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

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.

Answer 2

From WordPress core functions:

<?php
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 3

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 4

If the $string is a serialized false value, ie $string = 'b:0;' SoN9ne's function returns false, it's wrong

so the function would be

/**
 * Check if a string is serialized
 *
 * @param string $string
 *
 * @return bool
 */
function is_serialized_string($string)
{
    return ($string == 'b:0;' || @unserialize($string) !== false);
}

Answer 5

Despite Pascal MARTIN's excellent answer, I was curious if you could approach this another way, so I did this just as a mental exercise

<?php

ini_set( 'display_errors', 1 );
ini_set( 'track_errors', 1 );
error_reporting( E_ALL );

$valueToUnserialize = serialize( false );
//$valueToUnserialize = "a"; # uncomment this for another test

$unserialized = @unserialize( $valueToUnserialize );

if ( FALSE === $unserialized && isset( $php_errormsg ) && strpos( $php_errormsg, 'unserialize' ) !== FALSE )
{
  echo 'Value could not be unserialized<br>';
  echo $valueToUnserialize;
} else {
  echo 'Value was unserialized!<br>';
  var_dump( $unserialized );
}

And it actually works. The only caveat is that it will likely break if you have a registered error handler because of how $php_errormsg works.

Answer 6

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

Correctly handles the case of serialize(false). :)

Answer 7

build in to a function

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

Answer 8

There is WordPress solution: (detail is here)

    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 9

/**
 * some people will look down on this little puppy
 */
function isSerialized($s){
if(
    stristr($s, '{' ) != false &&
    stristr($s, '}' ) != false &&
    stristr($s, ';' ) != false &&
    stristr($s, ':' ) != false
    ){
    return true;
}else{
    return false;
}

}

Answer 10

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 11

I would just try to unserialize it. This is how i would solve it

public static function is_serialized($string)
{
    try {
        unserialize($string);
    } catch (\Exception $e) {
        return false;
    }

    return true;
}

Or more like a helper function

function is_serialized($string) {
  try {
        unserialize($string);
    } catch (\Exception $e) {
        return false;
    }

    return true;
}

Answer 12

• The mentionned WordPress function does not really detect arrays (a:1:{42} is considered to be serialized) and falsely returns true on escaped strings like a:1:{s:3:\"foo\";s:3:\"bar\";} (although unserialize does not work)

• If you use the @unserialize way on the other side WordPress for example adds an ugly margin at the top of the backend when using define('WP_DEBUG', true);

• A working solution that solves both problems and circumvents the stfu-operator is:

function __is_serialized($var)
{
    if (!is_string($var) || $var == '') {
        return false;
    }
    set_error_handler(function ($errno, $errstr) {});
    $unserialized = unserialize($var);
    restore_error_handler();
    if ($var !== 'b:0;' && $unserialized === false) {
        return false;
    }
    return true;
}

Answer 13

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;

}