How to check if directory contents has changed with PHP?

Question

I'm writing a photo gallery script in PHP and have a single directory where the user will store their pictures. I'm attempting to set up page caching and have the cache refresh only if the contents of the directory has changed. I thought I could do this by caching the last modified time of the directory using the filemtime() function and compare it to the current modified time of the directory. However, as I've come to realize, the directory modified time does not change as files are added or removed from that directory (at least on Windows, not sure about Linux machines yet).

So my questions is, what is the simplest way to check if the contents of a directory have been modified?

Answer 1

Here's what you may try. Store all pictures in a single directory (or in /username subdirectories inside it to speed things up and to lessen the stress on the FS) and set up Apache (or whaterver you're using) to serve them as static content with "expires-on" set to 100 years in the future. File names should contain some unique prefix or suffix (timestamp, SHA1 hash of file content, etc), so whenever uses changes the file its name gets changed and Apache will serve a new version, which will get cached along the way.

Answer 2

You're thinking the wrong way.

You should execute your directory indexer script as soon as someone's uploaded a new file and it's moved to the target location.

Answer 3

What about touching the directory after a user has submitted his image? Changelog says: Requires php 5.3 for windows to work, but I think it should work on all other environments

Answer 4

Try deleting the cached version when a user uploads a file to his directory.

When someone tries to view the gallery, look if there's a cached version first. If there's a cached version, load it, otherwise, generate the page, cache it, done.

Answer 5

As already mentioned by others, a better way to solve this would be to trigger a function when particular events happen, that changes the folder. However, if your server is a unix, you can use inotifywait to watch the directory, and then invoke a PHP script.

Here's a simple example:

#!/bin/sh
inotifywait --recursive --monitor --quiet --event modify,create,delete,move --format '%f' /path/to/directory/to/watch |
  while read FILE ; do
    php /path/to/trigger.php $FILE
  done

See also: http://linux.die.net/man/1/inotifywait

Answer 6

Uh. I'd simply store the md5 of a directory listing. If the contents change, the md5(directory-listing) will change. You might get the very occasional md5 clash, but I think that chance is tiny enough..
Alternatively, you could store a little file in that directory that contains the "last modified" date. But I'd go with md5.

---

PS. on second thought, seeing as how you're looking at performance (caching) requesting and hashing the directory listing might not be entirely optimal..

Answer 7

I was looking for something similar and I just found this:

http://www.franzone.com/2008/06/05/php-script-to-monitor-ftp-directory-changes/

For me looks like a great solution since I'll have a lot of control (I'll be doing an AJAX call to see if anything changed).

Hope that this helps.

Answer 8

IMO edubem's answer is the way to go, however you can do something like this:

if (sha1(serialize(Map('/path/to/directory/', true))) != /* previous stored hash */)
{
    // directory contents has changed
}

Or a more weak / faster version:

if (Size('/path/to/directory/', true) != /* previous stored size */)
{
    // directory contents has changed
}

Here are the functions used:

function Map($path, $recursive = false)
{
    $result = array();

    if (is_dir($path) === true)
    {
     $path = Path($path);
     $files = array_diff(scandir($path), array('.', '..'));

     foreach ($files as $file)
     {
      if (is_dir($path . $file) === true)
      {
       $result[$file] = ($recursive === true) ? Map($path . $file, $recursive) : $this->Size($path . $file, true);
      }

      else if (is_file($path . $file) === true)
      {
       $result[$file] = Size($path . $file);
      }
     }
    }

    else if (is_file($path) === true)
    {
     $result[basename($path)] = Size($path);
    }

    return $result;
}

function Size($path, $recursive = true)
{
    $result = 0;

    if (is_dir($path) === true)
    {
     $path = Path($path);
     $files = array_diff(scandir($path), array('.', '..'));

     foreach ($files as $file)
     {
      if (is_dir($path . $file) === true)
      {
       $result += ($recursive === true) ? Size($path . $file, $recursive) : 0;
      }

      else if (is_file() === true)
      {
       $result += sprintf('%u', filesize($path . $file));
      }
     }
    }

    else if (is_file($path) === true)
    {
     $result += sprintf('%u', filesize($path));
    }

    return $result;
}

function Path($path)
{
    if (file_exists($path) === true)
    {
     $path = rtrim(str_replace('\\', '/', realpath($path)), '/');

     if (is_dir($path) === true)
     {
      $path .= '/';
     }

     return $path;
    }

    return false;
}