app_signal.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2022, 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 Channel signaling applications
 *
 * \author Naveen Albert <asterisk@phreaknet.org>
 *
 * \ingroup applications
 */
 
/*** MODULEINFO
    <support_level>extended</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/file.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/module.h"
#include "asterisk/app.h"
#include "asterisk/module.h"
 
/*** DOCUMENTATION
    <application name="Signal" language="en_US">
        <synopsis>
            Sends a signal to any waiting channels.
        </synopsis>
        <syntax>
            <parameter name="signalname" required="true">
                <para>Name of signal to send.</para>
            </parameter>
            <parameter name="payload" required="false">
                <para>Payload data to deliver.</para>
            </parameter>
        </syntax>
        <description>
            <para>Sends a named signal to any channels that may be
            waiting for one. Acts as a producer in a simple
            message queue.</para>
            <variablelist>
                <variable name="SIGNALSTATUS">
                    <value name="SUCCESS">
                        Signal was successfully sent to at least
                        one listener for processing.
                    </value>
                    <value name="FAILURE">
                        Signal could not be sent or nobody
                        was listening for this signal.
                    </value>
                </variable>
            </variablelist>
            <example title="Send a signal named workdone">
            same => n,Signal(workdone,Work has completed)
            </example>
        </description>
        <see-also>
            <ref type="application">WaitForSignal</ref>
        </see-also>
    </application>
    <application name="WaitForSignal" language="en_US">
        <synopsis>
            Waits for a named signal on a channel.
        </synopsis>
        <syntax>
            <parameter name="signalname" required="true">
                <para>Name of signal to send.</para>
            </parameter>
            <parameter name="signaltimeout" required="false">
                <para>Maximum time, in seconds, to wait for signal.</para>
            </parameter>
        </syntax>
        <description>
            <para>Waits for <replaceable>signaltimeout</replaceable> seconds on the current
            channel to receive a signal with name <replaceable>signalname</replaceable>.
            Acts as a consumer in a simple message queue.</para>
            <para>Result of signal wait will be stored in the following variables:</para>
            <variablelist>
                <variable name="WAITFORSIGNALSTATUS">
                    <value name="SIGNALED">
                        Signal was received.
                    </value>
                    <value name="TIMEOUT">
                        Timed out waiting for signal.
                    </value>
                    <value name="HANGUP">
                        Channel hung up before signal was received.
                    </value>
                </variable>
                <variable name="WAITFORSIGNALPAYLOAD">
                    <para>Data payload attached to signal, if it exists</para>
                </variable>
            </variablelist>
            <example title="Wait for the workdone signal, indefinitely, and print out payload">
            same => n,WaitForSignal(workdone)
            same => n,NoOp(Received: ${WAITFORSIGNALPAYLOAD})
            </example>
        </description>
        <see-also>
            <ref type="application">Signal</ref>
        </see-also>
    </application>
 ***/
 
static const char * const app = "Signal";
static const char * const app2 = "WaitForSignal";
 
struct signalitem {
    ast_mutex_t lock;
    char name[AST_MAX_CONTEXT];
    int sig_alert_pipe[2];
    int watchers;
    unsigned int signaled:1;
    char *payload;
    AST_LIST_ENTRY(signalitem) entry;       /*!< Next Signal item */
};
 
static AST_RWLIST_HEAD_STATIC(signals, signalitem);
 
static struct signalitem *alloc_signal(const char *sname)
{
    struct signalitem *s;
 
    if (!(s = ast_calloc(1, sizeof(*s)))) {
        return NULL;
    }
 
    ast_mutex_init(&s->lock);
    ast_copy_string(s->name, sname, sizeof(s->name));
 
    s->sig_alert_pipe[0] = -1;
    s->sig_alert_pipe[1] = -1;
    s->watchers = 0;
    s->payload = NULL;
    ast_alertpipe_init(s->sig_alert_pipe);
 
    return s;
}
 
static int dealloc_signal(struct signalitem *s)
{
    if (s->watchers) { /* somebody is still using us... refuse to go away */
        ast_debug(1, "Signal '%s' is still being used by %d listener(s)\n", s->name, s->watchers);
        return -1;
    }
    ast_alertpipe_close(s->sig_alert_pipe);
    ast_mutex_destroy(&s->lock);
    if (s->payload) {
        ast_free(s->payload);
        s->payload = NULL;
    }
    ast_free(s);
    s = NULL;
    return 0;
}
 
static int remove_signal(char *sname)
{
    int res = -1;
    struct signalitem *s;
 
    AST_LIST_TRAVERSE_SAFE_BEGIN(&signals, s, entry) {
        if (!strcmp(s->name, sname)) {
            AST_LIST_REMOVE_CURRENT(entry);
            res = dealloc_signal(s);
            ast_debug(1, "Removed signal '%s'\n", sname);
        }
    }
    AST_LIST_TRAVERSE_SAFE_END;
 
    return res;
}
 
static struct signalitem *get_signal(char *sname, int addnew)
{
    struct signalitem *s = NULL;
    AST_RWLIST_WRLOCK(&signals);
    AST_LIST_TRAVERSE(&signals, s, entry) {
        if (!strcasecmp(s->name, sname)) {
            ast_debug(1, "Using existing signal item '%s'\n", sname);
            break;
        }
    }
    if (!s) {
        if (addnew) { /* signal doesn't exist, so create it */
            s = alloc_signal(sname);
            /* Totally fail if we fail to find/create an entry */
            if (s) {
                ast_debug(1, "Created new signal item '%s'\n", sname);
                AST_RWLIST_INSERT_HEAD(&signals, s, entry);
            } else {
                ast_log(LOG_WARNING, "Failed to create signal item for '%s'\n", sname);
            }
        } else {
            ast_debug(1, "Signal '%s' doesn't exist, and not creating it\n", sname);
        }
    }
    AST_RWLIST_UNLOCK(&signals);
    return s;
}
 
static int wait_for_signal_or_hangup(struct ast_channel *chan, char *signame, int timeout)
{
    struct signalitem *s = NULL;
    int ms, remaining_time, res = 1, goaway = 0;
    struct timeval start;
    struct ast_frame *frame = NULL;
 
    remaining_time = timeout;
    start = ast_tvnow();
 
    s = get_signal(signame, 1);
 
    ast_mutex_lock(&s->lock);
    s->watchers = s->watchers + 1; /* we unlock, because a) other people need to use this and */
    ast_mutex_unlock(&s->lock); /* b) the signal will be available to us as long as watchers > 0 */
 
    while (timeout == 0 || remaining_time > 0) {
        int ofd, exception;
 
        ms = 1000;
        errno = 0;
        if (ast_waitfor_nandfds(&chan, 1, &s->sig_alert_pipe[0], 1, &exception, &ofd, &ms)) { /* channel won */
            if (!(frame = ast_read(chan))) { /* channel hung up */
                ast_debug(1, "Channel '%s' did not return a frame; probably hung up.\n", ast_channel_name(chan));
                res = -1;
                break;
            } else {
                ast_frfree(frame); /* handle frames */
            }
        } else if (ofd == s->sig_alert_pipe[0]) { /* fd won */
            if (ast_alertpipe_read(s->sig_alert_pipe) == AST_ALERT_READ_SUCCESS) {
                ast_debug(1, "Alert pipe has data for us\n");
                res = 0;
                break;
            } else {
                ast_debug(1, "Alert pipe does not have data for us\n");
            }
        } else { /* nobody won */
            if (ms && (ofd < 0)) {
                if (!((errno == 0) || (errno == EINTR))) {
                    ast_log(LOG_WARNING, "Something bad happened while channel '%s' was polling.\n", ast_channel_name(chan));
                    break;
                }
            } /* else, nothing happened */
        }
        if (timeout) {
            remaining_time = ast_remaining_ms(start, timeout);
        }
    }
 
    /* WRLOCK the list so that if we're going to destroy the signal now, nobody else can grab it before that happens. */
    AST_RWLIST_WRLOCK(&signals);
    ast_mutex_lock(&s->lock);
    if (s->payload) {
        pbx_builtin_setvar_helper(chan, "WAITFORSIGNALPAYLOAD", s->payload);
    }
    s->watchers = s->watchers - 1;
    if (s->watchers) { /* folks are still waiting for this, pass it on... */
        int save_errno = errno;
        if (ast_alertpipe_write(s->sig_alert_pipe)) {
            ast_log(LOG_WARNING, "%s: write() failed: %s\n", __FUNCTION__, strerror(errno));
        }
        errno = save_errno;
    } else { /* nobody else is waiting for this */
        goaway = 1; /* we were the last guy using this, so mark signal item for destruction */
    }
    ast_mutex_unlock(&s->lock);
 
    if (goaway) {
        /* remove_signal calls ast_mutex_destroy, so don't call it with the mutex itself locked. */
        remove_signal(signame);
    }
    AST_RWLIST_UNLOCK(&signals);
 
    return res;
}
 
static int send_signal(char *signame, char *payload)
{
    struct signalitem *s;
    int save_errno = errno;
    int res = 0;
 
    s = get_signal(signame, 0); /* if signal doesn't exist already, no point in creating it, because nobody could be waiting for it! */
 
    if (!s) {
        return -1; /* this signal didn't exist, so we can't send a signal for it */
    }
 
    /* at this point, we know someone is listening, since signals are destroyed when watchers gets down to 0 */
    ast_mutex_lock(&s->lock);
    s->signaled = 1;
    if (payload && *payload) {
        int len = strlen(payload);
        if (s->payload) {
            ast_free(s->payload); /* if there was already a payload, replace it */
            s->payload = NULL;
        }
        s->payload = ast_malloc(len + 1);
        if (!s->payload) {
            ast_log(LOG_WARNING, "Failed to allocate signal payload '%s'\n", payload);
        } else {
            ast_copy_string(s->payload, payload, len + 1);
        }
    }
    if (ast_alertpipe_write(s->sig_alert_pipe)) {
        ast_log(LOG_WARNING, "%s: write() failed: %s\n", __FUNCTION__, strerror(errno));
        s->signaled = 0; /* okay, so we didn't send a signal after all... */
        res = -1;
    }
    errno = save_errno;
    ast_debug(1, "Sent '%s' signal to %d listeners\n", signame, s->watchers);
    ast_mutex_unlock(&s->lock);
 
    return res;
}
 
static int waitsignal_exec(struct ast_channel *chan, const char *data)
{
    char *argcopy;
    int r = 0, timeoutms = 0;
    double timeout = 0;
 
    AST_DECLARE_APP_ARGS(args,
        AST_APP_ARG(signame);
        AST_APP_ARG(sigtimeout);
    );
 
    if (ast_strlen_zero(data)) {
        ast_log(LOG_WARNING, "Signal() requires arguments\n");
        return -1;
    }
 
    argcopy = ast_strdupa(data);
    AST_STANDARD_APP_ARGS(args, argcopy);
 
    if (ast_strlen_zero(args.signame)) {
        ast_log(LOG_WARNING, "Missing signal name\n");
        return -1;
    }
    if (strlen(args.signame) >= AST_MAX_CONTEXT) {
        ast_log(LOG_WARNING, "Signal name '%s' is too long\n", args.signame);
        return -1;
    }
    if (!ast_strlen_zero(args.sigtimeout)) {
        if (sscanf(args.sigtimeout, "%30lg", &timeout) != 1 || timeout < 0) {
            ast_log(LOG_WARNING, "Invalid timeout provided: %s. Defaulting to no timeout.\n", args.sigtimeout);
        } else {
            timeoutms = timeout * 1000; /* sec to msec */
        }
    }
 
    if (timeout > 0) {
        ast_debug(1, "Waiting for signal '%s' for %d ms\n", args.signame, timeoutms);
    } else {
        ast_debug(1, "Waiting for signal '%s', indefinitely\n", args.signame);
    }
 
    r = wait_for_signal_or_hangup(chan, args.signame, timeoutms);
 
    if (r == 1) {
        ast_verb(3, "Channel '%s' timed out, waiting for signal '%s'\n", ast_channel_name(chan), args.signame);
        pbx_builtin_setvar_helper(chan, "WAITFORSIGNALSTATUS", "TIMEOUT");
    } else if (!r) {
        ast_verb(3, "Received signal '%s' on channel '%s'\n", args.signame, ast_channel_name(chan));
        pbx_builtin_setvar_helper(chan, "WAITFORSIGNALSTATUS", "SIGNALED");
    } else {
        pbx_builtin_setvar_helper(chan, "WAITFORSIGNALSTATUS", "HANGUP");
        ast_verb(3, "Channel '%s' hung up\n", ast_channel_name(chan));
        return -1;
    }
 
    return 0;
}
 
static int signal_exec(struct ast_channel *chan, const char *data)
{
    char *argcopy;
    AST_DECLARE_APP_ARGS(args,
        AST_APP_ARG(signame);
        AST_APP_ARG(payload);
    );
 
    if (ast_strlen_zero(data)) {
        ast_log(LOG_WARNING, "Signal() requires arguments\n");
        return -1;
    }
 
    argcopy = ast_strdupa(data);
    AST_STANDARD_APP_ARGS(args, argcopy);
 
    if (ast_strlen_zero(args.signame)) {
        ast_log(LOG_WARNING, "Missing signal name\n");
        return -1;
    }
    if (strlen(args.signame) >= AST_MAX_CONTEXT) {
        ast_log(LOG_WARNING, "Signal name '%s' is too long\n", args.signame);
        return -1;
    }
 
    if (send_signal(args.signame, args.payload)) {
        pbx_builtin_setvar_helper(chan, "SIGNALSTATUS", "FAILURE");
    } else {
        pbx_builtin_setvar_helper(chan, "SIGNALSTATUS", "SUCCESS");
    }
 
    return 0;
}
 
static int unload_module(void)
{
    struct signalitem *s;
    int res = 0;
 
    /* To avoid a locking nightmare, and for logistical reasons, this module
     * will refuse to unload if watchers > 0. That way we know a signal's
     * pipe won't disappear while it's being used. */
 
    AST_RWLIST_WRLOCK(&signals);
    /* Don't just use AST_RWLIST_REMOVE_HEAD, because if dealloc_signal fails, it should stay in the list. */
    AST_LIST_TRAVERSE_SAFE_BEGIN(&signals, s, entry) {
        int mres = dealloc_signal(s);
        res |= mres;
        if (!mres) {
            AST_LIST_REMOVE_CURRENT(entry);
        }
    }
    AST_LIST_TRAVERSE_SAFE_END;
    AST_RWLIST_UNLOCK(&signals);
 
    /* One or more signals still has watchers. */
    if (res) {
        ast_log(LOG_WARNING, "One or more signals is currently in use. Unload failed.\n");
        return res;
    }
 
    res |= ast_unregister_application(app);
    res |= ast_unregister_application(app2);
 
    return res;
}
 
static int load_module(void)
{
    int res;
 
    res = ast_register_application_xml(app, signal_exec);
    res |= ast_register_application_xml(app2, waitsignal_exec);
 
    return res;
}
 
AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "Channel Signaling Applications");