app_signal: Add signaling applications

Adds the Signal and WaitForSignal
applications, which can be used for inter-channel
signaling in the dialplan.

Signal supports sending a signal to other channels
listening for a signal of the same name, with an
optional data payload. The signal is received by
all channels waiting for that named signal.

ASTERISK-29810 #close

Change-Id: Ic34439de3d60f8609357666a465c354d81f5fef3

apps/app_signal.c

+/*
+ * 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");

doc/CHANGES-staging/app_signal.txt

+Subject: app_signal
+
+Adds Signal and WaitForSignal applications
+which can be used for signaling or as a
+simple message queue in the dialplan.