Creating temporary files in PHP

#!/usr/bin/env php
<?php

/**
 * Make a temporary file or directory in $prefix
 *
 * If $prefix is Null, sys_get_temp_dir() is used
 *
 * The template can be any file name, all sequences of two or more subsequent
 * X's are replaced by random alphanumeric characters
 *
 * If $dir is True, a directory is created
 *
 * A MktempError is thrown if an error occurs
 *
 * We return the full path to the created file or directory.
 *
 * This implementation is written by Martin Tournoij <martin@arp242.net>, while
 * peeking at FreeBSD's implementation of mkstemp (src/lib/libc/stdio/mktemp.c)
 * http://www.arp242.net/php-mktemp.html
 */
function mktemp($template=Null, $prefix=Null, $dir=False)
{
    if ($template === Null)
        $template = 'XXXXXX';
    if ($prefix === Null)
        $prefix = sys_get_temp_dir();

    # Check if we can write to $prefix, we will *not* create this directory!
    $oprefix = $prefix;
    $prefix = realpath($prefix);
    if ($prefix === False || !is_dir($prefix))
        throw new MktempError("Prefix `$oprefix' doesn't exists or isn't a directory");
    if (!is_writable($prefix))
        throw new MktempError("Prefix `$prefix' isn't writable");

    # Some sanity checks in $template
    if (strpos($template, '/') !== False)
        throw new MktempException("Template `$template' contains a slash (/) character");
    if (strlen($template) > PHP_MAXPATHLEN)
        throw new MktempException("Template `$template' is longer than PHP_MAXPATHLEN");

    # Replacement characters for the X's
    $padchars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

    # Replace two or more XX's with a random choice from $padchars
    $name = '';
    $doreplace = False;
    $Xs = [];
    foreach (range(0, strlen($template)) as $i) {
        $c = substr($template, $i, 1);
        if ($c !== 'X')
            $doreplace = False;
        elseif ($c === 'X' && substr($template, $i + 1, 1) === 'X')
            $doreplace = True;

        if ($doreplace) {
            $c = $padchars[mt_rand(0, strlen($padchars) - 1)];
            $Xs[] = $i;
        }

        $name .= $c;
    }

    if (count($Xs) === 0)
        throw new MktempError("No sequence of two or more X characters in template `$template'");

    $maxpermutations = pow(strlen($padchars), count($Xs));
    $permutation = 0;
    $curpos = array_shift($Xs);
    $startchr = strpos($padchars, substr($name, $curpos, 1)) - 1;
    $trychr = $startchr;
    while (true) {
        if ($permutation >= $maxpermutations)
            throw new MktempError("Unable to create $prefix/$template; all possible file permutations already exist");

        # Try to create file/directory
        if ($dir) {
            $s = @mkdir("$prefix/$name", 0700);

            # What we *really* want to do is do something along the lines of
            # `errno == EEXISTS' in C. In PHP there is, as far as I can see, no
            # way to do this.
            # The only thing we can do is run error_get_last(), and get a text
            # message, which is locale-dependent and may change in future PHP
            # versions.
            #
            # This check is needed, because all sort of things can go wrong (
            # permissions of $prefix changed, signal caught, symlink loop, max
            # file descriptors, etc).
            #
            # The file_exists() sort of solves the problem, I can't think of any
            # serious drawbacks, but it's extra disk I/O, and in very, *VERY*
            # rare cases it's not reliable (fopen() failed for another reason &
            # this file is created before we arrive at this check)
            #
            # There's a bug for this, but it doesn't seem to be considered much
            # of a priority...  https://bugs.php.net/bug.php?id=49396
            if (!$s && file_exists("$prefix/$name")) {
                $err = error_get_last();
                throw new MktempError("Error creating `$prefix/$name': {$err['message']}");
            }
            if ($s) break;
        }
        else {
            $s = @fopen("$prefix/$name", 'x');

            if ($s === False && !file_exists("$prefix/$name")) {
                $err = error_get_last();
                throw new MktempError("Error creating `$prefix/$name': {$err['message']}");
            }

            if ($s !== False) {
                fclose($s);
                chmod("$prefix/$name", 0600);
                break;
            }
        }

        # Loop over each X we replaced, and try the next character from
        # $padchars
        $permutation += 1;
        $trychr += 1;
        if ($trychr > strlen($padchars) - 1)
            $trychr = 0;

        if ($trychr === $startchr) {
            $curpos = array_shift($Xs);
            $startchr = strpos($padchars, substr($name, $curpos, 1)) - 1;
            $trychr = $startchr + 1;
        }

        $name = substr_replace($name, $padchars[$trychr], $curpos, 1);
    }

    return "$prefix/$name";
}

class MktempError extends Exception { }

<?php
error_reporting(E_ALL);
ini_set('display_errors', 'on');

foreach (range(0, 10) as $i) {
    try {
        mktemp('nonexistent', '/nonexistent');
        print("We excpected an exception\n");
        exit(1);
    }
    catch (MktempError $exc) { }

    try {
        mktemp('NoXCharacters');
        print("We excpected an exception\n");
        exit(1);
    }
    catch (MktempError $exc) { }

    try {
        mktemp('ohnoes.XXXXXX', '../../../../../etc/passwd');
        print("We excpected an exception\n");
        exit(1);
    }
    catch (MktempError $exc) { }

    $path = mktemp('hello XXXXXX world');
    print "$path\n";
    unlink($path);

    $dir = mktemp('dir.XXXXX', Null, True);
    print "$dir\n";
    rmdir($dir);

    $path = mktemp("-> XXX TEST XXXX <- &|\n    asdf XXXX");
    print "$path\n";
    unlink($path);

    print "\n";
}