Date: Wed, 20 Nov 2024 09:35:33 -0600
From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: adam@labkey.com, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>,
	pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18711: Attempting a connection with a database name longer
 than 63 characters now fails
Message-ID: <Zz4BxVqAZnWHFXFB@nathan>
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On Tue, Nov 19, 2024 at 11:23:13PM -0500, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> I'm admittedly not an expert in the multi-byte code, but since there are
>> encodings like LATIN1 that use a byte per character, don't we need to do
>> multiple lookups any time the NAMEDATALEN-1'th byte is non-ASCII?
> 
> I don't think so, but maybe I'm missing something.  An important
> property of backend-legal encodings is that all bytes of a multibyte
> character have their high bits set.  Thus if the NAMEDATALEN-2'th
> byte does not have that, it is not part of a multibyte character.
> That's also the reason we can stop if we reach a high-bit-clear
> byte while backing up to earlier bytes.

That's good to know.  If we can assume that 1) all bytes of a multibyte
character have the high bit set and 2) all multibyte characters actually
require multiple bytes, then there are just a handful of cases that require
multiple lookups, and we can restrict even those to some extent, too.

-- 
nathan