app_waitforcond: New application

While several applications exist to wait for
a certain event to occur, none allow waiting
for any generic expression to become true.
This application allows for waiting for a condition
to become true, with configurable timeout and
checking interval.

ASTERISK-29444

Change-Id: I08adf2824b8bc63405778cf355963b5005612f41

apps/app_waitforcond.c

@@ -0,0 +1,234 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2021, Naveen Albert
+ *
+ * Naveen Albert <asterisk@phreaknet.org>
+ *
+ * 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 Sleep until a condition is true
+ *
+ * \author Naveen Albert <asterisk@phreaknet.org>
+ *
+ * \ingroup applications
+ */
+
+/*** MODULEINFO
+	<support_level>extended</support_level>
+ ***/
+
+#include "asterisk.h"
+
+#include "asterisk/logger.h"
+#include "asterisk/channel.h"
+#include "asterisk/pbx.h"
+#include "asterisk/module.h"
+#include "asterisk/app.h"
+
+/*** DOCUMENTATION
+	<application name="WaitForCondition" language="en_US">
+		<synopsis>
+			Wait (sleep) until the given condition is true.
+		</synopsis>
+		<syntax>
+			<parameter name="replacementchar" required="true">
+				<para>Specifies the character in the expression used to replace the <literal>$</literal>
+				character. This character should not be used anywhere in the expression itself.</para>
+			</parameter>
+			<parameter name="expression" required="true">
+				<para>A modified logical expression with the <literal>$</literal> characters replaced by
+				<replaceable>replacementchar</replaceable>. This is necessary to pass the expression itself
+				into the application, rather than its initial evaluation.</para>
+			</parameter>
+			<parameter name="timeout">
+				<para>The maximum amount of time, in seconds, this application should wait for a condition
+				to become true before dialplan execution continues automatically to the next priority.
+				By default, there is no timeout.</para>
+			</parameter>
+			<parameter name="interval">
+				<para>The frequency, in seconds, of polling the condition, which can be adjusted depending
+				on how time-sensitive execution needs to be. By default, this is 0.05.</para>
+			</parameter>
+		</syntax>
+		<description>
+			<para>Waits until <replaceable>expression</replaceable> evaluates to true, checking every
+			<replaceable>interval</replaceable> seconds for up to <replaceable>timeout</replaceable>. Default
+			is evaluate <replaceable>expression</replaceable> every 50 milliseconds with no timeout.</para>
+			<example title="Wait for ${condition} to become 1 for up to 40 seconds, checking every 500ms">
+			 same => n,WaitForCondition(#,#["#{condition}"="1"],40,0.5)
+			</example>
+			<para>Sets <variable>WAITFORCONDITIONSTATUS</variable> to one of the following values:</para>
+			<variablelist>
+				<variable name="WAITFORCONDITIONSTATUS">
+					<value name="TRUE">
+						Condition evaluated to true before timeout expired.
+					</value>
+					<value name="FAILURE">
+						Invalid argument.
+					</value>
+					<value name="TIMEOUT">
+						Timeout elapsed without condition evaluating to true.
+					</value>
+					<value name="HANGUP">
+						Channel hung up before condition became true.
+					</value>
+				</variable>
+			</variablelist>
+		</description>
+	</application>
+ ***/
+
+static char *app = "WaitForCondition";
+
+static int waitforcond_exec(struct ast_channel *chan, const char *data)
+{
+	int ms, i;
+	double timeout = 0, poll = 0;
+	int timeout_ms = 0;
+	int poll_ms = 50; /* default is evaluate the condition every 50ms */
+	struct timeval start = ast_tvnow();
+	char dollarsignrep;
+	int brackets = 0;
+	char *pos, *open_bracket, *expression, *optargs = NULL;
+	char condition[512];
+
+	AST_DECLARE_APP_ARGS(args,
+		AST_APP_ARG(timeout);
+		AST_APP_ARG(interval);
+	);
+
+	pos = ast_strdupa(data);
+
+	if (ast_strlen_zero(pos)) {
+		ast_log(LOG_ERROR, "WaitForCondition requires a condition\n");
+		pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "FAILURE");
+		return 0;
+	}
+
+	/* is there at least a [ followed by a ] somewhere ? */
+	if (!(open_bracket = strchr(pos, '[')) || !strchr(open_bracket, ']')) {
+		ast_log(LOG_ERROR, "No expression detected. Did you forget to replace the $ signs?\n");
+		pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "FAILURE");
+		return 0;
+	}
+
+	dollarsignrep = pos[0];
+	if (dollarsignrep == '$' || dollarsignrep == '[' || dollarsignrep == ']'
+		|| dollarsignrep == '{' || dollarsignrep == '}') {
+		ast_log(LOG_ERROR, "Dollar sign replacement cannot be %c.\n", dollarsignrep);
+		pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "FAILURE");
+		return 0;
+	}
+	++pos;
+	if (pos[0] != ',') {
+		ast_log(LOG_ERROR, "Invalid separator: %c\n", pos[0]);
+		pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "FAILURE");
+		return 0;
+	}
+	++pos;
+	if (pos[0] != dollarsignrep) {
+		ast_log(LOG_ERROR, "Expression start does not match provided replacement: %c\n", pos[0]);
+		pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "FAILURE");
+		return 0;
+	}
+
+	expression = pos; /* we're at the start of the expression */
+
+	/* commas may appear within the expression, so go until we've encountered as many closing brackets as opening */
+	while (++pos) {
+		if (pos[0] == '\0') {
+			ast_log(LOG_ERROR, "Could not parse end of expression.\n");
+			pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "FAILURE");
+			return 0;
+		}
+		if (pos[0] == '[') {
+			brackets++;
+		} else if (pos[0] == ']') {
+			brackets--;
+		}
+		if (brackets == 0) { /* reached end of expression */
+			break;
+		}
+	}
+	++pos;
+	if (pos[0] != '\0') {
+		++pos; /* eat comma separator */
+		if (pos[0] != '\0') {
+			optargs = ast_strdupa(pos);
+			AST_STANDARD_APP_ARGS(args, optargs);
+			if (!ast_strlen_zero(args.timeout)) {
+				if (sscanf(args.timeout, "%30lg", &timeout) != 1) {
+					ast_log(LOG_WARNING, "Invalid timeout provided: %s. No timeout set.\n", args.timeout);
+					return -1;
+				}
+				timeout_ms = timeout * 1000.0;
+			}
+
+			if (!ast_strlen_zero(args.interval)) {
+				if (sscanf(args.interval, "%30lg", &poll) != 1) {
+					ast_log(LOG_WARNING, "Invalid polling interval provided: %s. Default unchanged.\n", args.interval);
+					return -1;
+				}
+				if (poll < 0.001) {
+					ast_log(LOG_WARNING, "Polling interval cannot be less than 1ms. Default unchanged.\n");
+					return -1;
+				}
+				poll_ms = poll * 1000.0;
+			}
+		}
+	}
+
+	for (i = 0; expression[i] != '\0'; i++) {
+		if (expression[i] == dollarsignrep) {
+			expression[i] = '$'; /* replace $s back into expression for variable parsing */
+		}
+	}
+
+	if (timeout_ms > 0) {
+		ast_debug(1, "Waiting for condition for %f seconds: %s (checking every %d ms)", timeout, expression, poll_ms);
+	} else {
+		ast_debug(1, "Waiting for condition, forever: %s (checking every %d ms)", expression, poll_ms);
+	}
+
+	while (1) {
+		/* Substitute variables now */
+		pbx_substitute_variables_helper(chan, expression, condition, sizeof(condition) - 1);
+		if (pbx_checkcondition(condition)) {
+			pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "TRUE");
+			return 0;
+		}
+		/* If a timeout was specified, check that it hasn't expired */
+		if ((timeout_ms > 0) && !(ms = ast_remaining_ms(start, timeout_ms))) {
+			pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "TIMEOUT");
+			return 0;
+		}
+		if (ast_safe_sleep(chan, poll_ms)) { /* don't waste CPU, we don't need a super tight loop */
+			pbx_builtin_setvar_helper(chan, "WAITFORCONDITIONSTATUS", "HANGUP");
+			return -1; /* channel hung up */
+		}
+	}
+}
+
+static int unload_module(void)
+{
+	return ast_unregister_application(app);
+}
+
+static int load_module(void)
+{
+	return ast_register_application_xml(app, waitforcond_exec);
+}
+
+AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "Wait until condition is true");

doc/CHANGES-staging/app_waitforcond.txt

@@ -0,0 +1,5 @@
+Subject: WaitForCondition application
+
+This application provides a way to halt
+dialplan execution until a provided
+condition evaluates to true.