Re: Make COPY format extendable: Extract COPY TO format implementations

On Fri, Jan 26, 2024 at 6:02 PM Junwang Zhao <zhjwpku@gmail.com> wrote:
>
> On Fri, Jan 26, 2024 at 4:55 PM Sutou Kouhei <kou@clear-code.com> wrote:
> >
> > Hi,
> >
> > In <CAEG8a3KhS6s1XQgDSvc8vFTb4GkhBmS8TxOoVSDPFX+MPExxxQ@mail.gmail.com>
> >   "Re: Make COPY format extendable: Extract COPY TO format implementations" on Fri, 26 Jan 2024 16:41:50 +0800,
> >   Junwang Zhao <zhjwpku@gmail.com> wrote:
> >
> > > CopyToProcessOption()/CopyFromProcessOption() can only handle
> > > single option, and store the options in the opaque field,  but it can not
> > > check the relation of two options, for example, considering json format,
> > > the `header` option can not be handled by these two functions.
> > >
> > > I want to find a way when the user specifies the header option, customer
> > > handler can error out.
> >
> > Ah, you want to use a built-in option (such as "header")
> > value from a custom handler, right? Hmm, it may be better
> > that we call CopyToProcessOption()/CopyFromProcessOption()
> > for all options including built-in options.
> >
> Hmm, still I don't think it can handle all cases, since we don't know
> the sequence of the options, we need all the options been parsed
> before we check the compatibility of the options, or customer
> handlers will need complicated logic to resolve that, which might
> lead to ugly code :(
>

Does it make sense to pass only non-builtin options to the custom
format callback after parsing and evaluating the builtin options? That
is, we parse and evaluate only the builtin options and populate
opts_out first, then pass each rest option to the custom format
handler callback. The callback can refer to the builtin option values.
The callback is expected to return false if the passed option is not
supported. If one of the builtin formats is specified and the rest
options list has at least one option, we raise "option %s not
recognized" error.  IOW it's the core's responsibility to ranse the
"option %s not recognized" error, which is in order to raise a
consistent error message. Also, I think the core should check the
redundant options including bultiin and custom options.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com