Re: pg should ignore u+200b zero width space

On 03/11/2020 16:52, Tom Lane wrote:
> Heikki Linnakangas <hlinnaka@iki.fi> writes:
>> On 03/11/2020 15:41, James Cloos wrote:
>>> pg should treat a no break space after whitespace as just more
>>> whitespace.
> 
>> Hmm. I'm not sure if change the behavior is a good idea, but a hint in
>> the error message would be nice. Something like:
> 
> The difficulty with doing anything in this space --- whether it be
> ignoring, throwing an error, or whatever --- is that it makes the
> lexer's behavior encoding-sensitive and potentially locale-sensitive.
> That's problematic for all sorts of reasons.  One of the worst is
> that frontend programs such as psql and ecpg also have SQL lexers,
> and there'd be no way to keep their behavior in precise sync with
> the backend's.  (They might not even be running in the same encoding,
> never mind locale.)  It might even be possible to build security
> holes around that; recall the fun we've had with trying to lock
> down quoting rules in encodings where backslash can be part of a
> multibyte character :-(.
> 
> Perhaps it'd be all right to confine the change in behavior to
> just modifying the error text in cases where we were going to
> throw an error anyway.  But I think this is much harder than
> it sounds to do in a valid, safe way.

Yeah, my thinking was to just add a hint when you're throwing a syntax 
error anyway. Something simple like check if client_encoding is utf8 and 
there is a U+200b in the query string, and add the hint if so. It 
doesn't need to catch all cases, and rare false positives are OK too.

- Heikki