[HIGH PRIORITY - Proposed fix to be included for ASP.NET Beta7]

This fixes a bug found with chunked uploads using custom content that repeatedly calls Flush() on the stream passed into SerializeToStreamAsync.

This bug was discovered by WCF tests and reported via GitHub: https://github.com/dotnet/corefx/issues/2897

It was a mistake to use the Flush() method on the stream to send the final terminating chunk for the upload since that method can be called by custom content via the SerializeToStreamAsync method. The typical use pattern is that depending on the actual streams involved, upper layer software typically can call Flush() one or more times when writing to a stream. The fix here is to simply leave Flush() as a no-op (which it basically is for the WinHttpRequestStream) and have an internal method to handle the writing of the final terminating chunk.

This fix is being checked into TFS instead of using a GitHub PR. The reason is that the tests for this need to use our current internal server that correctly echoes the request headers in order to verify 'Transfer-Encoding: chunked' was sent by the client. I tried to put this test into the current GitHub tests using the current "http://httpbin.org" test server, but I discovered that httpbin.org doesn't properly echo the request headers when 'Transfer-Encoding' is sent. Instead, it ends up replacing that header and sending back 'Content-Length' (even though we didn't send that in the request headers). We have a backlog work item to port our remaining ToF tests to GitHub over the next several weeks.

[tfs-changeset: 1516976]

Author: davidsh

src/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpHandler.cs

@@ -1190,7 +1190,7 @@ private async void StartRequest(object obj)
                         await state.RequestMessage.Content.CopyToAsync(
                             requestStream,
                             state.TransportContext).ConfigureAwait(false);
-                        requestStream.Flush();
+                        requestStream.EndUpload();
                     }
 
                     state.CancellationToken.ThrowIfCancellationRequested();

src/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpRequestStream.cs

@@ -77,10 +77,6 @@ public override long Position
 
         public override void Flush()
         {
-            if (_chunkedMode)
-            {
-                WriteData(s_endChunk, 0, s_endChunk.Length);
-            }
         }
 
         public override void Write(byte[] buffer, int offset, int count)
@@ -128,6 +124,14 @@ public override int Read(byte[] buffer, int offset, int count)
             throw new NotSupportedException();
         }
 
+        internal void EndUpload()
+        {
+            if (_chunkedMode)
+            {
+                WriteData(s_endChunk, 0, s_endChunk.Length);
+            }
+        }
+        
         protected override void Dispose(bool disposing)
         {
             if (disposing && !_disposed)