if (!mStreamIO)  return NS_ERROR_NOT_AVAILABLE;
if (mClosed)  return NS_ERROR_NOT_AVAILABLE;
nsDiskCacheInputStream::Available(PRUint32 * bytesAvailable){    if (!mStreamIO)  return NS_ERROR_NOT_AVAILABLE;    if (mStreamEnd < mPos)  return NS_ERROR_UNEXPECTED;        *bytesAvailable = mStreamEnd - mPos;    return NS_OK;}