if (!mStreamIO)  return NS_ERROR_NOT_AVAILABLE;
if (mClosed)  return NS_ERROR_NOT_AVAILABLE;
nsDiskCacheOutputStream::Write(const char *buf, PRUint32 count, PRUint32 *bytesWritten){    if (!mStreamIO)  return NS_ERROR_NOT_AVAILABLE;    return mStreamIO->Write(buf, count, bytesWritten);}