Download a file via FTP with auto-resume functionality in case of any disconnects.

php-ftp-download-auto-resume.php

<?php
/**
 * Copyright (C) <2012> <Corey Ballou>
 * @author Corey Ballou <http://www.craftblue.com>
 * @license MIT License
 */

/**
 * Handles FTP download of a remote file and stores it in a local file.
 *
 * @param   string  $ftpServer          The FTP server to connect to, i.e. ftp.server.com
 * @param   string  $username           The FTP username
 * @param   string  $password           The FTP password
 * @param   string  $remoteFilePath     The path to the remote file if necessary
 * @param   string  $localFilePath      The full path to the local file
 * @param   int     $port               The FTP server port, 21 is standard
 * @return  bool
 */
function download(
    $ftpServer,
    $username,
    $password,
    $remoteFilePath,
    $localFilePath,
    $port = 21,
    $timeout = 30)
{
    // set up basic connection
    $conn = ftp_connect($ftpServer, $port, $timeout)
        or die('Could not connect to FTP server.');

    // login with username and password
    if (@ftp_login($conn, $username, $password)) {
        // turn on PASV mode
        @ftp_pasv($conn, TRUE);

        // attempt to download the file, with retries
        return _download($conn, $remoteFilePath, $localFilePath);
    } else {
        if (!empty($conn)) {
            ftp_close($conn);
        }
        die('Access credential problem connecting to FTP server.');
    }

    if (!empty($conn)) {
        ftp_close($conn);
    }
    
    return false;
}

/**
 * Handle file downloads with attempted retries. Note that filesize() doesn't
 * work on all machines. Also, depending on the file type, you may need to swap
 * out FTP_BINARY for FTP_ASCII.
 *
 * @param   resource	$conn
 * @param   string      $remoteFilePath     The path to the remote file if necessary
 * @param   string      $localFilePath      The full path to the local file
 * @param   int		$retries
 */
function _download($conn, $remoteFilePath, $localFilePath, $retries = 1)
{
    // check if the local file already exists to determine resume d/l position
    $resumePosition = 0;
    if (file_exists($localFilePath)) {
        $resumePosition = filesize($localFilePath);
    }

    // attempt to download with auto-resume capabilities up to 5 retries
    if (@ftp_get($conn, $localFilePath, $remoteFilePath, FTP_BINARY, $resumePosition)) {
        if (!empty($conn)) {
            ftp_close($conn);
        }
        return true;
    } else if ($retries < 5) {
        // retry up to five times
        return _download($conn, $remoteFilePath, $localFilePath, $retries + 1);
    } else {
        die('There was a problem downloading the remote file.');
    }
}