static int blobVarDecodedLength(int len) {
    return ((len - 1) // 1-byte header
      * 7) // 7-bits of payload per encoded byte
      / 8; // 8-bits per byte
  }
Calculate the expected BlobVar decoded length based on encoded length.
hbase-common/src/main/java/org/apache/hadoop/hbase/util/OrderedBytes.java