Join a list of arbitrary strings together so they can be split apart again, ie split(join($x)) === $x for all $x

JoinSplit.php

<?php

namespace JoinSplit;

/**
 * @param string[] $a
 * @return string
 */
function join(array $a) {
    $r = '';
    foreach ($a as $x) {
        $x = str_replace('\\', '\\\\', $x);
        $x = str_replace(';', '\\;', $x);
        $r .= $x . ';';
    }
    return $r;
}

/**
 * @param string $s
 * @return string[]
 */
function split($s) {
    $r = array();
    $b = '';
    $l = strlen($s);
    $e = false;
    for ($i = 0; $i < $l; $i++) {
        $c = $s[$i];
        if ($e) {
            $b .= $c;
            $e = false;
        } else if ($c === '\\') {
            $e = true;
        } else if ($c === ';') {
            $r[] = $b;
            $b = '';
        } else {
            $b .= $c;
        }
    }
    return $r;
}

/**
 * @throws \Exception
 */
function test() {
    static $tests = array(
        array(),
        array(''),
        array('"'),
        array('""'),
        array(','),
        array(';'),
        array('\\'),
        array('\\"'),
        array("\n"),
        array("\r"),
        array("\v"),
        array("\t"),
        array(" "),
        array("\r\n"),
        array('"', '""', ';', '', ',', "\n"),
        array("\x00", 'lololol'),
        array("\x00", '0'),
        array("\x00"),
    );
    
    foreach ($tests as $test1) {
        $test2 = split(join($test1));
        
        if ($test1 !== $test2) {
            $test1 = var_export($test1, true);
            $test2 = var_export($test2, true);
            throw new \Exception("expected $test1, got $test2");
        }
    }
}

test();