Fixed non-decreasing count of stream on H3 connection. (#51742)

* Fixed HTTP/3 client hang after subsequent 100 streams.

Fixed testing H/3 loopback stream to properly close. Otherwise, the stream will end up in a bad state and the connection will eventually run out of available streams.

* Added assert.

src/libraries/Common/tests/System/Net/Http/Http3LoopbackStream.cs

@@ -227,6 +227,7 @@ public async Task SendResponseBodyAsync(byte[] content, bool isFinal = true)
             if (isFinal)
             {
                 await ShutdownSendAsync().ConfigureAwait(false);
+                await _stream.ShutdownCompleted().ConfigureAwait(false);
                 Dispose();
             }
         }

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3Connection.cs

@@ -285,7 +285,7 @@ private void CancelWaiters()
             }
         }
 
-        // TODO: how do we get this event?
+        // TODO: how do we get this event? -> HandleEventStreamsAvailable reports currently available Uni/Bi streams
         private void OnMaximumStreamCountIncrease(long newMaximumStreamCount)
         {
             lock (SyncObj)
@@ -295,15 +295,23 @@ private void OnMaximumStreamCountIncrease(long newMaximumStreamCount)
                     return;
                 }
 
-                _requestStreamsRemaining += (newMaximumStreamCount - _maximumRequestStreams);
+                IncreaseRemainingStreamCount(newMaximumStreamCount - _maximumRequestStreams);
                 _maximumRequestStreams = newMaximumStreamCount;
+            }
+        }
+
+        private void IncreaseRemainingStreamCount(long delta)
+        {
+            Debug.Assert(Monitor.IsEntered(SyncObj));
+            Debug.Assert(delta > 0);
 
-                while (_requestStreamsRemaining != 0 && _waitingRequests.TryDequeue(out TaskCompletionSourceWithCancellation<bool>? tcs))
+            _requestStreamsRemaining += delta;
+
+            while (_requestStreamsRemaining != 0 && _waitingRequests.TryDequeue(out TaskCompletionSourceWithCancellation<bool>? tcs))
+            {
+                if (tcs.TrySetResult(true))
                 {
-                    if (tcs.TrySetResult(true))
-                    {
-                        --_requestStreamsRemaining;
-                    }
+                    --_requestStreamsRemaining;
                 }
             }
         }
@@ -406,6 +414,8 @@ public void RemoveStream(QuicStream stream)
                 bool removed = _activeRequests.Remove(stream);
                 Debug.Assert(removed == true);
 
+                IncreaseRemainingStreamCount(1);
+
                 if (ShuttingDown)
                 {
                     CheckForShutdown();

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3RequestStream.cs

@@ -312,7 +312,7 @@ private async Task ReadResponseAsync(CancellationToken cancellationToken)
                 {
                     if (NetEventSource.Log.IsEnabled())
                     {
-                        Trace($"Expected HEADERS as first response frame; recieved {frameType}.");
+                        Trace($"Expected HEADERS as first response frame; received {frameType}.");
                     }
                     throw new HttpRequestException(SR.net_http_invalid_response);
                 }

src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http3.cs

@@ -78,6 +78,43 @@ public async Task ClientSettingsReceived_Success(int headerSizeLimit)
             await new[] { clientTask, serverTask }.WhenAllOrAnyFailed(20_000);
         }
 
+        [Theory]
+        [InlineData(100)]
+        public async Task SendMoreThanStreamLimitRequests_Succeeds(int streamLimit)
+        {
+            using Http3LoopbackServer server = CreateHttp3LoopbackServer();
+
+            Task serverTask = Task.Run(async () =>
+            {
+                using Http3LoopbackConnection connection = (Http3LoopbackConnection)await server.EstablishGenericConnectionAsync();
+                for (int i = 0; i < streamLimit + 1; ++i)
+                {
+                    using Http3LoopbackStream stream = await connection.AcceptRequestStreamAsync();
+                    await stream.HandleRequestAsync();
+                }
+            });
+
+            Task clientTask = Task.Run(async () =>
+            {
+                using HttpClient client = CreateHttpClient();
+
+                for (int i = 0; i < streamLimit + 1; ++i)
+                {
+                    using HttpRequestMessage request = new()
+                    {
+                        Method = HttpMethod.Get,
+                        RequestUri = server.Address,
+                        Version = HttpVersion30,
+                        VersionPolicy = HttpVersionPolicy.RequestVersionExact
+                    };
+                    using var response = await client.SendAsync(request).WaitAsync(TimeSpan.FromSeconds(10));
+                }
+            });
+
+            await new[] { clientTask, serverTask }.WhenAllOrAnyFailed(20_000);
+        }
+
+
         [Fact]
         public async Task ReservedFrameType_Throws()
         {

src/libraries/System.Net.Quic/src/System/Net/Quic/Implementations/MsQuic/MsQuicStream.cs

@@ -298,7 +298,7 @@ internal override async ValueTask<int> ReadAsync(Memory<byte> destination, Cance
                 }
             }, _state);
 
-            // TODO there could potentially be a perf gain by storing the buffer from the inital read
+            // TODO there could potentially be a perf gain by storing the buffer from the initial read
             // This reduces the amount of async calls, however it makes it so MsQuic holds onto the buffers
             // longer than it needs to. We will need to benchmark this.
             int length = (int)await _state.ReceiveResettableCompletionSource.GetValueTask().ConfigureAwait(false);