Unable to assign attribute to nested node if already assigned higher-up

[mcab]

Describe the bug
I'm trying to assign a particular attribute (xmlns:ds) with the same key, value pairing, which has also been previously defined on a higher-level element. It applies correctly for the node closest to the root, but not for the lower nodes nodes.

To Reproduce

const { create } = require('xmlbuilder2');

function convertor(cert) {
    return {
        '@use': 'signing',
        'foobar': {
            '@xmlns:ds': 'att',
            'foobaz': {
                'foobarbaz': cert,
            }
        },
    }
}

function create_metadata(certs) {
    let final_certs = []
    for (cert in certs) {
        final_certs.push(convertor(certs[cert]))
    }

    xml = create({
        'foo': {
            '@xmlns:ds': 'att',
            'bar': {
                'baz': final_certs
            }
        }
    }).end({ prettyPrint: true })
    console.log(xml);
}

create_metadata(['cert1', 'cert2'])

Expected behavior
I expect each foobar to have @xmlns:ds as an attribute, but they do not.

The current output (2.4.0) looks like:

<?xml version="1.0"?>
<foo xmlns:ds="att">
  <bar>
    <baz use="signing">
      <foobar>
        <foobaz>
          <foobarbaz>cert1</foobarbaz>
        </foobaz>
      </foobar>
    </baz>
    <baz use="signing">
      <foobar>
        <foobaz>
          <foobarbaz>cert2</foobarbaz>
        </foobaz>
      </foobar>
    </baz>
  </bar>
</foo>

What I'm expecting:

<?xml version="1.0"?>
<foo xmlns:ds="att">
  <bar>
    <baz use="signing">
      <foobar xmlns:ds="att">
        <foobaz>
          <foobarbaz>cert1</foobarbaz>
        </foobaz>
      </foobar>
    </baz>
    <baz use="signing">
      <foobar xmlns:ds="att">
        <foobaz>
          <foobarbaz>cert2</foobarbaz>
        </foobaz>
      </foobar>
    </baz>
  </bar>
</foo>

Before passing to create(), the structure hints that the attribute should be set:

[
  {
    '@use': 'signing',
    foobar: {
      '@xmlns:ds': 'att',
      foobaz: [Object]
    }
  },
  {
    '@use': 'signing',
    foobar: {
      '@xmlns:ds': 'att',
      foobaz: [Object]
    }
  }
]

Version:

• node.js: [12.4.1]
• xmlbuilder2 [2.4.0]

[mcab]

Ah, it seems to be #20, but in reverse. 😅

Ideally, xmlns(:ds) is set on the child nodes too.

[oozcitak]

This is not a bug but a feature of the serializer.

xmlbuilder2 keeps a record of namespaces while serializing the document. It can add, modify and even remove namespace prefixes. But it preserves the meaning of the document.

In your case, the parent foo element node declares the namespace att with the prefix ds. So, foo and all of its child elements have access to this namespace. Redeclaring the namespace under the child foobar element node is superfluous as it is already declared by foo. If you would canonicalize both documents you would see they are identical.