Pascal (Lazarus/Delphi)

S3 Resume Download

See more Amazon S3 (new) Examples

Suppose an S3 download of a very large file failed for some reason and you have a partial file on disk. Rather than restart the entire download, you wish to download the remaining portion. This example demonstrates how to finish a previously failed download.

Note: This example requires Chilkat v9.5.0.83 or above.

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.FileAccess,
  Chilkat.AuthAws,
  Chilkat.Rest,
  Chilkat.StringBuilder,
  Chilkat.Stream;

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

procedure RunDemo;
var
  success: Boolean;
  rest: TRest;
  bTls: Boolean;
  port: Integer;
  bAutoReconnect: Boolean;
  authAws: TAuthAws;
  fac: TFileAccess;
  localFilepath: string;
  sz: Integer;
  sbRange: TStringBuilder;
  responseStatusCode: Integer;
  bodyStream: TStream;
  errResponse: string;

begin
  success := False;

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

  rest := TRest.Create;

  //  Connect to the Amazon AWS REST server.
  bTls := True;
  port := 443;
  bAutoReconnect := True;
  success := rest.Connect('s3.amazonaws.com',port,bTls,bAutoReconnect);

  //  ---------------------------------------------------------------------------
  //  Important: For buckets created in regions outside us-east-1,
  //  there are three important changes that need to be made.
  //  See Working with S3 Buckets in Non-us-east-1 Regions for the details.
  //  ---------------------------------------------------------------------------

  //  Provide AWS credentials for the REST call.
  authAws := TAuthAws.Create;
  authAws.AccessKey := 'AWS_ACCESS_KEY';
  authAws.SecretKey := 'AWS_SECRET_KEY';
  authAws.ServiceName := 's3';
  success := rest.SetAuthAws(authAws);

  //  Set the bucket name via the HOST header.
  //  In this case, the bucket name is "chilkat100".
  rest.Host := 'chilkat100.s3.amazonaws.com';

  //  We want to continue downloading a file.
  //  The relative local filepath of our previously partially downoaded file is: qa_output/hamlet.xml
  //  Let's find out how many bytes are already downloaded.
  fac := TFileAccess.Create;
  localFilepath := 'qa_output/hamlet.xml';
  //  Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
  //  the size of the file as a string, then convert to an integer value.
  sz := fac.FileSize(localFilepath);
  if (sz > 0) then
    begin
      WriteLn('sz = ' + sz);

      //  If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
      //  Range: bytes=42375-
      sbRange := TStringBuilder.Create;
      sbRange.Append('bytes=');
      sbRange.AppendInt(sz);
      sbRange.Append('-');
      rest.AddHeader('Range',sbRange.GetAsString());
      WriteLn('Added Range: ' + sbRange.GetAsString());
    end;

  //  Send the request to download the remainder of the file.
  success := rest.SendReqNoBody('GET','/hamlet.xml');
  if (success <> True) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  //  Read the response header.
  responseStatusCode := rest.ReadResponseHeader();
  if (responseStatusCode < 0) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  WriteLn('Response status code = ' + responseStatusCode);

  //  We expect a 200 or 206 response status if the file data is coming.
  //  Otherwise, we'll get a string response body with an error message(or no response body).
  if ((responseStatusCode = 200) or (responseStatusCode = 206)) then
    begin

      bodyStream := TStream.Create;

      //  The stream's sink will be a file.
      //  We will append to the file..
      bodyStream.SinkFile := localFilepath;

      //  Indicate that we wish to append to the output file.
      //  The SinkFileAppend property was added in Chilkat v9.50.83
      bodyStream.SinkFileAppend := True;

      //  Read the response body to the stream.  Given that we've
      //  set the stream's sink to a file, it will stream directly
      //  to the file.
      success := rest.ReadRespBodyStream(bodyStream,True);
      if (success <> True) then
        begin
          WriteLn(rest.LastErrorText);
          Exit;
        end;

      WriteLn('Successfully downloaded the file.');

    end
  else
    begin
      errResponse := rest.ReadRespBodyString();
      if (rest.LastMethodSuccess <> True) then
        begin
          WriteLn(rest.LastErrorText);
        end
      else
        begin
          WriteLn(errResponse);
        end;
    end;


  rest.Free;
  authAws.Free;
  fac.Free;
      sbRange.Free;
      bodyStream.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.