HEAD response can include Content-Length header.

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

@@ -617,6 +617,21 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Http
             _responseBytesWritten += count;
         }
 
+        protected void VerifyResponseContentLength()
+        {
+            var responseHeaders = FrameResponseHeaders;
+
+            if (!HttpMethods.IsHead(Method) &&
+                !responseHeaders.HasTransferEncoding &&
+                responseHeaders.HeaderContentLengthValue.HasValue &&
+                _responseBytesWritten < responseHeaders.HeaderContentLengthValue.Value)
+            {
+                _keepAlive = false;
+                ReportApplicationError(new InvalidOperationException(
+                    $"Response Content-Length mismatch: too few bytes written ({_responseBytesWritten} of {responseHeaders.HeaderContentLengthValue.Value})."));
+            }
+        }
+
         private void WriteChunked(ArraySegment<byte> data)
         {
             SocketOutput.Write(data, chunk: true);

src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameOfT.cs

@@ -5,6 +5,7 @@ using System;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Http
@@ -92,16 +93,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Http
                         try
                         {
                             await _application.ProcessRequestAsync(context).ConfigureAwait(false);
-
+                            VerifyResponseContentLength();
-                            var responseHeaders = FrameResponseHeaders;
-                            if (!responseHeaders.HasTransferEncoding &&
-                                responseHeaders.HasContentLength &&
-                                _responseBytesWritten < responseHeaders.HeaderContentLengthValue.Value)
-                            {
-                                _keepAlive = false;
-                                ReportApplicationError(new InvalidOperationException(
-                                    $"Response Content-Length mismatch: too few bytes written ({_responseBytesWritten} of {responseHeaders.HeaderContentLengthValue.Value})."));
-                            }
                         }
                         catch (Exception ex)
                         {

test/Microsoft.AspNetCore.Server.Kestrel.FunctionalTests/ResponseTests.cs

@@ -607,6 +607,62 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
             Assert.Equal(0, testLogger.ApplicationErrorsLogged);
         }
 
+        [Fact]
+        public async Task HeadResponseCanContainContentLengthHeader()
+        {
+            var testLogger = new TestApplicationErrorLogger();
+            var serviceContext = new TestServiceContext { Log = new TestKestrelTrace(testLogger) };
+
+            using (var server = new TestServer(httpContext =>
+            {
+                httpContext.Response.ContentLength = 42;
+                return TaskCache.CompletedTask;
+            }, serviceContext))
+            {
+                using (var connection = server.CreateConnection())
+                {
+                    await connection.SendEnd(
+                        "HEAD / HTTP/1.1",
+                        "",
+                        "");
+                    await connection.ReceiveEnd(
+                        $"HTTP/1.1 200 OK",
+                        $"Date: {server.Context.DateHeaderValue}",
+                        "Content-Length: 42",
+                        "",
+                        "");
+                }
+            }
+        }
+
+        [Fact]
+        public async Task HeadResponseCanContainContentLengthHeaderButBodyNotWritten()
+        {
+            var testLogger = new TestApplicationErrorLogger();
+            var serviceContext = new TestServiceContext { Log = new TestKestrelTrace(testLogger) };
+
+            using (var server = new TestServer(async httpContext =>
+            {
+                httpContext.Response.ContentLength = 12;
+                await httpContext.Response.WriteAsync("hello, world");
+            }, serviceContext))
+            {
+                using (var connection = server.CreateConnection())
+                {
+                    await connection.SendEnd(
+                        "HEAD / HTTP/1.1",
+                        "",
+                        "");
+                    await connection.ReceiveEnd(
+                        $"HTTP/1.1 200 OK",
+                        $"Date: {server.Context.DateHeaderValue}",
+                        "Content-Length: 12",
+                        "",
+                        "");
+                }
+            }
+        }
+
         public static TheoryData<string, StringValues, string> NullHeaderData
         {
             get