Re: regclass and format('%I')

On 15 March 2015 at 08:44, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> > ​IOW, as long as the output string matches: ^"(?:"{2})*"$ I do not see
> how
> > it is possible ​for format to lay in a value at %I that is any more
> > insecure than the current behavior. If the input string already matches
> > that pattern then it could be output as-is without any additional risk
> and
> > with the positive benefit of making this case work as expected. The
> broken
> > case then exists when someone actually intends to name their identifier
> > <"something"> which then correctly becomes <"""something"""> on output.
>
> But that's exactly the problem: you just broke a case that used to work.
> format('%I') is not supposed to guess at what the user intends; it is
> supposed to produce a string that, after being passed through identifier
> parsing (dequoting or downcasing), will match the input. It is not
> format's business to break that contract just because the input has
> already got some double quotes in it.
>
> An example of where this might be important is if you're trying to
> construct a query with arbitrary column headers in the output. You
> can do
> format('... AS %I ...', ..., column_label, ...)
> and be confident that the label will be exactly what you've got in
> column_label. This proposed change would break that for labels that
> happen to already have double-quotes --- but who are we to say that
> that can't have been what you wanted?
>

I agree with Tom that we shouldn't key off of contents in the string to
determine whether or not to quote. Introducing the behave I describe in an
intuitive way would require some kind of type-specific handling in
format(). I'm not sure what the cost of this is to the project, but David
makes the very reasonable point that imposing the burden of choosing
between `%s` and `%I` opens up the possibility of confusing vulnerabilities.

Kind Regards,
Jason Dusek