I am trying to validate a simple document in the terminal (with the nu.validator.client.SimpleCommandLineValidator). Passing a schema URL starting with https always fails.

Here is a simple input document:

<?xml version="1.0" encoding="utf-8"?>
<section xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
    <title>Title</title>
    <para>Some text</para>
</section>

And the command:

java -cp vnu.jar nu.validator.client.SimpleCommandLineValidator \
    --schema https://docbook.org/xml/5.1/rng/docbook.rng \
    --xml \
    --stdout \
    --format json \
    file.xml

This results in error: The "--schema" option requires a URL for a schema.

Looking at the source code, it seems that this restriction is hard coded.

Running the Vnu validator as a web service, you actually can specify a schema with https. Is there any particular reason for this restriction? http is discouraged for many years now. And I don't see any workaround at this moment (besides providing some kind of proxy from localhost).

Any help would be greatly appreciated. Thanks!