public int length() {
        int length = 1 + 2 + deviceToken.length + 2 + payload.length;
        final int marshalledLength = marshall().length;
        assert marshalledLength == length;
        return length;
    }
Returns the length of the message in bytes as it is encoded on the wire.

Apple require the message to be of length 255 bytes or less.

@return length of encoded message in bytes
src/main/java/com/notnoop/apns/SimpleApnsNotification.java