be called on an active channel\n");
        return -1;
    }
 
    AST_STANDARD_RAW_ARGS(args, data);
 
    if (ast_strlen_zero(args.n) || ast_strlen_zero(args.name)) {
        ast_log(LOG_ERROR, "LOCAL_PEEK requires parameters n and varname\n");
        return -1;
    }
 
    n = atoi(args.n);
    *buf = '\0';
 
    ast_channel_lock(chan);
    AST_LIST_TRAVERSE(ast_channel_varshead(chan), variables, entries) {
        if (!strcmp(args.name, ast_var_name(variables)) && ++found > n) {
            ast_copy_string(buf, ast_var_value(variables), len);
            break;
        }
    }
    ast_channel_unlock(chan);
    return 0;
}
 
static struct ast_custom_function peek_function = {
    .name = "LOCAL_PEEK",
    .read = peek_read,
};
 
static int stackpeek_read(struct ast_channel *chan, const char *cmd, char *data, struct ast_str **str, ssize_t len)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_list *oldlist;
    struct gosub_stack_frame *frame;
    int n;
    AST_DECLARE_APP_ARGS(args,
        AST_APP_ARG(n);
        AST_APP_ARG(which);
        AST_APP_ARG(suppress);
    );
 
    if (!chan) {
        ast_log(LOG_ERROR, "STACK_PEEK must be called on an active channel\n");
        return -1;
    }
 
    data = ast_strdupa(data);
    AST_STANDARD_APP_ARGS(args, data);
 
    if (ast_strlen_zero(args.n) || ast_strlen_zero(args.which)) {
        ast_log(LOG_ERROR, "STACK_PEEK requires parameters n and which\n");
        return -1;
    }
 
    n = atoi(args.n);
    if (n <= 0) {
        ast_log(LOG_ERROR, "STACK_PEEK must be called with a positive peek value\n");
        return -1;
    }
 
    ast_channel_lock(chan);
    if (!(stack_store = ast_channel_datastore_find(chan, &stack_info, NULL))) {
        if (!ast_true(args.suppress)) {
            ast_log(LOG_ERROR, "STACK_PEEK called on a channel without a gosub stack\n");
        }
        ast_channel_unlock(chan);
        return -1;
    }
 
    oldlist = stack_store->data;
 
    AST_LIST_LOCK(oldlist);
    AST_LIST_TRAVERSE(oldlist, frame, entries) {
        if (--n == 0) {
            break;
        }
    }
 
    if (!frame) {
        /* Too deep */
        if (!ast_true(args.suppress)) {
            ast_log(LOG_ERROR, "Stack peek of '%s' is more stack frames than I have\n", args.n);
        }
        AST_LIST_UNLOCK(oldlist);
        ast_channel_unlock(chan);
        return -1;
    }
 
    args.which = ast_skip_blanks(args.which);
 
    switch (args.which[0]) {
    case 'l': /* label */
        ast_str_set(str, len, "%s,%s,%d", frame->context, frame->extension, frame->priority - 1);
        break;
    case 'c': /* context */
        ast_str_set(str, len, "%s", frame->context);
        break;
    case 'e': /* extension */
        ast_str_set(str, len, "%s", frame->extension);
        break;
    case 'p': /* priority */
        ast_str_set(str, len, "%d", frame->priority - 1);
        break;
    default:
        ast_log(LOG_ERROR, "Unknown argument '%s' to STACK_PEEK\n", args.which);
        break;
    }
 
    AST_LIST_UNLOCK(oldlist);
    ast_channel_unlock(chan);
 
    return 0;
}
 
static struct ast_custom_function stackpeek_function = {
    .name = "STACK_PEEK",
    .read2 = stackpeek_read,
};
 
/*!
 * \internal
 * \brief Pop stack frames until remove a special return location.
 * \since 11.0
 *
 * \param chan Channel to balance stack on.
 *
 * \note The channel is already locked when called.
 */
static void balance_stack(struct ast_channel *chan)
{
    struct ast_datastore *stack_store;
    struct gosub_stack_list *oldlist;
    struct gosub_stack_frame *oldframe;
    int found;
 
    stack_store = ast_channel_datastore_find(chan, &stack_info, NULL);
    if (!stack_store) {
        ast_log(LOG_WARNING, "No %s stack allocated.\n", app_gosub);
        return;
    }
 
    oldlist = stack_store->data;
    AST_LIST_LOCK(oldlist);
    do {
        oldframe = AST_LIST_REMOVE_HEAD(oldlist, entries);
        if (!oldframe) {
            break;
        }
        found = oldframe->is_special;
        gosub_release_frame(chan, oldframe);
    } while (!found);
    AST_LIST_UNLOCK(oldlist);
}
 
/*!
 * \internal
 * \brief Run a subroutine on a channel.
 * \since 11.0
 *
 * \note Absolutely _NO_ channel locks should be held before calling this function.
 *
 * \param chan Channel to execute subroutine on.
 * \param sub_args Gosub application argument string.
 * \param ignore_hangup TRUE if a hangup does not stop execution of the routine.
 *
 * \retval 0 success
 * \retval -1 on error
 */
static int gosub_run(struct ast_channel *chan, const char *sub_args, int ignore_hangup)
{
    const char *saved_context;
    const char *saved_exten;
    int saved_priority;
    int saved_hangup_flags;
    int saved_autoloopflag;
    int saved_in_subroutine;
    int res;
 
    ast_channel_lock(chan);
 
    ast_verb(3, "%s Internal %s(%s) start\n",
        ast_channel_name(chan), app_gosub, sub_args);
 
    /* Save non-hangup softhangup flags. */
    saved_hangup_flags = ast_channel_softhangup_internal_flag(chan)
        & AST_SOFTHANGUP_ASYNCGOTO;
    if (saved_hangup_flags) {
        ast_channel_clear_softhangup(chan, AST_SOFTHANGUP_ASYNCGOTO);
    }
 
    /* Save autoloop flag */
    saved_autoloopflag = ast_test_flag(ast_channel_flags(chan), AST_FLAG_IN_AUTOLOOP);
    ast_set_flag(ast_channel_flags(chan), AST_FLAG_IN_AUTOLOOP);
 
    /* Save current dialplan location */
    saved_context = ast_strdupa(ast_channel_context(chan));
    saved_exten = ast_strdupa(ast_channel_exten(chan));
    saved_priority = ast_channel_priority(chan);
 
    /* Save whether or not we are in a subroutine */
    saved_in_subroutine = ast_test_flag(ast_channel_flags(chan), AST_FLAG_SUBROUTINE_EXEC);
 
    ast_debug(4, "%s Original location: %s,%s,%d\n", ast_channel_name(chan),
        saved_context, saved_exten, saved_priority);
 
    ast_channel_unlock(chan);
    res = gosub_exec(chan, sub_args);
    ast_debug(4, "%s exited with status %d\n", app_gosub, res);
    ast_channel_lock(chan);
    if (!res) {
        struct ast_datastore *stack_store;
 
        /* Mark the return location as special. */
        stack_store = ast_channel_datastore_find(chan, &stack_info, NULL);
        if (!stack_store) {
            /* Should never happen! */
            ast_log(LOG_ERROR, "No %s stack!\n", app_gosub);
            res = -1;
        } else {
            struct gosub_stack_list *oldlist;
            struct gosub_stack_frame *cur;
 
            oldlist = stack_store->data;
            cur = AST_LIST_FIRST(oldlist);
            cur->is_special = 1;
        }
    }
    if (!res) {
        int found = 0;  /* set if we find at least one match */
 
        /*
         * Run gosub body autoloop.
         *
         * Note that this loop is inverted from the normal execution
         * loop because we just executed the Gosub application as the
         * first extension of the autoloop.
         */
        do {
            /* Check for hangup. */
            if (ast_check_hangup(chan)) {
                if (ast_channel_softhangup_internal_flag(chan) & AST_SOFTHANGUP_ASYNCGOTO) {
                    ast_log(LOG_ERROR, "%s An async goto just messed up our execution location.\n",
                        ast_channel_name(chan));
                    break;
                }
                if (!ignore_hangup) {
                    break;
                }
            }
 
            /* Next dialplan priority. */
            ast_channel_priority_set(chan, ast_channel_priority(chan) + 1);
 
            ast_channel_unlock(chan);
            res = ast_spawn_extension(chan, ast_channel_context(chan),
                ast_channel_exten(chan), ast_channel_priority(chan),
                S_COR(ast_channel_caller(chan)->id.number.valid,
                    ast_channel_caller(chan)->id.number.str, NULL),
                &found, 1);
            ast_channel_lock(chan);
        } while (!res);
        if (found && res) {
            /* Something bad happened, or a hangup has been requested. */
            ast_debug(1, "Spawn extension (%s,%s,%d) exited with %d on '%s'\n",
                ast_channel_context(chan), ast_channel_exten(chan),
                ast_channel_priority(chan), res, ast_channel_name(chan));
            ast_verb(2, "Spawn extension (%s, %s, %d) exited non-zero on '%s'\n",
                ast_channel_context(chan), ast_channel_exten(chan),
                ast_channel_priority(chan), ast_channel_name(chan));
        }
 
        /* Did the routine return? */
        if (ast_channel_priority(chan) == saved_priority
            && !strcmp(ast_channel_context(chan), saved_context)
            && !strcmp(ast_channel_exten(chan), saved_exten)) {
            ast_verb(3, "%s Internal %s(%s) complete GOSUB_RETVAL=%s\n",
                ast_channel_name(chan), app_gosub, sub_args,
                S_OR(pbx_builtin_getvar_helper(chan, "GOSUB_RETVAL"), ""));
        } else {
            ast_log(LOG_WARNING, "%s Abnormal '%s(%s)' exit.  Popping routine return locations.\n",
                ast_channel_name(chan), app_gosub, sub_args);
            balance_stack(chan);
            pbx_builtin_setvar_helper(chan, "GOSUB_RETVAL", "");
        }
 
        /* We executed the requested subroutine to the best of our ability. */
        res = 0;
    }
 
    ast_debug(4, "%s Ending location: %s,%s,%d\n", ast_channel_name(chan),
        ast_channel_context(chan), ast_channel_exten(chan),
        ast_channel_priority(chan));
 
    /* Restore dialplan location */
    if (!(ast_channel_softhangup_internal_flag(chan) & AST_SOFTHANGUP_ASYNCGOTO)) {
        ast_channel_context_set(chan, saved_context);
        ast_channel_exten_set(chan, saved_exten);
        ast_channel_priority_set(chan, saved_priority);
    }
 
    /* Restore autoloop flag */
    ast_set2_flag(ast_channel_flags(chan), saved_autoloopflag, AST_FLAG_IN_AUTOLOOP);
 
    /* Restore subroutine flag */
    ast_set2_flag(ast_channel_flags(chan), saved_in_subroutine, AST_FLAG_SUBROUTINE_EXEC);
 
    /* Restore non-hangup softhangup flags. */
    if (saved_hangup_flags) {
        ast_softhangup_nolock(chan, saved_hangup_flags);
    }
 
    ast_channel_unlock(chan);
 
    return res;
}
 
static int handle_gosub(struct ast_channel *chan, AGI *agi, int argc, const char * const *argv)
{
    int res;
    int priority;
    int old_autoloopflag;
    int old_in_subroutine;
    int old_priority;
    const char *old_context;
    const char *old_extension;
    char *gosub_args;
 
    if (argc < 4 || argc > 5) {
        return RESULT_SHOWUSAGE;
    }
 
    ast_debug(1, "Gosub called with %d arguments: 0:%s 1:%s 2:%s 3:%s 4:%s\n", argc, argv[0], argv[1], argv[2], argv[3], argc == 5 ? argv[4] : "");
 
    if (sscanf(argv[3], "%30d", &priority) != 1 || priority < 1) {
        /* Lookup the priority label */
        priority = ast_findlabel_extension(chan, argv[1], argv[2], argv[3],
            S_COR(ast_channel_caller(chan)->id.number.valid, ast_channel_caller(chan)->id.number.str, NULL));
        if (priority < 0) {
            ast_log(LOG_ERROR, "Priority '%s' not found in '%s@%s'\n", argv[3], argv[2], argv[1]);
            ast_agi_send(agi->fd, chan, "200 result=-1 Gosub label not found\n");
            return RESULT_FAILURE;
        }
    } else if (!ast_exists_extension(chan, argv[1], argv[2], priority,
        S_COR(ast_channel_caller(chan)->id.number.valid, ast_channel_caller(chan)->id.number.str, NULL))) {
        ast_agi_send(agi->fd, chan, "200 result=-1 Gosub label not found\n");
        return RESULT_FAILURE;
    }
 
    if (argc == 5) {
        if (ast_asprintf(&gosub_args, "%s,%s,%d(%s)", argv[1], argv[2], priority, argv[4]) < 0) {
            gosub_args = NULL;
        }
    } else {
        if (ast_asprintf(&gosub_args, "%s,%s,%d", argv[1], argv[2], priority) < 0) {
            gosub_args = NULL;
        }
    }
    if (!gosub_args) {
        ast_agi_send(agi->fd, chan, "503 result=-2 Memory allocation failure\n");
        return RESULT_FAILURE;
    }
 
    ast_channel_lock(chan);
 
    ast_verb(3, "%s AGI %s(%s) start\n", ast_channel_name(chan), app_gosub, gosub_args);
 
    /* Save autoloop flag */
    old_autoloopflag = ast_test_flag(ast_channel_flags(chan), AST_FLAG_IN_AUTOLOOP);
    ast_set_flag(ast_channel_flags(chan), AST_FLAG_IN_AUTOLOOP);
 
    /* Save subroutine flag */
    old_in_subroutine = ast_test_flag(ast_channel_flags(chan), AST_FLAG_SUBROUTINE_EXEC);
 
    /* Save previous location, since we're going to change it */
    old_context = ast_strdupa(ast_channel_context(chan));
    old_extension = ast_strdupa(ast_channel_exten(chan));
    old_priority = ast_channel_priority(chan);
 
    ast_debug(4, "%s Original location: %s,%s,%d\n", ast_channel_name(chan),
        old_context, old_extension, old_priority);
    ast_channel_unlock(chan);
 
    res = gosub_exec(chan, gosub_args);
    if (!res) {
        struct ast_datastore *stack_store;
 
        /* Mark the return location as special. */
        ast_channel_lock(chan);
        stack_store = ast_channel_datastore_find(chan, &stack_info, NULL);
        if (!stack_store) {
            /* Should never happen! */
            ast_log(LOG_ERROR, "No %s stack!\n", app_gosub);
            res = -1;
        } else {
            struct gosub_stack_list *oldlist;
            struct gosub_stack_frame *cur;
 
            oldlist = stack_store->data;
            cur = AST_LIST_FIRST(oldlist);
            cur->is_special = 1;
        }
        ast_channel_unlock(chan);
    }
    if (!res) {
        struct ast_pbx *pbx;
        struct ast_pbx_args args;
        int abnormal_exit;
 
        memset(&args, 0, sizeof(args));
        args.no_hangup_chan = 1;
 
        ast_channel_lock(chan);
 
        /* Next dialplan priority. */
        ast_channel_priority_set(chan, ast_channel_priority(chan) + 1);
 
        /* Suppress warning about PBX already existing */
        pbx = ast_channel_pbx(chan);
        ast_channel_pbx_set(chan, NULL);
        ast_channel_unlock(chan);
 
        ast_agi_send(agi->fd, chan, "100 result=0 Trying...\n");
        ast_pbx_run_args(chan, &args);
 
        ast_channel_lock(chan);
        ast_free(ast_channel_pbx(chan));
        ast_channel_pbx_set(chan, pbx);
 
        /* Did the routine return? */
        if (ast_channel_priority(chan) == old_priority
            && !strcmp(ast_channel_context(chan), old_context)
            && !strcmp(ast_channel_exten(chan), old_extension)) {
            ast_verb(3, "%s AGI %s(%s) complete GOSUB_RETVAL=%s\n",
                ast_channel_name(chan), app_gosub, gosub_args,
                S_OR(pbx_builtin_getvar_helper(chan, "GOSUB_RETVAL"), ""));
            abnormal_exit = 0;
        } else {
            ast_log(LOG_NOTICE, "%s Abnormal AGI %s(%s) exit.  Popping routine return locations.\n",
                ast_channel_name(chan), app_gosub, gosub_args);
            balance_stack(chan);
            pbx_builtin_setvar_helper(chan, "GOSUB_RETVAL", "");
            abnormal_exit = 1;
        }
        ast_channel_unlock(chan);
 
        ast_agi_send(agi->fd, chan, "200 result=0 Gosub complete%s\n",
            abnormal_exit ? " (abnormal exit)" : "");
    } else {
        ast_agi_send(agi->fd, chan, "200 result=%d Gosub failed\n", res);
    }
 
    ast_free(gosub_args);
 
    ast_channel_lock(chan);
    ast_debug(4, "%s Ending location: %s,%s,%d\n", ast_channel_name(chan),
        ast_channel_context(chan), ast_channel_exten(chan),
        ast_channel_priority(chan));
 
    /* Restore previous location */
    ast_channel_context_set(chan, old_context);
    ast_channel_exten_set(chan, old_extension);
    ast_channel_priority_set(chan, old_priority);
 
    /* Restore autoloop flag */
    ast_set2_flag(ast_channel_flags(chan), old_autoloopflag, AST_FLAG_IN_AUTOLOOP);
 
    /* Restore subroutine flag */
    ast_set2_flag(ast_channel_flags(chan), old_in_subroutine, AST_FLAG_SUBROUTINE_EXEC);
    ast_channel_unlock(chan);
 
    return RESULT_SUCCESS;
}
 
static struct agi_command gosub_agi_command =
    { { "gosub", NULL }, handle_gosub, NULL, NULL, 0 };
 
static int unload_module(void)
{
    ast_install_stack_functions(NULL);
 
    ast_agi_unregister(&gosub_agi_command);
 
    ast_unregister_application(app_return);
    ast_unregister_application(app_pop);
    ast_unregister_application(app_gosubif);
    ast_unregister_application(app_gosub);
    ast_custom_function_unregister(&local_function);
    ast_custom_function_unregister(&peek_function);
    ast_custom_function_unregister(&stackpeek_function);
 
    return 0;
}
 
static int load_module(void)
{
    /* Setup the stack application callback functions. */
    static struct ast_app_stack_funcs funcs = {
        .run_sub = gosub_run,
        .expand_sub_args = expand_gosub_args,
    };
 
    ast_agi_register(ast_module_info->self, &gosub_agi_command);
 
    ast_register_application_xml(app_pop, pop_exec);
    ast_register_application_xml(app_return, return_exec);
    ast_register_application_xml(app_gosubif, gosubif_exec);
    ast_register_application_xml(app_gosub, gosub_exec);
    ast_custom_function_register(&local_function);
    ast_custom_function_register(&peek_function);
    ast_custom_function_register(&stackpeek_function);
 
    funcs.module = ast_module_info->self,
    ast_install_stack_functions(&funcs);
 
    return 0;
}
 
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT | AST_MODFLAG_LOAD_ORDER, "Dialplan subroutines (Gosub, Return, etc)",
    .support_level = AST_MODULE_SUPPORT_CORE,
    .load = load_module,
    .unload = unload_module,
    .load_pri = AST_MODPRI_APP_DEPEND,
    .optional_modules = "res_agi",
);