Write callback function in cURL

<?php
 // Init curl session
 $ch = curl_init();
 // Set URL
 curl_setopt($ch, CURLOPT_URL, "http://www.php.net/");
 // Set callback function for headers
 curl_setopt($ch, CURLOPT_HEADERFUNCTION, "read_header");
 // Set callback function for body
 curl_setopt($ch, CURLOPT_WRITEFUNCTION, "read_body");
 // Execute curl
 curl_exec($ch);

 // close curl session
 curl_close($ch);

 // Callback function for header
 function read_header($ch, $string) {
  $length = strlen($string);
  echo "Header: $string\n";
  return $length;
 }

 // Callback function for body
 function read_body($ch, $string) {
  curl_close($ch);
  $length = strlen($string);
  echo "Received $length bytes\n";
  return $length;
 }
?>