Use WebHeaderEncoding to encode status description text

Author: stephentoub

src/System.Net.HttpListener/src/System.Net.HttpListener.csproj

@@ -94,6 +94,9 @@
     <Compile Include="$(CommonPath)\System\Net\UriScheme.cs">
       <Link>Common\System\Net\UriScheme.cs</Link>
     </Compile>
+    <Compile Include="$(CommonPath)\System\Net\WebHeaderEncoding.cs">
+      <Link>Common\System\Net\WebHeaderEncoding.cs</Link>
+    </Compile>
     <Compile Include="$(CommonPath)\System\Net\WebSockets\WebSocketValidate.cs">
       <Link>Common\System\Net\WebSockets\WebSocketValidate.cs</Link>
     </Compile>
@@ -125,9 +128,6 @@
     <Compile Include="$(CommonPath)\System\Net\InternalException.cs">
       <Link>Common\System\Net\InternalException.cs</Link>
     </Compile>
-    <Compile Include="$(CommonPath)\System\Net\WebHeaderEncoding.cs">
-      <Link>Common\System\Net\WebHeaderEncoding.cs</Link>
-    </Compile>
     <Compile Include="System\Net\Windows\HttpResponseStream.Windows.cs" />
     <Compile Include="System\Net\Windows\HttpResponseStreamAsyncResult.cs" />
     <Compile Include="System\Net\Windows\WebSockets\ServerWebSocket.cs" />

src/System.Net.HttpListener/src/System/Net/Managed/HttpListenerResponse.Managed.cs

@@ -266,9 +266,13 @@ internal void SendHeaders(bool closing, MemoryStream ms, bool isWebSocketHandsha
 
             Encoding encoding = Encoding.Default;
             StreamWriter writer = new StreamWriter(ms, encoding, 256);
-            writer.Write("HTTP/{0} {1} {2}\r\n", _version, _statusCode, StatusDescription);
-            string headers_str = FormatHeaders(_webHeaders);
-            writer.Write(headers_str);
+            writer.Write("HTTP/{0} {1} ", _version, _statusCode);
+            writer.Flush();
+            byte[] statusDescriptionBytes = WebHeaderEncoding.GetBytes(StatusDescription);
+            ms.Write(statusDescriptionBytes, 0, statusDescriptionBytes.Length);
+            writer.Write("\r\n");
+
+            writer.Write(FormatHeaders(_webHeaders));
             writer.Flush();
             int preamble = encoding.GetPreamble().Length;
             EnsureResponseStream();

src/System.Net.HttpListener/tests/HttpListenerResponseTests.Headers.cs

@@ -333,8 +333,7 @@ public async Task StatusDescription_GetWithCustomStatusCode_ReturnsExpected(int
         [InlineData("A !#\t1\u1234", "A !#\t14", 125)] // 
         [InlineData("StatusDescription", "StatusDescription", 135)]
         [InlineData("  StatusDescription  ", "  StatusDescription  ", 139)]
-        // The managed implementation should use WebHeaderEncoding to encode unicode headers.
-        [ConditionalTheory(nameof(Helpers) + "." + nameof(Helpers.IsWindowsImplementation))] // [ActiveIssue(19976, TestPlatforms.AnyUnix)]
+        [ConditionalTheory(nameof(PlatformDetection) + "." + nameof(PlatformDetection.IsNotOneCoreUAP))]
         public async Task StatusDescription_SetCustom_Success(string statusDescription, string expectedStatusDescription, int expectedNumberOfBytes)
         {
             using (HttpListenerResponse response = await GetResponse())