Example of how to use the Stasis message bus

In order to get people familiar with the Stasis message bus, it would
be useful to have something of a tutorial. Since I'm not clever enough
to think of some cool integration we could do with Twitter, I settled
for something that might actually be useful.

This patch adds a res_statsd.so module, which implements a basic
statsd[1] client. Statsd is a very simple statistics gathering server,
which can publish its results to a backend graphing engine, like
Graphite[2]. There are several different Statsd server
implementations[3], so you can pick what works best for your
environment.

The actual example of how to use the Stasis message bus is in
res_chan_stats.so. This module demonstrates how to use subscriptions
and the message router by monitoring messages and posting channels
stats to the statsd server.

A wiki page walking through res_chan_stats.so is forthcoming.

 [1]: https://github.com/etsy/statsd/
 [2]: http://graphite.readthedocs.org/en/latest/
 [3]: http://joemiller.me/2011/09/21/list-of-statsd-server-implementations/

Review: https://reviewboard.asterisk.org/r/2460/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@386624 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 188 insertions, 0 deletions

diff --git a/res/res_chan_stats.c b/res/res_chan_stats.c
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+++ b/res/res_chan_stats.c
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+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2013, Digium, Inc.
+ *
+ * David M. Lee, II <dlee@digium.com>
+ *
+ * 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.
+ */
+
+/*!
+ * \brief Statsd channel stats. Exmaple of how to subscribe to Stasis events.
+ *
+ * This module subscribes to the channel caching topic and issues statsd stats
+ * based on the received messages.
+ *
+ * \author David M. Lee, II <dlee@digium.com>
+ * \since 12
+ */
+
+/*** MODULEINFO
+	<depend>res_statsd</depend>
+	<defaultenabled>no</defaultenabled>
+	<support_level>extended</support_level>
+ ***/
+
+#include "asterisk.h"
+
+ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
+
+#include "asterisk/module.h"
+#include "asterisk/stasis_channels.h"
+#include "asterisk/stasis_message_router.h"
+#include "asterisk/statsd.h"
+#include "asterisk/time.h"
+
+/*! Regular Stasis subscription */
+static struct stasis_subscription *sub;
+/*! Stasis message router */
+static struct stasis_message_router *router;
+
+/*!
+ * \brief Subscription callback for all channel messages.
+ * \param data Data pointer given when creating the subscription.
+ * \param sub This subscription.
+ * \param topic The topic the message was posted to. This is not necessarily the
+ *              topic you subscribed to, since messages may be forwarded between
+ *              topics.
+ * \param message The message itself.
+ */
+static void statsmaker(void *data, struct stasis_subscription *sub,
+	struct stasis_topic *topic, struct stasis_message *message)
+{
+	RAII_VAR(struct ast_str *, metric, NULL, ast_free);
+
+	if (stasis_subscription_final_message(sub, message)) {
+		/* Normally, data points to an object that must be cleaned up.
+		 * The final message is an unsubscribe notification that's
+		 * guaranteed to be the last message this subscription receives.
+		 * This would be a safe place to kick off any needed cleanup.
+		 */
+		return;
+	}
+
+	/* For no good reason, count message types */
+	metric = ast_str_create(80);
+	if (metric) {
+		ast_str_set(&metric, 0, "stasis.message.%s",
+			stasis_message_type_name(stasis_message_type(message)));
+		ast_statsd_log(ast_str_buffer(metric), AST_STATSD_METER, 1);
+	}
+}
+
+/*!
+ * \brief Router callback for \ref stasis_cache_update messages.
+ * \param data Data pointer given when added to router.
+ * \param sub This subscription.
+ * \param topic The topic the message was posted to. This is not necessarily the
+ *              topic you subscribed to, since messages may be forwarded between
+ *              topics.
+ * \param message The message itself.
+ */
+static void updates(void *data, struct stasis_subscription *sub,
+	struct stasis_topic *topic, struct stasis_message *message)
+{
+	/* Since this came from a message router, we know the type of the
+	 * message. We can cast the data without checking its type.
+	 */
+	struct stasis_cache_update *update = stasis_message_data(message);
+
+	/* We're only interested in channel snapshots, so check the type
+	 * of the underlying message.
+	 */
+	if (ast_channel_snapshot_type() != update->type) {
+		return;
+	}
+
+	/* There are three types of cache updates.
+	 * !old && new -> Initial cache entry
+	 * old && new -> Updated cache entry
+	 * old && !new -> Cache entry removed.
+	 */
+
+	if (!update->old_snapshot && update->new_snapshot) {
+		/* Initial cache entry; count a channel creation */
+		ast_statsd_log("channels.count", AST_STATSD_COUNTER, 1);
+	} else if (update->old_snapshot && !update->new_snapshot) {
+		/* Cache entry removed. Compute the age of the channel and post
+		 * that, as well as decrementing the channel count.
+		 */
+		struct ast_channel_snapshot *last;
+		int64_t age;
+
+		last = stasis_message_data(update->old_snapshot);
+		age = ast_tvdiff_ms(*stasis_message_timestamp(message),
+			last->creationtime);
+		ast_statsd_log("channels.calltime", AST_STATSD_TIMER, age);
+
+		/* And decrement the channel count */
+		ast_statsd_log("channels.count", AST_STATSD_COUNTER, -1);
+	}
+}
+
+/*!
+ * \brief Router callback for any message that doesn't otherwise have a route.
+ * \param data Data pointer given when added to router.
+ * \param sub This subscription.
+ * \param topic The topic the message was posted to. This is not necessarily the
+ *              topic you subscribed to, since messages may be forwarded between
+ *              topics.
+ * \param message The message itself.
+ */
+static void default_route(void *data, struct stasis_subscription *sub,
+	struct stasis_topic *topic, struct stasis_message *message)
+{
+	if (stasis_subscription_final_message(sub, message)) {
+		/* Much like with the regular subscription, you may need to
+		 * perform some cleanup when done with a message router. You
+		 * can look for the final message in the default route.
+		 */
+		return;
+	}
+}
+
+static int load_module(void)
+{
+	/* You can create a message router to route messages by type */
+	router = stasis_message_router_create(
+		stasis_caching_get_topic(ast_channel_topic_all_cached()));
+	if (!router) {
+		return AST_MODULE_LOAD_FAILURE;
+	}
+	stasis_message_router_add(router, stasis_cache_update_type(),
+		updates, NULL);
+	stasis_message_router_set_default(router, default_route, NULL);
+
+	/* Or a subscription to receive all of the messages from a topic */
+	sub = stasis_subscribe(ast_channel_topic_all(), statsmaker, NULL);
+	if (!sub) {
+		return AST_MODULE_LOAD_FAILURE;
+	}
+	return AST_MODULE_LOAD_SUCCESS;
+}
+
+static int unload_module(void)
+{
+	stasis_unsubscribe(sub);
+	sub = NULL;
+	stasis_message_router_unsubscribe(router);
+	router = NULL;
+	return 0;
+}
+
+AST_MODULE_INFO(ASTERISK_GPL_KEY,
+	AST_MODFLAG_DEFAULT,
+	"Example of how to use Stasis",
+	.load = load_module,
+	.unload = unload_module,
+	.nonoptreq = "res_statsd"
+	);