#838 review of 91e28e87:
1. Ghost events. The deferred report ran the SDK walk off Lock with no
liveness check, so an event waiting behind a full channel when a deploy
removed its condition still reached i=2253 subscribers after the NodeDeleted
(a ghost Retain alarm for ScadaBridge) and folder items. Delivery now walks
the SDK path itself (OnReportEvent, OnReportEventAsync, inverse notifiers,
then the Parent as BaseInstanceState does) re-checking before EVERY hop that
the condition is the live instance; OnConditionReportEvent checks the same,
which also stops a non-live scripted condition being admitted through its
old equipment folder (#808). A guard test pins that only NodeState and
BaseInstanceState define the walk. New wire test removes the condition in
the same Lock hold as a flood; the flag-off variant fails without the checks.
2. Back-pressure. Deferral is per condition (one condition's events stay
ordered; others are not held up). Overflow policy: coalesce, newest wins --
past 1024 waiting per condition or 65,536 total, the oldest not-yet-started
event is discarded (a condition event carries full state). Warning on
entering deferral (<=1/min), Information on draining, meters
otopcua.opcua.condition_events.deferred / .discarded{reason}.
3. Verified by decompiling SDK 2.0.1: the notifier list is snapshotted under the
node's own lock, MonitoredNode2.Dispose completes its writer (pending writes
fail with ChannelClosedException, swallowed), and the consumer catches
per-event exceptions -- no fix needed; documented.
4. ConditionRefresh does not flush deferrals; documented as a residual.
#844 review: DescribeCredential canonicalises the key id (trim, lowercase;
non-hex ids fold into one identity) and the username, since ConfigDbApiKeyStore
matches with SQL Server's case-insensitive, trailing-space-blind `=`.
#838(a): each notifier's SDK MonitoredNode2 drains a bounded channel (4096,
FullMode=Wait) and the synchronous NodeState.ReportEvent blocks when it is
full. Condition events are reported under Lock, and the delivery task takes
Lock on a verdict-cache miss (the SDK's own GetNodeMetadata, flag off too, and
#826's IsNotifierEventVisibleTo). A burst of >4096 events under one Lock hold
therefore deadlocked the node manager -- FolderEventFloodWireTests stalled at
exactly 4097 events with enforcement on AND off (so it predates #826).
ReportConditionEvent now goes through ReportEventWithoutBlocking:
ReportEventAsync completes inline while channels have room (unchanged normal
path); on overflow the report continues asynchronously holding no thread or
lock, and later reports queue behind it so events keep report order. The
deferred work holds only frozen snapshots and drains once Lock is released;
client delivery stays bounded by each item's queue.
#838(b): documented in docs/security.md that Part 3 ReceiveEvents applies to
the event's EventType and SourceNode (the SDK check, kept first), not to the
notifier; our decision is layered on top and non-condition events on a folder
item fail closed under enforcement. The reflection item stays open.
Joseph Doherty