code: def build_request(headers: Headers) -> str:
      
      raw_key = bytes(random.getrandbits(8) for _ in range(16))
      key = base64.b64encode(raw_key).decode()
      headers["Upgrade"] = "websocket"
      headers["Connection"] = "Upgrade"
      headers["Sec-WebSocket-Key"] = key
      headers["Sec-WebSocket-Version"] = "13"
      return key
docs: Build a handshake request to send to the server.
  
      Return the ``key`` which must be passed to :func:`check_response`.