code: public ClientFactoryBuilder idleTimeout(Duration idleTimeout) {
          requireNonNull(idleTimeout, "idleTimeout");
          checkArgument(!idleTimeout.isNegative(), "idleTimeout: %s (expected: >= 0)", idleTimeout);
          return idleTimeoutMillis(idleTimeout.toMillis());
      }
docs: Sets the idle timeout of a socket connection. The connection is closed if there is no request in
  progress for this amount of time.