Turn off synchronous IO by default

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Http/Frame.FeatureCollection.cs

@@ -22,6 +22,7 @@ public partial class Frame : IFeatureCollection,
                                  IHttpConnectionFeature,
                                  IHttpRequestLifetimeFeature,
                                  IHttpRequestIdentifierFeature,
+                                 IHttpBodyControlFeature,
                                  IHttpMaxRequestBodySizeFeature,
                                  IHttpRequestBodyMinimumDataRateFeature
     {
@@ -205,6 +206,12 @@ string IHttpRequestIdentifierFeature.TraceIdentifier
             set => TraceIdentifier = value;
         }
 
+        bool IHttpBodyControlFeature.AllowSynchronousIO
+        {
+            get => AllowSynchronousIO;
+            set => AllowSynchronousIO = value;
+        }
+
         bool IHttpMaxRequestBodySizeFeature.IsReadOnly => HasStartedConsumingRequestBody || _wasUpgraded;
 
         long? IHttpMaxRequestBodySizeFeature.MaxRequestBodySize

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Http/Frame.Generated.cs

@@ -25,6 +25,7 @@ public partial class Frame
         private static readonly Type ISessionFeatureType = typeof(global::Microsoft.AspNetCore.Http.Features.ISessionFeature);
         private static readonly Type IHttpMaxRequestBodySizeFeatureType = typeof(global::Microsoft.AspNetCore.Http.Features.IHttpMaxRequestBodySizeFeature);
         private static readonly Type IHttpRequestBodyMinimumDataRateFeatureType = typeof(global::Microsoft.AspNetCore.Server.Kestrel.Core.Features.IHttpRequestBodyMinimumDataRateFeature);
+        private static readonly Type IHttpBodyControlFeatureType = typeof(global::Microsoft.AspNetCore.Http.Features.IHttpBodyControlFeature);
         private static readonly Type IHttpSendFileFeatureType = typeof(global::Microsoft.AspNetCore.Http.Features.IHttpSendFileFeature);
 
         private object _currentIHttpRequestFeature;
@@ -44,6 +45,7 @@ public partial class Frame
         private object _currentISessionFeature;
         private object _currentIHttpMaxRequestBodySizeFeature;
         private object _currentIHttpRequestBodyMinimumDataRateFeature;
+        private object _currentIHttpBodyControlFeature;
         private object _currentIHttpSendFileFeature;
 
         private void FastReset()
@@ -56,6 +58,7 @@ private void FastReset()
             _currentIHttpConnectionFeature = this;
             _currentIHttpMaxRequestBodySizeFeature = this;
             _currentIHttpRequestBodyMinimumDataRateFeature = this;
+            _currentIHttpBodyControlFeature = this;
 
             _currentIServiceProvidersFeature = null;
             _currentIHttpAuthenticationFeature = null;
@@ -139,6 +142,10 @@ internal object FastFeatureGet(Type key)
             {
                 return _currentIHttpRequestBodyMinimumDataRateFeature;
             }
+            if (key == IHttpBodyControlFeatureType)
+            {
+                return _currentIHttpBodyControlFeature;
+            }
             if (key == IHttpSendFileFeatureType)
             {
                 return _currentIHttpSendFileFeature;
@@ -235,6 +242,11 @@ internal void FastFeatureSet(Type key, object feature)
                 _currentIHttpRequestBodyMinimumDataRateFeature = feature;
                 return;
             }
+            if (key == IHttpBodyControlFeatureType)
+            {
+                _currentIHttpBodyControlFeature = feature;
+                return;
+            }
             if (key == IHttpSendFileFeatureType)
             {
                 _currentIHttpSendFileFeature = feature;
@@ -313,6 +325,10 @@ private IEnumerable<KeyValuePair<Type, object>> FastEnumerable()
             {
                 yield return new KeyValuePair<Type, object>(IHttpRequestBodyMinimumDataRateFeatureType, _currentIHttpRequestBodyMinimumDataRateFeature as global::Microsoft.AspNetCore.Server.Kestrel.Core.Features.IHttpRequestBodyMinimumDataRateFeature);
             }
+            if (_currentIHttpBodyControlFeature != null)
+            {
+                yield return new KeyValuePair<Type, object>(IHttpBodyControlFeatureType, _currentIHttpBodyControlFeature as global::Microsoft.AspNetCore.Http.Features.IHttpBodyControlFeature);
+            }
             if (_currentIHttpSendFileFeature != null)
             {
                 yield return new KeyValuePair<Type, object>(IHttpSendFileFeatureType, _currentIHttpSendFileFeature as global::Microsoft.AspNetCore.Http.Features.IHttpSendFileFeature);

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Http/Frame.cs

@@ -123,6 +123,7 @@ public Frame(FrameContext frameContext)
         public string ConnectionIdFeature { get; set; }
         public bool HasStartedConsumingRequestBody { get; set; }
         public long? MaxRequestBodySize { get; set; }
+        public bool AllowSynchronousIO { get; set; }
 
         /// <summary>
         /// The request id. <seealso cref="HttpContext.TraceIdentifier"/>
@@ -306,7 +307,7 @@ public void InitializeStreams(MessageBody messageBody)
         {
             if (_frameStreams == null)
             {
-                _frameStreams = new Streams(this);
+                _frameStreams = new Streams(this, this);
             }
 
             (RequestBody, ResponseBody) = _frameStreams.Start(messageBody);
@@ -330,6 +331,7 @@ public void Reset()
 
             HasStartedConsumingRequestBody = false;
             MaxRequestBodySize = ServerOptions.Limits.MaxRequestBodySize;
+            AllowSynchronousIO = ServerOptions.AllowSynchronousIO;
             TraceIdentifier = null;
             Scheme = null;
             Method = null;

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Http/FrameRequestStream.cs

@@ -7,17 +7,20 @@
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure;
 using Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal;
+using Microsoft.AspNetCore.Http.Features;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
 {
     internal class FrameRequestStream : ReadOnlyStream
     {
+        private readonly IHttpBodyControlFeature _bodyControl;
         private MessageBody _body;
         private FrameStreamState _state;
         private Exception _error;
 
-        public FrameRequestStream()
+        public FrameRequestStream(IHttpBodyControlFeature bodyControl)
         {
+            _bodyControl = bodyControl;
             _state = FrameStreamState.Closed;
         }
 
@@ -34,13 +37,12 @@ public override long Position
 
         public override void Flush()
         {
-            // No-op.
+            throw new NotSupportedException();
         }
 
         public override Task FlushAsync(CancellationToken cancellationToken)
         {
-            // No-op.
-            return Task.CompletedTask;
+            throw new NotSupportedException();
         }
 
         public override long Seek(long offset, SeekOrigin origin)
@@ -55,8 +57,12 @@ public override void SetLength(long value)
 
         public override int Read(byte[] buffer, int offset, int count)
         {
-            // ValueTask uses .GetAwaiter().GetResult() if necessary
-            return ReadAsync(buffer, offset, count).Result;
+            if (!_bodyControl.AllowSynchronousIO)
+            {
+                throw new InvalidOperationException("Synchronous operations are disallowed. Call ReadAsync or set AllowSynchronousIO to true instead.");
+            }
+
+            return ReadAsync(buffer, offset, count).GetAwaiter().GetResult();
         }
 
         public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, object state)

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Http/FrameResponseStream.cs

@@ -6,16 +6,19 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure;
+using Microsoft.AspNetCore.Http.Features;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
 {
     internal class FrameResponseStream : WriteOnlyStream
     {
-        private IFrameControl _frameControl;
+        private readonly IHttpBodyControlFeature _bodyControl;
+        private readonly IFrameControl _frameControl;
         private FrameStreamState _state;
 
-        public FrameResponseStream(IFrameControl frameControl)
+        public FrameResponseStream(IHttpBodyControlFeature bodyControl, IFrameControl frameControl)
         {
+            _bodyControl = bodyControl;
             _frameControl = frameControl;
             _state = FrameStreamState.Closed;
         }
@@ -31,6 +34,7 @@ public override long Position
             set => throw new NotSupportedException();
         }
 
+        // REVIEW: Should Flush() throw?
         public override void Flush()
         {
             FlushAsync(default(CancellationToken)).GetAwaiter().GetResult();
@@ -58,6 +62,11 @@ public override void SetLength(long value)
 
         public override void Write(byte[] buffer, int offset, int count)
         {
+            if (!_bodyControl.AllowSynchronousIO)
+            {
+                throw new InvalidOperationException("Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.");
+            }
+
             WriteAsync(buffer, offset, count, default(CancellationToken)).GetAwaiter().GetResult();
         }
 

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Infrastructure/Streams.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure
@@ -17,11 +18,11 @@ private static readonly ThrowingWriteOnlyStream _throwingResponseStream
         private readonly FrameRequestStream _emptyRequest;
         private readonly Stream _upgradeStream;
 
-        public Streams(IFrameControl frameControl)
+        public Streams(IHttpBodyControlFeature bodyControl, IFrameControl frameControl)
         {
-            _request = new FrameRequestStream();
-            _emptyRequest = new FrameRequestStream();
-            _response = new FrameResponseStream(frameControl);
+            _request = new FrameRequestStream(bodyControl);
+            _emptyRequest = new FrameRequestStream(bodyControl);
+            _response = new FrameResponseStream(bodyControl, frameControl);
             _upgradeableResponse = new WrappingStream(_response);
             _upgradeStream = new FrameDuplexStream(_request, _response);
         }

src/Microsoft.AspNetCore.Server.Kestrel.Core/KestrelServerOptions.cs

@@ -35,6 +35,11 @@ public class KestrelServerOptions
         /// <remarks>The default mode is <see cref="SchedulingMode.Default"/></remarks>
         public SchedulingMode ApplicationSchedulingMode { get; set; } = SchedulingMode.Default;
 
+        /// <summary>
+        /// Gets or sets a value that controls whether synchronous IO is allowed for the <see cref="Http.Features.IHttpRequestFeature.Body"/> and <see cref="Http.Features.IHttpResponseFeature.Body"/> 
+        /// </summary>
+        public bool AllowSynchronousIO { get; set; }
+
         /// <summary>
         /// Enables the Listen options callback to resolve and use services registered by the application during startup.
         /// Typically initialized by UseKestrel()"/>.