mLastError = rv;
    NS_IMETHOD Write(const char *aBuf, PRUint32 aCount, PRUint32 *aBytesWritten) {        nsresult rv = mSink->Write(aBuf, aCount, aBytesWritten);        if (NS_SUCCEEDED(rv))            mBytesWritten += *aBytesWritten;        return rv;    }