PR feedback.

Author: Cesar Blum Silveira

src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameHeaders.Generated.cs

@@ -3404,7 +3404,6 @@ protected override bool RemoveFast(string key)
                         {
                             if (((_bits & 2048L) != 0))
                             {
-                                _contentLength = null;
                                 _bits &= ~2048L;
                                 _headers._ContentLength = StringValues.Empty;
                                 return true;
@@ -3701,7 +3700,7 @@ protected override void ClearFast()
         {
             _bits = 0;
             _headers = default(HeaderReferences);
-            _contentLength = null;
+            
             MaybeUnknown?.Clear();
         }
 

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

@@ -499,16 +499,22 @@ await connection.ReceiveEnd(
                 errorMessage.Exception.Message);
         }
 
-        [Fact]
-        public async Task WhenAppSetsContentLengthToZeroAndDoesNotWriteNoErrorIsThrown()
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task WhenAppSetsContentLengthToZeroAndDoesNotWriteNoErrorIsThrown(bool flushResponse)
         {
             var testLogger = new TestApplicationErrorLogger();
             var serviceContext = new TestServiceContext { Log = new TestKestrelTrace(testLogger) };
 
-            using (var server = new TestServer(httpContext =>
+            using (var server = new TestServer(async httpContext =>
             {
                 httpContext.Response.ContentLength = 0;
-                return TaskCache.CompletedTask;
+
+                if (flushResponse)
+                {
+                    await httpContext.Response.Body.FlushAsync();
+                }
             }, serviceContext))
             {
                 using (var connection = server.CreateConnection())

tools/Microsoft.AspNetCore.Server.Kestrel.GeneratedCode/KnownHeaders.cs

@@ -361,7 +361,7 @@ protected override bool RemoveFast(string key)
                         if (""{header.Name}"".Equals(key, StringComparison.OrdinalIgnoreCase))
                         {{
                             if ({header.TestBit()})
-                            {{{If(header.Identifier == "ContentLength", () => $@"
+                            {{{If(loop.ClassName == "FrameResponseHeaders" && header.Identifier == "ContentLength", () => $@"
                                 _contentLength = null;")}
                                 {header.ClearBit()};
                                 _headers._{header.Identifier} = StringValues.Empty;{(header.EnhancedSetter == false ? "" : $@"
@@ -382,7 +382,7 @@ protected override void ClearFast()
         {{
             _bits = 0;
             _headers = default(HeaderReferences);
-            _contentLength = null;
+            {(loop.ClassName == "FrameResponseHeaders" ? "_contentLength = null;" : "")}
             MaybeUnknown?.Clear();
         }}