Bump `jackson-bom` to version 2.19.x

[ppkarwasz]

Description

Due to changes in Jackson 2.19.x, the XmlLayout tests fail. The tests are not very verbose about the nature of the failure: it might be a breaking change in the format or just a problem in the test. Anyway the upgrade can not be done manually.

[rschmitt]

Judging from testAdditionalFields(), it looks like a namespacing issue. The assertions are:

assertTrue(str, str.contains("<KEY1>VALUE1</KEY1>"));
assertTrue(str, str.contains("<KEY2>" + new JavaLookup().getRuntime() + "</KEY2>"));

But Jackson 2.19.0 is emitting:

  <Event xmlns="http://logging.apache.org/log4j/2.0/events" timeMillis="1" thread="MyThreadName" level="DEBUG" loggerName="a.B" endOfBatch="false" loggerFqcn="f.q.c.n" threadId="1" threadPriority="5">
    <!-- lots of stuff -->
    <KEY1 xmlns="">VALUE1</KEY1>
    <KEY2 xmlns="">OpenJDK Runtime Environment (build 17.0.15+6-LTS) from Amazon.com Inc.</KEY2>
  </Event>

[ppkarwasz]

@rschmitt,

Thanks for investigating and diagnosing this.

While I can't say definitively whether this constitutes a breaking change for all users, I’m inclined to treat this as a non-breaking difference and adjust the test to match the layout's actual output.

A few points supporting this:

• This discrepancy is only likely to affect users who explicitly validate the output of the XML layout.
• The current Log4j-events.xsd schema is outdated and no longer validates the layout output. Even if it did, the schema doesn’t permit additional fields, meaning users relying on strict validation would already need to maintain their own custom schemas.

@garydgregory, I would like to hear your opinion on this matter.

[vy]

Upgrading to Jackson 2.19.x causes all (non-root?) elements to contain an extra (empty?) xmlns attribute. @rschmitt, have I understood correctly? Would you mind assessing the impact of this upgrade in the overall XmlLayout, please? That is, are additional fields the only affected component?

[ppkarwasz]

That is, are additional fields the only affected component?

Yes, the additional fields are the only XML elements without an associated namespace. All other elements in the LogEventMixIn are explicitly assigned to the http://logging.apache.org/log4j/2.0/events namespace.

The issue arises during the serialization of LogEventWithAdditionalFields:

logging-log4j2/log4j-core/src/main/java/org/apache/logging/log4j/core/layout/AbstractJacksonLayout.java

Lines 386 to 408 in 138404a

	@JsonRootName(XmlConstants.ELT_EVENT)
	@JacksonXmlRootElement(namespace = XmlConstants.XML_NAMESPACE, localName = XmlConstants.ELT_EVENT)
	public static class LogEventWithAdditionalFields {
	private final Object logEvent;
	private final Map<String, String> additionalFields;
	public LogEventWithAdditionalFields(final Object logEvent, final Map<String, String> additionalFields) {
	this.logEvent = logEvent;
	this.additionalFields = additionalFields;
	}
	@JsonUnwrapped
	public Object getLogEvent() {
	return logEvent;
	}
	@JsonAnyGetter
	@SuppressWarnings("unused")
	public Map<String, String> getAdditionalFields() {
	return additionalFields;
	}
	}

It's possible that simply annotating the additional fields with @JacksonXmlProperty(namespace = "http://logging.apache.org/log4j/2.0/events") would resolve the namespace issue. However, I believe the problem is broader: the current Log4j-events.xsd schema does not validate any log event, even those without additional fields.

If there are users who still rely on XML output and require schema validation, we should consider providing a way for them to extend our schema to support custom fields. Otherwise, we should just adapt the test to use XMLUnit and go on.

[vy]

@ppkarwasz, thanks so much for the elaborate explanation. Then I am inclined to just fix the tests and proceed with the upgrade. @rschmitt, would you like to submit a PR to fix the tests?