Decodes JSON string if needed

function-maybe_decode_json.php

<?php

/**
 * Decodes JSON string if needed
 *
 * @uses    json_decode()
 * @author  Martin Adamko   <@martin_adamko>
 * @licence The MIT Licence <http://opensource.org/licenses/MIT>
 * 
 * @param   string  $str        String to decode if needed
 * @param   bool    $assoc      When TRUE, returned objects will be converted into associative arrays
 * @param   int     $depth      User specified recursion depth
 * @param   int     $options    Bitmask of JSON decode options. Currently only JSON_BIGINT_AS_STRING is supported (default is to cast large integers as floats)
 * @returns mixed
 *
 */
function maybe_decode_json($str, $assoc = false, $depth = 512, $options = 0)
{
    if (!is_string($str)) {
        return $str;
    }

    // Trim it
    $str = trim($str);

    // Nothing to do with an empty string
    if (strlen($str)===0) {
        return '';
    }

    // Any "null" string would return NULL (decoding error returns also NULL)
    if ($str==='null') {
        return null;
    }

    // Decode it
    $data = json_decode($str, $assoc, $depth, $options);

    // Decoding error
    if ($data===null) {
        return $str;
    }

    // Success
    return $data;
}