Wait for positive HTTP/2 flow-control credit when stream window goes negative

src/httpcore2/CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## Unreleased
+
+### Fixed
+
+* Wait for positive flow-control credit when a peer's `SETTINGS` frame drives a stream's send window negative, instead of letting h2 raise `LocalProtocolError`. ([#935](https://github.com/pydantic/httpx2/pull/935))
+
 ## 2.0.0
 
 Official first release of `httpcore2`. No changes since `2.0.0b1`.

src/httpcore2/httpcore2/_async/http2.py

@@ -465,7 +465,7 @@ async def _wait_for_outgoing_flow(self, request: Request, stream_id: int) -> int
         local_flow: int = self._h2_state.local_flow_control_window(stream_id)
         max_frame_size: int = self._h2_state.max_outbound_frame_size
         flow = min(local_flow, max_frame_size)
-        while flow == 0:
+        while flow <= 0:
             await self._receive_events(request)
             local_flow = self._h2_state.local_flow_control_window(stream_id)
             max_frame_size = self._h2_state.max_outbound_frame_size

src/httpcore2/httpcore2/_sync/http2.py

@@ -465,7 +465,7 @@ def _wait_for_outgoing_flow(self, request: Request, stream_id: int) -> int:
         local_flow: int = self._h2_state.local_flow_control_window(stream_id)
         max_frame_size: int = self._h2_state.max_outbound_frame_size
         flow = min(local_flow, max_frame_size)
-        while flow == 0:
+        while flow <= 0:
             self._receive_events(request)
             local_flow = self._h2_state.local_flow_control_window(stream_id)
             max_frame_size = self._h2_state.max_outbound_frame_size

tests/httpcore2/_async/test_http2.py

@@ -202,6 +202,44 @@ async def test_http2_connection_with_goaway():
             await conn.request("GET", "https://example.com/")
 
 
+@pytest.mark.anyio
+async def test_http2_connection_with_negative_flow_control_window():
+    """A negative stream flow-control window must be awaited, not sent into.
+
+    After the 65535-byte window is exhausted, the server reduces INITIAL_WINDOW_SIZE
+    by 32767, which adjusts the just-exhausted stream window from 0 to -32767.
+    `_wait_for_outgoing_flow` must park the stream until WINDOW_UPDATE restores
+    positive credit; otherwise `h2` raises `LocalProtocolError` on the next send_data.
+    """
+    origin = httpcore2.Origin(b"https", b"example.com", 443)
+    reduce_settings = hyperframe.frame.SettingsFrame(stream_id=0)
+    reduce_settings.settings = {hyperframe.frame.SettingsFrame.INITIAL_WINDOW_SIZE: 32768}
+    stream = httpcore2.AsyncMockStream(
+        [
+            hyperframe.frame.SettingsFrame(stream_id=0).serialize(),
+            # This frame reduces INITIAL_WINDOW_SIZE to 32768, which adjusts the just-exhausted stream window to -32767.
+            reduce_settings.serialize(),
+            hyperframe.frame.WindowUpdateFrame(stream_id=0, window_increment=100_000).serialize(),
+            hyperframe.frame.WindowUpdateFrame(stream_id=1, window_increment=100_000).serialize(),
+            hyperframe.frame.HeadersFrame(
+                stream_id=1,
+                data=hpack.Encoder().encode(
+                    [
+                        (b":status", b"200"),
+                        (b"content-type", b"plain/text"),
+                    ]
+                ),
+                flags=["END_HEADERS"],
+            ).serialize(),
+            hyperframe.frame.DataFrame(stream_id=1, data=b"response", flags=["END_STREAM"]).serialize(),
+        ]
+    )
+    async with httpcore2.AsyncHTTP2Connection(origin=origin, stream=stream) as conn:
+        response = await conn.request("POST", "https://example.com/", content=b"x" * 100_000)
+        assert response.status == 200
+        assert response.content == b"response"
+
+
 @pytest.mark.anyio
 async def test_http2_connection_with_flow_control():
     origin = httpcore2.Origin(b"https", b"example.com", 443)

tests/httpcore2/_sync/test_http2.py

@@ -203,6 +203,44 @@ def test_http2_connection_with_goaway():
 
 
 
+def test_http2_connection_with_negative_flow_control_window():
+    """A negative stream flow-control window must be awaited, not sent into.
+
+    After the 65535-byte window is exhausted, the server reduces INITIAL_WINDOW_SIZE
+    by 32767, which adjusts the just-exhausted stream window from 0 to -32767.
+    `_wait_for_outgoing_flow` must park the stream until WINDOW_UPDATE restores
+    positive credit; otherwise `h2` raises `LocalProtocolError` on the next send_data.
+    """
+    origin = httpcore2.Origin(b"https", b"example.com", 443)
+    reduce_settings = hyperframe.frame.SettingsFrame(stream_id=0)
+    reduce_settings.settings = {hyperframe.frame.SettingsFrame.INITIAL_WINDOW_SIZE: 32768}
+    stream = httpcore2.MockStream(
+        [
+            hyperframe.frame.SettingsFrame(stream_id=0).serialize(),
+            # This frame reduces INITIAL_WINDOW_SIZE to 32768, which adjusts the just-exhausted stream window to -32767.
+            reduce_settings.serialize(),
+            hyperframe.frame.WindowUpdateFrame(stream_id=0, window_increment=100_000).serialize(),
+            hyperframe.frame.WindowUpdateFrame(stream_id=1, window_increment=100_000).serialize(),
+            hyperframe.frame.HeadersFrame(
+                stream_id=1,
+                data=hpack.Encoder().encode(
+                    [
+                        (b":status", b"200"),
+                        (b"content-type", b"plain/text"),
+                    ]
+                ),
+                flags=["END_HEADERS"],
+            ).serialize(),
+            hyperframe.frame.DataFrame(stream_id=1, data=b"response", flags=["END_STREAM"]).serialize(),
+        ]
+    )
+    with httpcore2.HTTP2Connection(origin=origin, stream=stream) as conn:
+        response = conn.request("POST", "https://example.com/", content=b"x" * 100_000)
+        assert response.status == 200
+        assert response.content == b"response"
+
+
+
 def test_http2_connection_with_flow_control():
     origin = httpcore2.Origin(b"https", b"example.com", 443)
     stream = httpcore2.MockStream(