runtime: Memory leak in SendAsync in HttpClient

In corefx/src/System.Net.Http/src/System/Net/Http/HttpClient.cs:SendAsync there seems to be a memory leak that is triggered when CancellationToken.None is used.

We have created HttpClient once and reuse it:

    var httpClientHandler = new HttpClientHandler();
    httpClientHandler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true;
    httpClient = new HttpClient(httpClientHandler);
    httpClient.Timeout = Timeout.InfiniteTimeSpan;

And are calling like this:

    using (var content = PrepareHttpContentJson(input))
    using (HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, new Uri(fullUrl, UriKind.RelativeOrAbsolute)))
    {
      request.Content = content;
      using (HttpResponseMessage result = await httpClient.SendAsync(request, CancellationToken.None))
      {
        // work on result
      }
    }

PrepareHttpContentJson returns a ByteArrayContent (json content) with ContentType set.

If this code is called repeatably, it leaks every ByteArrayContent created.

Looking to the memory using Diagnostic Tools in Visual Studio, this is what seems to lock the memory:

ByteArrayContent
   > Action<Stream>
    > HttpWebRequest
      > ConnectStream
      > ContextAwareResult
      > HttpClientHandler+RequestState
      > CancellationCallbackInfo

If I replace CancellationToken.None with cts.Token in SendAsync and create var cts = new CancellationTokenSource(); just before the first using, the memory leak stops.

I made this attempt as I checked the source code for HttpClient.cs and noticed some handling of cancellation tokens going on and figured this might be the cause.

Note: This MAY be an interaction issue with Autofac, but I don’t think so. The using code block is resolve by Autofac, but there is only ever 1 instance (registered as single instance) of it (so it wont be disposed between usages).

[EDIT] Add C# syntax highlighting by @karelz