endpoint/stasis: Eliminate duplicate events on endpoint status change

When an endpoint is created, its messages are forwarded to both the tech
endpoint topic and the all endpoints topic. This is done so that various
parties interested in endpoint messages can subscribe to just the tech
endpoint and receive all messages associated with that particular technology,
as opposed to subscribing to the all endpoints topic. Unfortunately, when the
tech endpoint is created, it also forwards all of its messages to the all
topic. This results in duplicate messages whenever an endpoint publishes its
messages.

This patch resolves the duplicate message issue by creating a new function
for Stasis caching topics, stasis_cp_sink_create. In most respects, this acts
as a normal caching topic, save that it no longer forwards messages it receives
to the all endpoints topic. This allows it to act as an aggregation "sink",
while preserving the necessary caching behaviour.

ASTERISK-25137 #close
Reported-by: Vitezslav Novy

ASTERISK-25116 #close
Reported-by: George Joseph <george.joseph@fairview5.com>
Tested-by: George Joseph <george.joseph@fairview5.com>

Change-Id: Ie47784adfb973ab0063e59fc18f390d7dd26d17b

include/asterisk/stasis_cache_pattern.h

@@ -109,6 +109,8 @@ struct stasis_cp_single;
 /*!
  * \brief Create the 'one' side of the cache pattern.
  *
+ * Create the 'one' and forward to all's topic and topic_cached.
+ *
  * Dispose of using stasis_cp_single_unsubscribe().
  *
  * \param all Corresponding all side.
@@ -118,6 +120,23 @@ struct stasis_cp_single;
 struct stasis_cp_single *stasis_cp_single_create(struct stasis_cp_all *all,
 	const char *name);
 
+/*!
+ * \brief Create a sink in the cache pattern
+ *
+ * Create the 'one' but do not automatically forward to the all's topic.
+ * This is useful when aggregating other topic's messages created with
+ * \c stasis_cp_single_create in another caching topic without replicating
+ * those messages in the all's topics.
+ *
+ * Dispose of using stasis_cp_single_unsubscribe().
+ *
+ * \param all Corresponding all side.
+ * \param name Base name for the topics.
+ * \return One side instance
+ */
+struct stasis_cp_single *stasis_cp_sink_create(struct stasis_cp_all *all,
+	const char *name);
+
 /*!
  * \brief Stops caching and forwarding messages.
  *

main/endpoints.c

@@ -303,13 +303,14 @@ static struct ast_endpoint *endpoint_internal_create(const char *tech, const cha
 		return NULL;
 	}
 
+	if (!ast_strlen_zero(resource)) {
+
 		endpoint->topics = stasis_cp_single_create(ast_endpoint_cache_all(),
 			endpoint->id);
 		if (!endpoint->topics) {
 			return NULL;
 		}
 
-	if (!ast_strlen_zero(resource)) {
 		endpoint->router = stasis_message_router_create_pool(ast_endpoint_topic(endpoint));
 		if (!endpoint->router) {
 			return NULL;
@@ -325,9 +326,16 @@ static struct ast_endpoint *endpoint_internal_create(const char *tech, const cha
 
 		endpoint->tech_forward = stasis_forward_all(stasis_cp_single_topic(endpoint->topics),
 			stasis_cp_single_topic(tech_endpoint->topics));
+
 		endpoint_publish_snapshot(endpoint);
 		ao2_link(endpoints, endpoint);
 	} else {
+		endpoint->topics = stasis_cp_sink_create(ast_endpoint_cache_all(),
+			endpoint->id);
+		if (!endpoint->topics) {
+			return NULL;
+		}
+
 		ao2_link(tech_endpoints, endpoint);
 	}
 

main/stasis_cache_pattern.c

@@ -138,6 +138,30 @@ struct stasis_cp_single *stasis_cp_single_create(struct stasis_cp_all *all,
 {
 	RAII_VAR(struct stasis_cp_single *, one, NULL, ao2_cleanup);
 
+	one = stasis_cp_sink_create(all, name);
+	if (!one) {
+		return NULL;
+	}
+
+	one->forward_topic_to_all = stasis_forward_all(one->topic, all->topic);
+	if (!one->forward_topic_to_all) {
+		return NULL;
+	}
+	one->forward_cached_to_all = stasis_forward_all(
+		stasis_caching_get_topic(one->topic_cached), all->topic_cached);
+	if (!one->forward_cached_to_all) {
+		return NULL;
+	}
+
+	ao2_ref(one, +1);
+	return one;
+}
+
+struct stasis_cp_single *stasis_cp_sink_create(struct stasis_cp_all *all,
+	const char *name)
+{
+	RAII_VAR(struct stasis_cp_single *, one, NULL, ao2_cleanup);
+
 	one = ao2_t_alloc(sizeof(*one), one_dtor, name);
 	if (!one) {
 		return NULL;
@@ -152,16 +176,6 @@ struct stasis_cp_single *stasis_cp_single_create(struct stasis_cp_all *all,
 		return NULL;
 	}
 
-	one->forward_topic_to_all = stasis_forward_all(one->topic, all->topic);
-	if (!one->forward_topic_to_all) {
-		return NULL;
-	}
-	one->forward_cached_to_all = stasis_forward_all(
-		stasis_caching_get_topic(one->topic_cached), all->topic_cached);
-	if (!one->forward_cached_to_all) {
-		return NULL;
-	}
-
 	ao2_ref(one, +1);
 	return one;
 }