diff --git a/src/Microsoft.AspNetCore.Server.HttpSys/HttpSysOptions.cs b/src/Microsoft.AspNetCore.Server.HttpSys/HttpSysOptions.cs
index cf34e6e..0d8a6b4 100644
--- a/src/Microsoft.AspNetCore.Server.HttpSys/HttpSysOptions.cs
+++ b/src/Microsoft.AspNetCore.Server.HttpSys/HttpSysOptions.cs
@@ -61,6 +61,15 @@ namespace Microsoft.AspNetCore.Server.HttpSys
///
public bool ThrowWriteExceptions { get; set; }
+ ///
+ /// Enable buffering of response data in the Kernel.
+ /// It should be used by an application doing synchronous I/O or by an application doing asynchronous I/O with
+ /// no more than one outstanding write at a time, and can significantly improve throughput over high-latency connections.
+ /// Applications that use asynchronous I/O and that may have more than one send outstanding at a time should not use this flag.
+ /// Enabling this can results in higher CPU and memory usage by Http.Sys.
+ ///
+ public bool EnableKernelResponseBuffering { get; set; }
+
///
/// Gets or sets the maximum number of concurrent connections to accept, -1 for infinite, or null to
/// use the machine wide setting from the registry. The default value is null.
diff --git a/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/ResponseBody.cs b/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/ResponseBody.cs
index 87ae976..4024c5e 100644
--- a/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/ResponseBody.cs
+++ b/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/ResponseBody.cs
@@ -43,6 +43,8 @@ namespace Microsoft.AspNetCore.Server.HttpSys
internal bool ThrowWriteExceptions => RequestContext.Server.Options.ThrowWriteExceptions;
+ internal bool EnableKernelResponseBuffering => RequestContext.Server.Options.EnableKernelResponseBuffering;
+
internal bool IsDisposed => _disposed;
public override bool CanSeek
@@ -436,6 +438,10 @@ namespace Microsoft.AspNetCore.Server.HttpSys
else if (!endOfRequest && _leftToWrite != writeCount)
{
flags |= HttpApiTypes.HTTP_FLAGS.HTTP_SEND_RESPONSE_FLAG_MORE_DATA;
+ if (EnableKernelResponseBuffering)
+ {
+ flags |= HttpApiTypes.HTTP_FLAGS.HTTP_SEND_RESPONSE_FLAG_BUFFER_DATA;
+ }
}
// Update _leftToWrite now so we can queue up additional async writes.
diff --git a/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/ResponseBodyTests.cs b/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/ResponseBodyTests.cs
index a42071b..10eec93 100644
--- a/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/ResponseBodyTests.cs
+++ b/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/ResponseBodyTests.cs
@@ -38,6 +38,41 @@ namespace Microsoft.AspNetCore.Server.HttpSys
}
}
+ [ConditionalTheory]
+ [InlineData(true)]
+ [InlineData(false)]
+ public async Task ResponseBody_WriteNoHeaders_SetsChunked_LargeBody(bool enableKernelBuffering)
+ {
+ const int WriteSize = 1024 * 1024;
+ const int NumWrites = 32;
+
+ string address;
+ using (Utilities.CreateHttpServer(
+ baseAddress: out address,
+ configureOptions: options => { options.EnableKernelResponseBuffering = enableKernelBuffering; },
+ app: async httpContext =>
+ {
+ httpContext.Features.Get().AllowSynchronousIO = true;
+ for (int i = 0; i < NumWrites - 1; i++)
+ {
+ httpContext.Response.Body.Write(new byte[WriteSize], 0, WriteSize);
+ }
+ await httpContext.Response.Body.WriteAsync(new byte[WriteSize], 0, WriteSize);
+ }))
+ {
+ var response = await SendRequestAsync(address);
+ Assert.Equal(200, (int)response.StatusCode);
+ Assert.Equal(new Version(1, 1), response.Version);
+ IEnumerable ignored;
+ Assert.False(response.Content.Headers.TryGetValues("content-length", out ignored), "Content-Length");
+ Assert.True(response.Headers.TransferEncodingChunked.HasValue, "Chunked");
+
+ var bytes = await response.Content.ReadAsByteArrayAsync();
+ Assert.Equal(WriteSize * NumWrites, bytes.Length);
+ Assert.True(bytes.All(b => b == 0));
+ }
+ }
+
[ConditionalFact]
public async Task ResponseBody_WriteNoHeadersAndFlush_DefaultsToChunked()
{