Consolidate OutputStream implementation

Move Windows implementation to shared, then use that from managed, which means moving the core of the managed implementation to a private EnsureResponseStream helper.

Author: stephentoub

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

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Diagnostics;
+using System.IO;
 using System.Text;
 
 namespace System.Net
@@ -11,6 +12,7 @@ public sealed unsafe partial class HttpListenerResponse : IDisposable
     {
         private CookieCollection _cookies;
         private bool _keepAlive = true;
+        private HttpResponseStream _responseStream;
         private string _statusDescription;
         private WebHeaderCollection _webHeaders = new WebHeaderCollection();
 
@@ -62,6 +64,16 @@ public bool KeepAlive
             }
         }
 
+        public Stream OutputStream
+        {
+            get
+            {
+                CheckDisposed();
+                EnsureResponseStream();
+                return _responseStream;
+            }
+        }
+
         public string RedirectLocation
         {
             get => Headers[HttpResponseHeader.Location];

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

@@ -39,7 +39,6 @@ public sealed partial class HttpListenerResponse : IDisposable
     {
         private long _contentLength;
         private bool _clSet;
-        private HttpResponseStream _outputStream;
         private Version _version = HttpVersion.Version11;
         private int _statusCode = 200;
         private bool _chunked;
@@ -70,13 +69,11 @@ public long ContentLength64
             }
         }
 
-        public Stream OutputStream
+        private void EnsureResponseStream()
         {
-            get
+            if (_responseStream == null)
             {
-                if (_outputStream == null)
-                    _outputStream = _context.Connection.GetResponseStream();
-                return _outputStream;
+                _responseStream = _context.Connection.GetResponseStream();
             }
         }
 
@@ -275,8 +272,7 @@ internal void SendHeaders(bool closing, MemoryStream ms, bool isWebSocketHandsha
             writer.Write(headers_str);
             writer.Flush();
             int preamble = encoding.GetPreamble().Length;
-            if (_outputStream == null)
-                _outputStream = _context.Connection.GetResponseStream();
+            EnsureResponseStream();
 
             /* Assumes that the ms was at position 0 */
             ms.Position = preamble;

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

@@ -25,7 +25,6 @@ private enum ResponseState
 
         private ResponseState _responseState;
 
-        private HttpResponseStream _responseStream;
         private long _contentLength;
         private BoundaryType _boundaryType;
         private Interop.HttpApi.HTTP_RESPONSE _nativeResponse;
@@ -53,16 +52,6 @@ internal HttpListenerResponse(HttpListenerContext httpContext) : this()
 
         private HttpListenerRequest HttpListenerRequest => HttpListenerContext.Request;
 
-        public Stream OutputStream
-        {
-            get
-            {
-                CheckDisposed();
-                EnsureResponseStream();
-                return _responseStream;
-            }
-        }
-
         public int StatusCode
         {
             get => _nativeResponse.StatusCode;

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

@@ -126,8 +126,7 @@ public async Task ContentType_SetAfterHeadersSent_DoesNothing()
             Assert.DoesNotContain("Content-Type", clientResponse);
         }
 
-        // The managed implementation should throw an ObjectDisposedException getting OutputStream when disposed.
-        [ConditionalFact(nameof(Helpers) + "." + nameof(Helpers.IsWindowsImplementation))] // [ActiveIssue(19971, TestPlatforms.AnyUnix)]
+        [ConditionalFact(nameof(PlatformDetection) + "." + nameof(PlatformDetection.IsNotOneCoreUAP))]
         public async Task OutputStream_GetDisposed_ThrowsObjectDisposedException()
         {
             HttpListenerResponse response = await GetResponse();