Since WebClient's uploadData doesn't encode data, then what will be the effect of adding a “Content-Type”, “multipart/form-data” header to it

Question

C#'s uploadData method doesn't encode the data that is being sent. So, if I send a file over (after converting it into bytes) using this method, and the receiving side is looking for a multiform/form-data post, then it will obviously not work. Will adding a header like :

WebClient c = new WebClient();
c.Headers.Add("Content-Type", "multipart/form-data");

make it send the data encrypted as multiform, or will the data be still not encrypted (and hence unparseable by servers expecting multiform data) ?

Note that I can't use WebClient's uploadFile, as I don't have permission to get the file path location on the client side (I just have a stream, that I can convert to bytes)

Answer 1

Why don't you use UploadFile of WebClient over https if you want it to be secure? and that will automatically take care of adding multipart/form-data.

Example using UploadFile

http://msdn.microsoft.com/en-us/library/36s52zhs.aspx

And one more thing, encoding and encrypting are 2 different things.

Edit:

You should probably tag your question as Silverlight if you you are using WebClient in your WebClient project. Anyways, WebClient class in SL doesn't have any UploadData method. See this for more info:

http://msdn.microsoft.com/en-us/library/system.net.webclient%28v=vs.95%29.aspx

Anyways, here is the working solution to your problem:

In your button click, have this code:

OpenFileDialog dialog = new OpenFileDialog();
            bool? retVal = dialog.ShowDialog();
            if (retVal.HasValue && retVal == true)
            {
                using (Stream stream = dialog.File.OpenRead())
                {
                    MemoryStream memoryStream = new MemoryStream();
                    stream.CopyTo(memoryStream);
                    WebClient webClient = new WebClient();
                    webClient.Headers["Content-type"] = "multipart/form-data; boundary=---------------------------" + _boundaryNo;
                    webClient.OpenWriteAsync(new Uri("http://localhost:1463/Home/File", UriKind.Absolute), "POST", new { Stream = memoryStream, FileName = dialog.File.Name });
                    webClient.OpenWriteCompleted += new OpenWriteCompletedEventHandler(webClient_OpenWriteCompleted);
                }
            } 

and the event itself:

void webClient_OpenWriteCompleted(object sender, OpenWriteCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                Stream responseStream = e.Result as Stream;                
                dynamic obj = e.UserState;
                MemoryStream memoryStream = obj.Stream as MemoryStream;
                string fileName = obj.FileName;
                if (responseStream != null && memoryStream != null)
                {
                    string headerTemplate = string.Format("-----------------------------{0}\r\n", _boundaryNo);

                    memoryStream.Position = 0;
                    byte[] byteArr = memoryStream.ToArray();
                    string data = headerTemplate + string.Format("Content-Disposition: form-data; name=\"pic\"; filename=\"{0}\"\r\nContent-Type: application/octet-stream\r\n\r\n", fileName);
                    byte[] header = Encoding.UTF8.GetBytes(data);
                    responseStream.Write(header, 0, header.Length);

                    responseStream.Write(byteArr, 0, byteArr.Length);
                    header = Encoding.UTF8.GetBytes("\r\n");
                    responseStream.Write(byteArr, 0, byteArr.Length);

                    byte[] trailer = System.Text.Encoding.UTF8.GetBytes(string.Format("-----------------------------{0}--\r\n", _boundaryNo));
                    responseStream.Write(trailer, 0, trailer.Length);                    
                }
                memoryStream.Close();
                responseStream.Close();
            }
        }

where _boundaryNo is private string _boundaryNo = DateTime.Now.Ticks.ToString("x");

I had it working with Asp.Net MVC 4 and Silverlight 5.

Good luck :)