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Re: Issue: Deprecation of the XML2 module 'xml_is_well_formed' function

From: David Fetter <david(at)fetter(dot)org>
To: Mike Berrow <mberrow(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Issue: Deprecation of the XML2 module 'xml_is_well_formed' function
Date: 2010-06-28 16:00:47
Message-ID: 20100628160047.GD1474@fetter.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Jun 28, 2010 at 08:08:53AM -0700, Mike Berrow wrote:
> We need to make extensive use of the 'xml_is_well_formed' function provided
> by the XML2 module.
> 
> Yet the documentation says that the xml2 module will be deprecated since
> "XML syntax checking and XPath queries"
> is covered by the XML-related functionality based on the SQL/XML standard in
> the core server from PostgreSQL 8.3 onwards.
> 
> However, the core function XMLPARSE does not provide equivalent
> functionality since when it detects an invalid XML document,
> it throws an error rather than returning a truth value (which is what we
> need and currently have with the 'xml_is_well_formed' function).
> 
> For example:
> 
> select xml_is_well_formed('<br></br2>');
>  xml_is_well_formed
> --------------------
>  f
> (1 row)
> 
> select XMLPARSE( DOCUMENT '<br></br2>' );
> ERROR:  invalid XML document
> DETAIL:  Entity: line 1: parser error : expected '>'
> <br></br2>
>         ^
> Entity: line 1: parser error : Extra content at the end of the document
> <br></br2>
>         ^
> 
> Is there some way to use the new, core XML functionality to simply
> return a truth value in the way that we need?.

Here's a PL/pgsql wrapper for it.  You could create a similar wrapper
for other commands.

CREATE OR REPLACE FUNCTION xml_is_well_formed(in_putative_xml TEXT)
STRICT /* Leave this line here if you want RETURNS NULL ON NULL INPUT behavior. */
RETURNS BOOLEAN
LANGUAGE plpgsql
AS $$
BEGIN
    PERFORM XMLPARSE(DOCUMENT(in_putative_xml));
    RETURN true;
    EXCEPTION
        WHEN invalid_xml_document THEN
            RETURN false;
END;
$$;

While tracking this down, I didn't see a way to get SQLSTATE or the
corresponding condition name via psql.  Is this an oversight?  A bug,
perhaps?

Cheers,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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