503 error with multipart upload GoogleDrive Api v2 - delphi

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 :-))

Answer 2

After changing two things in my code, and doing some substantial cleanup, I was able to get the upload working. The main changes I made were writing everything directly to the TMemoryStream rather than to a TStringStream then to a TMemoryStream and using AnsiStrings rather than strings. Here is my cleaned up code.
function TGoogleDriveApi.MultipartUpload(aStream: TStream; aFile: TGoogleDriveFileUp) : IGoogleDriveFile;
var
json, url, boundary, body : AnsiString;
lHttpHelper : IHttpHelper;
ms : TMemoryStream;
ss : TStringStream;
writer : IRtSerializeWriter;
reader : IRtSerializeReader;
begin
if(Token.IsExpired) then
Token.Refresh(TokenUrl, OAuth.ClientId, OAuth.ClientSecret);
lHttpHelper := THttpHelper.Create;
ss := TStringStream.Create;
writer := TRtJsonSerializeWriter.Create;
writer.SaveToStream(ss,aFile);
ss.Position := 0;
json := ss.ReadString(ss.Size);
FreeAndNil(ss);
url := 'https://www.googleapis.com/upload/drive/v2/files?uploadType=multipart&access_token='+lHttpHelper.UrlEncode(Token.access_token);
boundary := 'a_bondary';
body := '--'+boundary+sLineBreak;
body := body + 'Content-Type: application/json; charset=UTF-8' + sLineBreak + sLineBreak;
body := body + json + sLineBreak + sLineBreak +'--'+boundary;
body := body + sLineBreak + sLineBreak;
ms := TMemoryStream.Create;
ms.Write(body[1],Length(body));
ms.CopyFrom(aStream, aStream.Size);
body := sLineBreak + sLineBreak + '--' + boundary + '--';
ms.Write(body[1],Length(body));
ms.Position := 0;
json := lHttpHelper.PostResponse(url,'multipart/related; boundary="'+boundary+'"',ms);
ss := TStringStream.Create;
ss.WriteString(json);
ss.Position := 0;
reader := TRtJsonSerializeReader.Create;
Result := TGoogleDriveFileDown.Create;
reader.LoadFromStream(ss,Result as TGoogleDriveFileDown);
FreeAndNil(ms);
FreeAndNil(ss);
end;