Delphi: Using Google URL Shortener with IdHTTP - 400 Bad Request - delphi

Question

I'm trying to access the URL Shortener ( http://goo.gl/ ) via its API from within Delphi.
However, the only result I get is: HTTP/1.0 400 Bad Request (reason: parseError)
Here is my code (on a form with a Button1, Memo1 and IdHTTP1 that has IdSSLIOHandlerSocketOpenSSL1 as its IOHandler. I got the necessary 32-bit OpenSSL DLLs from http://indy.fulgan.com/SSL/ and put them in the .exe's directory):
procedure TFrmMain.Button1Click(Sender: TObject);
var html, actionurl: String;
makeshort: TStringList;
begin
try
makeshort := TStringList.Create;
actionurl := 'https://www.googleapis.com/urlshortener/v1/url';
makeshort.Add('{"longUrl": "http://slashdot.org/stories"}');
IdHttp1.Request.ContentType := 'application/json';
//IdHTTP1.Request.ContentEncoding := 'UTF-8'; //Using this gives error 415
html := IdHTTP1.Post(actionurl, makeshort);
memo1.lines.add(idHTTP1.response.ResponseText);
except on e: EIdHTTPProtocolException do
begin
memo1.lines.add(idHTTP1.response.ResponseText);
memo1.lines.add(e.ErrorMessage);
end;
end;
memo1.Lines.add(html);
makeshort.Free;
end;
Update: I have left off my API key in this example (should usually work well without one for a few tries), but if you want to try it with your own, you can substitute the actionurl string with
'https://www.googleapis.com/urlshortener/v1/url?key=<yourapikey>';
The ParseError message leads me to believe that there might be something wrong with the encoding of the longurl when it gets posted but I wouldn't know what to change.
I've been fuzzing over this for quite a while now and I'm sure the mistake is right before my eyes - I'm just not seeing it right now.
Any help is therefore greatly appreciated!
Thanks!

Answer 1

As you discovered, the TStrings overloaded version of the TIdHTTP.Post() method is the wrong method to use. It sends an application/x-www-form-urlencoded formatted request, which is not appropriate for a JSON formatted request. You have to use the TStream overloaded version of the TIdHTTP.Post() method instead`, eg:
procedure TFrmMain.Button1Click(Sender: TObject);
var
html, actionurl: String;
makeshort: TMemoryStream;
begin
try
makeshort := TMemoryStream.Create;
try
actionurl := 'https://www.googleapis.com/urlshortener/v1/url';
WriteStringToStream(makeshort, '{"longUrl": "http://slashdot.org/stories"}', IndyUTF8Encoding);
makeshort.Position := 0;
IdHTTP1.Request.ContentType := 'application/json';
IdHTTP1.Request.Charset := 'utf-8';
html := IdHTTP1.Post(actionurl, makeshort);
finally
makeshort.Free;
end;
Memo1.Lines.Add(IdHTTP1.Response.ResponseText);
Memo1.Lines.Add(html);
except
on e: Exception do
begin
Memo1.Lines.Add(e.Message);
if e is EIdHTTPProtocolException then
Memo1.lines.Add(EIdHTTPProtocolException(e).ErrorMessage);
end;
end;
end;

Answer 2

From the URL shortener API docs:
Every request your application sends to the Google URL Shortener API
needs to identify your application to Google. There are two ways to
identify your application: using an OAuth 2.0 token (which also
authorizes the request) and/or using the application's API key.
Your example does not contain code for OAuth or API key authentication.
To authenticate with an API key, the docs are clear:
After you have an API key, your application can append the query
parameter key=yourAPIKey to all request URLs.