Delphi DLL

Resume an Interrupted FTP Transfer

Demonstrates the RestartNext and PartialTransfer properties, which request that the next transfer resume from existing content and report whether a download was incomplete.

Note: The local paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: For a large transfer over a flaky link, restarting from zero after a drop is wasteful. Setting RestartNext makes the next download continue from the current local file size (and the next upload from the remote size); the flag is consumed by that one transfer and then reset. Afterward PartialTransfer tells you whether the download got only part of the file — the signal to set RestartNext again and resume once more.

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Delphi DLL

var
success: Boolean;
ftp: HCkFtp2;

begin
success := False;

ftp := CkFtp2_Create();

CkFtp2_putHostname(ftp,'ftp.example.com');
CkFtp2_putUsername(ftp,'myFtpLogin');

//  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.
CkFtp2_putPassword(ftp,'myPassword');

success := CkFtp2_Connect(ftp);
if (success = False) then
  begin
    Memo1.Lines.Add(CkFtp2__lastErrorText(ftp));
    Exit;
  end;

//  RestartNext requests that the NEXT transfer resume from existing content rather than starting
//  over.  It is consumed by that transfer and then automatically reset.
CkFtp2_putRestartNext(ftp,True);

//  Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
//  the current local file size.
success := CkFtp2_GetFile(ftp,'public_html/bigfile.zip','qa_output/bigfile.zip');
if (success = False) then
  begin
    Memo1.Lines.Add(CkFtp2__lastErrorText(ftp));
    Exit;
  end;

//  PartialTransfer indicates whether the most recent download received some, but not all, of the
//  remote file -- distinguishing a mid-transfer failure from other outcomes.
if (CkFtp2_getPartialTransfer(ftp)) then
  begin
    Memo1.Lines.Add('Only part of the file was received; another resume may be needed.');
  end
else
  begin
    Memo1.Lines.Add('The file was fully received.');
  end;

success := CkFtp2_Disconnect(ftp);
if (success = False) then
  begin
    Memo1.Lines.Add(CkFtp2__lastErrorText(ftp));
    Exit;
  end;

CkFtp2_Dispose(ftp);