bridge_native_rtp/bridge_channel: Fix direct media issues due to frame hook

This patch fixes issues with direct media bridges that occur after a blind
transfer. These issues were caught by the (currently failing)
pjsip/transfers/blind_transfer/caller_direct_media test.

The test currently fails primarily for two reasons:
(1) When Bob and Charlie (the transfer target and the transfer destination)
    enter a bridge together, the framehook remains on the transfer target
    channel until both channels are in the bridge. As it consumes voice frames,
    the initial bridge type is a simple bridge. The framehook is removed when
    both channels are in the bridge; however, this does not currently cause the
    bridging framework to re-evaluate the bridge. This patch adds a
    AST_SOFTHANGUP_UNBRIDGE poke to the transfer target channel when a
    framehook is removed so the bridge can re-evaluate itself.

(2) When a channel leaves a native RTP bridge, it may be leaving due to being
    hung up. Sending a re-INVITE to a channel that is about to be hung up is
    not nice - in fact, there's a good chance we'll send the BYE request before
    the channel has had a chance to send back a 200 OK. To be somewhat nicer,
    this patch adds a function to channel.h that allows the bridging framework
    to query for exactly why a channel is leaving a bridge via the channel's
    soft hangup flags. This allows it to only send the re-INVITE if there's a
    chance the channel will survive the native bridging experience.

Review: https://reviewboard.asterisk.org/r/3535/
........

Merged revisions 414122 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@414123 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 16 insertions, 0 deletions

diff --git a/include/asterisk/channel.h b/include/asterisk/channel.h
index a4ad2ae01..c2d8b39c9 100644
--- a/include/asterisk/channel.h
+++ b/include/asterisk/channel.h
@@ -4273,6 +4273,22 @@ struct ast_bridge *ast_channel_get_bridge(const struct ast_channel *chan);
 int ast_channel_is_bridged(const struct ast_channel *chan);
 
 /*!
+ * \brief Determine if a channel is leaving a bridge, but \em not hung up
+ * \since 12.3.0
+ *
+ * \param chan The channel to test
+ *
+ * \note If a channel is hung up, it is implicitly leaving any bridge it
+ * may be in. This function is used to test if a channel is leaving a bridge
+ * but may survive the experience, if it has a place to go to (dialplan or
+ * otherwise)
+ *
+ * \retval 0 The channel is not leaving the bridge or is hung up
+ * \retval non-zero The channel is leaving the bridge
+ */
+int ast_channel_is_leaving_bridge(struct ast_channel *chan);
+
+/*!
  * \brief Get the channel's bridge peer only if the bridge is two-party.
  * \since 12.0.0
  *