Non-English Locale breaks ZADD #1893

Expected behaviour

Given this code:

<?php

setlocale(LC_ALL, 'de_DE');

$redis = new \Redis();
$redis->connect('127.0.0.1');

$redis->zadd('tmp_set', -1607954792.2, 'foo');

var_dump($redis->getLastError());

I expect this code to return NULL as the last error.

Actual behaviour

I get ERR value is not a valid float as the last error.

I'm seeing this behaviour on

• OS: all
• Redis: all versions
• PHP: all versions
• phpredis: 5.3.2

I've checked

• There is no similar issue from other users
• Issue isn't fixed in develop branch

Details

As far as I can tell, this is because redis_zadd_cmd uses redis_cmd_append_sstr_dbl which in turn uses snprintf to convert the float to string:

snprintf depends on the application locale when selecting the decimal separator which for the German language is , instead of .. Changing the system/application locale to English fixes it.

This seems issue seems to have been reported and addressed before in #33 / 1d6133d but it seems that subsequent changes broke this again.