Fifth PR of the alarms-over-gateway epic
(docs/plans/alarms-over-gateway.md). Depends on PR C.1
(AahClientManagedAlarmEventWriter), already merged.
Today HistorianFrameHandler is constructed at Program.cs line 57
without an alarmWriter, so every WriteAlarmEvents frame replies
"Sidecar not configured with an alarm-event writer" and the lmxopcua
side keeps the row queued. C.2 wires a real writer behind a new
OTOPCUA_HISTORIAN_ALARM_WRITE_ENABLED toggle.
- Program.BuildAlarmWriter — gated on the env var (default true,
fail-open under accidental misconfiguration). Constructs an
AahClientManagedAlarmEventWriter wrapping a
SdkAlarmHistorianWriteBackend with the same connection config the
read path uses.
- Install-Services.ps1 — appends OTOPCUA_HISTORIAN_ALARM_WRITE_ENABLED=true
to the OtOpcUaWonderwareHistorian service env block when the
sidecar is installed. Read-only deployments flip it to false at
service-config edit time without re-installing.
- HistorianFrameHandler signature already accepts
IAlarmEventWriter? — supplying non-null at line 57 lights up
the WriteAlarmEvents reply path that's been dormant since PR 3.3.
Until PR D.1 pins the live aahClientManaged entry point, the
SdkAlarmHistorianWriteBackend reports RetryPlease for every event
with a structured diagnostic. The lmxopcua-side
SqliteStoreAndForwardSink retains queued events; same effective
behaviour as today's NullAlarmHistorianSink fallback but with
visible diagnostics rather than silent discard.
Tests:
- 6 BuildAlarmWriter env-var cases — unset / true / false /
unrecognized → default-on / capitalization variants.
- Full sidecar test suite: 56 passed (was 48; 8 new).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
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