<?php

// This implementation doesn't do any validation and just splits at the first colon in each line.
function parse(string $rawHeaders): array
{
    $lines = explode("\r\n", $rawHeaders);
    $headers = [];

    foreach ($lines as $line) {
        if (empty($line)) {
            break;
        }

        if (strpos($line, ':') !== false) {
            $parts = explode(':', $line, 2);
            $headers[strtolower($parts[0])][] = trim($parts[1] ?? '');
        }
    }

    return $headers;
}

$rawHeaders = "Server: Microsoft-IIS/5.0
Date: Tue, 31 Oct 2006 08:00:29 GMT
Connection: close
Allow: GET, HEAD, POST, TRACE, OPTIONS
Content-Length: 0
X-No-Value:
X-No-Whitespace: Test
X-Trailing-Whitespace:  	Foobar		  
";

$start = microtime(true);

for ($i = 0; $i < 300000; $i++) {
    parse($rawHeaders);
}

print(microtime(true) - $start) . PHP_EOL;