ARI/PJSIP: Add the ability to redirect (transfer) a channel in a Stasis app

This patch adds a new feature to ARI to redirect a channel to another server,
and fixes a few bugs in PJSIP's handling of the Transfer dialplan
application/ARI redirect capability.

*New Feature*
A new operation has been added to the ARI channels resource, redirect. With
this, a channel in a Stasis application can be redirected to another endpoint
of the same underlying channel technology.

*Bug fixes*
In the process of writing this new feature, two bugs were fixed in the PJSIP
stack:
(1) The existing .transfer channel callback had the limitation that it could
    only transfer channels to a SIP URI, i.e., you had to pass
    'PJSIP/sip:foo@my_provider.com' to the dialplan application. While this is
    still supported, it is somewhat unintuitive - particularly in a world full
    of endpoints. As such, we now also support specifying the PJSIP endpoint to
    transfer to.
(2) res_pjsip_multihomed was, unfortunately, trying to 'help' a 302 redirect by
    updating its Contact header. Alas, that resulted in the forwarding
    destination set by the dialplan application/ARI resource/whatever being
    rewritten with very incorrect information. Hence, we now don't bother
    updating an outgoing response if it is a 302. Since this took a looong time
    to find, some additional debug statements have been added to those modules
    that update the Contact headers.

Review: https://reviewboard.asterisk.org/r/4316/

ASTERISK-24015 #close
Reported by: Private Name

ASTERISK-24703 #close
Reported by: Matt Jordan
........

Merged revisions 431717 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@431718 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 32 insertions, 0 deletions

diff --git a/res/stasis/control.c b/res/stasis/control.c
index 7dc1220cf..e239de29b 100644
--- a/res/stasis/control.c
+++ b/res/stasis/control.c
@@ -428,6 +428,38 @@ int stasis_app_control_continue(struct stasis_app_control *control, const char *
 	return 0;
 }
 
+static int app_control_redirect(struct stasis_app_control *control,
+	struct ast_channel *chan, void *data)
+{
+	char *endpoint = data;
+	int res;
+
+	ast_assert(control->channel != NULL);
+	ast_assert(endpoint != NULL);
+
+	res = ast_transfer(control->channel, endpoint);
+	if (!res) {
+		ast_log(LOG_NOTICE, "Unsupported transfer requested on channel '%s'\n",
+			ast_channel_name(control->channel));
+		return 0;
+	}
+
+	return 0;
+}
+
+int stasis_app_control_redirect(struct stasis_app_control *control, const char *endpoint)
+{
+	char *endpoint_data = ast_strdup(endpoint);
+
+	if (!endpoint_data) {
+		return -1;
+	}
+
+	stasis_app_send_command_async(control, app_control_redirect, endpoint_data, ast_free_ptr);
+
+	return 0;
+}
+
 struct stasis_app_control_dtmf_data {
 	int before;
 	int between;