Monitoring upload progress with HttpWebRequest

Question

I've recently written a C# function that does a multi part form post for uploading files. To track the progress, I'd write the form data to the request stream at 4096 bytes at a time and call back with each write. However, it seems that the request does not even get sent until GetResponseAsync() is called.

If this is the case, is the reporting of every 4096 bytes written to the request stream an accurate reporting of upload progress?

If not, how can I accurately report progress? WebClient is out of the question for me, this is in a PCL Xamarin project.

    private async Task<string> PostFormAsync (string postUrl, string contentType, byte[] formData)
    {
        try {
            HttpWebRequest request = WebRequest.Create (postUrl) as HttpWebRequest;

            request.Method = "POST";
            request.ContentType = contentType;

            request.Headers ["Cookie"] = Constants.Cookie;

            byte[] buffer = new byte[4096];
            int count = 0;
            int length = 0;
            using (Stream requestStream = await request.GetRequestStreamAsync ()) {
                using (Stream inputStream = new MemoryStream (formData)) {

                    while ((count = await inputStream.ReadAsync (buffer, 0, buffer.Length)) > 0) {
                        await requestStream.WriteAsync (buffer, 0, count);
                        length += count;
                        Device.BeginInvokeOnMainThread (() => {
                            _progressBar.Progress = length / formData.Length;
                        });
                    }   
                }
            }
            _progressBar.Progress = 0;

            WebResponse resp = await request.GetResponseAsync ();

            using (Stream stream = resp.GetResponseStream ()) {
                StreamReader respReader = new StreamReader (stream);
                return respReader.ReadToEnd ();
            }

        } catch (Exception e) {

            Debug.WriteLine (e.ToString ());
            return String.Empty;
        }
    }

Please note that I am asking about monitoring progress of an upload at 4096 bytes at a time, not a download

Answer 1

I ended up accomplishing this by setting the AllowWriteStreamBuffering property of the WebRequest equal to false and the SendChunked property to true.

HOWEVER Xamarin.PCL (Profile 78) does not allow you to access these properties of the HttpWebRequest, so I had to instantiate my HttpWebRequest and return it from a dependency service in my platform specific project (only tested in iOS).

public class WebDependency : IWebDependency
{
    public HttpWebRequest GetWebRequest(string uri)
    {
        var request = WebRequest.Create (uri) as HttpWebRequest;
        request.SendChunked = true;
        request.AllowWriteStreamBuffering = false;

        return request;

    }

}

And then to instantiate my web request -

HttpWebRequest request = DependencyService.Get<IWebDependency>().GetWebRequest(uri);