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Developing SevenDrops - A Dropbox-based photo uploader for Windows Phone 7 [5/6]


It's now time to work on the actual upload mechanism for the application. It still relies on OAuth, but as it was shown in the previous article, the foundation for it is already created.

The first thing that I did is create the Upload method - the one that will actually be performing the procedure. Here is what it looks like:

public static void Upload(string name, byte[] content, string token, string apiKey, string consumerSecret, string tokenSecret)
    Dictionary<string, string> parameters = new Dictionary<string, string>();

    parameters.Add("oauth_consumer_key", apiKey);
    parameters.Add("oauth_signature_method", "HMAC-SHA1");
    parameters.Add("oauth_timestamp", CurrentUNIXTimestamp.Get());
    parameters.Add("oauth_nonce", Guid.NewGuid().ToString().Replace("-", ""));
    parameters.Add("oauth_token", token);
    parameters.Add("oauth_version", "1.0");
    parameters.Add("file", name);

    string OAuthHeader = GetOAuthHeader(parameters, "POST", "https://api-content.dropbox.com/0/files/dropbox/SevenDrops", consumerSecret, tokenSecret);

    string boundary = Guid.NewGuid().ToString();
    string header = "--" + boundary;
    string footer = "--" + boundary + "--";

    HttpWebRequest uploadRequest = (HttpWebRequest)WebRequest.Create("https://api-content.dropbox.com/0/files/dropbox/SevenDrops");
    uploadRequest.ContentType = "multipart/form-data; boundary=" + boundary;
    uploadRequest.Method = "POST";
    uploadRequest.Headers["Authorization"] = OAuthHeader;

    StringBuilder headers = new StringBuilder();
    headers.AppendLine("Content-Disposition: file; name=\"file\"; filename=\""+ name +"\"");
    headers.AppendLine("Content-Type: application/octet-stream");
    headers.AppendLine(Encoding.GetEncoding("iso-8859-1").GetString(content, 0, content.Length));

    byte[] contents = Encoding.GetEncoding("iso-8859-1").GetBytes(headers.ToString());

    object[] data = new object[2] { uploadRequest, contents };
    uploadRequest.BeginGetRequestStream(new AsyncCallback(GetData), data);

There are a couple of things you should notice about this method. I am using the same standard set of parameters to create the OAuth signature. However, there is a new one - file. That's where I am setting the file name for the uploaded file.

REMINDER: I will not be operating with direct paths here. I already have an ImageUnit class that contains the byte array (file contents).

Take a look at the URL I am using. I am executing a POST request to https://api-content.dropbox.com/0/files/dropbox/SevenDrops - this is a different subdomain. For other API calls api.dropbox.com was invoked. Here there is api-content. According to the official documentation, this was introduced for performance conservation reasons.

The request itself will be passing multipart data and I am following a standard pattern to build the HTTP headers.

NOTE: Even though you can be uploading different files that have different file types, the MIME type used for the request should always be application/octet-stream.

I am using the ISO 8859-1 charset for conversion purposes. This is the standard character set used in HTML documents and it is one of the recommended charsets to be used for transmitted encoded data.

When I am invoking the asynchronous BeginGetRequestStream, I am passing the state that is in fact an object array, that will contain both the image array and the request, so that I won't have to make the bytes publicly accessible across the class.

The callback is this:

static void GetData(IAsyncResult result)
    object[] data = (object[])result.AsyncState;
    byte[] content = (byte[])data[1];

    HttpWebRequest request = (HttpWebRequest)data[0];

    Stream requestStream = request.EndGetRequestStream(result);
    requestStream.Write(content, 0, content.Length);

    request.BeginGetResponse(new AsyncCallback(GetResponse), request);

The moment the callback is invoked, I am getting the state information and attempting to write the data to the request stream. Once that process is complete and the stream is closed, I am trying to get the response:

static void GetResponse(IAsyncResult result)
    HttpWebRequest request = (HttpWebRequest)result.AsyncState;
    HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result);

    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
        string responseText = reader.ReadToEnd();

A successful web response means that the file upload is complete. Now the uploading core is in place and is added to the OAuthClient static class. All that is left now is put everything together in the main view and wire it.


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