Ensure HttpSys request header dictionary removes known headers when Remove is called before Get dotnet#43230 (dotnet#44860)

Author: singh733

src/Servers/HttpSys/src/RequestProcessing/RequestHeaders.Generated.tt

@@ -166,13 +166,17 @@ namespace Microsoft.AspNetCore.HttpSys.Internal
 <# foreach(var length in lengths) { #>
                 case <#=length.Key#>:
 <# foreach(var prop in length) { #>
-                    if (_<#=prop.Name#>.Count > 0
-                        && string.Equals(key, HeaderNames.<#=prop.Name#>, StringComparison.Ordinal))
+                    if(string.Equals(key, HeaderNames.<#=prop.Name#>, StringComparison.Ordinal))
                     {
-					    bool wasSet = <#=IsRead(prop.Index)#>;
-                        <#=prop.Name#> = StringValues.Empty;
-                        return wasSet;
+                         if ((<#=IsRead(prop.Index)#> && <#=prop.Name#>.Count > 0)
+                            || (!<#=IsRead(prop.Index)#> && HasKnownHeader(<#=prop.ID#>)))                            
+                        {					        
+                            <#=prop.Name#> = StringValues.Empty;
+                            return true;
+                        }
+                        return false;
                     }
+                    
 <# } #>
                    break;
 <# } #>

src/Servers/HttpSys/test/FunctionalTests/Listener/RequestHeaderTests.cs

@@ -15,6 +15,46 @@ namespace Microsoft.AspNetCore.Server.HttpSys.Listener;
 
 public class RequestHeaderTests
 {
+    [ConditionalFact]
+    public async Task RequestHeaders_RemoveHeaders_Success()
+    {
+        string address;
+        using (var server = Utilities.CreateHttpServer(out address))
+        {
+            string[] customValues = new string[] { "custom1, and custom测试2", "custom3" };
+            Task responseTask = SendRequestAsync(address, "Custom-Header", customValues, Encoding.UTF8);
+
+            var context = await server.AcceptAsync(Utilities.DefaultTimeout);
+            var requestHeaders = context.Request.Headers;
+
+            var headers = context.Request.Headers;
+            bool removed = headers.Remove("Connection");
+            Assert.False(headers.TryGetValue("Connection", out _));
+            Assert.True(StringValues.IsNullOrEmpty(headers["Connection"]));
+            Assert.True(StringValues.IsNullOrEmpty(headers.Connection));
+
+            removed = headers.Remove("Custom-Header");
+            Assert.True(removed);
+            Assert.False(headers.TryGetValue("Custom-Header", out _));
+            Assert.True(StringValues.IsNullOrEmpty(headers["Custom-Header"]));
+
+            headers["Connection"] = "foo";
+            Assert.True(headers.TryGetValue("Connection", out var connectionValue));
+            Assert.Equal("foo", connectionValue);
+            Assert.Equal("foo", headers["Connection"]);
+
+            bool removedAfterAssignValue = headers.Remove("Connection");
+            bool removedAgain = headers.Remove("Connection");
+
+            Assert.True(removed);
+            Assert.True(removedAfterAssignValue);
+            Assert.False(removedAgain);
+
+            context.Dispose();
+
+            await responseTask;
+        }
+    }
 
     [ConditionalFact]
     public async Task RequestHeaders_ClientSendsUtf8Headers_Success()

src/Shared/HttpSys/RequestProcessing/NativeRequestContext.cs

@@ -307,6 +307,38 @@ private static string GetAuthTypeFromRequest(HttpApiTypes.HTTP_REQUEST_AUTH_TYPE
         }
     }
 
+    internal bool HasKnownHeader(HttpSysRequestHeader header)
+    {
+        if (PermanentlyPinned)
+        {
+            return HasKnowHeaderHelper(header, 0, _nativeRequest);
+        }
+        else
+        {
+            fixed (byte* pMemoryBlob = _backingBuffer.Memory.Span)
+            {
+                var request = (HttpApiTypes.HTTP_REQUEST*)(pMemoryBlob + _bufferAlignment);
+                long fixup = pMemoryBlob - (byte*)_originalBufferAddress;
+                return HasKnowHeaderHelper(header, fixup, request);
+            }
+        }
+    }
+
+    private bool HasKnowHeaderHelper(HttpSysRequestHeader header, long fixup, HttpApiTypes.HTTP_REQUEST* request)
+    {
+        int headerIndex = (int)header;        
+
+        HttpApiTypes.HTTP_KNOWN_HEADER* pKnownHeader = (&request->Headers.KnownHeaders) + headerIndex;
+        // For known headers, when header value is empty, RawValueLength will be 0 and
+        // pRawValue will point to empty string ("\0")
+        if (pKnownHeader->RawValueLength > 0)
+        {
+            return true;
+        }
+
+        return false;
+    }
+
     // These methods are for accessing the request structure after it has been unpinned. They need to adjust addresses
     // in case GC has moved the original object.
 
@@ -325,7 +357,7 @@ private static string GetAuthTypeFromRequest(HttpApiTypes.HTTP_REQUEST_AUTH_TYPE
                 return GetKnowHeaderHelper(header, fixup, request);
             }
         }
-    }
+    }  
 
     private string? GetKnowHeaderHelper(HttpSysRequestHeader header, long fixup, HttpApiTypes.HTTP_REQUEST* request)
     {