Check to see if a string is serialized?

Question

What\'s the best way to determine whether or not a string is the result of the serialize() function?

https://www.php.net/manual/en/function.serialize

Answer 1

Optimizing Pascal MARTIN's response

/**
 * Check if a string is serialized
 * @param string $string
 */
public static function is_serial($string) {
    return (@unserialize($string) !== false);
}

Answer 2

I didn't write this code, it's from WordPress actually. Thought I'd include it for anybody interested, it might be overkill but it works :)

<?php
function is_serialized( $data ) {
    // if it isn't a string, it isn't serialized
    if ( !is_string( $data ) )
        return false;
    $data = trim( $data );
    if ( 'N;' == $data )
        return true;
    if ( !preg_match( '/^([adObis]):/', $data, $badions ) )
        return false;
    switch ( $badions[1] ) {
        case 'a' :
        case 'O' :
        case 's' :
            if ( preg_match( "/^{$badions[1]}:[0-9]+:.*[;}]\$/s", $data ) )
                return true;
            break;
        case 'b' :
        case 'i' :
        case 'd' :
            if ( preg_match( "/^{$badions[1]}:[0-9.E-]+;\$/", $data ) )
                return true;
            break;
    }
    return false;
}

Answer 3

build in to a function

function isSerialized($value)
{
   return preg_match('^([adObis]:|N;)^', $value);
}

Answer 4

see the wordpress function is_serialized

function is_serialized( $data, $strict = true ) {
// If it isn't a string, it isn't serialized.
if ( ! is_string( $data ) ) {
    return false;
}
$data = trim( $data );
if ( 'N;' === $data ) {
    return true;
}
if ( strlen( $data ) < 4 ) {
    return false;
}
if ( ':' !== $data[1] ) {
    return false;
}
if ( $strict ) {
    $lastc = substr( $data, -1 );
    if ( ';' !== $lastc && '}' !== $lastc ) {
        return false;
    }
} else {
    $semicolon = strpos( $data, ';' );
    $brace     = strpos( $data, '}' );
    // Either ; or } must exist.
    if ( false === $semicolon && false === $brace ) {
        return false;
    }
    // But neither must be in the first X characters.
    if ( false !== $semicolon && $semicolon < 3 ) {
        return false;
    }
    if ( false !== $brace && $brace < 4 ) {
        return false;
    }
}
$token = $data[0];
switch ( $token ) {
    case 's':
        if ( $strict ) {
            if ( '"' !== substr( $data, -2, 1 ) ) {
                return false;
            }
        } elseif ( false === strpos( $data, '"' ) ) {
            return false;
        }
        // Or else fall through.
    case 'a':
    case 'O':
        return (bool) preg_match( "/^{$token}:[0-9]+:/s", $data );
    case 'b':
    case 'i':
    case 'd':
        $end = $strict ? '$' : '';
        return (bool) preg_match( "/^{$token}:[0-9.E+-]+;$end/", $data );
}
return false;

}

Answer 5

This works fine for me

<?php

function is_serialized($data){
    return (is_string($data) && preg_match("#^((N;)|((a|O|s):[0-9]+:.*[;}])|((b|i|d):[0-9.E-]+;))$#um", $data));
    }

?>

Answer 6

I'd say, try to unserialize it ;-)

Quoting the manual :

In case the passed string is not unserializeable, FALSE is returned and E_NOTICE is issued.

So, you have to check if the return value is false or not (with === or !==, to be sure not to have any problem with 0 or null or anything that equals to false, I'd say).

Just beware the notice : you might want/need to use the @ operator.

For instance :

$str = 'hjkl';
$data = @unserialize($str);
if ($data !== false) {
    echo "ok";
} else {
    echo "not ok";
}

Will get you :

not ok

EDIT : Oh, and like @Peter said (thanks to him!), you might run into trouble if you are trying to unserialize the representation of a boolean false :-(

So, checking that your serialized string is not equal to "b:0;" might be helpful too ; something like this should do the trick, I suppose :

$data = @unserialize($str);
if ($str === 'b:0;' || $data !== false) {
    echo "ok";
} else {
    echo "not ok";
}

testing that special case before trying to unserialize would be an optimization -- but probably not that usefull, if you don't often have a false serialized value.