app_stack.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (c) 2004-2006 Tilghman Lesher <[email protected]>.
 *
 * 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 <[email protected]>
 *
 * \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">
 <synopsis>
 Jump to label, saving return address.
 </synopsis>
 <syntax>
 <parameter name="context" />
 <parameter name="exten" />
 <parameter name="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">Macro</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">
 <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="application">MacroIf</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">
 <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">
 <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">
 <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">
 <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">
 <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">
 <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, "Attempt to reach a non-existent destination for %s: (Context:%s, Extension:%s, Priority:%d)\n",
 app_gosub, dest_context, dest_exten, dest_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.
 *
 * \return Nothing
 */
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_NOTICE, "%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",
);