func_export: Add EXPORT function

Adds the EXPORT function, which allows write
access to variables and functions on other
channels.

ASTERISK-29432 #close

Change-Id: I7492645ae4307553d0f586d78e13a4f586231fdf

doc/CHANGES-staging/func_export.txt

@@ -0,0 +1,5 @@
+Subject: New EXPORT function
+
+A new function, EXPORT, allows writing variables
+and functions on other channels, the complement
+of the IMPORT function.

funcs/func_export.c

@@ -0,0 +1,107 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2021-2022, Naveen Albert
+ *
+ * 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 Set variables and functions on other channels
+ *
+ * \author Naveen Albert <asterisk@phreaknet.org>
+ *
+ * \ingroup functions
+ */
+
+/*** MODULEINFO
+	<support_level>extended</support_level>
+ ***/
+
+#include "asterisk.h"
+
+#include "asterisk/module.h"
+#include "asterisk/channel.h"
+#include "asterisk/pbx.h"
+#include "asterisk/utils.h"
+#include "asterisk/app.h"
+#include "asterisk/stringfields.h"
+
+/*** DOCUMENTATION
+	<function name="EXPORT" language="en_US">
+		<synopsis>
+			Set variables or dialplan functions on any arbitrary channel that exists.
+		</synopsis>
+		<syntax>
+			<parameter name="channel" required="true">
+				<para>The complete channel name: <literal>SIP/12-abcd1234</literal>.</para>
+			</parameter>
+			<parameter name="var" required="true">
+				<para>Variable name</para>
+			</parameter>
+		</syntax>
+		<description>
+			<para>Allows setting variables or functions on any existing channel if it exists.</para>
+		</description>
+		<see-also>
+			<ref type="function">IMPORT</ref>
+			<ref type="function">MASTER_CHANNEL</ref>
+			<ref type="function">SHARED</ref>
+		</see-also>
+	</function>
+ ***/
+
+static int func_export_write(struct ast_channel *chan, const char *function, char *data, const char *value)
+{
+	struct ast_channel *ochan;
+
+	AST_DECLARE_APP_ARGS(args,
+		AST_APP_ARG(channel);
+		AST_APP_ARG(var);
+	);
+	AST_STANDARD_APP_ARGS(args, data);
+
+	if (!args.channel) {
+		ast_log(LOG_WARNING, "No channel was provided to %s function.\n", function);
+		return -1;
+	}
+	if (!args.var) {
+		ast_log(LOG_WARNING, "No variable name was provided to %s function.\n", function);
+		return -1;
+	}
+	ochan = ast_channel_get_by_name(args.channel);
+	if (!ochan) {
+		ast_log(LOG_WARNING, "Channel '%s' not found! '%s' not set.\n", args.channel, args.var);
+		return -1;
+	}
+
+	pbx_builtin_setvar_helper(ochan, data, value);
+	ast_channel_unref(ochan);
+	return 0;
+}
+
+static struct ast_custom_function export_function = {
+	.name = "EXPORT",
+	.write = func_export_write,
+};
+
+static int unload_module(void)
+{
+	return ast_custom_function_unregister(&export_function);
+}
+
+static int load_module(void)
+{
+	return ast_custom_function_register(&export_function);
+}
+
+AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "Set variables and functions on other channels");