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From: Kirill Reshke <reshkekirill@gmail.com>
Date: Sun, 7 Dec 2025 12:34:22 +0500
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 <CALdSSPjxLU+zhWx+CgwN+VHoHTso33trY6mse1A6Jks7hWAdrA@mail.gmail.com>
Subject: Re: WIP - xmlvalidate implementation from TODO list
To: Marcos Magueta <maguetamarcos@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
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On Sun, 7 Dec 2025 at 04:38, Marcos Magueta <maguetamarcos@gmail.com> wrote=
:
>
> Hello!
>
> I am likely one of the few people still using XML, but I noticed XSD sche=
ma validation is still a TODO on postgresql, which I have some personal use=
 cases for.
>
> In this patch I attempt to implement XMLVALIDATE with the already in use =
libxml following a version I got my hands on of the SQL/XML standard of 201=
6.
>
> In short, I had to add the ACCORDING word to comply with it and completel=
y ignored the version that was already in the src that fetches arbitrary sc=
hemas (it refers to validations of dtds, which is another more troublesome =
TODO).
>
> I had problems running the regression tests on my machine, so I could onl=
y test the feature by spawning a modified instance of postgresql and issuin=
g queries through psql, therefore I am marking it as WIP. If anyone can ass=
ert the tests pass, I would be glad.
>
> Also, this is my first patch, so I might have not followed standard pract=
ices as best as I could, so please pay particular attention to that on revi=
ew.
>
> Cheers,
> Marcos Magueta.

HI!

1)
> + // Default case since nothing got returned
> + // out of the normal path for validation calls to libxml

PostgreSQL uses /**/ comments style.

2)
XML regression test suite fails, see attached. By the way, what are
your issues with running `make check` ?

3)
By the way, in [0] we have this

`
The function in PostgreSQL produces an =E2=80=9Cunimplemented=E2=80=9D erro=
r, because
PostgreSQL does not have any implementation of the mechanism assumed
in the standard for registering schemas in advance, which is necessary
to address the security implications of a function that could refer to
schemas from arbitrary locations.
`

How does your patch resolve this? I did not find any change in this area

4)
Also I want to mention that without a doc, the patch is not in a
commitable shape.

5) I am a bit surprised by this grammar rule:

>  XMLVALIDATE '(' document_or_content a_expr ACCORDING TO XMLSCHEMA a_expr=
 ')'

this allow a wide class of expressions accepted by parser, like

`SELECT xmlvalidate(DOCUMENT  (select oid from pg_class) ACCORDING TO
XMLSCHEMA (select 32)) AS is_valid FROM xml_validation_test;`

Is this expected? a_expr is way more than string constants and column
references..  If yes, the regression test that you added, does not
test this..


p.s. I failed to find in google SQL/XML standard of 2016. So, I cannot
double-check if this feature is compliant with it...

[0] https://wiki.postgresql.org/wiki/PostgreSQL_vs_SQL/XML_Standards

--=20
Best regards,
Kirill Reshke

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