@Override
    public long getSize() throws IOException {
        if (raFile == null) {
            // LAZY empty
            return 0;
        } else {
            return raFile.size();
        }
    }
@param b   to fill
@param off offset
@param len length
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/UncompressedInputStream.java