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Marc Schier
0383472ebc
### Summary Three related gaps mean no `PublishedDataSet` can produce a message that is not a key frame or a derived delta frame. `PubSubDataSetMessageType.Event` and the `ua-event` wire tag of Part 14 §7.2.5.4 are modelled but unreachable. This PR also corrects the JSON `DataValue` status member to the Part 6 Table 42 name `Status`. ### 1. A dataset cannot declare what its sample is `PublishedDataSetSnapshot` carries a metadata version, fields and a timestamp. `WriterGroup.BuildDataSetMessageAsync` therefore decides the message kind alone: `KeyFrameCount <= 1` forces `KeyFrame`, otherwise it derives a delta by comparing the snapshot **positionally** against the previous one. That derivation assumes successive snapshots describe the same fields in the same order, which holds only for a source returning its complete current state every cycle. A source whose samples are *occurrences* — an event, a condition snapshot, or a delta it has already computed — cannot satisfy it: consecutive samples carry different fields, so field *i* of one occurrence is compared against field *i* of an unrelated earlier one, and `Math.Min` silently truncates when the counts differ. `PublishedDataSetSnapshot` now carries an optional `MessageType`. When set, the writer publishes exactly the supplied fields under the declared type and leaves its key-frame state untouched. When null — the default, and every existing caller — behaviour is unchanged. ### 2. The event writer was unreachable `EventDataSetWriter` and `EventPublishedDataSet` implement the Part 14 §6.2.4 event model correctly, but nothing could use them: - `EventPublishedDataSet` did not implement `IPublishedDataSet`, so `PubSubApplication` could not register an event dataset; - nothing in the library constructed `EventDataSetWriter`, and it was not an `IDataSetWriter`; - `WriterGroup` appends at most one message per writer per cycle, whereas an event writer produces one per occurrence. Now: `EventPublishedDataSet` is an `IPublishedDataSet` whose general `SampleAsync` drains one occurrence per cycle declared as an event; `EventDataSetWriter` is an `IDataSetWriter`; `PubSubApplication` builds an event dataset when the configured `DataSetSource` is a `PublishedEventsDataType` and the registered source is an `IEventSampler`; and a writer group drains every pending occurrence in one publish cycle. Event-writer sequence numbers now use the WriterGroup checkpoint state, so failover and restart resume above the shared checkpoint. The rows-returning `EventPublishedDataSet.SampleAsync` is renamed `SampleEventsAsync`, both to make room for the interface member and to match `IEventSampler.SampleEventsAsync`. ### 3. A metadata announcement hides its own payload `JsonMetaDataMessage` documents that the payload *"is exposed both on the base `PubSubNetworkMessage.MetaData` property and on `MetaDataPayload` so callers can use whichever accessor matches their fluent style."* `MetaDataPublisher` set only `MetaDataPayload`, so the documented contract was false: any consumer, transform or encoder hook reading the base property saw an announcement as a message carrying nothing. Both are now populated. Dataset subscriptions also use a dispose-safe subscribe/recheck handshake, preventing a concurrent shutdown from leaving a late handler attached. ### 4. JSON DataValue status used the wrong member name Part 6 section 5.4.2.18 Table 42 names the `DataValue` status member `Status`; `StatusCode` is its data type. `JsonEncoder` and `JsonDecoder` instead shared the member name `StatusCode`, so stack-to-stack round-trips passed while standards-conformant peers could not exchange non-Good status values. Both directions now use `Status`. The encoder regression test also verifies that `StatusCode` is absent from the emitted `DataValue` object. Fixes #4111. ### Compatibility The snapshot property is optional and defaults to null, so existing PubSub sources and current-state sampling behavior remain unchanged. The `EventPublishedDataSet.SampleAsync` rename is source-breaking on a type that could not previously be reached from the runtime. The JSON `DataValue` wire member intentionally changes from `StatusCode` to the specification-defined `Status`. No legacy alias is retained: the encoder emits `Status`, and the decoder expects `Status`. ### Testing `Opc.Ua.PubSub.Tests` on `net10.0`: 1341 passed, 1 skipped, 0 failed. New coverage: - `WriterGroupDeclaredMessageTypeTests` — a declared type is honoured, declared samples never become delta frames and are never suppressed as unchanged, and an undeclared source keeps the existing key-frame cadence. - `EventDataSetWriterTests.EventPublishedDataSet_SamplesOneOccurrencePerSnapshotAsync` — the general contract drains one occurrence per call, declares it as an event, and reports nothing when exhausted. - `WriterGroupEventWriterHotStandbyContinuesSequenceNumberFromSharedCheckpointAsync` — event messages share the checkpointed sequence state and continue monotonically after standby promotion. Issue #4111 validation: - `Opc.Ua.Types.Tests` JSON encoder/decoder fixtures on `net10.0`: 274 passed. - `Opc.Ua.Core.Encoders.Tests` JSON conformance cases on `net10.0`: 604 passed. - `Opc.Ua.PubSub.Tests` JSON fixtures on `net10.0`: 88 passed. - Targeted `net48` regression tests: 2 passed; core JSON conformance cases: 572 passed. - Review-feedback fixtures on `net48`: 11 passed. CI-fix validation: - `Opc.Ua.Core.Tests` on `net10.0`: 4145 passed, 86 skipped. - `Opc.Ua.Core.Tests` on `net48`: 4070 passed, 92 skipped. - Patch coverage check passes after adding targeted metadata and event publishing tests. --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1a300bc8-8bde-4a82-8fc3-476ef837bc6a Copilot-Session: 9f18bf87-795f-40a9-8494-b6e6334c4a97