proposal: lob conversion functionality

Hello

I had to enhance my older project, where XML documents are parsed and
created on server side - in PLpgSQL and PLPerl procedures. We would to
use a LO API for client server communication, but we have to
parse/serialize LO on server side.

I found so there are no simple API for working with LO from PL without
access to file system. I had to use a ugly hacks:

CREATE OR REPLACE FUNCTION parser.save_as_lob(bytea)
RETURNS oid AS $$
DECLARE _loid oid; _substr bytea;
BEGIN _loid := lo_creat(-1); FOR i IN 0..length($1)/2048 LOOP   _substr := substring($1 FROM i * 2048 + 1 FOR 2048);
IF_substr <> '' THEN     INSERT INTO pg_largeobject(loid, pageno, data)       VALUES(_loid, i, _substr);   END IF; END
LOOP;
 EXECUTE format('GRANT SELECT ON LARGE OBJECT %s TO ohs', _loid); RETURN _loid;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER STRICT SET search_path = 'pg_catalog';

and

CREATE OR REPLACE FUNCTION fbuilder.attachment_to_xml(attachment oid)
RETURNS xml AS $$
DECLARE b_cum bytea = ''; b bytea;
BEGIN FOR b IN SELECT l.data             FROM pg_largeobject l            WHERE l.loid = attachment_to_xml.attachment
        ORDER BY l.pageno LOOP   b_cum := b_cum || b; END LOOP; IF NOT FOUND THEN   RETURN NULL; ELSE   RETURN
xmlelement(NAME"attachment",                                      encode(b_cum, 'base64')); END IF;
 
END;
$$ LANGUAGE plpgsql STRICT SECURITY DEFINER SET search_path = 'pg_catalog';

These functions can be simplified if we supports some functions like
encode, decode for LO

So my proposal is creating functions:

* lo_encode(loid oid) .. returns bytea
* lo_encode(loid oid, encoding text) .. returns text
* lo_make(loid oid, data bytea)
* lo_make(loid oid, data text, encoding text)

This can simplify all transformation between LO and VARLENA. Known
limit is 1G for varlena, but it is still relative enough high.

Notes. comments?

Regards

Pavel