From ebf3aa046ef8ebb90850eb81029039b52f2af8c1 Mon Sep 17 00:00:00 2001
From: Bruce Liang <Bruce.Liang@Abilitycorp.com.tw>
Date: Wed, 24 Aug 2022 19:50:19 +0800
Subject: [PATCH] gst-rtsp-server: Fix pushing backlog to client

Check back pressure of a stream transport before popping buffer from its backlog.

If the stream transport is not experiencing back pressure, the buffer can be popped from backlog and pushed to client.

Fixes:#1298

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2998>
---
 .../gst/rtsp-server/rtsp-server-internal.h    |  2 ++
 .../gst/rtsp-server/rtsp-stream-transport.c   | 19 +++++++++++++++++++
 .../gst/rtsp-server/rtsp-stream.c             | 18 +++++++++++-------
 3 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-server-internal.h b/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-server-internal.h
index b5aaefffc7..6015d6840e 100644
--- a/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-server-internal.h
+++ b/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-server-internal.h
@@ -40,6 +40,8 @@ gboolean                 gst_rtsp_stream_transport_backlog_pop   (GstRTSPStreamT
                                                                   GstBufferList **buffer_list,
                                                                   gboolean *is_rtp);
 
+gboolean                 gst_rtsp_stream_transport_backlog_peek_is_rtp (GstRTSPStreamTransport * trans);
+
 gboolean                 gst_rtsp_stream_transport_backlog_is_empty (GstRTSPStreamTransport *trans);
 
 void                     gst_rtsp_stream_transport_clear_backlog (GstRTSPStreamTransport * trans);
diff --git a/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream-transport.c b/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream-transport.c
index d293a95138..4502ec1fd5 100644
--- a/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream-transport.c
+++ b/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream-transport.c
@@ -950,6 +950,25 @@ gst_rtsp_stream_transport_backlog_pop (GstRTSPStreamTransport * trans,
   return TRUE;
 }
 
+/* Not MT-safe, caller should ensure consistent locking.
+ * See gst_rtsp_stream_transport_lock_backlog() */
+gboolean
+gst_rtsp_stream_transport_backlog_peek_is_rtp (GstRTSPStreamTransport * trans)
+{
+  BackLogItem *item;
+  GstRTSPStreamTransportPrivate *priv;
+
+  g_return_val_if_fail (!gst_rtsp_stream_transport_backlog_is_empty (trans),
+      FALSE);
+
+  priv = trans->priv;
+
+  item = (BackLogItem *) gst_queue_array_peek_head_struct (priv->items);
+
+  return item->is_rtp;
+}
+
+
 /* Not MT-safe, caller should ensure consistent locking.
  * See gst_rtsp_stream_transport_lock_backlog() */
 gboolean
diff --git a/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream.c b/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream.c
index fed62d8c82..99d87e9d97 100644
--- a/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream.c
+++ b/subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-stream.c
@@ -2644,16 +2644,20 @@ check_transport_backlog (GstRTSPStream * stream, GstRTSPStreamTransport * trans)
     gboolean is_rtp;
     gboolean popped;
 
-    popped =
-        gst_rtsp_stream_transport_backlog_pop (trans, &buffer, &buffer_list,
-        &is_rtp);
+    is_rtp = gst_rtsp_stream_transport_backlog_peek_is_rtp (trans);
 
-    g_assert (popped == TRUE);
+    if (!gst_rtsp_stream_transport_check_back_pressure (trans, is_rtp)) {
+      popped =
+          gst_rtsp_stream_transport_backlog_pop (trans, &buffer, &buffer_list,
+          &is_rtp);
 
-    send_ret = push_data (stream, trans, buffer, buffer_list, is_rtp);
+      g_assert (popped == TRUE);
 
-    gst_clear_buffer (&buffer);
-    gst_clear_buffer_list (&buffer_list);
+      send_ret = push_data (stream, trans, buffer, buffer_list, is_rtp);
+
+      gst_clear_buffer (&buffer);
+      gst_clear_buffer_list (&buffer_list);
+    }
   }
 
   gst_rtsp_stream_transport_unlock_backlog (trans);