From 1e556e0b46d6ace8ad81d277fd9c396c70f11fdf Mon Sep 17 00:00:00 2001
From: "Chris Ross (ASP.NET)" <chrross@microsoft.com>
Date: Mon, 6 Nov 2017 22:15:19 -0800
Subject: [PATCH]  #1253 TestServer: mark response headers IsReadOnly on start

---
 src/Microsoft.AspNetCore.TestHost/ResponseFeature.cs          | 4 +++-
 .../ResponseFeatureTests.cs                                   | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/Microsoft.AspNetCore.TestHost/ResponseFeature.cs b/src/Microsoft.AspNetCore.TestHost/ResponseFeature.cs
index f736481810..2fb691619a 100644
--- a/src/Microsoft.AspNetCore.TestHost/ResponseFeature.cs
+++ b/src/Microsoft.AspNetCore.TestHost/ResponseFeature.cs
@@ -13,10 +13,11 @@ namespace Microsoft.AspNetCore.TestHost
     {
         private Func<Task> _responseStartingAsync = () => Task.FromResult(true);
         private Func<Task> _responseCompletedAsync = () => Task.FromResult(true);
+        private HeaderDictionary _headers = new HeaderDictionary();
 
         public ResponseFeature()
         {
-            Headers = new HeaderDictionary();
+            Headers = _headers;
             Body = new MemoryStream();
 
             // 200 is the default status code all the way down to the host, so we set it
@@ -69,6 +70,7 @@ namespace Microsoft.AspNetCore.TestHost
         {
             await _responseStartingAsync();
             HasStarted = true;
+            _headers.IsReadOnly = true;
         }
 
         public Task FireOnResponseCompletedAsync()
diff --git a/test/Microsoft.AspNetCore.TestHost.Tests/ResponseFeatureTests.cs b/test/Microsoft.AspNetCore.TestHost.Tests/ResponseFeatureTests.cs
index f50d68a815..8081f092a8 100644
--- a/test/Microsoft.AspNetCore.TestHost.Tests/ResponseFeatureTests.cs
+++ b/test/Microsoft.AspNetCore.TestHost.Tests/ResponseFeatureTests.cs
@@ -22,6 +22,7 @@ namespace Microsoft.AspNetCore.TestHost
             await responseInformation.FireOnSendingHeadersAsync();
 
             Assert.True(responseInformation.HasStarted);
+            Assert.True(responseInformation.Headers.IsReadOnly);
         }
 
         [Fact]