确保从Windows Phone到ASP.NET MVC 3的文件上载

Question

I am working on a Windows Phone app. This app will let users take pictures and upload them to my server. I have successfully implemented this. However, I've noticed that sometimes the picture does not get uploaded properly. I suspect this happens when someone puts the app to sleep before its done uploading. Or the connectivity gets interrupted. I'm really not sure how to do address this. I've included my code here. I'm hoping someone can provide some insight.

Client Side - Windows Phone App - Picture.cs
--------------------------------------------
public event EventHandler Upload_Succeeded;
public event EventHandler Upload_Failed;
public void Upload()
{
  try {
    WebRequest request = HttpWebRequest.Create(GetBackendPictureUploadUrl());
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";
    request.BeginGetRequestStream(new AsyncCallback(UploadBeginGetRequestStreamCallBack), request);
  } catch (Exception ex)
  {
    Upload_Failed(this, EventArgs.Empty);
  }
}

private void UploadBeginGetRequestStreamCallBack(IAsyncResult ar)
{
  try {
    StringBuilder sb = new StringBuilder();
    this.ImageBytes.ToList<byte>().ForEach(x => sb.AppendFormat("{0}.", Convert.ToUInt32(x)));

    Dictionary<string, string> parameters = new Dictionary<string, string>();
    parameters.Add("username", GetUsername());
    parameters.Add("pictureByts", sb.ToString());

    string data = string.Empty;
    foreach (string key in parameters.Keys)
    {
      data += key;
      data += "=";
      data += parameters[key];
      data += "&";
    }
    data = data.Substring(0, data.Length - 1);

    HttpWebRequest webRequest = (HttpWebRequest)(ar.AsyncState);
    using (Stream postStream = webRequest.EndGetRequestStream(ar))
    {
      byte[] byteArray = Encoding.UTF8.GetBytes(data);
      postStream.Write(byteArray, 0, byteArray.Length);
      postStream.Close();
    }
    webRequest.BeginGetResponse(new AsyncCallback(Upload_Completed), webRequest);
  } catch (Exception ex)
  {
    Upload_Failed(this, EventArgs.Empty);
  }
}

private void Upload_Completed(IAsyncResult result)
{
  Upload_Succeeded(this, EventArgs.Empty);
}

Server Size - ASP.NET MVC - MyController.cs
-------------------------------------------
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult AddPicture(string username, string pictureBytes)
{
  string path = ConfigurationManager.AppSettings["pictureDirectory"] + "/" + username + "/";
  if (Directory.Exists(path) == false)
    Directory.CreateDirectory(path);
  string filePath = path + "/" + Guid.NewGuid().ToString() + ".png";

  // Save the picture to the file system
  string[] bytesToConvert = pictureBytes.Split('.');
  List<byte> fileBytes = new List<byte>();
  bytesToConvert.ToList<string>().Where(x => !string.IsNullOrEmpty(x)).ToList<string>().ForEach(x => fileBytes.Add(Convert.ToByte(x)));

  using (FileStream fileStream = new FileStream(filePath, FileMode.Create))
  {
    byte[] bytes = fileBytes.ToArray();
    fileStream.Write(bytes, 0, bytes.Length);
    fileStream.Close();
  }
}

I'm so confused. This code looks right in my opinion. But I've noticed that files are being written on my server. Sometimes they are just grey images. Sometimes it looks like part of the image was written but not the whole thing. What am I doing wrong? How do I ensure that the file is completely uploaded / written properly? There has to be some way of doing this. Clearly Facebook etc. are doing this. What am I doing wrong?

Answer 1

You need to set ContentLength in your Upload method. To do that, you should compute your finished data buffer before you make the async request. Then you will have the length you need (after UTF8 encode). Then supply the data to the stream when the callback occurs.