Float locale issues

[ns3777k]

Prometheus can only deal with floats written with a dot (2.20 in en_EN for example). However if a project is set to use ru_RU, floats are written with a comma.

<?php
  
setlocale(LC_NUMERIC, 'en_EN');
printf("%f\n", 2.22); // prints 2.220000 which is correct

setlocale(LC_NUMERIC, 'ru_RU');
printf("%f\n", 2.22); // prints 2,220000 which is not correct

This can be fixed dropping the locale to C and returning it back after stringifying. Symfony guys fixed it in the VarDumper component here https://github.com/symfony/symfony/pull/23575/files .

Of course a project can drop locale when rendering the metrics, but IMO this should be handled by the library.

[amfleurke]

It's not only when rendering.
The APC.php storage handler has a function histogramBucketValueKey that just converts the float to string for naming the buckets, which causes the bucket to not be updated if the float is rendered with comma.