stasis: set a channel variable on websocket disconnect error

When an error occurs while writing to a web socket, the web socket is
disconnected and the event is logged. A side-effect of this, however, is that
any application on the other side waiting for a response from Stasis is left
hanging indefinitely (as there is no mechanism presently available for
notifying interested parties about web socket error states in Stasis).

To remedy this scenario, this patch introduces a new channel variable:
STASISSTATUS.

The possible values for STASISSTATUS are:
SUCCESS         - The channel has exited Stasis without any failures
FAILED          - Something caused Stasis to croak. Some (not all) possible
                  reasons for this:
                    - The app registry is not instantiated;
                    - The app requested is not registered;
                    - The app requested is not active;
                    - Stasis couldn't send a start message

ASTERISK-24802
Reported By: Kevin Harwell
Review: https://reviewboard.asterisk.org/r/4519/
........

Merged revisions 433839 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@433845 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_stasis.c

@@ -54,6 +54,25 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 				Invoke a Stasis application.
 			</para>
 		</description>
+		<para>This application will set the following channel variable upon
+		completion:</para>
+			<variablelist>
+				<variable name="STASISSTATUS">
+					<para>This indicates the status of the execution of the
+					Stasis application.</para>
+					<value name="SUCCESS">
+					The channel has exited Stasis without any failures in Stasis
+					</value>
+					<value name="FAILED">
+					A failure occurred when executing the Stasis application.
+					Some (not all) possible reasons for this:
+					    <para>The app registry is not instantiated</para>
+					    <para>The app requested is not registered</para>
+					    <para>The app requested is not active</para>
+					    <para>Stasis couldn't send a start message</para>
+					</value>
+				</variable>
+			</variablelist>
 	</application>
  ***/
 
@@ -67,6 +86,7 @@ static const char *stasis = "Stasis";
 static int app_exec(struct ast_channel *chan, const char *data)
 {
 	char *parse = NULL;
+	int ret = -1;
 
 	AST_DECLARE_APP_ARGS(args,
 		AST_APP_ARG(app_name);
@@ -76,17 +96,28 @@ static int app_exec(struct ast_channel *chan, const char *data)
 	ast_assert(chan != NULL);
 	ast_assert(data != NULL);
 
+	pbx_builtin_setvar_helper(chan, "STASISSTATUS", "");
+
 	/* parse the arguments */
 	parse = ast_strdupa(data);
 	AST_STANDARD_APP_ARGS(args, parse);
 
 	if (args.argc < 1) {
 		ast_log(LOG_WARNING, "Stasis app_name argument missing\n");
-		return -1;
+	} else {
+		ret = stasis_app_exec(chan,
+		                      args.app_name,
+		                      args.argc - 1,
+		                      args.app_argv);
+	}
+
+	if (ret == -1) {
+	    pbx_builtin_setvar_helper(chan, "STASISSTATUS", "FAILED");
+	} else {
+	    pbx_builtin_setvar_helper(chan, "STASISSTATUS", "SUCCESS");
 	}
 
-	return stasis_app_exec(
-		chan, args.app_name, args.argc - 1, args.app_argv);
+	return ret;
 }
 
 static int load_module(void)