app_waitforcond.c

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/*
 * 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">
        <since>
            <version>16.20.0</version>
            <version>18.6.0</version>
        </since>
        <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 dialplan variable/function 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");