Function to create an Apple APNS command 3 push payload

APNS command 3

// token: An apple token
// message: The message to push
// id: The push message identifier
// expiry: Push expiration date
// priority: Priority (5 or 10)

public function createPayload($token, $message, $identifier, $expiry, $priority)
{
  $body = json_encode(array('aps' => array('alert' => $message)), JSON_UNESCAPED_UNICODE);
  $packedToken = pack("H*", $token);
  $tokenData = chr(1) . pack('n',strlen($packedToken)) . $packedToken;
  $payloadBody = chr(2) . pack('n',strlen($body)) . $body;
  $packedIdentifier = pack("N", $identifier);
  $identifier = chr(3) . pack('n',strlen($packedIdentifier)) . $packedIdentifier;
  $packedExpiry = pack("N", $expiry);
  $expiry = chr(4) . pack('n',strlen($packedExpiry)) . $packedExpiry;
  $packedPriority = chr($priority);
  $priority = chr(5) . pack('n',strlen($packedPriority)) . $packedPriority;
  $payload = $tokenData.$payloadBody.$identifier.$expiry.$priority;
  
  return chr(2) . pack("N", strlen($payload)) . $payload;
}