Re: BUG #18711: Attempting a connection with a database name longer than 63 characters now fails

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(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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