Moxy 2.7.x - Serialising Object containing DOM Element with xmlns="" to XMLStreamWriter can emit duplicate xmlns tag, resulting in corrupt XML

[petergeneric]

(I originally reported this on Bugzilla as 576541 last year, but it has since received an automated reply that sounds like Bugzilla is no longer in use?)

I believe there is a long-standing bug in MOXy whereby if the Object being serialised contains a dom Element, and that Element (or any of its children) have an empty default namespace tag defined, serialisation will emit a duplicate xmlns="" tag when outputting to an XMLStreamWriter, resulting in invalid XML which cannot be parsed.

I have built a test case that demonstrates the simplest manifestation of the bug (and also my workaround, which is an XMLStreamWriter that detects and suppresses duplicate xmlns="" events).

https://github.com/petergeneric/moxybug-2021-10

Just run mvn test to demo the bug. The MOXy version is a variable, moxy.version. I've tested this against a range of versions between 2.5.0 and 2.7.11, and on Java 8 and 17.

My workaround works where the application is in control of the XMLStreamWriter, however there are other cases where it is not (e.g. in a JAX-RS context with, say, resteasy's fastinfoset provider, where the client/server generates invalid Fast Infoset XML where it would generate valid application/xml)

When tracing the calls to XMLStreamWriter.setDefaultNamespace as part of my test case when using moxy 2.7.11, the first call is from:

	at bugdemo.DuplicateNSFilteringXMLStreamWriter.writeDefaultNamespace(DuplicateNSFilteringXMLStreamWriter.java:148)
	at org.eclipse.persistence.internal.oxm.record.DomToXMLStreamWriter.writeElement(DomToXMLStreamWriter.java:111)
	at org.eclipse.persistence.internal.oxm.record.DomToXMLStreamWriter.writeToStream(DomToXMLStreamWriter.java:43)
	at org.eclipse.persistence.oxm.record.XMLStreamWriterRecord.node(XMLStreamWriterRecord.java:215)
	at org.eclipse.persistence.oxm.record.MarshalRecord.node(MarshalRecord.java:456)
	at org.eclipse.persistence.internal.oxm.XMLAnyObjectMappingNodeValue.marshalSimpleValue(XMLAnyObjectMappingNodeValue.java:280)
	at org.eclipse.persistence.internal.oxm.XMLAnyObjectMappingNodeValue.marshalSingleValue(XMLAnyObjectMappingNodeValue.java:104)
	at org.eclipse.persistence.internal.oxm.XMLAnyObjectMappingNodeValue.marshal(XMLAnyObjectMappingNodeValue.java:67)
	at org.eclipse.persistence.internal.oxm.NodeValue.marshal(NodeValue.java:104)
	at org.eclipse.persistence.internal.oxm.record.ObjectMarshalContext.marshal(ObjectMarshalContext.java:61)

And the second call (which is what results in the XML being invalid) is:

	at bugdemo.DuplicateNSFilteringXMLStreamWriter.writeDefaultNamespace(DuplicateNSFilteringXMLStreamWriter.java:148)
	at org.eclipse.persistence.internal.oxm.record.DomToXMLStreamWriter.writeElement(DomToXMLStreamWriter.java:135)
	at org.eclipse.persistence.internal.oxm.record.DomToXMLStreamWriter.writeToStream(DomToXMLStreamWriter.java:43)
	at org.eclipse.persistence.oxm.record.XMLStreamWriterRecord.node(XMLStreamWriterRecord.java:215)
	at org.eclipse.persistence.oxm.record.MarshalRecord.node(MarshalRecord.java:456)
	at org.eclipse.persistence.internal.oxm.XMLAnyObjectMappingNodeValue.marshalSimpleValue(XMLAnyObjectMappingNodeValue.java:280)
	at org.eclipse.persistence.internal.oxm.XMLAnyObjectMappingNodeValue.marshalSingleValue(XMLAnyObjectMappingNodeValue.java:104)
	at org.eclipse.persistence.internal.oxm.XMLAnyObjectMappingNodeValue.marshal(XMLAnyObjectMappingNodeValue.java:67)
	at org.eclipse.persistence.internal.oxm.NodeValue.marshal(NodeValue.java:104)
	at org.eclipse.persistence.internal.oxm.record.ObjectMarshalContext.marshal(ObjectMarshalContext.java:61)

[petergeneric]

N.B. this issue no longer appears in 4.0.0-RC2, but we have projects that cannot be migrated from javax to jakarta so we can't avail of this new major version currently.