public static FSDataInputStream getUnderlyingFileLinkInputStream(FSDataInputStream stream) {
    if (stream.getWrappedStream() instanceof FileLinkInputStream) {
      return ((FileLinkInputStream) stream.getWrappedStream()).getUnderlyingInputStream();
    }
    return null;
  }
If the passed FSDataInputStream is backed by a FileLink, returns the underlying InputStream for
the resolved link target. Otherwise, returns null.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/FileLink.java