(Delphi DLL) Download Binary File to In-Memory Bytes

This example demonstrates how to download the binary content of a file from Google Drive directly into local memory.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
gAuth: HCkAuthGoogle;
rest: HCkRest;
bAutoReconnect: Boolean;
gdCache: HCkCache;
fileId: PWideChar;
sbPath: HCkStringBuilder;
statusCode: Integer;
errResponseBody: PWideChar;
jpgBytes: HCkByteData;
fac: HCkFileAccess;

begin
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');

// To download to memory, we'll send the request in one call, then receive
// the response header, and then the response body.
// If the response header indicates failure or an unexpected response, then the
// body is not the data we desire.

// First send the HTTP request.
success := CkRest_SendReqNoBody(rest,'GET',CkStringBuilder__getAsString(sbPath));
if (success <> True) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    Exit;
  end;

// Get the response header.
statusCode := CkRest_ReadResponseHeader(rest);
if (statusCode <> 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));

    // Read the response body (which should be error text or HTML)
    errResponseBody := CkRest__readRespBodyString(rest);
    if (CkRest_getLastMethodSuccess(rest) = True) then
      begin
        Memo1.Lines.Add('response body: ' + errResponseBody);
      end;
    Exit;
  end;

// Read the response body, which should contain the file data.
jpgBytes := CkByteData_Create();
success := CkRest_ReadRespBodyBinary(rest,jpgBytes);
if (CkRest_getLastMethodSuccess(rest) <> True) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    Exit;
  end;

// Save jpgBytes to a file so we can examine the file to verify that it worked.
fac := CkFileAccess_Create();
CkFileAccess_WriteEntireFile(fac,'qa_output/penguins_out.jpg',jpgBytes);

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

CkAuthGoogle_Dispose(gAuth);
CkRest_Dispose(rest);
CkCache_Dispose(gdCache);
CkStringBuilder_Dispose(sbPath);
CkByteData_Dispose(jpgBytes);
CkFileAccess_Dispose(fac);

end;