Implement Event Subscription handling for channels by JonathanWhiteUK · Pull Request #746 · gopcua/opcua

JonathanWhiteUK · 2024-10-16T09:44:22Z

Hi, I have added event channel handling. This is a breaking change as it changes the signatures of some of the functions to allow for handling of both event messages and data change messages. Thanks :)

SCZwilling · 2024-11-25T07:07:00Z

Hello, I was trying to use your implementation of event subscription but i am getting error- "The attribute is not supported for the specified Node. StatusBadAttributeIDInvalid (0x80350000)". I am subscribing to an object node which has below configuration-

Attribute | Value
Nodeld | ins=2;s=Sinumerik
NamespaceIndex 2 |  
IdentifierType | String
Identifier | Sinumerik
NodeClass | Object
BrowseName | 2, "Sinumerik"
DisplayName | "en-US", "Sinumerik"
Description | "en-US", "An object with several features of Sinumerik"
EventNotifier | SubscribeToEvents

I have tested this node on UA Expert and there i am able to see the events and alarms. I believe i need to change some configuration to subscribe events on this node, could you help with it @Jwcode-uk ?

magiconair · 2024-12-03T19:57:34Z

Thank you @Jwcode-uk. I can see that one function in subscription.go gets an additional parameter. I think we could use a different pattern for functions like this. Not sure if we have more than just this one. Might be worthwhile to look. Would like to keep this consistent.

Not sure if this is complex enough to use the Option pattern for this constructor. What do you think?

// Deprectated: Use NewDefaultMonitoredItemCreateRequest instead. Will be removed with 0.8.0
func NewMonitoredItemCreateRequestWithDefaults(nodeID *ua.NodeID, attributeID ua.AttributeID, clientHandle uint32) *ua.MonitoredItemCreateRequest {
	return NewDefaultMonitoredItemCreateRequest(MICreateRequestArgs{
		NodeID:       nodeID,
		AttributeID:  attributeID,
		ClientHandle: clientHandle,
	})
}

type MonitoredItemCreateRequestArgs struct {
	NodeID       *ua.NodeID
	AttributeID  ua.AttributeID
	ClientHandle uint32
	Filter       *ua.ExtensionObject
}

func NewDefaultMonitoredItemCreateRequest(args MonitoredItemCreateRequestArgs) *ua.MonitoredItemCreateRequest {
	if args.AttributeID == 0 {
		args.AttributeID = ua.AttributeIDValue
	}
	return &ua.MonitoredItemCreateRequest{
		ItemToMonitor: &ua.ReadValueID{
			NodeID:       args.NodeID,
			AttributeID:  args.AttributeID,
			DataEncoding: &ua.QualifiedName{},
		},
		MonitoringMode: ua.MonitoringModeReporting,
		RequestedParameters: &ua.MonitoringParameters{
			ClientHandle:     args.ClientHandle,
			DiscardOldest:    true,
			Filter:           args.Filter,
			QueueSize:        10,
			SamplingInterval: 0.0,
		},
	}
}

magiconair

Did a first pass through the code and would like to see a change so that this implementation does not break existing code. See the comment on ChanSubscribe for a suggestion. I've also left some smaller style comments.

Some more comments would be useful since it isn't immediately obvious to me what the code does.

Lets do the refactor first - unless that isn't possible - and then I'll do another pass over the implementation and probably have a couple more questions.

magiconair · 2025-01-19T16:49:46Z

monitor/subscription.go

+							dataValue := &ua.DataValue{
+								Value:           field,
+								Status:          ua.StatusOK,
+								SourceTimestamp: time.Now(),


Shouldn't all dataValues have the same timestamp? Isn't there a timestamp in the item (e.g. ServerTimestamp)?

magiconair · 2025-01-19T16:53:02Z

monitor/subscription.go


 // internal func to read from internal channel and write to client provided channel
-func (s *Subscription) pump(ctx context.Context, notifyCh chan<- *DataChangeMessage, cb MsgHandler) {
+func (s *Subscription) pump(ctx context.Context, notifyCh chan<- Message, cb MsgHandler, sub bool) {


sub seems unused here and the name also collides with other usages of sub in this file where it usually denotes a *Subscription

magiconair · 2025-01-19T16:55:04Z

monitor/subscription.go


 // AddNodes adds nodes defined by their string representation
-func (s *Subscription) AddNodes(ctx context.Context, nodes ...string) error {
+func (s *Subscription) AddNodes(ctx context.Context, eventSub bool, filter *ua.ExtensionObject, nodes ...string) error {


What does eventSub do here? Also, see comment on ChanSubscribe for a way to add this functionality without breaking the signatures.

magiconair · 2025-01-19T16:55:36Z

monitor/subscription.go

+		return nil, nil
+	}
+
+	toAdd := make([]*ua.MonitoredItemCreateRequest, 0)


var toAdd []*ua.MonitoredItemCreateRequest

magiconair · 2025-01-19T16:56:40Z

monitor/subscription.go

+						out.EventFields = make([]*ua.DataValue, len(item.EventFields))
+
+						for i, field := range item.EventFields {
+							// Create a new DataValue


pls remove this comment as it does not have value

magiconair · 2025-01-19T16:59:35Z

monitor/subscription.go

+						}
+					}
+
+					if notifyCh != nil {


I prefer switch statements over if/else, e.g.

switch { case notifyCh != nil: select { ... } case cb != nil: cb(sb, out) atomic.AddUint64(&s.delivered, 1) default: panic(...) }

magiconair · 2025-01-19T17:00:59Z

subscription.go

 		MonitoringMode: ua.MonitoringModeReporting,
 		RequestedParameters: &ua.MonitoringParameters{
-			ClientHandle:     clientHandle,
+			ClientHandle:     args.ClientHandle,


Shouldn't the other parameters be configurable as well while providing sensible defaults?

magiconair · 2025-01-19T17:03:57Z

monitor/subscription.go

 // will also cause the subscription to stop, but `Unsubscribe` must still be called.
-func (m *NodeMonitor) ChanSubscribe(ctx context.Context, params *opcua.SubscriptionParameters, ch chan<- *DataChangeMessage, nodes ...string) (*Subscription, error) {
-	sub, err := newSubscription(ctx, m, params, 16, nodes...)
+func (m *NodeMonitor) ChanSubscribe(ctx context.Context, params *opcua.SubscriptionParameters, ch chan<- Message, eventSub bool, filter *ua.ExtensionObject, nodes ...string) (*Subscription, error) {


I am starting to think that an args parameter might be useful here. We did something similar with the WithContext versions of all functions where we dropped the WithContext suffix in a later version. So maybe we can refactor this change so that we add ChanSubscribeWithArgs(ctx context.Context, args ChanSubscribeArgs) (*Subscription, error) and drop the WithArgs in 0.8.0. Add a deprecation note to the other version. What do you think?

FelixTing · 2025-07-30T02:01:54Z

@magiconair Thank you for your review. I've synced the branch with the main branch and updated the code based on your suggestions. Could you please take another look when you have a moment? Thanks!

cloudxxx8 · 2025-08-12T02:20:46Z

this PR is ready for review again

Signed-off-by: FelixTing <felix@iotechsys.com>

github-actions · 2026-03-29T04:38:16Z

This pull request has been marked as stale due to inactivity. It will be closed in 7 days if no further activity occurs.

cloudxxx8 · 2026-03-29T11:24:02Z

may we review this PR for the next release?

jackchenjc force-pushed the DAN-11-branch branch from aa706a4 to 669ad21 Compare January 18, 2025 06:27

magiconair suggested changes Jan 19, 2025

View reviewed changes

magiconair added this to the v0.6.6 milestone Jan 22, 2025

magiconair modified the milestones: v0.7.1, v0.7.2 Feb 27, 2025

magiconair modified the milestones: v0.7.2, v0.7.4 Mar 17, 2025

magiconair modified the milestones: v0.7.4, v0.8.0 Apr 7, 2025

magiconair modified the milestones: v0.8.0, v0.8.1 Apr 24, 2025

FelixTing force-pushed the DAN-11-branch branch 3 times, most recently from 6837b18 to dad24e2 Compare July 30, 2025 02:00

Implement Event Subscription handling for channels

82ebd4c

Signed-off-by: FelixTing <felix@iotechsys.com>

cloudxxx8 force-pushed the DAN-11-branch branch from dad24e2 to 82ebd4c Compare August 12, 2025 02:21

JonathanWhiteUK requested a review from magiconair September 29, 2025 08:44

github-actions bot added the Stale label Mar 29, 2026

github-actions bot removed the Stale label Mar 30, 2026

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JonathanWhiteUK commented Oct 16, 2024

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FelixTing commented Jul 30, 2025

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SCZwilling commented Nov 25, 2024 •

edited by magiconair

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