FlickrNet.Flickr.ReplacePicture C# (CSharp) Method

        public string ReplacePicture(Stream stream, string photoId)
        {
            string boundary = "FLICKR_MIME_" + DateTime.Now.ToString("yyyyMMddhhmmss");

            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(ReplaceUrl);
            req.UserAgent = "Mozilla/4.0 FlickrNet API (compatible; MSIE 6.0; Windows NT 5.1)";
            req.Method = "POST";
            if( Proxy != null ) req.Proxy = Proxy;
            req.Referer = "http://www.flickr.com";
            req.KeepAlive = false;
            req.Timeout = HttpTimeout * 100;
            req.ContentType = "multipart/form-data; boundary=" + boundary + "";

            StringBuilder sb = new StringBuilder();

            Hashtable parameters = new Hashtable();

            parameters.Add("photo_id", photoId);
            parameters.Add("api_key", _apiKey);
            parameters.Add("auth_token", _apiToken);

            string[] keys = new string[parameters.Keys.Count];
            parameters.Keys.CopyTo(keys, 0);
            Array.Sort(keys);

            StringBuilder HashStringBuilder = new StringBuilder(_sharedSecret, 2 * 1024);

            foreach(string key in keys)
            {
                HashStringBuilder.Append(key);
                HashStringBuilder.Append(parameters[key]);
                sb.Append("--" + boundary + "\r\n");
                sb.Append("Content-Disposition: form-data; name=\"" + key + "\"\r\n");
                sb.Append("\r\n");
                sb.Append(parameters[key] + "\r\n");
            }

            sb.Append("--" + boundary + "\r\n");
            sb.Append("Content-Disposition: form-data; name=\"api_sig\"\r\n");
            sb.Append("\r\n");
            sb.Append(Md5Hash(HashStringBuilder.ToString()) + "\r\n");

            // Photo
            sb.Append("--" + boundary + "\r\n");
            sb.Append("Content-Disposition: form-data; name=\"photo\"; filename=\"image.jpeg\"\r\n");
            sb.Append("Content-Type: image/jpeg\r\n");
            sb.Append("\r\n");

            UTF8Encoding encoding = new UTF8Encoding();

            byte[] postContents = encoding.GetBytes(sb.ToString());

            byte[] photoContents = new byte[stream.Length];
            stream.Read(photoContents, 0, photoContents.Length);
            stream.Close();

            byte[] postFooter = encoding.GetBytes("\r\n--" + boundary + "--\r\n");

            byte[] dataBuffer = new byte[postContents.Length + photoContents.Length + postFooter.Length];
            Buffer.BlockCopy(postContents, 0, dataBuffer, 0, postContents.Length);
            Buffer.BlockCopy(photoContents, 0, dataBuffer, postContents.Length, photoContents.Length);
            Buffer.BlockCopy(postFooter, 0, dataBuffer, postContents.Length + photoContents.Length, postFooter.Length);

            req.ContentLength = dataBuffer.Length;

            Stream resStream = req.GetRequestStream();

            int j = 1;
            int uploadBit = Math.Max(dataBuffer.Length / 100, 50*1024);
            int uploadSoFar = 0;

            for(int i = 0; i < dataBuffer.Length; i=i+uploadBit)
            {
                int toUpload = Math.Min(uploadBit, dataBuffer.Length - i);
                uploadSoFar += toUpload;

                resStream.Write(dataBuffer, i, toUpload);

                if( (OnUploadProgress != null) && ((j++) % 5 == 0 || uploadSoFar == dataBuffer.Length) )
                {
                    OnUploadProgress(this, new UploadProgressEventArgs(i+toUpload, uploadSoFar == dataBuffer.Length));
                }
            }
            resStream.Close();

            HttpWebResponse res = (HttpWebResponse)req.GetResponse();

            XmlSerializer serializer = _uploaderSerializer;

            StreamReader sr = new StreamReader(res.GetResponseStream());
            string s= sr.ReadToEnd();
            sr.Close();

            StringReader str = new StringReader(s);

            FlickrNet.Uploader uploader = (FlickrNet.Uploader)serializer.Deserialize(str);

            if( uploader.Status == ResponseStatus.OK )
            {
                return uploader.PhotoId;
            }
            else
            {
                throw new FlickrException(uploader.Error);
            }
        }