HTTP/2 protocol handler: tweak receive window sizes

We were using the default ones, provided by RFC7540. It appears they are way
too restrictive and conservative: when downloading something relatively big,
a stream keeps spending the whole session/its own 'recv' windows and thus
we have to constantly send WINDOW_UPDATE frames. This significantly slows
down our HTTP/2 implementation, making it orders of magnitude slower than
HTTP/1.1. To fix this:

- We send SETTINGS_INITIAL_WINDOW_SIZE in the first SETTINGS frame
  to inform our peer that per-stream WINDOW is bigger than 64Kb
- We increase the session's receive window size.

Task-number: QTBUG-63722
Change-Id: I31312fcfd5f0fc0aee6aaa5d3562cc7d1b931adc
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/network/access/http2/http2protocol.cpp b/src/network/access/http2/http2protocol.cpp
index 54811aeab0..bb3d6bf575 100644
--- a/src/network/access/http2/http2protocol.cpp
+++ b/src/network/access/http2/http2protocol.cpp
@@ -216,6 +216,8 @@ Frame default_SETTINGS_frame()
     // MAX frame size (16 kb), disable/enable PUSH_PROMISE
     builder.append(Settings::MAX_FRAME_SIZE_ID);
     builder.append(quint32(maxFrameSize));
+    builder.append(Settings::INITIAL_WINDOW_SIZE_ID);
+    builder.append(initialStreamReceiveWindowSize);
     builder.append(Settings::ENABLE_PUSH_ID);
     builder.append(quint32(is_PUSH_PROMISE_enabled()));