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: mod.rs
    path of file: ./repos/aquatic/crates/udp/src/workers/socket/uring
    
    the code of the file until where you have to start completion: mod buf_ring;
mod recv_helper;
mod send_buffers;

use std::cell::RefCell;
use std::collections::VecDeque;
use std::net::UdpSocket;
use std::ops::DerefMut;
use std::os::fd::AsRawFd;
use std::sync::atomic::Ordering;

use anyhow::Context;
use aquatic_common::access_list::AccessListCache;
use crossbeam_channel::Sender;
use io_uring::opcode::Timeout;
use io_uring::types::{Fixed, Timespec};
use io_uring::{IoUring, Probe};

use aquatic_common::{
    access_list::create_access_list_cache, privileges::PrivilegeDropper, CanonicalSocketAddr,
    ValidUntil,
};
use aquatic_udp_protocol::*;
use rand::rngs::SmallRng;
use rand::SeedableRng;

use crate::common::*;
use crate::config::Config;

use self::buf_ring::BufRing;
use self::recv_helper::RecvHelper;
use self::send_buffers::{ResponseType, SendBuffers};

use super::validator::ConnectionValidator;
use super::{create_socket, EXTRA_PACKET_SIZE_IPV4, EXTRA_PACKET_SIZE_IPV6};

/// Size of each request buffer
///
/// Needs to fit recvmsg metadata in addition to the payload.
///
/// The payload of a scrape request with 20 info hashes fits in 256 bytes.
const REQUEST_BUF_LEN: usize = 512;

/// Size of each response buffer
///
/// Enough for:
/// - IPv6 announce response with 112 peers
/// - scrape response for 170 info hashes
const RESPONSE_BUF_LEN: usize = 2048;

const USER_DATA_RECV: u64 = u64::MAX;
const USER_DATA_PULSE_TIMEOUT: u64 = u64::MAX - 1;

const SOCKET_IDENTIFIER: Fixed = Fixed(0);

thread_local! {
    /// Store IoUring instance here so that it can be accessed in BufRing::drop
    pub static CURRENT_RING: CurrentRing = CurrentRing(RefCell::new(None));
}

pub struct CurrentRing(RefCell<Option<IoUring>>);

i
    
    fn handle_cqe(&mut self, cqe: io_uring::cqueue::Entry) {
        match cqe.user_data() {
            USER_DATA_RECV => {
                if let Some((addr, response)) = self.handle_recv_cqe(&cqe) {
                    self.local_responses.push_back((addr, response));
                }

                if !io_uring::cqueue::more(cqe.flags()) {
                    self.resubmittable_sqe_buf.push(self.recv_sqe.clone());
                }
            }
            USER_DATA_PULSE_TIMEOUT => {
                self.validator.update_elapsed();

                self.peer_valid_until = ValidUntil::new(
                    self.shared_state.server_start_instant,
                    self.config.cleaning.max_peer_age,
                );

                self.resubmittable_sqe_buf
                    .push(self.pulse_timeout_sqe.clone());
            }
            send_buffer_index => {
                let result = cqe.result();

                if result < 0 {
                    ::log::error!(
                        "Couldn't send response: {:#}",
                        ::std::io::Error::from_raw_os_error(-result)
                    );
                } else if self.config.statistics.active() {
                    let send_buffer_index = send_buffer_index as usize;

                    let (response_type, receiver_is_ipv4) =
                        self.send_buffers.response_type_and_ipv4(send_buffer_index);

                    let (statistics, extra_bytes) = if receiver_is_ipv4 {
                        (&self.statistics.ipv4, EXTRA_PACKET_SIZE_IPV4)
                    } else {
                        (&self.statistics.ipv6, EXTRA_PACKET_SIZE_IPV6)
                    };

                    statistics
                        .bytes_sent
                        .fetch_add(result as usize + extra_bytes, Ordering::Relaxed);

                    let response_counter = match response_type {
                        ResponseType::Connect => &statistics.responses_connect,
                        ResponseType::Announce => &statistics.responses_announce,
                        ResponseType::Scrape => &statistics.responses_scrape,
                        ResponseType::Error => &statistics.responses_error,
                    };

                    response_counter.fetch_add(1, Ordering::Relaxed);
                }

                // Safety: OK because cqe using buffer has been returned and
                // contents will no longer be accessed by kernel
                unsafe {
                    self.send_buffers
                        .mark_buffer_as_free(send_buffer_index as usize);
                }
            }
        }
    }