RFR: 4890732: GZIPOutputStream doesn't support, in fact thwarts, use of optional GZIP fields [v3]

[Lin Zang]

On Mon, 22 Mar 2021 20:06:33 GMT, Lance Andersen <lancea at openjdk.org> wrote:

>> Lin Zang has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - update copyright
>>  - reuse arguments constructor for non-argument one.
>
> src/java.base/share/classes/java/util/zip/GZIPOutputStream.java line 320:
> 
>> 318:              *     +---+---+=================================+
>> 319:              */
>> 320:             int xlen = extraFieldBytes.length;
> 
> On a quick look at the RFC,  I noticed the following:
> 
> ------------------------
> 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
>          <gzip at prep.ai.mit.edu> 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:
> 
> 
> ---------------
> 
> This does not seem to be accounted for or is it?

Yes, This should be considered, I will add logic in the code. 
However, I did some search and found that there is only one subfield defined, which is mentioned in RFC:
SI1         SI2         Data
----------  ----------  ----
0x41 ('A')  0x70 ('P')  Apollo file type information

or SI2 = 0  is reserved.

It seems this subfield definition is no longe maintained. (FYI, https://stackoverflow.com/questions/65188890/what-gzip-extra-field-subfields-exist) 

So is it ok if make it only accept these two cases for FLG.FEXTRA and reject others?

-------------

PR: https://git.openjdk.java.net/jdk/pull/3072