Docs · Observability

Event reference

The full event catalogue — 52 classes grouped by lifecycle. Each event carries a $client reference plus a handful of typed fields.

The library dispatches 52 event classes. Every event extends a common shape with a $client property; the per-event fields below are the additions on top of that.

All event classes live in PhpOpcua\Client\Event\.

Connection lifecycle (6)

Event	Fires when	Key fields
`ClientConnecting`	`connect()` starts	`endpoint`
`ClientConnected`	Session is activated	`endpoint`, `sessionId`
`ClientDisconnecting`	`disconnect()` starts	—
`ClientDisconnected`	Disconnect completed (clean or broken)	— (only `$client`)
`ClientReconnecting`	`reconnect()` starts	`endpoint`
`ConnectionFailed`	`connect()` raised	`endpoint`, `exception`

Secure channel (2)

Event	Fires when	Key fields
`SecureChannelOpened`	OPN exchange completed	`channelId`, `securityPolicy` (enum), `securityMode`
`SecureChannelClosed`	CLO sent or socket dropped	`channelId`

Session (3)

Event	Fires when	Key fields
`SessionCreated`	After CreateSession	`sessionId`, `sessionName`
`SessionActivated`	After ActivateSession	`sessionId`
`SessionClosed`	After CloseSession	`sessionId`

Read / Write (3)

Event	Fires when	Key fields
`NodeValueRead`	`read()` succeeded	`nodeId`, `attributeId`, `dataValue`
`NodeValueWritten`	`write()` returned Good	`nodeId`, `value`, `type`
`NodeValueWriteFailed`	`write()` returned non-Good	`nodeId`, `value`, `type`, `statusCode`

Write type detection (2)

Event	Fires when	Key fields
`WriteTypeDetecting`	Auto-detection started for a node	`nodeId`
`WriteTypeDetected`	Auto-detection produced a `BuiltinType`	`nodeId`, `detectedType`, `fromCache`

Browse (1)

Event	Fires when	Key fields
`NodeBrowsed`	`browse()` succeeded	`nodeId`, `direction`, `referenceCount`

Subscriptions (4)

Event	Fires when	Key fields
`SubscriptionCreated`	`createSubscription()` succeeded	`subscriptionId`, `revisedPublishingInterval`
`SubscriptionDeleted`	`deleteSubscription()` succeeded	`subscriptionId`
`SubscriptionKeepAlive`	Server sent an empty publish response	`subscriptionId`
`SubscriptionTransferred`	`transferSubscriptions()` returned Good	`subscriptionId`

Monitored items (3)

Event	Fires when	Key fields
`MonitoredItemCreated`	`createMonitoredItems()` returned Good	`subscriptionId`, `monitoredItemId`, `nodeId`, `statusCode`
`MonitoredItemModified`	`modifyMonitoredItems()` returned Good	`subscriptionId`, `monitoredItemId`
`MonitoredItemDeleted`	`deleteMonitoredItems()` returned Good	`subscriptionId`, `monitoredItemId`

Publish (3)

Event	Fires when	Key fields
`DataChangeReceived`	A data-change notification was delivered	`subscriptionId`, `sequenceNumber`, `clientHandle`, `dataValue`
`EventNotificationReceived`	An event notification was delivered	`subscriptionId`, `sequenceNumber`, `clientHandle`, `eventFields`
`PublishResponseReceived`	Any publish response (including keep-alives)	`subscriptionId`, `sequenceNumber`, `notificationCount`, `moreNotifications`

Triggering (1)

Event	Fires when	Key fields
`TriggeringConfigured`	`setTriggering()` returned Good	`subscriptionId`, `triggeringItemId`, `addResults`, `removeResults`

Alarms (9)

These are auto-deduced from event notification payloads — when an EventNotificationReceived event carries alarm-shaped fields, the library dispatches one of the specific events below in addition.

Event	Fires when	Key fields
`AlarmEventReceived`	Any alarm-shaped event	`sourceName`, `message`, `severity`, `eventType`
`AlarmActivated`	`ActiveState` → `Active`	`subscriptionId`, `clientHandle`, `sourceName`, `severity`, `message`
`AlarmDeactivated`	`ActiveState` → `Inactive`	`sourceName`
`AlarmAcknowledged`	`AckedState` → acknowledged	`sourceName`, `acknowledger`
`AlarmConfirmed`	`ConfirmedState` → confirmed	`sourceName`
`AlarmShelved`	Shelved/Unshelved state transition	`sourceName`, `shelved`
`AlarmSeverityChanged`	Severity changed	`sourceName`, `oldSeverity`, `newSeverity`
`LimitAlarmExceeded`	LimitAlarmType variants tripped a limit	`subscriptionId`, `clientHandle`, `sourceName`, `limitState`, `severity`
`OffNormalAlarmTriggered`	OffNormalAlarmType variants tripped	`subscriptionId`, `clientHandle`, `sourceName`, `severity`

Type discovery (1)

Event	Fires when	Key fields
`DataTypesDiscovered`	`discoverDataTypes()` completed	`namespaceIndex`, `count`

History updates (4)

Dispatched after each HistoryUpdate call returns. Added in v4.4.0.

Event	Fires when	Key fields
`HistoryDataUpdated`	`historyInsertData()` / `historyReplaceData()` / `historyUpdateData()` returned	`nodeId`, `operation` (`PerformUpdateType`), `valueCount`, `operationResults` (`int[]`)
`HistoryDataDeleted`	`historyDeleteRawModified()` (`kind: 'rawModified'`) or `historyDeleteAtTime()` (`kind: 'atTime'`) returned	`nodeId`, `kind` (`string`), `statusCode` (`int`), `operationResults` (`int[]`, populated only for `atTime`)
`HistoryEventUpdated`	`historyInsertEvent()` / `historyReplaceEvent()` / `historyUpdateEvent()` returned	`nodeId`, `operation` (`PerformUpdateType`), `eventCount`, `operationResults` (`int[]`)
`HistoryEventDeleted`	`historyDeleteEvent()` returned	`nodeId`, `eventCount`, `operationResults` (`int[]`)

PerformUpdateType is an int-backed enum (Insert=1, Replace=2, Update=3, Remove=4) — see Operations · History writes.

Aggregates (1)

Dispatched after the client-side aggregator finishes a windowed computation. Added in v4.4.0.

Event	Fires when	Key fields
`AggregateComputed`	`aggregate()` or `historyAggregate()` returned	`function` (`AggregateFunction`), `rawInputCount`, `intervalCount`, `nodeId` (`?NodeId`, null for in-memory)

See Operations · Client-side aggregates.

Cache (2)

Event	Fires when	Key fields
`CacheHit`	A cached value was returned	`key`, `operation`, `nodeId`
`CacheMiss`	A miss triggered a server round-trip	`key`, `operation`, `nodeId`

Retry (2)

Event	Fires when	Key fields
`RetryAttempt`	A retry is about to run	`operation`, `attempt`, `exception`
`RetryExhausted`	The retry budget is exhausted and the call fails	`operation`, `attempts`, `exception`

Trust store (5)

Event	Fires when	Key fields
`ServerCertificateTrusted`	Cert was already in store, accepted	`fingerprint`
`ServerCertificateAutoAccepted`	TOFU recorded a new cert	`fingerprint`
`ServerCertificateRejected`	Cert was rejected (validation failed)	`fingerprint`, `reason`
`ServerCertificateManuallyTrusted`	`trustCertificate()` was called	`fingerprint`
`ServerCertificateRemoved`	`untrustCertificate()` was called	`fingerprint`

Putting them in context

You want	Listen for
"Tell me when the connection is up"	`ClientConnected`
"Tell me when it breaks"	`ConnectionFailed` (raised exception); `ClientDisconnected` covers both clean and broken
"Count reads"	`NodeValueRead`
"Count failed writes"	`NodeValueWriteFailed`
"Page on critical alarms"	`AlarmActivated` filtered by `severity`
"Measure cache effectiveness"	`CacheHit` and `CacheMiss`
"Track retry behaviour"	`RetryAttempt`, `RetryExhausted`
"Audit certificate trust decisions"	The five trust-store events

For wiring patterns, see Events. For events you want to trigger programmatically (in tests), see Testing · MockClient.

Last updated · 2026-05-21

Edit on GitHub Report issue

← Previous

Events

Caching