code: @Override
      public void setObserver(HttpOutputStreamObserver obs) {
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled()) {
              Tr.debug(tc, "obs  ->" + obs);
          }
          this.obs = obs;
      }
docs: Sets an observer for this output stream. The observer will be
  notified when the stream is first written to.