Delphi: Using Google URL Shortener with IdHTTP - 4

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

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.

Answer 2

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;