PHP Function Calling Function

Question

Working on a link shortening script and I'm stumped. I figured the following code would function as needed however, I get an execution time out related to $str .= $charset[mt_rand(0, $count-1)];. I have scoured over the code several times, I can't find what I am doing wrong.

function randString($length, $charset='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789') {
    $str = '';
    $count = strlen($charset);
    while ($length--) {
        $str .= $charset[mt_rand(0, $count-1)];
    }
    return $str; 
}

function shrinkURL($url) {
    $is_unique = false;
    $num = 4;
    $random_string = randString($num);

    $count = 0;
    while (!$is_unique) {
        $q1 = "SELECT id FROM linkShortner WHERE short = '".$random_string."' LIMIT 1";
    $result = mysql_query($q1) or die(mysql_error());

        if ($result === false)   // if you don't get a result, then you're good
            $is_unique = true;
        else                     // if you DO get a result, keep trying
            $count++;

    if ($count >= 10) {
        $num = (strlen($random_string) + 1);
    $random_string = randString($num);
    $count = 0;
        }
    $random_string = randString($num);
    }

    $shortURL = "https://domain.com/l/".$random_string;

    $q2 = "INSERT INTO linkShortner (id, destination, short, shorURL, creationDate) VALUES (NULL, '".$url."', '".$random_string."', '".$shortURL."', '".$DateTime."')";
    $r2 = mysql_query($q2) or die(mysql_error());

    return $shortURL; 

}

$shortURL = shrinkURL('http://domain.com');
echo $shortURL;

Any help would be greatly appreciated, think maybe I am just burnt out.

I got the answer but I cant post it [the answer as answer] due to my reputation being under 10. So here I is: Changed if ($result === false) to if (!mysql_num_rows($result)) and all is well. if ($result === false) is for mysqli which is not being used here. Basically the shrinkURL function scours the DB for a matching string before trying to insert a unique string/row, if ($result === false) would never = false because the value of $result is MySQL_query($q1) therefore producing an endless loop. — Sabyre
– Sabyre, Commented Mar 26, 2014 at 16:35

Damien Overeem · Accepted Answer · 2014-03-26 15:35:01Z

1

My guess is that at some point your function randString() will be called with the $length argument being 0.

This would make:

while ($length--) {
    $str .= $charset[mt_rand(0, $count-1)];
}

get stuck, because the first iteration would be while (-1), which is true. And then while (-2), which is also true.. etc etc etc.

I would change your while ( $length-- ) to while ( $length-- >= 0 )

answered Mar 26, 2014 at 15:35

Damien Overeem

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4 Comments

Sabyre Over a year ago

If I add the following under the randString function It works.

Sabyre Over a year ago

$num = 4; $random_string = randString($num); echo $random_string; exit();

Damien Overeem Over a year ago

You are calling the randString() twice in your code. Since the exit makes it work, I'm guessing the second call (in the if ($count >=10)... bit) is the one ending up in an endless loop.

Sabyre Over a year ago

I did try your suggestions out of frustration, though I do appreciate the thought they were not helpful. Changing while ( $length-- ) to while ( $length-- >= 0 ) resulted in a string length of 5, I would prefer to start with 4 and only increase the length if there are no more unique strings available quickly. I probably should have been more informative with my question. You were right about the randString calls being the culprit due to improper use of $result (see comment under my question). Thanks for the help.

Sabyre · Accepted Answer · 2014-03-27 19:48:26Z

0

Changed if ($result === false) to if (!mysql_num_rows($result)) and all is well. if ($result === false) is for mysqli which is not being used here.

Basically the shrinkURL function scours the DB for a matching string before trying to insert a unique string/row, if ($result === false) would never = false because the value of $result is MySQL_query($q1) therefore producing an endless loop.

answered Mar 27, 2014 at 19:48

Sabyre

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