code: func Hijack(stream controlapi.Control_SessionServer) (net.Conn, <-chan struct{}, map[string][]string) {
  	md, _ := metadata.FromIncomingContext(stream.Context())
  	c, closeCh := streamToConn(stream)
  	return c, closeCh, md
  }
docs: // Hijack hijacks session to a connection.