Pascal (Lazarus/Delphi)

Refresh Access Token on 401 Unauthorized and Retry (Service Account)

See more Google Cloud Storage Examples

Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.) Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.AuthGoogle,
  Chilkat.Socket,
  Chilkat.FileAccess,
  Chilkat.BinData,
  Chilkat.StringBuilder,
  Chilkat.Http;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  sbToken: TStringBuilder;
  http: THttp;
  url: string;
  fileData: TBinData;
  responseCode: Integer;
  fac: TFileAccess;
  jsonKey: string;
  gAuth: TAuthGoogle;
  tlsSock: TSocket;
  sbErrorResponse: TStringBuilder;

begin
  success := False;

  //  This example requires the Chilkat API to have been previously unlocked.
  //  See Global Unlock Sample for sample code.

  //  This example uses a previously obtained access token having permission for the 
  //  scope "https://www.googleapis.com/auth/cloud-platform"

  //  In this example, Get Google Cloud Storage OAuth2 Access Token, 
  //  the service account access token was saved to a text file.  This example fetches the access token from the file..
  sbToken := TStringBuilder.Create;
  success := sbToken.LoadFile('qa_data/tokens/googleCloudStorageAccessToken.txt','utf-8');
  if (success = False) then
    begin
      WriteLn('Failed to load access token.');
      Exit;
    end;

  http := THttp.Create;

  http.AuthToken := sbToken.GetAsString();

  //  Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
  http.SetUrlVar('bucket_name','chilkat-ocean');
  http.SetUrlVar('object_name','starfish.jpg');
  url := 'https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media';

  //  If there is an error response, then we didn't actually download the file data,
  //  but instead we downloaded an error response..
  fileData := TBinData.Create;
  success := http.DownloadBd(url,fileData);
  responseCode := http.LastStatus;
  if ((success = False) and (responseCode <> 401)) then
    begin
      WriteLn(http.LastErrorText);
      Exit;
    end;

  if (responseCode = 401) then
    begin
      WriteLn('Received 401 Unauthorized response. Attempting to refresh the access token...');

      //  May be that the access token expired.
      //  Load our JSON key and request a new access token, then retry the original request.
      fac := TFileAccess.Create;
      jsonKey := fac.ReadEntireTextFile('qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json','utf-8');
      if (fac.LastMethodSuccess <> True) then
        begin
          WriteLn(fac.LastErrorText);
          Exit;
        end;

      gAuth := TAuthGoogle.Create;
      gAuth.JsonKey := jsonKey;
      gAuth.Scope := 'https://www.googleapis.com/auth/cloud-platform';
      gAuth.ExpireNumSeconds := 3600;
      gAuth.SubEmailAddress := '';

      tlsSock := TSocket.Create;
      success := tlsSock.Connect('www.googleapis.com',443,True,5000);
      if (success <> True) then
        begin
          WriteLn(tlsSock.LastErrorText);
          Exit;
        end;

      success := gAuth.ObtainAccessToken(tlsSock);
      if (success <> True) then
        begin
          WriteLn(gAuth.LastErrorText);
          Exit;
        end;

      fac.WriteEntireTextFile('qa_data/tokens/googleCloudStorageAccessToken.txt',gAuth.AccessToken,'utf-8',False);

      //  Retry the original request.
      http.AuthToken := gAuth.AccessToken;
      success := http.DownloadBd(url,fileData);
      if (success = False) then
        begin
          WriteLn(http.LastErrorText);
          Exit;
        end;

    end;

  if (responseCode <> 200) then
    begin
      //  Get the error response
      sbErrorResponse := TStringBuilder.Create;
      sbErrorResponse.AppendBd(fileData,'utf-8',0,0);
      WriteLn('Error response code = ' + responseCode);
      WriteLn('Error:');
      WriteLn(sbErrorResponse.GetAsString());
      Exit;
    end;

  WriteLn('Success.');

  //  Save the downloaded data to a file.
  success := fileData.WriteFile('qa_output/starfish.jpg');


  sbToken.Free;
  http.Free;
  fileData.Free;
      fac.Free;
      gAuth.Free;
      tlsSock.Free;
      sbErrorResponse.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.