Thread

Re: BUG #19354: JOHAB rejects valid byte sequences

Tom Lane <tgl@sss.pgh.pa.us> — 2025-12-16T15:41:46Z

Robert Haas <robertmhaas@gmail.com> writes:
> ... So I went looking for
> where we got the mapping tables from. UCS_to_JOHAB.pl expects to read
> from a file JOHAB.TXT, of which the latest version seems to be found
> here:
> https://www.unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/KSC/JOHAB.TXT
> And indeed, if I run UCS_to_JOHAB.pl on that JOHAB.txt file, it
> regenerates the current mapping files.

Thanks for doing that research!

> So apparently we've
> got the "right" mappings, but you can only actually the ones that
> match the code's rules for something to be a valid multi-byte
> character, which aren't actually in sync with the mapping table.

Yeah.  Looking at the code in wchar.c, it's clear that it thinks
that JOHAB has the same character-length rules as EUC_KR, which is
something that one might guess based on available documentation that
says it's related to that encoding.  So I can see how we got here.

However, that doesn't mean we can fix pg_johab_mblen() and we're done.
I'm still quite afraid that we'd be introducing security-grade
inconsistencies of interpretation between different PG versions.

> I'm
> left with the conclusions that (1) nobody ever actually tried using
> this encoding for anything real until 3 days ago and (2) we don't have
> any testing infrastructure that verifies that the characters in the
> mapping tables are actually accepted by pg_verifymbstr(). I wonder how
> many other encodings we have that don't actually work?

Indeed.  Anyone want to do some testing?

			regards, tom lane