Uploading a file via POST multipart/form-data from windows phone 8.1 Silverlight Httpclient to python server corrupts files

Question

Originally, I was using Windows Phone 8 System.Net.Http library to upload an image from SD card to a Python server with the following code:

    private async void UploadFile()
    {
        try
        {
            // Make sure there is a picture selected
            if (photoStream != null)
            {
                // initialize the client
                // need to make sure the server accepts network IP-based
                // requests. 
                // ensure correct IP and correct port address
                var fileUploadUrl = @"http://IPAddress/";
                var client = new HttpClient();

                // Reset the photoStream position
                // If you don't reset the position, the content lenght
                // sent will be 0
                photoStream.Position = 0;

                // This is the postdata
                MultipartFormDataContent content = new MultipartFormDataContent();
                content.Add(new StreamContent(photoStream), "fn", fileName);

                // upload the file sending the form info and ensure a result.
                // it will throw an exception if the service doesn't return 
                // a valid successful status code
                await client.PostAsync(fileUploadUrl, content)
                    .ContinueWith((postTask) =>
                    {
                        postTask.Result.EnsureSuccessStatusCode();
                    });
            }

            // Disable the Upload button
            btnUpload.IsEnabled = false;

            // reset the image control
            DisplayImage.Source = null;
        }
        catch
        {

        }
    }

In the server side, I used the following python code to decode the request:

ctype, pdict = cgi.parse_header(self.headers['content-type'])
data = cgi.parse_multipart(self.rfile, pdict)

It worked until I switched from Windows Phone 8 to Windows Phone 8.1 Silverlight. Since the System.Net.Http library is no longer supported in Windows Phone 8.1 Silverlight, I used Windows.Web.Http instead with modification of the code:

    private async void UploadFile()
    {
        try
        {
            // Make sure there is a picture selected
            if (file != null)
            {
                // initialize the client
                // need to make sure the server accepts network IP-based
                // requests. 
                // ensure correct IP and correct port address
                var fileUploadUrl = new Uri(@"http://IPAddress/", UriKind.Absolute);
                var client = new HttpClient();

                HttpMultipartFormDataContent content = new HttpMultipartFormDataContent();
                HttpStreamContent streamContent = new HttpStreamContent(photoStream);
                content.Add(streamContent, "fn", fileName);

                await client.PostAsync(fileUploadUrl, content);

            }

            // Disable the Upload button
            btnUpload.IsEnabled = false;

            // reset the image control
            DisplayImage.Source = null;
        }
        catch
        {

        }
    }

The server side is unchanged. However, the resulting file uploaded now has extra bytes inserted periodically that look something like '\r\n10000\r\n' or 0D 0A 31 30 30 30 30 0D 0A. The file also appears to begin and end with the same extra byte pattern. On the server pdict maps the boundary to something like xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, but this seems to be the same behavior from when the file was uploaded via System.Net.Http. I tried removing these bytes by hand on a smaller file which seemed to confirm that the file is otherwise correct.

Why are these extra bytes present? Is this a problem with the Python server mishandling the POST request?

Answer 1

Here's my solution when I encountered this issue:

Client:

 public async Task UploadImage(byte[] image, string url)
        {
            Stream stream = new System.IO.MemoryStream(image);
            HttpStreamContent streamContent = new HttpStreamContent(stream.AsInputStream());

            Uri resourceAddress = null;
            Uri.TryCreate(url.Trim(), UriKind.Absolute, out resourceAddress);
            Windows.Web.Http.HttpRequestMessage request = new Windows.Web.Http.HttpRequestMessage(Windows.Web.Http.HttpMethod.Post, resourceAddress);
            request.Content = streamContent;

            var httpClient = new Windows.Web.Http.HttpClient();
            var cts = new CancellationTokenSource();
            Windows.Web.Http.HttpResponseMessage response = await httpClient.SendRequestAsync(request).AsTask(cts.Token);
        }

Controller:

public async Task<HttpResponseMessage> Post()
{
    Stream requestStream = await this.Request.Content.ReadAsStreamAsync();
    byte[] byteArray = null;
    using (MemoryStream ms = new MemoryStream())
    {
        await requestStream.CopyToAsync(ms);
        byteArray = ms.ToArray();
    }
    .
    .
    .
    return Request.CreateResponse(HttpStatusCode.OK);
}