CAMEL-23516: camel-xmpp - Use dedicated HeaderFilterStrategy aligned with sibling components

[oscerd]

Summary

camel-xmpp defaulted its headerFilterStrategy to a bare
new DefaultHeaderFilterStrategy() with no configuration — at
XmppEndpoint.java:106 (the production path, passed into XmppBinding)
and in the XmppBinding() no-arg constructor. The base strategy with no
inFilter / inFilterPattern / inFilterStartsWith returns false for
every header, so inbound XMPP message properties (XmppBinding.extractHeadersFrom,
applyFilterToExternalHeaders) are copied onto the Camel Exchange
as-is — including Camel* / camel* / org.apache.camel.* keys that
drive component behaviour downstream.

This aligns camel-xmpp with the rest of the component catalog
(camel-kafka, camel-mail, camel-coap, camel-google-pubsub,
camel-jms, camel-sjms, and camel-nats via CAMEL-23515) which all
ship a dedicated HeaderFilterStrategy subclass.

Changes

• New XmppHeaderFilterStrategy following the
  KafkaHeaderFilterStrategy / MailHeaderFilterStrategy shape
  (setLowerCase(true), in/out setInFilterStartsWith(CAMEL_FILTER_STARTS_WITH)).
• XmppEndpoint and the XmppBinding no-arg constructor now default to
  new XmppHeaderFilterStrategy(); the now-unused
  DefaultHeaderFilterStrategy import is removed from both
  (XmppHeaderFilterStrategy is in the same package).
• Unit test covering inbound/outbound Camel* filtering, lowercase
  variants, and pass-through of non-Camel headers.
• 4.21 upgrade-guide entry (=== camel-xmpp).

Test plan

• Module build: mvn -pl components/camel-xmpp -DskipTests install
• New unit test: XmppHeaderFilterStrategyTest (4 tests, green)
• CI: full reactor build + existing camel-xmpp suite

JIRA

https://issues.apache.org/jira/browse/CAMEL-23516

Sibling of CAMEL-23515 (camel-nats, merged to main/4.18.x/4.14.x).
Backports to 4.18.x and 4.14.x planned per the fixVersions.

Claude Code on behalf of Andrea Cosentino

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🧪 CI tested the following changed modules:

• components/camel-xmpp
• docs

⚠️ Some tests are disabled on GitHub Actions (@DisabledIfSystemProperty(named = "ci.env.name")) and require manual verification:

• components/camel-xmpp: 6 test(s) disabled on GitHub Actions

All tested modules (8 modules)

• Camel :: JBang :: MCP
• Camel :: JBang :: Plugin :: Route Parser
• Camel :: JBang :: Plugin :: TUI
• Camel :: JBang :: Plugin :: Validate
• Camel :: Launcher :: Container
• Camel :: XMPP
• Camel :: YAML DSL :: Validator
• Camel :: YAML DSL :: Validator Maven Plugin

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