HttpWebRequest ReadWriteTimeout ignored in .NET; works in Mono

Question

When writing data to a web server, my tests show HttpWebRequest.ReadWriteTimeout is ignored, contrary to the MSDN spec. For example if I set ReadWriteTimeout to 1 (=1 msec), call myRequestStream.Write() passing in a buffer that takes 10 seconds to transfer, it transfers successfully and never times out using .NET 3.5 SP1. The same test running on Mono 2.6 times out immediately as expected. What could be wrong?

Answer 1

There appears to be a bug where the write timeout, when set on the Stream instance returned to you by BeginGetRequestStream(), is not propagated down to the native socket. I will be filing a bug to make sure this issue is corrected for a future release of the .NET Framework.

Here is a workaround.

private static void SetRequestStreamWriteTimeout(Stream requestStream, int timeout)
{
  // Work around a framework bug where the request stream write timeout doesn't make it
  // to the socket. The "m_Chunked" field indicates we are performing chunked reads. Since
  // this stream is being used for writes, the value of this field is irrelevant except
  // that setting it to true causes the Eof property on the ConnectStream object to evaluate
  // to false. The code responsible for setting the socket option short-circuits when it
  // sees Eof is true, and does not set the flag. If Eof is false, the write timeout
  // propagates to the native socket correctly.

  if (!s_requestStreamWriteTimeoutWorkaroundFailed)
  {
    try
    {
      Type connectStreamType = requestStream.GetType();
      FieldInfo fieldInfo = connectStreamType.GetField("m_Chunked", BindingFlags.NonPublic | BindingFlags.Instance);
      fieldInfo.SetValue(requestStream, true);
    }
    catch (Exception)
    {
      s_requestStreamWriteTimeoutWorkaroundFailed = true;
    }
  }

  requestStream.WriteTimeout = timeout;
}

private static bool s_requestStreamWriteTimeoutWorkaroundFailed;