JAXB non-reactive and reactive handle XML namespace prefixes differently

[gnieser]

Hello,

I am experiencing an unexpected difference in the way quarkus-resteasy-reactive-jaxb handles XML namespace prefixes when switching from non-reactive (io.quarkus:quarkus-resteasy-jaxb:2.16.4.Final) to reactive (io.quarkus:quarkus-resteasy-reactive-jaxb:2.16.4.Final).

Reproducer
The code defines (available at https://github.com/gnieser/quarkus-jaxb):

• A XML 'commons' namespace with prefix 'c' for a package org.acme.xml.commons.
  • Which contains an XML type. The NameType with a firstname and a lastname fields.

@javax.xml.bind.annotation.XmlSchema(namespace = "commons.xml.acme.org", elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED, xmlns = {
    @javax.xml.bind.annotation.XmlNs(namespaceURI = "commons.xml.acme.org", prefix = "c")
})
package org.acme.xml.commons;

The code also defines two additional namespaces that are exclusive to each other and never use in the same XML:

• A XML 'acme' namespace with prefix 'acme' for a package org.acme.xml.persons
  • Which contains a list of Persons. It's a list of objects of type NameType.

@javax.xml.bind.annotation.XmlSchema(namespace = "persons.xml.acme.org", elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED, xmlns = {
    @javax.xml.bind.annotation.XmlNs(namespaceURI = "persons.xml.acme.org", prefix = "acme")
})
package org.acme.xml.persons;

• A XML 'acme' namespace with prefix 'acme' for a package org.acme.xml.users
  • Which contains a list of Users. It's a list of objects of type NameType.

@javax.xml.bind.annotation.XmlSchema(namespace = "users.xml.acme.org", elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED, xmlns = {
    @javax.xml.bind.annotation.XmlNs(namespaceURI = "users.xml.acme.org", prefix = "acme")
})
package org.acme.xml.users;

Issue
The troublesome element is that while these two XML namespaces are never used together in the same response they define the same prefix for their respective namespace.
It may look weird, but this is a simplification of what a set of third party XSD schemas would produce through XJC. I have simplified to extreme and removed XJC from the equation.

Using quarkus-resteasy-jaxb
Only the namespaces in use in the Response are added to the XML so everything works fine:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<acme:users xmlns:acme="users.xml.acme.org" xmlns:c="commons.xml.acme.org">
  <acme:user>
    <c:firstName>Rosalind</c:firstName>
    <c:lastName>Franklin</c:lastName>
  </acme:user>
</acme:users>

Using quarkus-resteasy-reactive-jaxb
Even the namespaces not in use are added to the Response. So ensues a conflict in the prefixes, and one of them is set to ns2 and the XML response becomes:

<ns2:users xmlns:acme="persons.xml.acme.org" xmlns:ns2="users.xml.acme.org" xmlns:c="commons.xml.acme.org">
  <ns2:user>
    <c:firstName>Rosalind</c:firstName>
    <c:lastName>Franklin</c:lastName>
  </ns2:user>
</ns2:users>

Question
I understand that part of the issue is the conflicting prefixes, but I feel like something may be done to prevent:

• an unnecessary namespace definition from being added to the XML
• the behavior change between non-reactive to reactive

How can I guide quarkus-resteasy-reactive-jaxb to only add XML namespace definitions for the namespace that are actually part of the Response, and behave more like its non-reactive counterpart?

Note that even with a change to the prefixes (set to 'u' and 'p'), the unused namespace is still added to the XML:

<u:users xmlns:p="persons.xml.acme.org" xmlns:u="users.xml.acme.org" xmlns:c="commons.xml.acme.org">
  <u:user>
    <c:firstName>Rosalind</c:firstName>
    <c:lastName>Franklin</c:lastName>
  </u:user>
</u:users>

Thanks!

[quarkus-bot[bot]]

/cc @Sgitario (jaxb), @gsmet (jaxb)

[Sgitario]

That's a very fair request and makes total sense to me.
The logic that excludes classes is located here. Would you like to contribute with this enhancement? :)

[gnieser]

I would be honored to contribute, if I'm able to. I'm reading the guide, trying to compile a forked main branch (IDE seems pretty unresponsive though).

What would be the ideal solution?

• A quarkus.jaxb.exclude-packages. It excludes all classes within the packages (and sub-packages)
• A wildcard approach of some sort, with Java Regex or Ant-style (such as https://quarkus.io/guides/all-config#quarkus-arc_quarkus.arc.exclude-types or https://quarkus.io/guides/all-config#quarkus-core_quarkus.test.exclude-pattern) ? If so I suppose there may be an utility class I can leverage within the existing code base.

[gnieser]

I went for both. :)
Would this be suitable?

[Sgitario]

These changes sound really good! Many thanks!
Though, I would merge the exclude-classes and exclude-packages into exclude-classes (and use the startWith matching).
Moreover, I would not add pattern matching at least it's essential since we used not to try adding too many superficial configuration options.
But this is something we can discuss in a pull request, so we could incorporate more people's opinions.

[gnieser]

As per your suggestion, I have opened #31940
This is my first PR, hopefully I'm not doing anything wrong with the process.