Add test for remote max streams update

Improve testing for remote max streams update

This new test checks whether a change in the max streams setting is
properly handled. The max streams value is changed twice throughout the
mock stream. The first update increases the value while the second
update decreases it.

tests/_async/test_http2.py

@@ -294,3 +294,55 @@ async def test_http2_request_to_incorrect_origin():
     async with AsyncHTTP2Connection(origin=origin, stream=stream) as conn:
         with pytest.raises(RuntimeError):
             await conn.request("GET", "https://other.com/")
+
+
+@pytest.mark.anyio
+async def test_http2_remote_max_streams_update():
+    """
+    If the remote server updates the maximum concurrent streams value, we should
+    be adjusting how many streams we will allow.
+    """
+    origin = Origin(b"https", b"example.com", 443)
+    stream = AsyncMockStream(
+        [
+            hyperframe.frame.SettingsFrame(
+                settings={hyperframe.frame.SettingsFrame.MAX_CONCURRENT_STREAMS: 1000}
+            ).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"Hello, world!").serialize(),
+            hyperframe.frame.SettingsFrame(
+                settings={hyperframe.frame.SettingsFrame.MAX_CONCURRENT_STREAMS: 50}
+            ).serialize(),
+            hyperframe.frame.DataFrame(
+                stream_id=1, data=b"Hello, world...again!", flags=["END_STREAM"]
+            ).serialize(),
+        ]
+    )
+    async with AsyncHTTP2Connection(origin=origin, stream=stream) as conn:
+        async with conn.stream("GET", "https://example.com/") as response:
+            i = 0
+            async for chunk in response.aiter_stream():
+                if i == 0:
+                    assert chunk == b"Hello, world!"
+                    assert conn._h2_state.remote_settings.max_concurrent_streams == 1000
+                    assert conn._max_streams == min(
+                        conn._h2_state.remote_settings.max_concurrent_streams,
+                        conn._h2_state.local_settings.max_concurrent_streams,
+                    )
+                elif i == 1:
+                    assert chunk == b"Hello, world...again!"
+                    assert conn._h2_state.remote_settings.max_concurrent_streams == 50
+                    assert conn._max_streams == min(
+                        conn._h2_state.remote_settings.max_concurrent_streams,
+                        conn._h2_state.local_settings.max_concurrent_streams,
+                    )
+                i += 1

tests/_sync/test_http2.py

@@ -294,3 +294,55 @@ def test_http2_request_to_incorrect_origin():
     with HTTP2Connection(origin=origin, stream=stream) as conn:
         with pytest.raises(RuntimeError):
             conn.request("GET", "https://other.com/")
+
+
+
+def test_http2_remote_max_streams_update():
+    """
+    If the remote server updates the maximum concurrent streams value, we should
+    be adjusting how many streams we will allow.
+    """
+    origin = Origin(b"https", b"example.com", 443)
+    stream = MockStream(
+        [
+            hyperframe.frame.SettingsFrame(
+                settings={hyperframe.frame.SettingsFrame.MAX_CONCURRENT_STREAMS: 1000}
+            ).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"Hello, world!").serialize(),
+            hyperframe.frame.SettingsFrame(
+                settings={hyperframe.frame.SettingsFrame.MAX_CONCURRENT_STREAMS: 50}
+            ).serialize(),
+            hyperframe.frame.DataFrame(
+                stream_id=1, data=b"Hello, world...again!", flags=["END_STREAM"]
+            ).serialize(),
+        ]
+    )
+    with HTTP2Connection(origin=origin, stream=stream) as conn:
+        with conn.stream("GET", "https://example.com/") as response:
+            i = 0
+            for chunk in response.iter_stream():
+                if i == 0:
+                    assert chunk == b"Hello, world!"
+                    assert conn._h2_state.remote_settings.max_concurrent_streams == 1000
+                    assert conn._max_streams == min(
+                        conn._h2_state.remote_settings.max_concurrent_streams,
+                        conn._h2_state.local_settings.max_concurrent_streams,
+                    )
+                elif i == 1:
+                    assert chunk == b"Hello, world...again!"
+                    assert conn._h2_state.remote_settings.max_concurrent_streams == 50
+                    assert conn._max_streams == min(
+                        conn._h2_state.remote_settings.max_concurrent_streams,
+                        conn._h2_state.local_settings.max_concurrent_streams,
+                    )
+                i += 1