系统.OutOfMemoryException: FTP上传

我正在尝试将文件加载到FTP服务器。下面是我的代码:

                // Create the request.
                FtpWebRequest request = (FtpWebRequest)WebRequest.Create(appSettingsFTP.ftpUrl + @"/" + filename);
                request.Method = WebRequestMethods.Ftp.UploadFile;
                request.Timeout = 6000000; //set to 100 minutes
                // Add the login credentials.
                request.Credentials = new NetworkCredential(appSettingsFTP.ftpLogin, appSettingsFTP.ftpPassword);
                // Grab the file contents.
                StreamReader sourceStream = new StreamReader(appSettingsFTP.uploadFileDirectory + filename);
                byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());
                sourceStream.Close();
                request.ContentLength = fileContents.Length;
                // Copy the file contents to the outgoing stream.
                Stream requestStream = request.GetRequestStream();
                requestStream.Write(fileContents, 0, fileContents.Length);
                requestStream.Close();
                FtpWebResponse response = (FtpWebResponse)request.GetResponse();
                LoggerFTP.Log(filename.ToString() + " " + "Upload Complete, Status: " + response.StatusCode, false);

除了其中一个文件(有8个)之外，一切似乎都很好。不起作用的文件是最大的，大约有160,000 kB。我得到的错误是:

                System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
                     at System.String.ToCharArray()
                     at System.Text.Encoding.GetBytes(String s)
                     at CPMainSpringAPIExportsSC.UploadFTP.FTPUploadMethod(String viewname, String filename)

我相当确定错误发生在代码的这一行:

byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());

是否有一种方法可以在循环中读取蒸汽阅读器而不是一次读取所有内容?我想那会解决我的问题，但我想不出怎么做。

另外，我尝试使用+=操作符做一些事情，但后来意识到byte[]是静态的。

还有其他想法吗?提前感谢任何帮助。