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: sample5.rs
    path of file: ./repos/dnsguide/examples
    
    the code of the file until where you have to start completion: use std::net::UdpSocket;
use std::net::{Ipv4Addr, Ipv6Addr};

type Error = Box<dyn std::error::Error>;
type Result<T> = std::result::Result<T, Error>;

pub struct BytePacketBuffer {
    pub buf: [u8; 512],
    pub pos: usize,
}

impl BytePacketBuffer {
    pub fn new() -> BytePacketBuffer {
        BytePacketBuffer {
            buf: [0; 512],
            pos: 0,
        }
    }

    fn 
    
    fn get_ns<'a>(&'a self, qname: &'a str) -> impl Iterator<Item = (&'a str, &'a str)> {
        self.authorities
            .iter()
            // In practice, these are always NS records in well formed packages.
            // Convert the NS records to a tuple which has only the data we need
            // to make it easy to work with.
            .filter_map(|record| match record {
                DnsRecord::NS { domain, host, .. } => Some((domain.as_str(), host.as_str())),
                _ => None,
            })
            // Discard servers which aren't authoritative to our query
            .filter(move |(domain, _)| qname.ends_with(*domain))
    }