Description:
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PHP 7.3 introduced "syslog.filter" to control content send to syslog.
According to documentation (https://www.php.net/manual/en/errorfunc.configuration.php#ini.syslog.filter), "syslog.filter=all" should allow all characters (=same behavior like in PHP 7.2 or before). However, even when set "syslog.filter=all" to allow all characters including line breaks, when you now send a multi-line message via error_log() through syslog, PHP splits message on line break so you end up with multiple messages instead of sending one single message like before.

Test script:
---------------
<?php
$message = "This is line #1" . PHP_EOL;
$message .= "This is line #2";

$iniSetting = ini_get('error_log');
if ($iniSetting !== 'syslog') {
	die("You must set error_log=syslog!");
}

if (version_compare(phpversion(), '7.3', '>')) {
	$iniSetting = ini_get('syslog.filter');
	if ($iniSetting !== 'all') {
		die("You must set syslog.filter=all!");
	}
}

error_log($message);

print "Now please review your syslog!" . PHP_EOL;


Expected result:
----------------
When running test script like

> /usr/bin/php7.3 -d error_log=syslog -d syslog.filter=all test.php

I would expect one single syslog message like

> Apr 16 16:52:06 myhost php: This is line #1#012This is line #2

Actual result:
--------------
I am getting _two_ messages:

> Apr 16 16:53:20 myhost php: This is line #1
> Apr 16 16:53:20 myhost php: This is line #2