Stream Wrapper + Stream Filter cannot longer alter PHP file since PHP 7.4

[lyrixx]

Description

I created a minimal gist to reproduce the error since it need at least 3 files.

https://gist.github.com/lyrixx/13df9efcfd08fee999c6b2bac0106117

>…re/dev/labs/php/rename-legacy-function(main *) php7.2 index.php 
/home/gregoire/dev/labs/php/rename-legacy-function/test1.php
/home/gregoire/dev/labs/php/rename-legacy-function/test2.php

>…re/dev/labs/php/rename-legacy-function(main *) php7.3 index.php 
/home/gregoire/dev/labs/php/rename-legacy-function/test1.php
/home/gregoire/dev/labs/php/rename-legacy-function/test2.php

>…re/dev/labs/php/rename-legacy-function(main *) php7.4 index.php 
PHP Parse error:  syntax error, unexpected end of file, expecting ';' in /home/gregoire/dev/labs/php/rename-legacy-function/test1.php on line 8

Parse error: syntax error, unexpected end of file, expecting ';' in /home/gregoire/dev/labs/php/rename-legacy-function/test1.php on line 8

see this part of gist to understand : https://gist.github.com/lyrixx/13df9efcfd08fee999c6b2bac0106117#file-function-fixer-php-L290-L293

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The idea is to rename some functions (for dealing with a legacy and dirty codebase) with a stream filter. It used to work with older PHP version, but it seems it's broken since PHP 7.4.

PHP Version

7.4

Operating System

Ubuntu 20.04

[cmb69]

PHP 7.4 is no longer actively supported, but I can reproduce the reported behavior with PHP-8.0. However, this is not a bug in PHP, but rather a bug in the userland script. In StreamFilter::filter(), $consumed needs to be increased by the length of the modified stream contents; you can easily verify that by changing StreamFilter::doFilter():

$buffer = str_replace("foobar", "foob_$rand", $buffer);

[lyrixx]

@cmb69 Thanks for the feeback. Indeed I make the test with PHP 8.1 but I tried to find the version where it has broken.

I already tried to update the $consumed variable with the new new length but it did not work. I think something is broken in PHP :/
Of course, if I keep the same content length it works.

Did you manage to make it work?

[cmb69]

Okay, I had a closer look, and found that the behavioral change has been introduced by c2c5c9a. So the problem with the existing code is actually the StreamWrapper::stream_stat() implementation. At least the size needs to properly match the filtered output. Quick fix for the given script:

    public function stream_stat(): array
    {
        $stat = fstat($this->resource);
        $stat["size"] = $stat["size"] + 4;
        return $stat;
    }

Of course, that won't work in practice; instead the code needs to track the actual size.

[lyrixx]

So I'm not sure, is it bug in PHP, or something that need to be fixed in my script?

[cmb69]

You need to fix your script, so that StreamWrapper::stream_stat() returns the size of the filtered stream (not the original stream).