From: Bruce Momjian <bruce@momjian.us>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: adam@labkey.com
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18711: Attempting a connection with a database name longer than 63 characters now fails
Date: Thu, 21 Nov 2024 09:21:16 -0500
Message-ID: <Zz9B3KQGXFCGVPXy@momjian.us> (raw)
In-Reply-To: <Zz7g2s0GSBelWmpg@ip-10-97-1-34.eu-west-3.compute.internal>
References: <3976665.1732057784@sss.pgh.pa.us>
<Zz1bvchIEQPT6eTr@nathan>
<75265.1732076593@sss.pgh.pa.us>
<Zz4BxVqAZnWHFXFB@nathan>
<154104.1732118090@sss.pgh.pa.us>
<Zz4IJ041indld9jv@nathan>
<158506.1732120196@sss.pgh.pa.us>
<Zz4TcYSNWW1_Vj--@nathan>
<Zz5kfP7fIuoY8I45@nathan>
<Zz7g2s0GSBelWmpg@ip-10-97-1-34.eu-west-3.compute.internal>
On Thu, Nov 21, 2024 at 07:27:22AM +0000, Bertrand Drouvot wrote:
> + /*
> + * If the original name is too long and we see two consecutive bytes
> + * with their high bits set at the truncation point, we might have
> + * truncated in the middle of a multibyte character. In multibyte
> + * encodings, every byte of a multibyte character has its high bit
> + * set. So if IS_HIGHBIT_SET is true for both NAMEDATALEN-1 and
> + * NAMEDATALEN-2, we know we're in the middle of a multibyte
> + * character. We need to try truncating one more byte back to find the
> + * start of the next character.
> + */
...
> + /*
> + * If we've hit a byte with high bit clear (an ASCII byte), we
> + * know we can't be in the middle of a multibyte character,
> + * because all bytes of a multibyte character must have their
> + * high bits set. Any following byte must therefore be the
> + * start of a new character, so we can stop looking for
> + * earlier truncation points.
> + */
I don't understand this logic. Why are two bytes important? If we knew
it was UTF8 we could check for non-first bytes always starting with
bits 10, but we can't know that.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
When a patient asks the doctor, "Am I going to die?", he means
"Am I going to die soon?"
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To: pgsql-bugs@postgresql.org
Cc: bruce@momjian.us, bertranddrouvot.pg@gmail.com, nathandbossart@gmail.com, tgl@sss.pgh.pa.us, adam@labkey.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18711: Attempting a connection with a database name longer than 63 characters now fails
In-Reply-To: <Zz9B3KQGXFCGVPXy@momjian.us>
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