code: @Override
    public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method,
        CallOptions callOptions, Channel next) {
      return new CheckedForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
        @Override
        protected void checkedStart(Listener<RespT> responseListener, Metadata headers) {
          updateHeaders(headers);
          delegate().start(responseListener, headers);
        }
      };
    }
docs: {@inheritDoc}