code: public NettyServerBuilder maxConnectionIdle(long maxConnectionIdle, TimeUnit timeUnit) {
      checkArgument(maxConnectionIdle > 0L, "max connection idle must be positive");
      maxConnectionIdleInNanos = timeUnit.toNanos(maxConnectionIdle);
      if (maxConnectionIdleInNanos >= AS_LARGE_AS_INFINITE) {
        maxConnectionIdleInNanos = MAX_CONNECTION_IDLE_NANOS_DISABLED;
      }
      if (maxConnectionIdleInNanos < MIN_MAX_CONNECTION_IDLE_NANO) {
        maxConnectionIdleInNanos = MIN_MAX_CONNECTION_IDLE_NANO;
      }
      return this;
    }
docs: Sets a custom max connection idle time, connection being idle for longer than which will be
  gracefully terminated. Idleness duration is defined since the most recent time the number of
  outstanding RPCs became zero or the connection establishment. An unreasonably small value might
  be increased. {@code Long.MAX_VALUE} nano seconds or an unreasonably large value will disable
  max connection idle.
  
  @since 1.4.0