chan_websocket: Use leftover data if no frames are available when the timer fires.

When the 20ms channel timer fires but there are no frames available in
the queue, we now check for leftover data in the buffer and if there is
any, we create a frame with it and send it to the core. This resolves an
issue with the leftover data being delayed if a STOP_MEDIA_BUFFERING
command is delayed. Some existing comments were also clarified to
account for the new behavior.

Resolves: #2006

channels/chan_websocket.c

@@ -469,9 +469,7 @@ static struct ast_frame *dequeue_frame(struct websocket_pvt *instance)
 		AST_LIST_UNLOCK);
 
 	/*
-	 * If the queue is paused, don't read a frame.  Processing
-	 * will continue down the function and a silence frame will
-	 * be sent in its place.
+	 * If the queue is paused, don't read a frame.
 	 */
 	if (instance->queue_paused) {
 		return NULL;
@@ -493,10 +491,9 @@ static struct ast_frame *dequeue_frame(struct websocket_pvt *instance)
 	queued_frame = AST_LIST_REMOVE_HEAD(&instance->frame_queue, frame_list);
 
 	/*
-	 * If there are no frames in the queue, we need to
-	 * return NULL so we can send a silence frame.  We also need
-	 * to send the QUEUE_DRAINED notification if we were requested
-	 * to do so.
+	 * If there are no frames in the queue, we need to return NULL.
+	 * We also need to send the QUEUE_DRAINED notification if we
+	 * were requested to do so.
 	 */
 	if (!queued_frame) {
 		if (instance->report_queue_drained) {
@@ -550,8 +547,7 @@ static struct ast_frame *dequeue_frame(struct websocket_pvt *instance)
 
 	/*
 	 * If, after reading all control frames,  there are no frames
-	 * left in the queue, we need to return NULL so we can send
-	 * a silence frame.
+	 * left in the queue, we need to return NULL.
 	 */
 	if (!queued_frame) {
 		return NULL;
@@ -561,6 +557,30 @@ static struct ast_frame *dequeue_frame(struct websocket_pvt *instance)
 
 	return queued_frame;
 }
+
+static struct ast_frame *create_frame_from_buffer(struct websocket_pvt *instance,
+	char *buffer, size_t len)
+{
+	struct ast_frame fr = { 0, };
+	struct ast_frame *duped_frame = NULL;
+
+	AST_FRAME_SET_BUFFER(&fr, buffer, 0, len);
+	fr.frametype = AST_FRAME_VOICE;
+	fr.subclass.format = instance->native_format;
+	if (instance->native_codec->samples_count) {
+		fr.samples = instance->native_codec->samples_count(&fr);
+	}
+
+	duped_frame = ast_frisolate(&fr);
+	if (!duped_frame) {
+		ast_log(LOG_WARNING, "%s: Failed to isolate frame\n",
+			ast_channel_name(instance->channel));
+		return NULL;
+	}
+
+	return duped_frame;
+}
+
 /*!
  * \internal
  *
@@ -600,34 +620,34 @@ static struct ast_frame *webchan_read(struct ast_channel *ast)
 	}
 
 	native_frame = dequeue_frame(instance);
-
-	/*
-	 * No frame when the timer fires means we have to return a null frame in its place.
-	 */
 	if (!native_frame) {
-		ast_debug(4, "%s: WebSocket read timer fired with no frame available.  Returning NULL frame.\n",
+		if (instance->leftover_len > 0) {
+			native_frame = create_frame_from_buffer(instance, instance->leftover_data, instance->leftover_len);
+			if (native_frame) {
+				ast_debug(4, "%s: WebSocket read timer fired with no frame available but with %d bytes in leftover_data.  Returning partial frame.\n",
+					ast_channel_name(ast), (int)instance->leftover_len);
+				instance->leftover_len = 0;
+				return native_frame;
+			}
+		}
+		ast_debug(4, "%s: WebSocket read timer fired with no frame available and no data in leftover_data.  Returning NULL frame.\n",
 			ast_channel_name(ast));
 		return &ast_null_frame;
 	}
 
+	ast_debug(5, "%s: WebSocket read timer fired. Dequeued %d byte frame.  Left in buffer: %d\n",
+		ast_channel_name(ast), native_frame->datalen, (int)instance->leftover_len);
+
 	return native_frame;
 }
 
 static int queue_frame_from_buffer(struct websocket_pvt *instance,
 	char *buffer, size_t len)
 {
-	struct ast_frame fr = { 0, };
 	struct ast_frame *duped_frame = NULL;
 
-	AST_FRAME_SET_BUFFER(&fr, buffer, 0, len);
-	fr.frametype = AST_FRAME_VOICE;
-	fr.subclass.format = instance->native_format;
-	fr.samples = instance->native_codec->samples_count(&fr);
-
-	duped_frame = ast_frisolate(&fr);
+	duped_frame = create_frame_from_buffer(instance, buffer, len);
 	if (!duped_frame) {
-		ast_log(LOG_WARNING, "%s: Failed to isolate frame\n",
-			ast_channel_name(instance->channel));
 		return -1;
 	}