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: upgrade.rs
    path of file: ./repos/kube/kube-client/src/client
    
    the code of the file until where you have to start completion: use http::{self, Response, StatusCode};
use hyper::Body;
use thiserror::Error;
use tokio_tungstenite::tungstenite as ws;

// Binary subprotocol v4. See `Client::connect`.
pub const WS_PROTOCOL: &str = "v4.channel.k8s.io";

/// Possible errors from upgrading to a WebSocket connection
#[cfg(feature = "ws")]
#[cfg_attr(docsrs, doc(cfg(feature = "ws")))]
#[derive(Debug, Error)]
pub enum UpgradeConnectionError {
 
    
pub fn verify_response(res: &Response<Body>, key: &str) -> Result<(), UpgradeConnectionError> {
    if res.status() != StatusCode::SWITCHING_PROTOCOLS {
        return Err(UpgradeConnectionError::ProtocolSwitch(res.status()));
    }

    let headers = res.headers();
    if !headers
        .get(http::header::UPGRADE)
        .and_then(|h| h.to_str().ok())
        .map(|h| h.eq_ignore_ascii_case("websocket"))
        .unwrap_or(false)
    {
        return Err(UpgradeConnectionError::MissingUpgradeWebSocketHeader);
    }

    if !headers
        .get(http::header::CONNECTION)
        .and_then(|h| h.to_str().ok())
        .map(|h| h.eq_ignore_ascii_case("Upgrade"))
        .unwrap_or(false)
    {
        return Err(UpgradeConnectionError::MissingConnectionUpgradeHeader);
    }

    let accept_key = ws::handshake::derive_accept_key(key.as_ref());
    if !headers
        .get(http::header::SEC_WEBSOCKET_ACCEPT)
        .map(|h| h == &accept_key)
        .unwrap_or(false)
    {
        return Err(UpgradeConnectionError::SecWebSocketAcceptKeyMismatch);
    }

    // Make sure that the server returned the correct subprotocol.
    if !headers
        .get(http::header::SEC_WEBSOCKET_PROTOCOL)
        .map(|h| h == WS_PROTOCOL)
        .unwrap_or(false)
    {
        return Err(UpgradeConnectionError::SecWebSocketProtocolMismatch);
    }

    Ok(())
}