ARI/res_stasis: Subscribe to both Local channel halves when originating to app

This patch fixes two bugs:

1. When originating a channel into a Stasis application, we already create a
   subscription for the channel that is going into our Stasis app.
   Unfortunately, when you create a Local channel and pass it off to a Stasis
   app, you really aren't creating just one channel: you're creating two. This
   patch snags the second half of the Local channel pair (assuming it is a
   Local channel pair, but luckily core_local is kind about such assumptions)
   and subscribes to it as well.

2. Subscriptions are a bit sticky right now. If a subscription is made, the
   'interest' count gets bumped on the Stasis subscription - but unless
   something explicitly unsubscribes the channel, said subscription sticks
   around. This is not much of a problem is a user is creating the subscription
   - if they made it, they must want it. However, when we are creating
   implicit subscriptions, we need to make sure something clears them out.
   This patch takes a pessimistic approach: it watches the cache updates
   coming from Stasis and, if we notice that the cache just cleared out an
   object, we delete our subscription object. This keeps our ao2 container of
   Stasis forwards in an application from growing out of hand; it also is a
   bit more forgiving for end users who may not realize they were supposed to
   unsubscribe from that channel that just hung up.

Review: https://reviewboard.asterisk.org/r/3710/
#ASTERISK-23939 #close
........

Merged revisions 418089 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@418090 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 15 insertions, 0 deletions

diff --git a/include/asterisk/stasis_app.h b/include/asterisk/stasis_app.h
index 334155a5b..a7b204034 100644
--- a/include/asterisk/stasis_app.h
+++ b/include/asterisk/stasis_app.h
@@ -297,6 +297,21 @@ enum stasis_app_subscribe_res stasis_app_unsubscribe(const char *app_name,
 	const char **event_source_uris, int event_sources_count,
 	struct ast_json **json);
 
+/*!
+ * \brief Directly subscribe an application to a channel
+ *
+ * \param app_name Name of the application to subscribe.
+ * \param chan The channel to subscribe to
+ *
+ * \return \ref stasis_app_subscribe_res return code.
+ *
+ * \note This method can be used when you already hold a channel and its
+ *       lock. This bypasses the channel lookup that would normally be
+ *       performed by \ref stasis_app_subscribe.
+ */
+enum stasis_app_subscribe_res stasis_app_subscribe_channel(const char *app_name,
+	struct ast_channel *chan);
+
 /*! @} */
 
 /*! @{ */