You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: subscribe.rs
    path of file: ./repos/rumqtt/rumqttd/src/protocol/v5
    
    the code of the file until where you have to start completion: use super::*;
use bytes::{Buf, Bytes};
use core::fmt;

pub fn len(subscribe: &Subscribe, properties: &Option<SubscribeProperties>) -> usize {
    let mut len = 2 + subscribe.filters.iter().fold(0, |s, t| s + filter::len(t));

    if let Some(p) = properties {
        let properties_
    
    pub fn write(filter: &Filter, buffer: &mut BytesMut) {
        let mut options = 0;
        options |= filter.qos as u8;

        if filter.nolocal {
            options |= 0b0000_0100;
        }

        if filter.preserve_retain {
            options |= 0b0000_1000;
        }

        options |= match filter.retain_forward_rule {
            RetainForwardRule::OnEverySubscribe => 0b0000_0000,
            RetainForwardRule::OnNewSubscribe => 0b0001_0000,
            RetainForwardRule::Never => 0b0010_0000,
        };

        write_mqtt_string(buffer, filter.path.as_str());
        buffer.put_u8(options);
    }