Perl

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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Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

my $ftp = Chilkat2::Ftp2->new;

$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');

my $success = $ftp->Connect();
if (!$success) {
    print $ftp->LastErrorText, "\n";
    exit;
}

# 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(1);

# Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
# the current local file size.
$success = $ftp->GetFile('public_html/bigfile.zip', 'qa_output/bigfile.zip');
if (!$success) {
    print $ftp->LastErrorText, "\n";
    exit;
}

# 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.\n";
} else {
    print "The file was fully received.\n";
}

$success = $ftp->Disconnect();
if (!$success) {
    print $ftp->LastErrorText, "\n";
    exit;
}