PHP: Illegal string-offset

Introduction

I know this has been answered but Illegal string offset ERROR is not the only issue i see here. I belive they are better ways to introduce the flexibility you want and also still make elements save without all that complexity and using of $GLOBALS.

You can start by looking at :

• Are global variables in PHP considered bad practice? If so, why?
• PHP global in functions
• Why global state is the devil, and how to avoid using it

Quick Review

$input = new Input();                          <-- You add to initiate a class 
$server_name = $input->server("SERVER_NAME");
      ^                  ^           ^
      |                  |           |
    variable             |           |
                     Variable        |
                                  Variable 

Am not sure what stops you from just using

    $_SERVER['SERVER_NAME'] = makeSave($_SERVER['SERVER_NAME']);
                                  ^
                                  |- I guess this is what you want to introduce 

Assumption - You want fexibility

Lest assume you want flexibility and also recursion then your class call can be as flexible as :

print_r($input->SERVER_NAME);            |
print_r($input['SERVER_NAME']);          |----- Would Produce same result 
print_r($input->SERVER_NAME());          |

If this is the kind of flexibility you want the i would consider you combine __get , __call and ArrayAccess altogether ...

Lets Imagine

$var = array();
$var["name"] = "<b>" . $_SERVER['SERVER_NAME'] . "</b>";
$var["example"]['xss'] = '<IMG SRC=javascript:alert("XSS")>';
$var["example"]['sql'] = "x' AND email IS NULL; --";
$var["example"]['filter'] = "Let's meet  4:30am Ât the \tcafé\n";

$_SERVER['SERVER_NAME'] = $var ; // Just for example 

Now back to your format

$makeSave = new MakeSafe(MakeSafe::SAVE_XSS | MakeSafe::SAVE_FILTER);
$input = new Input($_SERVER, $makeSafe);

//You can 
print_r($input->SERVER_NAME);

//Or
print_r($input['SERVER_NAME']);

//Or
print_r($input->SERVER_NAME());

They would all output

Array
(
    [0] => <b>localhost</b>
    [1] => Array
        (
            [0] => <IMG SRC=javascript:alert("XSS")>
            [1] => x' AND email IS NULL; --
            [2] => Let's meet  4:30am Ât the 	café

        )

)

See Live DEMO

Your INPUT class modified

class INPUT implements \ArrayAccess {
    private $request = array();
    private $makeSafe;

    public function __construct(array $array, MakeSafe $makeSafe) {
        $this->request = $array;
        $this->makeSave = $makeSafe;
    }

    function __get($offset) {
        return $this->offsetGet($offset);
    }

    function __call($offset, $value) {
        return $this->offsetGet($offset);
    }

    public function setRequest(array $array) {
        $this->request = $array;
    }

    public function offsetSet($offset, $value) {
        trigger_error("Error: SUPER GLOBAL data cannot be modified");
    }

    public function offsetExists($offset) {
        return isset($this->request[$offset]);
    }

    public function offsetUnset($offset) {
        unset($this->request[$offset]);
    }

    public function offsetGet($offset) {
        return isset($this->request[$offset]) ? $this->makeSave->parse($this->request[$offset]) : null;
    }
}

Make your Save method a class

class MakeSafe {
    const SAVE_XSS = 1;
    const SAVE_SQL = 2;
    const SAVE_FILTER_HIGH = 4;
    const SAVE_FILTER_LOW = 8;
    const SAVE_FILTER = 16;

    private $options;

    function __construct($options) {
        $this->options = $options;
    }

    function escape($value) {
        if ($value = @mysql_real_escape_string($value))
            return $value;
        $return = '';
        for($i = 0; $i < strlen($value); ++ $i) {
            $char = $value[$i];
            $ord = ord($char);
            if ($char !== "'" && $char !== "\"" && $char !== '\\' && $ord >= 32 && $ord <= 126)
                $return .= $char;
            else
                $return .= '\\x' . dechex($ord);
        }
        return $return;
    }

    function parse($mixed) {
        if (is_string($mixed)) {
            $this->options & self::SAVE_XSS and $mixed = htmlspecialchars($mixed, ENT_QUOTES, 'UTF-8');
            $this->options & self::SAVE_SQL and $mixed = $this->escape($mixed);
            $this->options & self::SAVE_FILTER_HIGH and $mixed = filter_var($mixed, FILTER_SANITIZE_STRING, FILTER_FLAG_ENCODE_HIGH);
            $this->options & self::SAVE_FILTER_LOW and $mixed = filter_var($mixed, FILTER_SANITIZE_STRING, FILTER_FLAG_ENCODE_LOW);
            $this->options & self::SAVE_FILTER and $mixed = filter_var($mixed, FILTER_SANITIZE_STRING, FILTER_FLAG_ENCODE_HIGH | FILTER_FLAG_ENCODE_LOW);
            return $mixed;
        }

        if (is_array($mixed)) {
            $all = array();
            foreach ( $mixed as $data ) {
                $all[] = $this->parse($data);
            }
            return $all;
        }
        return $mixed;

        return $this->final;
    }
}

Conclusion

Has i said i know this has been answered but i hope this helps someone else not to write code like yours ...

PS : This has also fixed your PHP Warning: Illegal string offset ERROR