So, what I get from this is that what is troublesome is the possibility of an endless loop?When I wrote my recursive file system walking function every time it enters a directoryit bypasses . (self) and .. (parent dir) listings via a switch statement...
Note: the use of $_ in every variable name is my own practice. It helps me visually tospot variable references in code.
$_list = scandir($_targetDir);for( $_i = 0; $_i < count($_list); $_i++){switch($_list[$_i]){case '.':case '..':// add other case labels representing file names that should be bypassedbreak;default:// process every other item in the list// recursion comes when a directory is encountered and the loop enters and begins the next level.// the looping ends when the end of a directory listing is reached and all of the included directories have been processed// it pops back to a higher level and continues there. Eventually the whole file tree has been processed.break;}}
Note: It's unclear to me if you've actually encountered this
problem with your code, or you're trying to work out when it might
occur.
From a quick grep of the PHP source code[0], I believe the "Nesting level too deep" error does not refer to recursive function calls in the manner described above (which would likely result in either a SEGFAULT or an error referencing zend.max_allowed_stack_size such as in [1]). It specifically occurs when comparing arrays or objects in a manner that would result in an infinite loop due to self-references. See the .phpt results in the linked search for examples.
If you're encountering the "Nesting level too deep" error,
something else is going on in your code other than a
straight-forward recursive function call.
If objects aren't involved (where properties may directly or indirectly self-reference the object), explicit references (eg. `&$var`) almost certainly are.
Aside: When dealing with (Linux) filesystems, it may be possible
to encounter infinite loops even when ignoring the `.` and `..`
special entries if symlinks are involved. If you're sure symlinks
aren't involved (and specifically a symlink crafted to refer back
to a parent directory), you'll likely never encounter this issue.
The other solution is to limit the search depth - eg. never search
more than 5 directory levels deep. (This situation would result in
a stack overflow / stack size limit being reached as mentioned
above, and not "Nesting level too deep")
[0]
https://github.com/search?q=repo%3Aphp%2Fphp-src+%22Nesting+level+too+deep%22&type=code
[1]
https://github.com/php/php-src/blob/master/Zend/tests/stack_limit/gh16041_002.phpt
