Delphi DLL

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. Delphi DLL

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Cache, AuthGoogle, Stream, StringBuilder, Rest;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
gAuth: HCkAuthGoogle;
rest: HCkRest;
bAutoReconnect: Boolean;
gdCache: HCkCache;
fileId: PWideChar;
sbPath: HCkStringBuilder;
fileStream: HCkStream;
jsonResponse: PWideChar;

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 := CkAuthGoogle_Create();
CkAuthGoogle_putAccessToken(gAuth,'GOOGLE_DRIVE_ACCESS_TOKEN');

rest := CkRest_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 := CkRest_Connect(rest,'www.googleapis.com',443,True,bAutoReconnect);

// Provide the authentication credentials (i.e. the access token)
CkRest_SetAuthGoogle(rest,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 := CkCache_Create();
CkCache_putLevel(gdCache,0);
CkCache_AddRoot(gdCache,'C:/ckCache/googleDrive');

fileId := CkCache__fetchText(gdCache,'testFolder/abc/123/penguins.jpg');
if (CkCache_getLastMethodSuccess(gdCache) <> True) then
  begin
    Memo1.Lines.Add('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 := CkStringBuilder_Create();
CkStringBuilder_Append(sbPath,'/drive/v3/files/');
CkStringBuilder_Append(sbPath,fileId);
CkRest_AddQueryParam(rest,'alt','media');

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

// Download the file, streaming the content to the SinkFile.
jsonResponse := CkRest__fullRequestNoBody(rest,'GET',CkStringBuilder__getAsString(sbPath));
if (CkRest_getLastMethodSuccess(rest) <> True) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    Exit;
  end;

// A successful response will have a status code equal to 200.
if (CkRest_getResponseStatusCode(rest) <> 200) then
  begin
    Memo1.Lines.Add('response status code = ' + IntToStr(CkRest_getResponseStatusCode(rest)));
    Memo1.Lines.Add('response status text = ' + CkRest__responseStatusText(rest));
    Memo1.Lines.Add('response header: ' + CkRest__responseHeader(rest));
    Exit;
  end;

Memo1.Lines.Add('File downloaded.');

CkAuthGoogle_Dispose(gAuth);
CkRest_Dispose(rest);
CkCache_Dispose(gdCache);
CkStringBuilder_Dispose(sbPath);
CkStream_Dispose(fileStream);

end;