func_json: Adds JSON_DECODE function

Adds the JSON_DECODE function for parsing JSON in the
dialplan. JSON parsing already exists in the Asterisk
core and is used for many different things. This
function exposes the basic parsing capability to
the user in the dialplan, for instance, in conjunction
with CURL for using API responses.

ASTERISK-29706 #close

Change-Id: Iea60c49a7358dfdc2db60803cdc9a742f808ba2c

Author: InterLinked1

doc/CHANGES-staging/func_json.txt

@@ -0,0 +1,5 @@
+Subject: func_json
+
+The JSON_DECODE dialplan function can now be used
+to parse JSON strings, such as in conjunction with
+CURL for using API responses.

funcs/func_json.c

@@ -0,0 +1,228 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2021, 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 JSON parsing function
+ *
+ * \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/test.h"
+#include "asterisk/app.h"
+#include "asterisk/conversions.h"
+
+/*** DOCUMENTATION
+	<function name="JSON_DECODE" language="en_US">
+		<synopsis>
+			Returns the string value of a JSON object key from a string containing a
+			JSON array.
+		</synopsis>
+		<syntax>
+			<parameter name="varname" required="true">
+				<para>The name of the variable containing the JSON string to parse.</para>
+			</parameter>
+			<parameter name="item" required="true">
+				<para>The name of the key whose value to return.</para>
+			</parameter>
+		</syntax>
+		<description>
+			<para>The JSON_DECODE function retrieves the value of the given variable name
+			and parses it as JSON, returning the value at a specified key. If the key cannot
+			be found, an empty string is returned.</para>
+		</description>
+		<see-also>
+			<ref type="function">CURL</ref>
+		</see-also>
+	</function>
+ ***/
+
+AST_THREADSTORAGE(result_buf);
+
+static int json_decode_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
+{
+	struct ast_json *json, *jsonval;
+	AST_DECLARE_APP_ARGS(args,
+		AST_APP_ARG(varname);
+		AST_APP_ARG(key);
+	);
+	char *varsubst, *result2;
+	const char *result = NULL;
+	struct ast_str *str = ast_str_thread_get(&result_buf, 16);
+
+	AST_STANDARD_APP_ARGS(args, data);
+
+	if (ast_strlen_zero(args.varname)) {
+		ast_log(LOG_WARNING, "%s requires a variable name\n", cmd);
+		return -1;
+	}
+	if (ast_strlen_zero(args.key)) {
+		ast_log(LOG_WARNING, "%s requires a key\n", cmd);
+		return -1;
+	}
+
+	varsubst = ast_alloca(strlen(args.varname) + 4); /* +4 for ${} and null terminator */
+	if (!varsubst) {
+		ast_log(LOG_ERROR, "Failed to allocate string\n");
+		return -1;
+	}
+	sprintf(varsubst, "${%s}", args.varname); /* safe, because of the above allocation */
+	ast_str_substitute_variables(&str, 0, chan, varsubst);
+	if (ast_str_strlen(str) == 0) {
+		ast_debug(1, "Variable '%s' contains no data, nothing to search!\n", args.varname);
+		return -1; /* empty json string */
+	}
+
+	ast_debug(1, "Parsing JSON: %s\n", ast_str_buffer(str));
+
+	json = ast_json_load_str(str, NULL);
+
+	if (!json) {
+		ast_log(LOG_WARNING, "Failed to parse as JSON: %s\n", ast_str_buffer(str));
+		return -1;
+	}
+
+	jsonval = ast_json_object_get(json, args.key);
+	if (!jsonval) { /* no error or warning should be thrown */
+		ast_debug(1, "Could not find key '%s' in parsed JSON\n", args.key);
+		ast_json_free(json);
+		return -1;
+	}
+	switch(ast_json_typeof(jsonval)) {
+		int r;
+		case AST_JSON_STRING:
+			result = ast_json_string_get(jsonval);
+			snprintf(buf, len, "%s", result);
+			break;
+		case AST_JSON_INTEGER:
+			r = ast_json_integer_get(jsonval);
+			snprintf(buf, len, "%d", r); /* the snprintf below is mutually exclusive with this one */
+			break;
+		default:
+			result2 = ast_json_dump_string(jsonval);
+			snprintf(buf, len, "%s", result2);
+			ast_json_free(result2);
+			break;
+	}
+	ast_json_free(json);
+
+	return 0;
+}
+
+static struct ast_custom_function json_decode_function = {
+	.name = "JSON_DECODE",
+	.read = json_decode_read,
+};
+
+#ifdef TEST_FRAMEWORK
+AST_TEST_DEFINE(test_JSON_DECODE)
+{
+	int i, res = AST_TEST_PASS;
+	struct ast_channel *chan; /* dummy channel */
+	struct ast_str *str; /* fancy string for holding comparing value */
+
+	const char *test_strings[][5] = {
+		{"{\"city\": \"Anytown\", \"state\": \"USA\"}", "city", "Anytown"},
+		{"{\"city\": \"Anytown\", \"state\": \"USA\"}", "state", "USA"},
+		{"{\"city\": \"Anytown\", \"state\": \"USA\"}", "blah", ""},
+		{"{\"key1\": \"123\", \"key2\": \"456\"}", "key1", "123"},
+		{"{\"key1\": 123, \"key2\": 456}", "key1", "123"},
+	};
+
+	switch (cmd) {
+	case TEST_INIT:
+		info->name = "func_JSON_DECODE";
+		info->category = "/funcs/func_json/";
+		info->summary = "Test JSON_DECODE function";
+		info->description = "Verify JSON_DECODE behavior";
+		return AST_TEST_NOT_RUN;
+	case TEST_EXECUTE:
+		break;
+	}
+
+	if (!(chan = ast_dummy_channel_alloc())) {
+		ast_test_status_update(test, "Unable to allocate dummy channel\n");
+		return AST_TEST_FAIL;
+	}
+
+	if (!(str = ast_str_create(64))) {
+		ast_test_status_update(test, "Unable to allocate dynamic string buffer\n");
+		ast_channel_release(chan);
+		return AST_TEST_FAIL;
+	}
+
+	for (i = 0; i < ARRAY_LEN(test_strings); i++) {
+		char tmp[512], tmp2[512] = "";
+
+		struct ast_var_t *var = ast_var_assign("test_string", test_strings[i][0]);
+		if (!var) {
+			ast_test_status_update(test, "Unable to allocate variable\n");
+			ast_free(str);
+			ast_channel_release(chan);
+			return AST_TEST_FAIL;
+		}
+
+		AST_LIST_INSERT_HEAD(ast_channel_varshead(chan), var, entries);
+
+		snprintf(tmp, sizeof(tmp), "${JSON_DECODE(%s,%s)}", "test_string", test_strings[i][1]);
+
+		ast_str_substitute_variables(&str, 0, chan, tmp);
+		if (strcmp(test_strings[i][2], ast_str_buffer(str))) {
+			ast_test_status_update(test, "Format string '%s' substituted to '%s'.  Expected '%s'.\n", test_strings[i][0], tmp2, test_strings[i][2]);
+			res = AST_TEST_FAIL;
+		}
+	}
+
+	ast_free(str);
+	ast_channel_release(chan);
+
+	return res;
+}
+#endif
+
+static int unload_module(void)
+{
+	int res;
+
+	AST_TEST_UNREGISTER(test_JSON_DECODE);
+	res = ast_custom_function_unregister(&json_decode_function);
+
+	return res;
+}
+
+static int load_module(void)
+{
+	int res;
+
+	AST_TEST_REGISTER(test_JSON_DECODE);
+	res = ast_custom_function_register(&json_decode_function);
+
+	return res;
+}
+
+AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "JSON decoding function");