Override IIS headers in inproc (#1409)

Author: pakrym

src/Microsoft.AspNetCore.Server.IIS/Core/IISHttpContext.cs

@@ -318,29 +318,23 @@ public unsafe void SetResponseHeaders()
             {
                 var headerValues = headerPair.Value;
                 var knownHeaderIndex = HttpApiTypes.HTTP_RESPONSE_HEADER_ID.IndexOfKnownHeader(headerPair.Key);
-                if (knownHeaderIndex == -1)
+                for (var i = 0; i < headerValues.Count; i++)
                 {
-                    var headerNameBytes = Encoding.UTF8.GetBytes(headerPair.Key);
-                    for (var i = 0; i < headerValues.Count; i++)
+                    var isFirst = i == 0;
+                    var headerValueBytes = Encoding.UTF8.GetBytes(headerValues[i]);
+                    fixed (byte* pHeaderValue = headerValueBytes)
                     {
-                        var headerValueBytes = Encoding.UTF8.GetBytes(headerValues[i]);
-                        fixed (byte* pHeaderName = headerNameBytes)
+                        if (knownHeaderIndex == -1)
                         {
-                            fixed (byte* pHeaderValue = headerValueBytes)
+                            var headerNameBytes = Encoding.UTF8.GetBytes(headerPair.Key);
+                            fixed (byte* pHeaderName = headerNameBytes)
                             {
-                                NativeMethods.HttpResponseSetUnknownHeader(_pInProcessHandler, pHeaderName, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: false);
+                                NativeMethods.HttpResponseSetUnknownHeader(_pInProcessHandler, pHeaderName, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: isFirst);
                             }
                         }
-                    }
-                }
-                else
-                {
-                    for (var i = 0; i < headerValues.Count; i++)
-                    {
-                        var headerValueBytes = Encoding.UTF8.GetBytes(headerValues[i]);
-                        fixed (byte* pHeaderValue = headerValueBytes)
+                        else
                         {
-                            NativeMethods.HttpResponseSetKnownHeader(_pInProcessHandler, knownHeaderIndex, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: false);
+                            NativeMethods.HttpResponseSetKnownHeader(_pInProcessHandler, knownHeaderIndex, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: isFirst);
                         }
                     }
                 }

test/Common.FunctionalTests/Inprocess/ResponseHeaderTests.cs

@@ -74,5 +74,12 @@ public async Task CustomErrorCodeWorks(int code, string reason, string expectedR
             // ReadAsStringAsync returns empty string for empty results
             Assert.Equal(body ?? string.Empty, await response.Content.ReadAsStringAsync());
         }
+
+        [ConditionalFact]
+        public async Task ServerHeaderIsOverriden()
+        {
+            var response = await _fixture.Client.GetAsync("OverrideServer");
+            Assert.Equal("MyServer/7.8", response.Headers.Server.Single().Product.ToString());
+        }
     }
 }

test/WebSites/shared/SharedStartup/Startup.shared.cs

@@ -82,5 +82,11 @@ public async Task ApplicationInitialization(HttpContext context)
             }
             await context.Response.WriteAsync(_applicationInitializationCalled.ToString());
         }
+
+        public Task OverrideServer(HttpContext context)
+        {
+            context.Response.Headers["Server"] = "MyServer/7.8";
+            return Task.CompletedTask;
+        }
     }
 }