lmxopcua/docs/reqs/OpcUaServerReqs.md

OPC UA Server — Component Requirements

Parent: HLR-001, HLR-002, HLR-004

OPC-001: Server Endpoint

The OPC UA server shall listen on a configurable TCP port (default 4840) using the OPC Foundation .NET Standard stack.

Acceptance Criteria

• Server starts and accepts TCP connections on the configured port.
• Port is read from appsettings.json under OpcUa:Port; defaults to 4840 if absent.
• Endpoint URL format: opc.tcp://<hostname>:<port>/LmxOpcUa.
• If the port is in use at startup, log an Error and fail to start (do not silently pick another port).
• Security policy: None (no certificate validation). This is an internal plant-floor service.

Details

• Configurable items: port (default 4840), endpoint path (default /LmxOpcUa), server application name (default LmxOpcUa).
• Server shall use the OPCFoundation.NetStandard.Opc.Ua.Server NuGet package.
• On startup, log the endpoint URL at Information level.

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OPC-002: Address Space Structure

The server shall create folder nodes for areas and object nodes for automation objects, organized in the same parent-child hierarchy as the Galaxy.

Acceptance Criteria

• The root folder node has BrowseName ZB (hardcoded Galaxy name).
• Objects where is_area = 1 are created as FolderType nodes (organizational).
• Objects where is_area = 0 are created as BaseObjectType nodes.
• Parent-child relationships use Organizes references (for areas) and HasComponent references (for contained objects).
• A client browsing Root → Objects → ZB → DEV → TestArea → TestMachine_001 → DelmiaReceiver sees the same structure as gr/layout.md.

Details

• NodeIds use a string-based identifier scheme: ns=1;s=<tag_name> for object nodes, ns=1;s=<tag_name>.<attribute_name> for variable nodes.
• Infrastructure objects (AppEngines, Platforms) are included in the tree but may have no variable children.
• When contained_name is null or empty, fall back to tag_name as the BrowseName.

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OPC-003: Variable Nodes for Attributes

Each user-defined attribute on a deployed object shall be represented as an OPC UA variable node under its parent object node.

Acceptance Criteria

• Each row from attributes.sql creates one variable node under the matching object node (matched by gobject_id).
• Variable node BrowseName and DisplayName are set to attribute_name.
• Variable node stores full_tag_reference as its runtime MXAccess address.
• Variable node AccessLevel is set based on the attribute's security_classification per the mapping in gr/data_type_mapping.md.
• FreeAccess (0), Operate (1), Tune (4), Configure (5) → AccessLevel = CurrentRead | CurrentWrite (3).
• SecuredWrite (2), VerifiedWrite (3), ViewOnly (6) → AccessLevel = CurrentRead (1).
• Objects with no user-defined attributes still appear as object nodes with zero children.

Details

• Security classification determines the OPC UA AccessLevel and UserAccessLevel attributes on each variable node. The OPC UA stack enforces read-only access for nodes with CurrentRead-only access level.
• Attributes whose names start with _ are already filtered by the SQL query.

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OPC-004: Browse Name Translation

Browse names shall use contained names (human-readable, scoped to parent). The server shall internally translate browse paths to tag_name references for MXAccess operations.

Acceptance Criteria

• A variable node browsed as ZB/DEV/TestArea/TestMachine_001/DelmiaReceiver/DownloadPath correctly translates to MXAccess reference DelmiaReceiver_001.DownloadPath.
• Translation uses the tag_name stored on the parent object node, not the browse path.
• No runtime path parsing — the mapping is baked into each node at build time.

Details

• Each variable node stores its full_tag_reference (e.g., DelmiaReceiver_001.DownloadPath) at address-space build time. Read/write operations use this stored reference directly.

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OPC-005: Data Type Mapping

Variable nodes shall use OPC UA data types mapped from Galaxy mx_data_type values per the mapping in gr/data_type_mapping.md.

Acceptance Criteria

• Every mx_data_type value in the mapping table produces the correct OPC UA DataType NodeId on the variable node.
• Unknown/unmapped mx_data_type values default to String (i=12).
• ElapsedTime (type 7) maps to Double representing seconds.

Details

• Full mapping table in gr/data_type_mapping.md.
• DateTime conversion: Galaxy may store local time; convert to UTC for OPC UA.
• LocalizedText (type 15): use empty locale string with the text value.

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OPC-006: Array Support

Attributes marked as arrays shall have ValueRank=1 and ArrayDimensions set to the attribute's array_dimension value.

Acceptance Criteria

• is_array = 1 produces ValueRank = 1 (OneDimension) and ArrayDimensions = [array_dimension].
• is_array = 0 produces ValueRank = -1 (Scalar) and no ArrayDimensions.
• MXAccess reference for array attributes uses tag_name.attribute[] (whole array) format.

Details

• Individual array element access (tag_name.attribute[n]) is not required for initial implementation. Whole-array read/write only.
• If array_dimension is null or 0 when is_array = 1, log a Warning and default to ArrayDimensions = [0] (variable-length).

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OPC-007: Read Operations

The server shall fulfill OPC UA Read requests by reading the corresponding tag value from MXAccess using the tag_name.AttributeName reference.

Acceptance Criteria

• OPC UA Read request for a variable node results in a read via MXAccess using the node's stored full_tag_reference.
• Returned value is converted from the COM variant to the OPC UA data type specified on the node.
• OPC UA StatusCode reflects MXAccess quality: Good maps to Good, Bad/Uncertain map appropriately.
• If MXAccess is not connected, return StatusCode = Bad_NotConnected.
• Read timeout: configurable, default 5 seconds. On timeout, return Bad_Timeout.

Details

• Prefer cached subscription-delivered values over on-demand reads to reduce COM round-trips.
• If no subscription is active for the tag, perform an on-demand read (AddItem, AdviseSupervisory, wait for first OnDataChange, then UnAdvise/RemoveItem).
• Concurrency: semaphore-limited to configurable max (default 10) concurrent MXAccess operations.

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OPC-008: Write Operations

The server shall fulfill OPC UA Write requests by writing to the corresponding tag via MXAccess.

Acceptance Criteria

• OPC UA Write request results in an MXAccess Write() call with completion confirmed via OnWriteComplete() callback.
• Write timeout: configurable, default 5 seconds. On timeout, log Warning and return Bad_Timeout.
• MXSTATUS_PROXY with success = 0 causes the OPC UA write to return Bad_InternalError with the detail message.
• MXAccess errors 1008 (no permission), 1012 (secured write), 1013 (verified write) return Bad_UserAccessDenied.
• Write to a non-existent tag returns Bad_NodeIdUnknown.
• The server shall attempt to convert the written value to the expected Galaxy data type before passing to Write().

Details

• Write uses security classification -1 (no security). Galaxy runtime handles security enforcement.
• Write sequence: uses existing subscription handle if available, otherwise AddItem + AdviseSupervisory + Write + await OnWriteComplete + cleanup.
• Concurrent write limit: same semaphore as reads (configurable, default 10).

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OPC-009: Subscriptions

The server shall support OPC UA subscriptions by mapping them to MXAccess advisory subscriptions and forwarding data change notifications.

Acceptance Criteria

• OPC UA CreateMonitoredItems results in MXAccess AdviseSupervisory() subscriptions for the requested tags.
• Data changes from OnDataChange callback are forwarded as OPC UA notifications to all subscribed clients.
• Shared subscriptions: if two OPC UA clients subscribe to the same tag, only one MXAccess subscription exists (ref-counted).
• Last subscriber unsubscribing triggers UnAdvise/RemoveItem on the MXAccess side.
• After MXAccess reconnect, all active MXAccess subscriptions are re-established automatically.

Details

• Publishing interval from the OPC UA subscription request is honored on the OPC UA side; MXAccess delivers changes as fast as it receives them.
• OPC UA quality mapping from MXAccess quality integers: 192+ = Good, 64-191 = Uncertain, 0-63 = Bad.
• OnDataChange with MXSTATUS_PROXY failure: deliver notification with Bad quality to subscribed clients.

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OPC-010: Address Space Rebuild

When a Galaxy deployment change is detected, the server shall rebuild the address space without dropping existing OPC UA client connections where possible.

Acceptance Criteria

• When Galaxy Repository detects a deployment change, the OPC UA address space is updated.
• Only changed gobject subtrees are torn down and rebuilt; unchanged nodes, subscriptions, and alarm tracking remain intact.
• Existing OPC UA client sessions are preserved — clients stay connected.
• Subscriptions for tags on unchanged objects continue to work without interruption.
• Subscriptions for tags that no longer exist receive a Bad_NodeIdUnknown status notification.
• Sync is logged at Information level with the number of changed gobjects.

Details

• Uses incremental subtree sync: compares previous hierarchy+attributes with new, identifies changed gobject IDs, expands to include child subtrees, tears down only affected subtrees, and rebuilds them.
• First build (no cached state) performs a full build.
• If no changes are detected, the sync is a no-op (logged and skipped).
• Alarm tracking and MXAccess subscriptions for unchanged objects are not disrupted.
• Falls back to full rebuild behavior if the entire hierarchy changes.

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OPC-011: Server Diagnostics Node

The server shall expose a ServerStatus node under the standard OPC UA Server object with ServerState, CurrentTime, and StartTime. This is required by the OPC UA specification for compliant servers.

Acceptance Criteria

• ServerState reports Running during normal operation.
• CurrentTime returns the server's current UTC time.
• StartTime returns the UTC time when the service started.

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OPC-012: Namespace Configuration

The server shall register a namespace URI at namespace index 1. All application-specific NodeIds shall use this namespace.

Acceptance Criteria

• Namespace URI: urn:ZB:LmxOpcUa (Galaxy name is configurable).
• All object and variable NodeIds created from Galaxy data use namespace index 1.
• Standard OPC UA nodes remain in namespace 0.

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OPC-013: Session Management

The server shall support multiple concurrent OPC UA client sessions.

Acceptance Criteria

• Maximum concurrent sessions: configurable, default 100.
• Session timeout: configurable, default 30 minutes of inactivity.
• Expired sessions are cleaned up and their subscriptions removed.
• Session count is reported to the status dashboard.