Improper long path support for relative paths

[lunter2]

Description

The following code:

<?php
 chdir('C:\\');print(getcwd()); // C:\ (ok)

 var_dump(mkdir('C:\\'.str_repeat('a',255))); // true (absolute path - directory name with 255 characters created)
 var_dump(mkdir(str_repeat('b',255))); // false (relative path - directory name with 255 characters NOT created - max 247 characters works)
?>

Resulted in this output:

C:\
bool(true)
bool(false)

But I expected this output instead:

C:\
bool(true)
bool(true)

PHP Version

PHP 8.2.4

Operating System

Windows 10 Pro 22H2 (10.0.19045.2788)

[iluuu1994]

Are expected and actual result reversed here?

[lunter2]

I corrected it.

[nielsdos]

I tried to reproduce this on my Windows VM (Win10 22H2 so same as yours). I cannot reproduce this behaviour (I tried both with LongPathsEnabled 0 and 1).
Are you sure the reproduction code works on its own and is correct (*)? Can you also try this with extensions disabled (php -n)?. How long is the path of the current working directory, maybe that has some influence?

(*) I can't create a file/directory with 256 or more characters. But in that case the behaviour of mkdir and file_put_contents is the same.

[lunter2]

I change test script. Try again.

[lunter2]

New test script.

<?php
 chdir('C:\\');print(getcwd()); // C:\ (ok)

 var_dump(mkdir('C:\\'.str_repeat('a',255))); // true (absolute path - directory name with 255 characters created)
 var_dump(mkdir(str_repeat('b',255))); // false (relative path - directory name with 255 characters NOT created - max 247 characters works)
?>

I can confirm it on another computer.

c:\php>php -n mkdir.php
C:\bool(true)

Warning: mkdir(): No such file or directory in C:\php\mkdir.php on line 5
bool(false)

[nielsdos]

I can reproduce it, and I have found the root cause.
You'll be able to reproduce it on NTS builds, but not on ZTS builds. I was using ZTS which is the reason I couldn't reproduce it earlier.

What happens is that for long paths we rely on Windows's path canonicalization to prepend \\?\ to the path. The caveat here is that the path needs to be an absolute path for the \\?\ to work. In the 'b' example the path is not absolute, but relative, so the path lookup in Windows fails. On NTS when mkdir is called we directly call php_win32_ioutil_mkdir.

But why does it work on ZTS then? Well, on ZTS we do #define VIRTUAL_DIR (*). This makes sure that when we create a directory we call virtual_mkdir instead of php_win32_ioutil_mkdir. This first transforms the path to an absolute path by calling virtual_file_ex and only then calls php_win32_ioutil_mkdir. This indirectly makes the \\?\ style paths work because the paths that are sent to php_win32_ioutil_mkdir are always absolute in this case.

I suspect that most path-related functions suffer from this problem. I guess we should somehow make it absolute on NTS if we do a canonicalization transformation. (Side question: why is VIRTUAL_DIR ZTS-only?)

(*)

php-src/Zend/zend_virtual_cwd.h

Lines 52 to 54 in bf123da

	#ifdef ZTS
	#define VIRTUAL_DIR
	#endif

[lunter2]

Yes, I use NTS.