NS_IMETHOD SetObserver(nsIOutputStreamObserver *aObserver) { return mSink->SetObserver(aObserver);
NS_IMETHOD SetObserver(nsIInputStreamObserver *aObserver) { return mSource->SetObserver(aObserver);
    NS_IMETHOD SetObserver(nsIOutputStreamObserver *aObserver) {        return mSink->SetObserver(aObserver);    }