Xml_write to a zipfile

General
1

I want to write an xml to a zip file, this is what I tried:

zip_open("new.zip", write, Z, []), 
zipper_open_new_file_in_zip(Z, "imsmanifest.xml", S, []), 
xml_write(S, element(elem, [], []), []), 
close(S), 
close(Z).

An error is raised on the encoding:

Call: (15) sgml_write:xml_write(<stream>(000002284659f7e0), element(elem, [], []), []) ? skip
ERROR: Domain error: `xml_encoding' expected, found `octet'

Can I specify this somewhere?

2

xml_write/3 wants a text stream. This works fine.

t :-
    setup_call_cleanup(
        zip_open("new.zip", write, Z, []),
        setup_call_cleanup(
            zipper_open_new_file_in_zip(Z, "imsmanifest.xml", S, []),
            ( set_stream(S, encoding(utf8)),
              xml_write(S, element(elem, [], []), [])
            ),
            close(S)),
        zip_close(Z)).

You may like to use library(archive) though. library(zip) is a small public layer with a much more limited interface than library(archive) that exposes the built-in zip functionality (SWI-Prolog saved states are zip files).