Question

I’m attempting to work with the Google Drive API in Delphi XE2, and thus far, I have just about everything working. One thing I’m struggling with is the multipart upload. When I attempt to upload a file, I get a 503 error. Normally, that should indicate a problem with the server. However, when I send an upload request with the same body and headers to the same URL using fiddler rather than my API, the file is uploaded successfully. This tells me there has to be a problem with my code. This particular function is a mess, but here it is.

function TGoogleDriveApi.MultipartUpload(aStream : TStream; aTitle : string = 'Untitled';
  aDescription : string = ''; mimeType : string = 'application/octet-stream';
  indexableText : IGoogleDriveIndexableText = nil;
  lastViewedByMeDate : string = ''; modifiedDate : string = '';
  parents : IGoogleDriveParentList = nil) : IGoogleDriveFile;
var
  json, url, body, boundry, contentType : string;
  ss : TStringStream;
  ms : TMemoryStream;
  lHttpHelper : IHttpHelper;
  streamBytes : TBytes;
begin
  boundry := 'a_boundry';
  body := '--'+boundry+sLineBreak;
  body := body + 'Content-Type: application/json; charset=UTF-8';
  lHttpHelper := THttpHelper.Create;
  if(Token.IsExpired) then
    Token.Refresh(TokenUrl, OAuth.ClientId, OAuth.ClientSecret);
  url := 'https://www.googleapis.com/upload/drive/v2/files?uploadType=multipart&access_token='+lHttpHelper.UrlEncode(Token.access_token);
  json := '{';
  json := json + '"title": "'+aTitle+'"';
  if(aDescription <> '') then
    json := json + ', "description": "'+aDescription+'"';
  if(lastViewedByMeDate <> '') then
    json := json + ', "lastViewedByMeDate": "'+lastViewedByMeDate+'"';
  json := json + ', "mimeType": "'+mimeType+'"';
  if(modifiedDate <> '') then
    json := json + ', "modifiedDate": "'+modifiedDate+'"';
  json := json + '}';
  body := body + sLineBreak + sLineBreak + json + sLineBreak + sLineBreak + '--'+boundry;
  body := body + sLineBreak + 'Content-Type: '+mimeType + sLineBreak  + sLineBreak;
  body := body + 'some test text from the api' + sLineBreak + sLineBreak + '--'+boundry+'--';

  ss := TStringStream.Create;
  ss.WriteString(body);
  ss.Position := 0;
  ms := TMemoryStream.Create;
  ms.Write(ss,ss.Size);
  SetLength(streamBytes,aStream.Size);
  aStream.Read(streamBytes,aStream.Size);
  ms.Write(streamBytes[0],aStream.Size);
  ss.Clear;
  ss.Position := 0;
  ss.WriteString(sLineBreak + sLineBreak + '--'+boundry+'--');
  ss.Position := 0;
  ms.Write(ss,ss.Size);

  contentType := 'multipart/related; boundary="'+boundry+'"';
  json := lHttpHelper.PostResponse(url,contentType,ms);
  FreeAndNil(ss);
  FreeAndNil(ms);
  Result := nil;
end;

The line that causes problems is the lHttpHelper.PostResponse call. The code for that is shown here:

function THttpHelper.PostResponse(url, contentType : string; aStream : TStream) : string;
var
  lHTTP: TIdHTTP;
  lStream : TStringStream;
  handler : TIdSSLIOHandlerSocketOpenSSL;
begin
  lStream := TStringStream.Create;
  lHTTP := TIdHTTP.Create(nil);
  handler := TidSSLIOHandlerSocketOpenSSL.Create(nil);
  handler.SSLOptions.Method := sslvSSLv3;
  lHTTP.IOHandler := handler;
  try
    lHTTP.Request.ContentType := contentType;
    lHTTP.Post(url,aStream,lStream);
    lStream.Position := 0;
    Result := lStream.ReadString(lStream.Size);
      //except
  finally
    lStream.Free;
    lHTTP.Free;
    handler.Free;

    lStream := nil;
    lHTTP := nil;
    handler := nil;
  end;
end;

I’m currently calling the MultipartUpload function from my test, shown here

procedure TestIGoogleDriveApi.TestMultipartUpload;
var
  ReturnValue : IGoogleDriveFile;
  fs : TFileStream;
begin
  fs := TFileStream.Create('testupload.jpg',fmOpenRead);
  ReturnValue := FIGoogleDriveApi.MultipartUpload(fs,'Test Multipart Image Upload from API.txt','test file','image/jpeg');
  FreeAndNil(fs);
  if(ReturnValue = nil) then
    fail('ReturnValue cannot be nil');
end;

Any ideas what might be causing the problems? I’m not even sure what to suspect at this point.

Answer 1

You’ll need to somehow follow @RobKennedy’s advice. You need to see what’s happening on the wire to debug this. Try replacing the https drive url with http and then trace with Wireshark.

@Hendra is also correct, that generally your app needs to implement exponential backoff and retry for 500 errors, although I suspect that isn’t your specific problem (yet :-))