有个网络库叫gorilla, gorilla有个包叫websocket, websocket包有个方法叫upgrade, 这个upgrade方法的第三个参数怎么用的?

我的目标是, 当与客户端建立连接时, 发送一个cookie到客户端去, 必须在这个wss里, 不能使用普通http方法. 我是这么调用的: ``` var responseHeader http.Header //这里我不知道怎么写了 // responseHeader.Set("Set-Cookie", "SS=Q0=5Lb_nQ; path=/search") var conn, err = upgrader.Upgrade(w, r, responseHeader) ``` 方法的原型是这样的 ``` // Upgrade upgrades the HTTP server connection to the WebSocket protocol. // // The responseHeader is included in the response to the client's upgrade // request. Use the responseHeader to specify cookies (Set-Cookie) and the // application negotiated subprotocol (Sec-WebSocket-Protocol). // // If the upgrade fails, then Upgrade replies to the client with an HTTP error // response. func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header) (*Conn, error) { const badHandshake = "websocket: the client is not using the websocket protocol: " ```