Question

I’m using some of the code I found on here to POST an image to a server. The problem is that I am not receiving the Json response that I should be, instead I’m getting the ol’ SERVER NOT FOUND response in my “ResponseReady” callback. (EDIT: Turns out it was just my parameters, this code works perfectly fine.)

Here is the class I am using to make the POST

    public class PostSubmitter
    {

       public string url { get; set; }
       public Dictionary<string, object> parameters { get; set; }
       string boundary = "----------" + DateTime.Now.Ticks.ToString();
       HttpWebRequest webRequest;

       public void Submit()
       {
           // Prepare web request...
           webRequest = WebRequest.CreateHttp(url);
           webRequest.Method = "POST";
           webRequest.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);
           webRequest.BeginGetRequestStream(new AsyncCallback(RequestReady), webRequest);

       }

       private void RequestReady(IAsyncResult asynchronousResult)
       {
           using (Stream postStream = webRequest.EndGetRequestStream(asynchronousResult))
           {
                writeMultipartObject(postStream, parameters);
           }

           webRequest.BeginGetResponse(new AsyncCallback(ResponseReady), webRequest);

       }

       private void ResponseReady(IAsyncResult asynchronousResult)
       {
           try
           {
               using (var response =
                (HttpWebResponse)webRequest.EndGetResponse(asynchronousResult))
               using (var streamResponse = response.GetResponseStream())
               using (var streamRead = new StreamReader(streamResponse))
               {
                   var responseString = streamRead.ReadToEnd();
                   var success = response.StatusCode == HttpStatusCode.OK;

                   if (responseString != null)
                   {
                       //JObject comes from Newtonsoft.Json ddl. This is a good one if your working with json
                       JObject jsonResponse = JObject.Parse(responseString);
                       //Do stuff with json.....
                   }
               }
           }
           catch (Exception e)
           {
               if (e.Message == "The remote server returned an error: NotFound.")
               {
                   webRequest.Abort();
                   Deployment.Current.Dispatcher.BeginInvoke(delegate() { MessageBox.Show("Unable to connect to server at this time, please try again later"); });
               }
               else
                   Deployment.Current.Dispatcher.BeginInvoke(delegate() { MessageBox.Show("Unable to upload photo at this time, please try again later"); });
               return;
           }
       }


       public void writeMultipartObject(Stream stream, object data)
       {
           using (StreamWriter writer = new StreamWriter(stream))
           {
               if (data != null)
               {
                   foreach (var entry in data as Dictionary<string, object>)
                   {
                       WriteEntry(writer, entry.Key, entry.Value);
                   }
               }
               writer.Write("--");
               writer.Write(boundary);
               writer.WriteLine("--");
               writer.Flush();
           }
       }

       private void WriteEntry(StreamWriter writer, string key, object value)
       {
           if (value != null)
           {
               writer.Write("--");
               writer.WriteLine(boundary);
               if (value is byte[])
               {
                   byte[] ba = value as byte[];

                   writer.WriteLine(@"Content-Disposition: form-data; name=""{0}""; filename=""{1}""", key, "sentPhoto.jpg");
                   writer.WriteLine(@"Content-Type: application/octet-stream");
                   writer.WriteLine(@"Content-Type: image / jpeg");
                   writer.WriteLine(@"Content-Length: " + ba.Length);
                   writer.WriteLine();
                   writer.Flush();
                   Stream output = writer.BaseStream;

                   output.Write(ba, 0, ba.Length);
                   output.Flush();
                   writer.WriteLine();
               }
               else
               {
                   writer.WriteLine(@"Content-Disposition: form-data; name=""{0}""", key);
                   writer.WriteLine();
                   writer.WriteLine(value.ToString());
               }
           }
       }
    }

Using this class we can then make a simple POST to the server with the following lines of code:

    Dictionary<string, object> postData = new Dictionary<string, object>()
                                                {
                                                    {"file", byteArrayOfImage}
                                                    //You can add other parameters here
                                                };
    PostSubmitter postToServer = new PostSubmitter() { url = getPicturePostUrl(), parameters = postData };
    postToServer.Submit();

There are so many questions out there on this… you’d think they’d make it easier to do complex web requests….

Thanks in advance for your helpful comments or feel free to ask a question.

Answer 1

Well this code actually works perfectly. I just didn’t have one of the required parameters so the server was rejecting the request.