Re: JSON and unicode surrogate pairs

On Mon, Jun 10, 2013 at 11:20:13AM -0400, Andrew Dunstan wrote:
>
> On 06/10/2013 10:18 AM, Tom Lane wrote:
>> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>>> After thinking about this some more I have come to the conclusion that
>>> we should only do any de-escaping of \uxxxx sequences, whether or not
>>> they are for BMP characters, when the server encoding is utf8. For any
>>> other encoding, which is already a violation of the JSON standard
>>> anyway, and should be avoided if you're dealing with JSON, we should
>>> just pass them through even in text output. This will be a simple and
>>> very localized fix.
>> Hmm. I'm not sure that users will like this definition --- it will seem
>> pretty arbitrary to them that conversion of \u sequences happens in some
>> databases and not others.

Yep. Suppose you have a LATIN1 database. Changing it to a UTF8 database
where everyone uses client_encoding = LATIN1 should not change the semantics
of successful SQL statements. Some statements that fail with one database
encoding will succeed in the other, but a user should not witness a changed
non-error result. (Except functions like decode() that explicitly expose byte
representations.) Having "SELECT '["\u00e4"]'::json ->> 0" emit 'ä' in the
UTF8 database and '\u00e4' in the LATIN1 database would move PostgreSQL in the
wrong direction relative to that ideal.

> Then what should we do when there is no matching codepoint in the
> database encoding? First we'll have to delay the evaluation so it's not
> done over-eagerly, and then we'll have to try the conversion and throw
> an error if it doesn't work. The second part is what's happening now,
> but the delayed evaluation is not.

+1 for doing it that way.

Thanks,
nm

--
Noah Misch
EnterpriseDB http://www.enterprisedb.com