Reading boolean configuration values via php.ini is impossible due to architecture

[gdaszuta]

So because my application works with spawning some sub-processes in a manner that doesn't pass full environment verbatim, I've tried to move configuration to php.ini, and it does seem that it's impossible to do so in a consistent way.

The issue is, that some values are boolean:

    OTEL_SDK_DISABLED
    OTEL_PHP_INTERNAL_METRICS_ENABLED
    OTEL_PHP_AUTOLOAD_ENABLED
    OTEL_PHP_EXPERIMENTAL_AUTO_ROOT_SPAN

and php function https://www.php.net/manual/en/function.get-cfg-var.php used in OpenTelemetry\Config\SDK\Configuration\Environment\PhpIniEnvSource to read configuration from ini file has some undocumented, but consistent behaviour where any value considered by php developers as a 'truthy' is returned as string of value '1'.

The behaviour is apparently consistent between all php versions since at least 2013, probably since forever.

$ for PHP in 5.6 8.0 8.1 8.2 8.3 8.4 ; do 
    docker run -it --rm php:$PHP \
        php -d 'TEST_VALUE=true' -r 'echo phpversion() . " => " . json_encode(get_cfg_var("TEST_VALUE")) . "\n";' ;
done
5.6.40 => "1"
8.0.30 => "1"
8.1.31 => "1"
8.2.26 => "1"
8.3.14 => "1"
8.4.1 => "1"

This makes OpenTelemetry\SDK\Common\Configuration\Parser\BooleanParser always throw InvalidArgumentException, as only acceptable values are 'true' and 'false', log warning Invalid boolean value "%s" interpreted as "false" for %s', and not enable instrumentation.

This, unfortunately makes the php.ini way of configuration mentioned in documentation impossible, and as I can see in git history it was impossible since #870, so for good two years.

I see three ways to fix the issue – either revert the change to allow string "1" as a valid boolean value, reimplement php configuration parser to return verbatim configuration variable values, or drop this path of configuration altogether from documentation.

FYI @brettmc

[gdaszuta]

So I did some poking around php internals and available solutions, and it does seem that reimplementation of get_cfg_var() is suprisingly the most sane solution:

function get_raw_cfg_var(string $option) {
    $ini_files = array_map("trim", explode(",", php_ini_scanned_files()));

    foreach ($ini_files as $file) {
        $values = parse_ini_file($file, false, INI_SCANNER_RAW );

        if(isset($values[$option])) {
            return $values[$option];
        }
    }

    return false;
}

It could be fractionally slower than the native function (wasn't in my tests, but in theory it could), but it's specification-friendly, working, and drop-in. I can prepare PR later, please just someone let me know if you like this approach.

[brettmc]

if it's not possible to quote the values in php.ini (eg TEST_VALUE="true" in the example above), then your proposed solution looks ok to me. I'm not concerned about it being slightly slower, it's not heavily used.

[gdaszuta]

Ok, you got me here :) I was so focused on debugging the issue, I hadn't even consider quoting of this string could be mandatory.

I see one drawback of my solution – it won't work with parameters defined by php -d ..., and as far as I understand there is no way to gather runtime execution parameters from inside the script, so it also wouldn't be consistent. Maybe updating documentation would be the best way.

[brettmc]

Maybe updating documentation would be the best way.

Great! We could probably add some phpdoc to the ini processing class, as folks might look there. It's been some time since I went over our documentation over in opentelemetry.io, but it's very briefly mentioned in https://opentelemetry.io/docs/languages/php/sdk/#autoloading and maybe that section could be improved.