[backport camel-4.22.x] CAMEL-25694: camel-milo - fix write/call service failures being reported as success - #28367

TL;DR

The production change and the tests are the same as #27956. Two of the new tests do not compile on camel-4.22.x, and the upgrade-guide note is in an older section.

Blockers

• MiloClientProducerWriteFailureTest.java:68 calls super(new MiloClientConfiguration()). On camel-4.22.x the only MiloClientConnection constructor also takes a MonitorFilterConfiguration. The one-argument constructor came with CAMEL-25145, which is on main only. super(new MiloClientConfiguration(), new MonitorFilterConfiguration()) fixes it.
• SubscriptionManagerExceptionPropagationTest.java:155, :173 and :193 call new SubscriptionManager(config, executor, executor, 10_000). On camel-4.22.x the constructor is (MiloClientConfiguration, ScheduledExecutorService, long). The four-argument form came with CAMEL-25812 (#28111), which is on main only. new SubscriptionManager(new MiloClientConfiguration(), executor, 10_000) fixes it.

Other findings: 2

• The note === camel-milo - an awaited write, call or read that fails now fails the exchange is at camel-4x-upgrade-guide-4_22.adoc:2106, inside "Upgrading Camel 4.21 to 4.22". The change ships in 4.22.3, so the note belongs under "Upgrading from 4.22.2 to 4.22.3" (line 14).
• The 4.22 guide on main does not have this note yet. It should go under "Upgrading from 4.22.2 to 4.22.3" there too. One small PR on main can add it to the 4.22 and 4.18 guides together.

The CI failure is this compile error. The build (25, false) job failed, and the JDK 17 job was cancelled after it. A re-run will not help until the tests are fixed. The rest of the code the new tests use is the same on this branch, so I expect them to pass after these two changes, but CI has not run them yet.

Reviewed with Claude Code on behalf of @davsclaus. This review was generated by an AI agent and may contain inaccuracies; please verify all suggestions before applying.

Following up on @davsclaus's review — the two constructor blockers are resolved in this push. One structural issue remains.

✅ Resolved:

• MiloClientProducerWriteFailureTest: now calls super(new MiloClientConfiguration(), null) — compiles on camel-4.22.x (2-arg constructor; null is safe, the field is null-guarded at all usage sites).
• SubscriptionManagerExceptionPropagationTest: now calls new SubscriptionManager(new MiloClientConfiguration(), executor, 10_000) — 3-arg form matches the branch constructor.

🔴 Remaining — upgrade guide section (blocker):
The camel-milo note was appended at line 2106, inside the "Upgrading Camel 4.21 to 4.22" section. This fix ships in 4.22.3, so the note belongs under "Upgrading from 4.22.2 to 4.22.3" (the section that starts at line 14).

Please delete the block from lines 2105–2116 (end of file) and insert it between the camel-azure-eventhubs note and == Upgrading from 4.22.1 to 4.22.2, so the result reads:

== Upgrading from 4.22.2 to 4.22.3

=== camel-azure-eventhubs - an event that completes...
...set. Routes that read this header can now see `timeout` as well as `size`.

=== camel-milo - an awaited write, call or read that fails now fails the exchange

An awaited `milo-client` write, method call or read that fails at the service or transport level, for example a
request that times out (`Bad_Timeout`) or a lost connection, now fails the exchange and lets the route's error
handler run. Before, the exchange completed without an error and with a `null` body, silently discarding the failure.
A bad status for the node itself, such as `Bad_TypeMismatch` on a write, is not a failure of the operation and is
still returned as the body.

An awaited `call` that succeeds now returns the `CallMethodResult` as the exchange body. Before, the body was
always `null` even on success. A route that reads the result of an awaited call must be updated to read the
`CallMethodResult` from the body instead of expecting `null`.

== Upgrading from 4.22.1 to 4.22.2

⚠️ Note (low, non-blocker):
MiloClientProducerWriteFailureTest uses getDeclaredField("connection") to inject the stub connection. This is fragile — a field rename silently breaks the test at runtime. Consider a package-private setter or constructor parameter for testability.

Production fix: The handleAsync → whenCompleteAsync change is correct. whenCompleteAsync runs the side-effect (handleConnectionFailure) without consuming the future's result or exception — downstream callers see the original completion state unmodified. The test coverage is thorough: SubscriptionManagerExceptionPropagationTest validates the contract directly (including a documentation test for the old buggy behaviour), MiloClientProducerWriteFailureTest validates end-to-end through the producer, and testAwaitedCallReturnsResult validates that the call result is now returned on success.

This review was generated by an AI agent, Hermès on behalf of @gnodet.

All blockers resolved in the latest push.

✅ Fixed:

• Upgrade guide: camel-milo note now correctly placed under "Upgrading from 4.22.2 to 4.22.3" (moved from the 4.21→4.22 section at the end of the file).
• Merge with camel-4.22.x resolved — the branch is no longer conflicting.

The production fix and tests are identical to #27956. CI should be green after the push.

This review was generated by an AI agent, Hermès on behalf of @gnodet.

TL;DR

Approve: looks good.
Blockers: None.
Other findings: 1 docs follow-up on main.

The production change and the tests now match #27956 line for line, apart from the constructor calls that had to change for this branch:

• MiloClientProducerWriteFailureTest.java:68: super(new MiloClientConfiguration(), null) matches the only constructor on 4.22.x, MiloClientConnection(MiloClientConfiguration, MonitorFilterConfiguration). null is fine here: the field is only read in monitorValue, which the stub never reaches.
• SubscriptionManagerExceptionPropagationTest.java:155/173/193: new SubscriptionManager(config, executor, 10_000) matches SubscriptionManager(MiloClientConfiguration, ScheduledExecutorService, long) on 4.22.x.
• The guide note is now under "Upgrading from 4.22.2 to 4.22.3" (camel-4x-upgrade-guide-4_22.adoc:29), which is correct: the latest tag is camel-4.22.2.

Follow-up (not for this PR)

• Main's camel-4x-upgrade-guide-4_22.adoc still has no "camel-milo - an awaited write, call or read that fails now fails the exchange" note in its 4.22.3 section, and main's 4_18 guide misses the 4.18.6 one (#28368 put it on camel-4.18.x). Main only has it in the 4_24 guide. One small PR on main can add both notes.

Earlier points

• MiloClientConnection one-argument constructor does not exist on 4.22.x: fixed.
• SubscriptionManager four-argument constructor does not exist on 4.22.x: fixed.
• Note in the 4.21 to 4.22 section: moved to 4.22.2 to 4.22.3.

Claude Code on behalf of davsclaus. This review was generated by an AI agent and may contain inaccuracies; please verify all suggestions before applying.