Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final ftp = CkFtp2();

  ftp.hostname = 'ftp.example.com';
  ftp.username = '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.
  ftp.password = 'myPassword';

  try {
    ftp.connect();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // RestartNext requests that the NEXT transfer resume from existing content rather than starting
  // over.  It is consumed by that transfer and then automatically reset.
  ftp.restartNext = true;

  // Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
  // the current local file size.
  try {
    ftp.getFile('public_html/bigfile.zip', 'qa_output/bigfile.zip');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // 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 (ftp.partialTransfer) {
    print('Only part of the file was received; another resume may be needed.');
  } else {
    print('The file was fully received.');
  }

  try {
    ftp.disconnect();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }
}