Increase HTTP/2 default flow control window. (#7317)

* increase default flow control window

* fix tests

* fix test

* update changelog

* [autofix.ci] apply automated fixes

* simpler way to override default settings

* acknowledge settings

* document hyper-h2 workaround

* quote RFC

* [autofix.ci] apply automated fixes

* increase MAX_FRAME_SIZE

* update comment

* max out initial window size

* [autofix.ci] apply automated fixes

* increment connection control window

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Maximilian Hils <github@maximilianhils.com>

CHANGELOG.md

@@ -22,6 +22,8 @@
   This may break users of `modify_headers` that rely on filters referencing the message body.
   We expect this to be uncommon, but please make yourself heard if that's not the case.
   ([#7286](https://github.com/mitmproxy/mitmproxy/pull/7286), @lukant)
+- Increase HTTP/2 default flow control window size.
+  ([#7317](https://github.com/mitmproxy/mitmproxy/pull/7317), @sujaldev)
 - Fix a crash when handling corrupted compressed body in savehar addon and its tests.
   ([#7320](https://github.com/mitmproxy/mitmproxy/pull/7320), @8192bytes)
 - Remove dependency on `protobuf` library as it was no longer being used.

mitmproxy/proxy/layers/http/_http_h2.py

@@ -49,9 +49,20 @@ class BufferedH2Connection(h2.connection.H2Connection):
 
     def __init__(self, config: h2.config.H2Configuration):
         super().__init__(config)
+        self.local_settings.initial_window_size = 2**31 - 1
+        self.local_settings.max_frame_size = 2**17
+        self.max_inbound_frame_size = 2**17
+        # hyper-h2 pitfall: we need to acknowledge here, otherwise its sends out the old settings.
+        self.local_settings.acknowledge()
         self.stream_buffers = collections.defaultdict(collections.deque)
         self.stream_trailers = {}
 
+    def initiate_connection(self):
+        super().initiate_connection()
+        # We increase the flow-control window for new streams with a setting,
+        # but we need to increase the overall connection flow-control window as well.
+        self.increment_flow_control_window(2**31 - 1 - 65535)  # maximum - default
+
     def send_data(
         self,
         stream_id: int,

test/mitmproxy/proxy/layers/http/test_http2.py

@@ -116,6 +116,7 @@ def test_simple(tctx):
     frames = decode_frames(initial())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
     ]
     sff = FrameFactory()
@@ -258,6 +259,7 @@ def test_request_trailers(tctx: Context, open_h2_server_conn: Server, stream):
     frames = decode_frames(server_data1.setdefault(b"") + server_data2())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
         hyperframe.frame.DataFrame,
         hyperframe.frame.HeadersFrame,
@@ -323,6 +325,7 @@ def test_long_response(tctx: Context, trailers):
     frames = decode_frames(initial())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
     ]
     sff = FrameFactory()
@@ -349,11 +352,6 @@ def test_long_response(tctx: Context, trailers):
             server,
             sff.build_data_frame(b"a" * 10000, flags=[]).serialize(),
         )
-        << SendData(
-            server,
-            sff.build_window_update_frame(0, 40000).serialize()
-            + sff.build_window_update_frame(1, 40000).serialize(),
-        )
         >> DataReceived(
             server,
             sff.build_data_frame(b"a" * 10000, flags=[]).serialize(),
@@ -590,10 +588,11 @@ def test_no_normalization(tctx, normalize):
     frames = decode_frames(initial())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
     ]
     assert (
-        hpack.hpack.Decoder().decode(frames[1].data, True) == request_headers_lower
+        hpack.hpack.Decoder().decode(frames[2].data, True) == request_headers_lower
         if normalize
         else request_headers
     )
@@ -666,9 +665,10 @@ def test_end_stream_via_headers(tctx, stream):
     frames = decode_frames(forwarded_request_frames())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
     ]
-    assert "END_STREAM" in frames[1].flags
+    assert "END_STREAM" in frames[2].flags
 
     frames = decode_frames(forwarded_response_frames())
     assert [type(x) for x in frames] == [
@@ -861,6 +861,7 @@ def test_stream_concurrency(tctx):
     frames = decode_frames(data_req2())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
     ]
     frames = decode_frames(data_req1())
@@ -920,7 +921,7 @@ def test_max_concurrency(tctx):
         )
         << SendData(tctx.client, Placeholder(bytes))
     )
-    settings, req1 = decode_frames(req1_bytes())
+    settings, _, req1 = decode_frames(req1_bytes())
     (settings_ack,) = decode_frames(settings_ack_bytes())
     (req2,) = decode_frames(req2_bytes())
 
@@ -961,6 +962,7 @@ def test_stream_concurrent_get_connection(tctx):
     frames = decode_frames(data())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
         hyperframe.frame.HeadersFrame,
     ]
@@ -1013,6 +1015,7 @@ def test_kill_stream(tctx):
     frames = decode_frames(data_req1())
     assert [type(x) for x in frames] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.HeadersFrame,
     ]
 
@@ -1120,6 +1123,7 @@ def test_early_server_data(tctx):
     )
     assert [type(x) for x in decode_frames(server1())] == [
         hyperframe.frame.SettingsFrame,
+        hyperframe.frame.WindowUpdateFrame,
         hyperframe.frame.SettingsFrame,
     ]
     assert [type(x) for x in decode_frames(server2())] == [

test/mitmproxy/proxy/layers/http/test_http_version_interop.py

@@ -45,7 +45,8 @@ def h2_client(tctx: Context) -> tuple[h2.connection.H2Connection, Playbook]:
     server_preamble = Placeholder(bytes)
     assert playbook << SendData(tctx.client, server_preamble)
     assert event_types(conn.receive_data(server_preamble())) == [
-        h2.events.RemoteSettingsChanged
+        h2.events.RemoteSettingsChanged,
+        h2.events.WindowUpdated,
     ]
 
     settings_ack = Placeholder(bytes)
@@ -134,6 +135,7 @@ def test_h1_to_h2(tctx):
     events = conn.receive_data(request())
     assert event_types(events) == [
         h2.events.RemoteSettingsChanged,
+        h2.events.WindowUpdated,
         h2.events.RequestReceived,
         h2.events.StreamEnded,
     ]