存在哪些 GZip 额外字段子字段？

Question

RFC 1952（GZIP 文件格式规范）section 2.3.1.1 读取：

2.3.1.1. Extra field

   If the FLG.FEXTRA bit is set, an "extra field" is present in
   the header, with total length XLEN bytes.  It consists of a
   series of subfields, each of the form:

      +---+---+---+---+==================================+
      |SI1|SI2|  LEN  |... LEN bytes of subfield data ...|
      +---+---+---+---+==================================+

   SI1 and SI2 provide a subfield ID, typically two ASCII letters
   with some mnemonic value.  Jean-Loup Gailly
   <email@hidden> is maintaining a registry of subfield
   IDs; please send him any subfield ID you wish to use.  Subfield
   IDs with SI2 = 0 are reserved for future use.  The following
   IDs are currently defined:

      SI1         SI2         Data
      ----------  ----------  ----
      0x41 ('A')  0x70 ('P')  Apollo file type information

   LEN gives the length of the subfield data, excluding the 4
   initial bytes.

除了 RFC 中给出的 AP 之外，是否存在任何子字段类型？网络搜索找不到列表； GZip 的维基百科页面、GNU 主页、gzip 源代码或 Stack Overflow 上也没有任何提及。

Answer 1

据我所知，没有维护这样的注册表。 Jean-loup 不再适用于 gzip。

Answer 2

这里还有一个正在使用的子字段：

为在生物信息学中使用而开发的 BGZF 格式（符合 gzip 格式）使用子字段类型“BC”来指示当前块的大小。这用于使并行解压缩变得容易。

来自 http://samtools.github.io/hts-specs/SAMv1.pdf 的规范：

Each BGZF block contains a standard gzip file header with the following standard-compliant extensions:

The F.EXTRA bit in the header is set to indicate that extra fields are present.

The extra field used by BGZF uses the two subfield ID values 66 and 67 (ASCII ‘BC’).

The length of the BGZF extra field payload (field LEN in the gzip specification) is 2 (two bytes of payload).

The payload of the BGZF extra field is a 16-bit unsigned integer in little endian format. This integer gives the size of the containing BGZF block minus one.

存在哪些 GZip 额外字段子字段？

What GZip extra field subfields exist?

gzip

file-format