ftp访问空目录的返回

protected override bool DirectoryExists(string path)
        {
            bool exists = false;
            if (path.LastIndexOf('/') != path.Length - 1)
            {
                path = path + '/';
            }
            FtpWebResponse response = null;
            FtpWebRequest request = null;
            int retryCount = 0;
            while (true)
            {
                try
                {
                    request = CreateFtpRequest("ftp://" + HostIP + path);
                    request.Method = WebRequestMethods.Ftp.ListDirectory;
                    response = (FtpWebResponse)request.GetResponse();
                    using (TextReader tr = new StreamReader(response.GetResponseStream()))
                    {
                        string text = tr.ReadToEnd();
                        exists = true;
                    }
                    break;
                }
                catch (WebException e)
                {
                    if (response != null && response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable)
                    {
                        exists = false;
                        break;
                    }
                    else
                    {
                        response = e.Response as FtpWebResponse;
                        if (response != null && response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable)
                        {
                            exists = false;
                            break;
                        }
                    }
                    
                    if (HandleWebException(e, ++retryCount))
                    {
                        continue;
                    }
                }
                finally
                {
                    if (response != null)
                    {
                        response.Close();
                        response = null;
                    }
                }
            }

            return exists;
        }

这个方法是用来判断ftp路径是否存在，一开始并没有去判断path变量末尾有没有"/"，后来发现，如果末尾没有"/"，即使访问了一个空目录，也不会抛出异常，也就是说会返回一个550，但是不会抛出异常。