private void readHeaderMarker() throws IOException {
        fillFromRawStreamBuffer(headerMarkerRawBuffer);
        if (!checkEqualBuffer(BlockGZIPConstants.BLOCK_GZIP_V1_IDENTIFIER, headerMarkerRawBuffer)) {
            invalid("Does not look like a Block GZIP V1 Stream");
        }
    }
Read a header marker from the stream.
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/BlockGZIPInput.java