ftp cannot be rewound

[mvorisek]

Description

The following code:

<?php

$iter = new RecursiveDirectoryIterator('ftp://ftp.belnet.be/', \RecursiveDirectoryIterator::SKIP_DOTS);

var_dump($iter->current());
$iter->next();
var_dump($iter->current());
$iter->rewind();

Resulted in this output:

Warning: FilesystemIterator::rewind(): stream does not support seeking

But I expected this output instead:

support should not be related with seeking support

PHP Version

any

Operating System

any

[KapitanOczywisty]

What ftp wrapper does is sending NLST command and streaming response buffer and this is not seekable nor rewindable. It's possible to resend NLST command on rewind, though I don't know what side-effects this would have.

https://github.com/php/php-src/blob/master/ext/standard/ftp_fopen_wrapper.c#L724

[mvorisek]

As any file iterator is not buffered, ie. the results will change if the filesystem changes, there is no reason to not rewind the ftp iterator as well. Basically a rewind operation imply the state after an iterator is created.

[nielsdos]

Rewinding is implemented as seeking back to position 0. The entry for seek in php_ftp_dirstream_ops is non-existent. Perhaps an implementation could be made for seeking to 0.
The question then is what the FTP spec says about an NLST being interrupted by another NLST.