Pascal (Lazarus/Delphi)

Download File (Stream to Local Filesystem)

See more Google Drive Examples

This example demonstrates how to download the content of a file from Google Drive. The file is streamed to the local filesystem. 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.Cache,
  Chilkat.AuthGoogle,
  Chilkat.Stream,
  Chilkat.StringBuilder,
  Chilkat.Rest;

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

procedure RunDemo;
var
  success: Boolean;
  gAuth: TAuthGoogle;
  rest: TRest;
  bAutoReconnect: Boolean;
  gdCache: TCache;
  fileId: string;
  sbPath: TStringBuilder;
  fileStream: TStream;
  jsonResponse: string;

begin
  success := False;

  success := True;

  //  It 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 
  //  Google Drive scope.

  gAuth := TAuthGoogle.Create;
  gAuth.AccessToken := 'GOOGLE_DRIVE_ACCESS_TOKEN';

  rest := TRest.Create;

  //  Connect using TLS.
  //  A single REST object, once connected, can be used for many Google Drive REST API calls.
  //  The auto-reconnect indicates that if the already-established HTTPS connection is closed,
  //  then it will be automatically re-established as needed.
  bAutoReconnect := True;
  success := rest.Connect('www.googleapis.com',443,True,bAutoReconnect);

  //  Provide the authentication credentials (i.e. the access token)
  rest.SetAuthGoogle(gAuth);

  //  ------------------------------------------------------------------------------
  //  To download a file, we must know the file ID.
  //  In a previous example (see Build Local Metadata Cache
  //  we built a local cache to make it easy to lookup file IDs given a file path.
  //  Let's say we want to download "testFolder/abc/123/penguins.jpg".
  //  First we lookup the fileId in the cache.  With the fileId, we can download the file.
  gdCache := TCache.Create;
  gdCache.Level := 0;
  gdCache.AddRoot('C:/ckCache/googleDrive');

  fileId := gdCache.FetchText('testFolder/abc/123/penguins.jpg');
  if (gdCache.LastMethodSuccess <> True) then
    begin
      WriteLn('Filepath not found in cache.');
      Exit;
    end;

  //  We need to send a GET request like this:
  //  GET https://www.googleapis.com/drive/v3/files/fileId?alt=media
  //  The fileId is part of the path.
  sbPath := TStringBuilder.Create;
  sbPath.Append('/drive/v3/files/');
  sbPath.Append(fileId);
  rest.AddQueryParam('alt','media');

  //  Create a stream object with a SinkFile set to the path where the downloaded file will go.
  fileStream := TStream.Create;
  fileStream.SinkFile := 'qa_output/penguins.jpg';
  //  Indicate that the response body should stream directly to fileStream,
  //  but only if the response status is 200.  
  rest.SetResponseBodyStream(200,True,fileStream);

  //  Download the file, streaming the content to the SinkFile.
  jsonResponse := rest.FullRequestNoBody('GET',sbPath.GetAsString());
  if (rest.LastMethodSuccess <> True) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  //  A successful response will have a status code equal to 200.
  if (rest.ResponseStatusCode <> 200) then
    begin
      WriteLn('response status code = ' + rest.ResponseStatusCode);
      WriteLn('response status text = ' + rest.ResponseStatusText);
      WriteLn('response header: ' + rest.ResponseHeader);
      Exit;
    end;

  WriteLn('File downloaded.');


  gAuth.Free;
  rest.Free;
  gdCache.Free;
  sbPath.Free;
  fileStream.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.