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>res_agi</use>
   <support_level>core</support_level>
 ***/

#include "asterisk.h"
 
ASTERISK_FILE_VERSION(__FILE__, "$Revision: 396279 $")

#include "asterisk/pbx.h"
#include "asterisk/module.h"
#include "asterisk/app.h"
#include "asterisk/manager.h"
#include "asterisk/channel.h"
#include "asterisk/agi.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>
   </agi>
 ***/

static const char * const app_gosub = "Gosub";
static const char * const app_gosubif = "GosubIf";
static const char * const app_return = "Return";
static const char * const 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;
   unsigned int is_agi:1;
   char *context;
   char extension[0];
};

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;

   /* 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);
   }

   manager_event(EVENT_FLAG_DIALPLAN, "VarSet",
      "Channel: %s\r\n"
      "Variable: LOCAL(%s)\r\n"
      "Value: %s\r\n"
      "Uniqueid: %s\r\n",
      chan->name, var, value, chan->uniqueid);
   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, unsigned char arguments)
{
   struct gosub_stack_frame *new = NULL;
   int len_extension = strlen(extension), len_context = strlen(context);

   if ((new = ast_calloc(1, sizeof(*new) + 2 + len_extension + len_context))) {
      AST_LIST_HEAD_INIT_NOLOCK(&new->varshead);
      strcpy(new->extension, extension);
      new->context = new->extension + len_extension + 1;
      strcpy(new->context, context);
      new->priority = priority;
      new->arguments = arguments;
   }
   return new;
}

static void gosub_free(void *data)
{
   AST_LIST_HEAD(, gosub_stack_frame) *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;
   AST_LIST_HEAD(, gosub_stack_frame) *oldlist;

   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_REMOVE_HEAD(oldlist, entries);
   AST_LIST_UNLOCK(oldlist);

   if (oldframe) {
      gosub_release_frame(chan, oldframe);
   } else {
      ast_debug(1, "%s called with an empty gosub stack\n", app_pop);
   }
   ast_channel_unlock(chan);
   return 0;
}

static int return_exec(struct ast_channel *chan, const char *data)
{
   struct ast_datastore *stack_store;
   struct gosub_stack_frame *oldframe;
   AST_LIST_HEAD(, gosub_stack_frame) *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;
   } else if (oldframe->is_agi) {
      /* Exit from AGI */
      res = -1;
   }

   ast_explicit_goto(chan, oldframe->context, oldframe->extension, oldframe->priority);
   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;
}

static int gosub_exec(struct ast_channel *chan, const char *data)
{
   struct ast_datastore *stack_store;
   AST_LIST_HEAD(, gosub_stack_frame) *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_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(chan->context);
   orig_exten = ast_strdupa(chan->exten);
   orig_priority = chan->priority;
   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(chan->context);
   dest_exten = ast_strdupa(chan->exten);
   dest_priority = chan->priority;
   if (ast_test_flag(chan, AST_FLAG_IN_AUTOLOOP)) {
      ++dest_priority;
   }
   caller_id = S_COR(chan->caller.id.number.valid, chan->caller.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",
         chan->name);
      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, 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), "%d", args2.argc);
   frame_set_var(chan, newframe, "ARGC", argname);

   /* 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_copy_string(chan->context, orig_context, sizeof(chan->context));
   ast_copy_string(chan->exten, orig_exten, sizeof(chan->exten));
   chan->priority = 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;
   AST_LIST_HEAD(, gosub_stack_frame) *oldlist;
   struct gosub_stack_frame *frame;
   struct ast_var_t *variables;

   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;
   AST_LIST_HEAD(, gosub_stack_frame) *oldlist;
   struct gosub_stack_frame *frame;

   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);
   n = atoi(args.n);
   *buf = '\0';

   ast_channel_lock(chan);
   AST_LIST_TRAVERSE(&chan->varshead, 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;
   AST_LIST_HEAD(, gosub_stack_frame) *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);

   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_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);
   }

   AST_LIST_UNLOCK(oldlist);
   ast_channel_unlock(chan);

   return 0;
}

static struct ast_custom_function stackpeek_function = {
   .name = "STACK_PEEK",
   .read2 = stackpeek_read,
};

static int handle_gosub(struct ast_channel *chan, AGI *agi, int argc, const char * const *argv)
{
   int old_priority, priority;
   char old_context[AST_MAX_CONTEXT], old_extension[AST_MAX_EXTENSION];
   struct ast_app *theapp;
   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(chan->caller.id.number.valid, chan->caller.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(chan->caller.id.number.valid, chan->caller.id.number.str, NULL))) {
      ast_agi_send(agi->fd, chan, "200 result=-1 Gosub label not found\n");
      return RESULT_FAILURE;
   }

   /* Save previous location, since we're going to change it */
   ast_copy_string(old_context, chan->context, sizeof(old_context));
   ast_copy_string(old_extension, chan->exten, sizeof(old_extension));
   old_priority = chan->priority;

   if (!(theapp = pbx_findapp("Gosub"))) {
      ast_log(LOG_ERROR, "Gosub() cannot be found in the list of loaded applications\n");
      ast_agi_send(agi->fd, chan, "503 result=-2 Gosub is not loaded\n");
      return RESULT_FAILURE;
   }

   /* Apparently, if you run ast_pbx_run on a channel that already has a pbx
    * structure, you need to add 1 to the priority to get it to go to the
    * right place.  But if it doesn't have a pbx structure, then leaving off
    * the 1 is the right thing to do.  See how this code differs when we
    * call a Gosub for the CALLEE channel in Dial or Queue.
    */
   if (argc == 5) {
      if (ast_asprintf(&gosub_args, "%s,%s,%d(%s)", argv[1], argv[2], priority + (chan->pbx ? 1 : 0), argv[4]) < 0) {
         gosub_args = NULL;
      }
   } else {
      if (ast_asprintf(&gosub_args, "%s,%s,%d", argv[1], argv[2], priority + (chan->pbx ? 1 : 0)) < 0) {
         gosub_args = NULL;
      }
   }

   if (gosub_args) {
      int res;

      ast_debug(1, "Trying gosub with arguments '%s'\n", gosub_args);

      if ((res = pbx_exec(chan, theapp, gosub_args)) == 0) {
         struct ast_pbx *pbx = chan->pbx;
         struct ast_pbx_args args;
         struct ast_datastore *stack_store = ast_channel_datastore_find(chan, &stack_info, NULL);
         AST_LIST_HEAD(, gosub_stack_frame) *oldlist;
         struct gosub_stack_frame *cur;
         if (!stack_store) {
            ast_log(LOG_WARNING, "No GoSub stack remaining after AGI GoSub execution.\n");
            ast_free(gosub_args);
            return RESULT_FAILURE;
         }
         oldlist = stack_store->data;
         cur = AST_LIST_FIRST(oldlist);
         cur->is_agi = 1;

         memset(&args, 0, sizeof(args));
         args.no_hangup_chan = 1;
         /* Suppress warning about PBX already existing */
         chan->pbx = NULL;
         ast_agi_send(agi->fd, chan, "100 result=0 Trying...\n");
         ast_pbx_run_args(chan, &args);
         ast_agi_send(agi->fd, chan, "200 result=0 Gosub complete\n");
         if (chan->pbx) {
            ast_free(chan->pbx);
         }
         chan->pbx = pbx;
      } else {
         ast_agi_send(agi->fd, chan, "200 result=%d Gosub failed\n", res);
      }
      ast_free(gosub_args);
   } else {
      ast_agi_send(agi->fd, chan, "503 result=-2 Memory allocation failure\n");
      return RESULT_FAILURE;
   }

   /* Restore previous location */
   ast_copy_string(chan->context, old_context, sizeof(chan->context));
   ast_copy_string(chan->exten, old_extension, sizeof(chan->exten));
   chan->priority = old_priority;

   return RESULT_SUCCESS;
}

static struct agi_command gosub_agi_command =
   { { "gosub", NULL }, handle_gosub, NULL, NULL, 0 };

static int unload_module(void)
{
   ast_agi_unregister(ast_module_info->self, &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)
{
   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);

   return 0;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT | AST_MODFLAG_LOAD_ORDER, "Dialplan subroutines (Gosub, Return, etc)",
      .load = load_module,
      .unload = unload_module,
      .load_pri = AST_MODPRI_APP_DEPEND,
      .nonoptreq = "res_agi",
      );