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: handler.rs
    path of file: ./repos/freenet-core/crates/core/src/contract
    
    the code of the file until where you have to start completion: use std::collections::BTreeMap;
use std::hash::Hash;
use std::sync::atomic::{AtomicU64, Ordering::SeqCst};
use std::time::Duration;

use freenet_stdlib::client_api::{ClientError, ClientRequest, HostResponse};
use freenet_stdlib::prelude::*;
use futures::{future::BoxFuture, FutureExt};
use serde::{Deserialize, Serialize};
use tokio::sync::mpsc::{self, UnboundedReceiver, UnboundedSender};

use super::executor::{ExecutorHalve, ExecutorToEventLoopChannel};
use super::ExecutorError;
use super::{
    executor::{ContractExecutor, Executor},
    ContractError,
};
use crate::client_events::HostResult;
use crate::message::Transaction;
use crate::{client_events::ClientId, node::PeerCliConfig, wasm_runtime::Runtime, DynError};

pub(crate) struct ClientResponsesReceiver(UnboundedReceiver<(ClientId, HostResult)>);

pub(crate) fn client_responses_channel() -> (ClientResponsesReceiver, ClientResponsesSender) {
    let (tx, rx) = mpsc::unbounded_channel();
    (ClientResponsesReceiver(rx), ClientResponsesSender(tx))
}

impl std::ops::Deref for ClientResponsesReceiver {
    type Target = UnboundedReceiver<(ClientId, HostResult)>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl std::ops::DerefMut for ClientResponsesReceiver {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &m
    
    async fn channel_test() -> Result<(), anyhow::Error> {
        let (send_halve, mut rcv_halve, _) = contract_handler_channel();

        let contract = ContractContainer::Wasm(ContractWasmAPIVersion::V1(WrappedContract::new(
            Arc::new(ContractCode::from(vec![0, 1, 2, 3])),
            Parameters::from(vec![4, 5]),
        )));

        let h = GlobalExecutor::spawn(async move {
            send_halve
                .send_to_handler(ContractHandlerEvent::PutQuery {
                    key: contract.key(),
                    state: vec![6, 7, 8].into(),
                    related_contracts: RelatedContracts::default(),
                    contract: Some(contract),
                })
                .await
        });
        let (id, ev) =
            tokio::time::timeout(Duration::from_millis(100), rcv_halve.recv_from_sender())
                .await??;

        let ContractHandlerEvent::PutQuery { state, .. } = ev else {
            anyhow::bail!("invalid event");
        };
        assert_eq!(state.as_ref(), &[6, 7, 8]);

        tokio::time::timeout(
            Duration::from_millis(100),
            rcv_halve.send_to_sender(
                id,
                ContractHandlerEvent::PutResponse {
                    new_value: Ok(vec![0, 7].into()),
                },
            ),
        )
        .await??;
        let ContractHandlerEvent::PutResponse { new_value } = h.await?? else {
            anyhow::bail!("invalid event!");
        };
        let new_value = new_value.map_err(|e| anyhow::anyhow!(e))?;
        assert_eq!(new_value.as_ref(), &[0, 7]);

        Ok(())
    }