zlib streams should support locking

[githubyiti]

Description

The following code:

<?php
			$gz = gzopen($cachefileb,'w9');
			gzwrite($gz, $towrite);
			gzclose($gz);

Resulted in this output:
Current function caused disk error while multiple sessions is writing to the same file.

But I expected this output instead:
can the file be locked while the file is being written?

### PHP Version

PHP 7.4

### Operating System

Almalinux

[cmb69]

https://www.php.net/flock

[githubyiti]

Thanks for the response!
Yes, someone is reporting the same problem on exactly the page you gave, has the issue been solved?
https://www.php.net/flock#111443

[cmb69]

No, that issue still persists. From a quick look at the implementation, the actual file stream is an "inner stream".

Workaround: use fopen() instead of gzopen() (and use ini_set("zlib.output_compression", 9")).

PS: probably better anyway: use a separate lock file (.lck).

[githubyiti]

Thanks.

The old code in use has already created a lot of data, fear rewriting the old code may unexpectly corrupt the old data.
new scripts are using the way you suggested.

Hope if can have something like gz_lock to patch to the old code.

Regards,

[cmb69]

This cannot be implemented for PHP < 8.5, and I would assume that upgrading to PHP 8 already requires quite some changes to your code base, so possibly tough luck.

Anyway, let's turn this into a proper feature request, since it generally makes sense to be able to lock zlib streams.

[cmb69]

Implementation would need to start at

php-src/ext/zlib/zlib_fopen_wrapper.c

Line 105 in ff80ec7

NULL /* set_option */

[githubyiti]

Thanks for moderating the title.
Hope will have gz_lock in the future.

[cmb69]

Hope will have gz_lock in the future.

Well, you would rather be able to use flock().

[githubyiti]

Added an external file lock as below
not sure will the problem be fixed.

if(file_exists($cachefileb."-lock") and time()-filemtime($cachefileb."-lock")<3){@set_time_limit(10);sleep(rand(0,8));}
clearstatcache();
if(!file_exists($cachefileb."-lock") or time()-filemtime($cachefileb."-lock")>3){
touch($cachefileb."-lock");
$gz = gzopen($cachefileb,'w9');
gzwrite($gz, $towrite);
gzclose($gz);
unlink($cachefileb."-lock");
}

[cmb69]

No, I've meant just flock() another file. Something like:

$lock = fopen($gz . ".lck", "w+");
flock($lock, LOCK_EX);
$gz = gzopen($cachefileb,'w9');
gzwrite($gz, $towrite);
gzclose($gz);
flock($lock, LOCK_UN);

[githubyiti]

Thanks!
Seems your flock is better.
I just code for hobby and not familiar with the behavior of how flock works.
Will the below work?

$lock = fopen($gz . ".lck", "w+");
if(!$lock ){@set_time_limit(10);
sleep(rand(0,8));
$lock = fopen($gz . ".lck", "w+");}
if($lock ){flock($lock, LOCK_EX);
$gz = gzopen($cachefileb,'w9');
gzwrite($gz, $towrite);
gzclose($gz);
flock($lock, LOCK_UN);
fclose($gz . ".lck");
}

[nielsdos]

Implemented in PHP 8.5 via 5acff0e

[githubyiti]

I found the problem perhaps can be solved by gz witing the file to tmp file then rename it back to the disk.
Even if the tmp file is corrupted when the lock failed, disk error can be prevented.
testing the code now, so far no disk error occurred.