在PHP中仅从FTP服务器下载新图像

Question

I made a little script which allows me to download images from FTP server. But, the thing is, whenever I execute the script, ALL images are downloaded. Is there any way to rewrite the code so that it only downloads new images?

My script looks like this:

$ftp_server = "my_server_ip";
$ftp_user = "my_user_name";
$ftp_pass = "my_password";
$DIR="my_path_to_images_folder";

$conn = ftp_connect($ftp_server);
if(!$conn)
{
    exit("Can not connect to server: $ftp_server
");
}

if(!ftp_login($conn,$ftp_user,$ftp_pass))
{
    ftp_quit($conn);
    exit("Can't login
");
}

ftp_chdir($conn,$DIR);

$files = ftp_nlist($conn,'.');
for($i=0;$i<count($files);$i++)
{
    if(!ftp_get($conn,$files[$i],$files[$i],FTP_BINARY))
    {
        echo "Can't download {$files[$i]}
";
    }
    else
    {
        echo "Successfully transferred images!";
    }
}

ftp_quit($conn);

Thank you.

Answer 1

To download only files that do not exist locally yet, or are newer than the local copy, use:

$files = ftp_nlist($conn, '.');

foreach ($files as $file)
{
    $remote_time = ftp_mdtm($conn, $file);

    if (!file_exists($file) ||
        (filemtime($file) < $remote_time))
    {
        ftp_get($conn, $file, $file, FTP_BINARY);
        touch($file, $remote_time);
    }
}

---

If your server supports MLSD command and you have PHP 7.2 and newer, you can replace ftp_nlist and repeated call to ftp_mdtm with one efficient call to ftp_mlsd function.