docs: HttpServerExchange terminateResponse() {
          int oldVal = state;
          if (allAreSet(oldVal, FLAG_RESPONSE_TERMINATED)) {
              // idempotent
              return this;
          }
          if(responseChannel != null) {
              responseChannel.responseDone();
          }
          this.state = oldVal | FLAG_RESPONSE_TERMINATED;
          if (anyAreSet(oldVal, FLAG_REQUEST_TERMINATED)) {
              invokeExchangeCompleteListeners();
          }
          return this;
      }