Ftp上传文件，文件名为啥变成了小写的

[仙剑]

最近用FtpWebRequest做文件上传下载程序，奇怪，待上传的文件名子是大写的，上传到服务器后就成了小写了。
我的主要代码如下：

//通过FTP下载并上传录音文件
private bool DownloadAndUpload(string sourcefile, string targetfile, FileServerInfo fileserver_source, FileServerInfo fileserver_target)
{
bool returnValue = false;
try
{
FtpWebRequest req_download, req_upload;
string url_download = string.Format("ftp://{0}:{1}{2}", fileserver_source.Host, fileserver_source.Port, sourcefile);
string url_upload = string.Format("ftp://{0}:{1}{2}", fileserver_target.Host, fileserver_target.Port, targetfile);
WriteLog("CopyFile", "Start copy file.from " + url_download + " to " + url_upload);

req_download = (FtpWebRequest)FtpWebRequest.Create(url_download);
req_download.Credentials = new NetworkCredential(fileserver_source.LoginUser, fileserver_source.LoginPwd);
req_download.Method = WebRequestMethods.Ftp.DownloadFile;
req_download.UseBinary = true;
FtpWebResponse response_download = (FtpWebResponse)req_download.GetResponse();
Stream stream_download = response_download.GetResponseStream();
req_upload = (FtpWebRequest)FtpWebRequest.Create(url_upload);
req_upload.Credentials = new NetworkCredential(fileserver_target.LoginUser, fileserver_target.LoginPwd);
req_upload.Method = WebRequestMethods.Ftp.UploadFile;
req_upload.UseBinary = true;
Stream stream_upload = req_upload.GetRequestStream();
int buffer_size = 2048;
int read_count = 0;
byte[] buffer = new byte[buffer_size];
read_count = stream_download.Read(buffer, 0, buffer_size);
while (read_count > 0)
{
stream_upload.Write(buffer, 0, read_count);
read_count = stream_download.Read(buffer, 0, buffer_size);
}
stream_upload.Flush();
stream_upload.Close();
stream_download.Close();
response_download.Close();
returnValue = true;
}
catch (Exception ex)
{
//WriteLog("DownLoadAndUpload", "Operation fail.\n\t" + ex.ToString());
returnValue = false;
}
return returnValue;
}

比如，原来的文件名是C010002011121323.wav，上传之后文件就成了c010002011121323.wav。