how to format json with array of json

//Using some loop here
{
  $response[] = array('url' => 'url_value','size' => 'file_size');
}

//without loop hardcoded values:

$response = array ( array('url' => "www.google.com/raj.png",'size' => "12.344KB"),
array('url' => "www.google.com/img2.png",'size' => "10.344KB") );

return json_encode($response);

$out= Array(
 Array('url'=>'www.goog', 'size'=>'12KB'),
 Array('url'=>'moogle', 'size'=>'13KB')
);
echo Json_encode($out);

Not sure how you are formatting your array, but if you define it like this it should do the trick:

$response_array = array(
  'response' => array(
    array(
      'url'  => 'www.google.com/raj.png',
      'size' => '12.344KB',
    ),
    array(
      'url'  => 'www.google.com/raj.png',
      'size' => '12.344KB',
    ),
    array(
      'url'  => 'www.google.com/raj.png',
      'size' => '12.344KB',
    ),
  ),
);

$respose_json = json_encode($response_array);
echo($response_json);

For looping through some results, try something like this:

$response_array = array('response' => array());
foreach($result_set as $result_item) {
  $response_item = array();
  $response_item['url'] = $result_item['url'];
  $response_item['size'] = $result_item['size'];
  $response_array['response'][] = $response_item;
}

$respose_json = json_encode($response_array);
echo($response_json);

With the $result_set above being whatever data you've pulled from a DB, server, etc.