问如何使用Drive 3.0下载Google的修订版？

EN

   private async Task GetRevisionStream(string accessToken, string fileId, string revId)
    {
        Log("Making API Call to get revision binary stream...");

        // builds the  request
        string userinfoRequestUri = "https://docs.google.com/feeds/download/documents/export/Export?id=" + fileId + "&revision=" + revId + "&exportFormat=docx";

        // sends the request
        HttpWebRequest userinfoRequest = (HttpWebRequest)WebRequest.Create(userinfoRequestUri);
        userinfoRequest.Method = "GET";
        userinfoRequest.Headers.Add(string.Format("Authorization: Bearer {0}", accessToken));
        userinfoRequest.ContentType = "application/x-www-form-urlencoded";
        userinfoRequest.Accept = "Accept=text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";

        // gets the response
        WebResponse userinfoResponse = await userinfoRequest.GetResponseAsync();
        using (StreamReader userinfoResponseReader = new StreamReader(userinfoResponse.GetResponseStream()))
        {
            // reads response body
            System.IO.Stream streamDoc = userinfoResponseReader.BaseStream;
            var fileStream = File.Create("d:\\test.docx");
            streamDoc.CopyTo(fileStream);
            fileStream.Flush();
            fileStream.Close();
        }
    }