Nick's Cache-Control header parser

parser.php

<?php
function parse($string)
{
    $string = trim($string);

    $directives = array();

    // handle empty string early so we don't need a separate start state
    if ($string == '') {
        return $directives;
    }

    $lastMatch = null;
    
    state_directive:
    switch (match(array('[a-zA-Z][a-zA-Z_-]*'), $string, $lastMatch)) {
        case 0:
            $directive = $lastMatch;
            goto state_value;
            break;

        default:
            throw new Exception('expected DIRECTIVE');
            break;
    }

    state_value:
    switch (match(array('="[^"]*"', '=([^",][^,]*)?'), $string, $lastMatch)) {
        case 0:
            $directives[$directive] = substr($lastMatch, 2, -1);
            goto state_separator;
            break;

        case 1:
            $directives[$directive] = rtrim(substr($lastMatch, 1));
            goto state_separator;
            break;

        default:
            $directives[$directive] = true;
            goto state_separator;
            break;
    }

    state_separator:
    switch (match(array('\s*,\s*', '$'), $string, $lastMatch)) {
        case 0:
            goto state_directive;
            break;

        case 1:
            return $directives;
            break;

        default:
            throw new Exception('expected SEPARATOR or END');
            break;

    }
}

function match($tokens, &$string, &$lastMatch)
{
    foreach ($tokens as $i => $token) {
        if (preg_match('/^'.$token.'/', $string, $matches)) {
            $lastMatch = $matches[0];
            $string = substr($string, strlen($matches[0]));
            return $i;
        }
    }
    return -1;
}
try {
    var_dump(parse('no-store& private=test, no-cache="a,b,c"'));
} catch (Exception $e) {
    var_dump($e->getMessage());
}

$start = microtime(true);
for ($i=0; $i<10000; $i++) {
    parse('no-store, private=test, no-cache="a,b,c"');
}
var_dump(microtime(true) - $start);

PHP Fatal error: Uncaught Exception: expected SEPARATOR or END when call with parse(' = 31536000')