Pascal (Lazarus/Delphi)

Resume an Interrupted SFTP Download

Demonstrates the Chilkat SFtp.ResumeDownloadFileByName method, which resumes an interrupted download. The first argument is the remote file path and the second is the local file path. Chilkat uses the existing local file size as the remote starting offset.

Note: This example uses relative local paths, which are resolved against the application's current working directory. Absolute local paths may also be used. Supply the paths appropriate to your own environment.

Background: The download counterpart to resuming an upload: it compares the local file size against the remote and fetches only what is missing — a full download if the local file is absent or empty, the remaining bytes appended if it is shorter, and nothing if it is already complete. As with resumed uploads, the check is size-based and assumes the partial file is a correct prefix of the remote file.

Chilkat Pascal (Lazarus/Delphi) Downloads

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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.SFtp;

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

procedure RunDemo;
var
  success: Boolean;
  sftp: TSFtp;
  port: Integer;
  password: string;

begin
  success := False;

  //  Demonstrates the SFtp.ResumeDownloadFileByName method, which resumes an interrupted download.
  //  The 1st argument is the remote file path and the 2nd is the local file path.

  sftp := TSFtp.Create;

  //  Connect, authenticate, and initialize the SFTP subsystem.
  port := 22;
  success := sftp.Connect('sftp.example.com',port);
  if (success = False) then
    begin
      WriteLn(sftp.LastErrorText);
      Exit;
    end;

  //  Normally you would not hard-code the password in source.  You should instead obtain it
  //  from an interactive prompt, environment variable, or a secrets vault.
  password := 'mySshPassword';

  success := sftp.AuthenticatePw('mySshLogin',password);
  if (success = False) then
    begin
      WriteLn(sftp.LastErrorText);
      Exit;
    end;

  success := sftp.InitializeSftp();
  if (success = False) then
    begin
      WriteLn(sftp.LastErrorText);
      Exit;
    end;

  //  Resume downloading the remote file.  Chilkat uses the existing local file size as the remote
  //  starting offset, so only the remaining bytes are appended.  If the local file is missing or
  //  empty, a normal full download is performed.
  success := sftp.ResumeDownloadFileByName('subdir/largefile.zip','qa_output/largefile.zip');
  if (success = False) then
    begin
      WriteLn(sftp.LastErrorText);
      Exit;
    end;
  WriteLn('Download resumed and completed.');

  sftp.Disconnect();


  sftp.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.