bridge: Add a deferred queue.

This change adds a deferred queue to bridging. If a bridge
technology determines that a frame can not be written and
should be deferred it can indicate back to bridging to do so.
Bridging will then requeue any deferred frames upon a new
channel joining the bridge.

This change has been leveraged for T.38 request negotiate
control frames. Without the deferred queue there is a race
condition between the bridge receiving the T.38 request
negotiate and the second channel joining and being in the
bridge. If the channel is not yet in the bridge then the T.38
negotiation fails.

A unit test has also been added that confirms that a T.38
request negotiate control frame is deferred when no other
channel is in the bridge and that it is requeued when a new
channel joins the bridge.

ASTERISK-26923

Change-Id: Ie05b08523f399eae579130f4a5f562a344d2e415

2 files changed, 62 insertions, 2 deletions

diff --git a/bridges/bridge_native_rtp.c b/bridges/bridge_native_rtp.c
index 77e321f4f..4af93bfca 100644
--- a/bridges/bridge_native_rtp.c
+++ b/bridges/bridge_native_rtp.c
@@ -508,7 +508,37 @@ static void native_rtp_bridge_leave(struct ast_bridge *bridge, struct ast_bridge
 
 static int native_rtp_bridge_write(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel, struct ast_frame *frame)
 {
-	return ast_bridge_queue_everyone_else(bridge, bridge_channel, frame);
+	const struct ast_control_t38_parameters *t38_parameters;
+	int defer = 0;
+
+	if (!ast_bridge_queue_everyone_else(bridge, bridge_channel, frame)) {
+		/* This frame was successfully queued so no need to defer */
+		return 0;
+	}
+
+	/* Depending on the frame defer it so when the next channel joins it receives it */
+	switch (frame->frametype) {
+	case AST_FRAME_CONTROL:
+		switch (frame->subclass.integer) {
+		case AST_CONTROL_T38_PARAMETERS:
+			t38_parameters = frame->data.ptr;
+			switch (t38_parameters->request_response) {
+			case AST_T38_REQUEST_NEGOTIATE:
+				defer = -1;
+				break;
+			default:
+				break;
+			}
+			break;
+		default:
+			break;
+		}
+		break;
+	default:
+		break;
+	}
+
+	return defer;
 }
 
 static struct ast_bridge_technology native_rtp_bridge = {
diff --git a/bridges/bridge_simple.c b/bridges/bridge_simple.c
index 3bf040380..a49bc39f3 100644
--- a/bridges/bridge_simple.c
+++ b/bridges/bridge_simple.c
@@ -71,7 +71,37 @@ static int simple_bridge_join(struct ast_bridge *bridge, struct ast_bridge_chann
 
 static int simple_bridge_write(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel, struct ast_frame *frame)
 {
-	return ast_bridge_queue_everyone_else(bridge, bridge_channel, frame);
+	const struct ast_control_t38_parameters *t38_parameters;
+	int defer = 0;
+
+	if (!ast_bridge_queue_everyone_else(bridge, bridge_channel, frame)) {
+		/* This frame was successfully queued so no need to defer */
+		return 0;
+	}
+
+	/* Depending on the frame defer it so when the next channel joins it receives it */
+	switch (frame->frametype) {
+	case AST_FRAME_CONTROL:
+		switch (frame->subclass.integer) {
+		case AST_CONTROL_T38_PARAMETERS:
+			t38_parameters = frame->data.ptr;
+			switch (t38_parameters->request_response) {
+			case AST_T38_REQUEST_NEGOTIATE:
+				defer = -1;
+				break;
+			default:
+				break;
+			}
+			break;
+		default:
+			break;
+		}
+		break;
+	default:
+		break;
+	}
+
+	return defer;
 }
 
 static struct ast_bridge_technology simple_bridge = {