# Description A Part 16 cause is a Method, and whether it may fire depends on the state the machine is in. Part 3 defines `Executable` / `UserExecutable` as exactly that question, and Part 4 has `Call` refuse a non-executable Method with `Bad_NotExecutable`. `FiniteStateMachineState` already knows the answer — `IsCausePermitted(context, causeId, checkUserAccessRights)` — but nothing outside alarm shelving connected the two. Across the library, `OnReadExecutable` was assigned in exactly three places, all in `AlarmConditionState`. Everywhere else a cause method kept the `true` its node was constructed with, so a client could not tell which causes currently apply and found out only by calling one and being refused with `Bad_NotSupported` from `DoCause`. ## What changed **`StateMachineBuilder.WithCause`** now answers both attributes from `IsCausePermitted` alongside installing the call handler — on the unified builder (via the dispatcher's `InstallCauseMethod`) and on the `Opc.Ua.Server.Fluent` surface reached through `INodeBuilder.AsStateMachine()`, which had the identical gap. `Executable` ignores user rights; `UserExecutable` also runs the machine's `OnCheckUserPermission` callback. Per the issue's note about servers that deliberately keep methods executable and answer at call time, both overloads take `reportExecutable: false` to opt out. **`ProgramStateMachineState`** wires its own `Start` / `Suspend` / `Resume` / `Halt` / `Reset` in `OnAfterCreate`, so a Program server no longer repeats the boilerplate the class already shipped handlers for. The Boiler quickstart's copy of it is deleted rather than left as an example. **Generator-emitted `*StateMachineState` subclasses** are left alone. The generator emits no Part 16 `StateTable` / `TransitionTable` / `CauseMappings` overrides — the same gap that makes the DI software-update dispatcher write `CurrentState` directly instead of going through `SetState` (see `docs/SoftwareUpdate.md`) — so there is nothing to derive executability from. A vendor machine from a NodeSet gets its causes through `StateMachineBuilder.For(...).WithCause(...)`, which the first change covers. Worth revisiting if the generator gains table emission. ## Notes for reviewers Two details behind the `ProgramStateMachineState` change: - The five methods are `OptionalPlaceholder` on `ProgramStateMachineType`, so the generated class has no typed properties for them. They are matched on browse name **without** the namespace index, because a subtype that redeclares them puts them in its own namespace — the Boiler model uses `1:Start`, not `0:Start`. - `NodeState.Create` rebuilds the child list from the type template, so a method added by hand before it is gone by the time `OnAfterCreate` runs. `WireCauseMethods(ISystemContext)` is public for that case. **Behaviour change worth flagging:** a `WithCause` against a machine whose `CauseMappings` lack that cause now reports the method non-executable where it previously reported executable. Such a call was already failing with `Bad_NotSupported` inside `DoCause`, so it fails earlier with the code Part 4 specifies rather than newly failing — but it is visible to clients that read the attribute. ## Related Issues - Fixes #4363 ## Checklist - [x] I have signed the [CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf) and read the [CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md) doc. - [x] I have added tests that prove my fix is effective or that my feature works and increased code coverage. - [x] I have added all necessary documentation. - [x] I have verified that my changes do not introduce (new) build or analyzer warnings. - [ ] I ran **all** tests locally using the **UA.slnx** solution against at least .net **framework** and .net **10**, and all passed. - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received. ### Tests New: `StateMachineBuilderCauseExecutableTests` (definition mode, the opt-out, `OnCheckUserPermission` affecting `UserExecutable` only, suspended machines) and `ProgramStateMachineStateTests`, plus two cases added to the existing fluent-builder fixture. All read through `MethodState.ReadAttribute`, so a handler that is installed but never consulted fails the test. Run locally on **net10.0**: `Opc.Ua.Server.Tests` (4797), `Opc.Ua.Core.Tests` (4374), `Opc.Ua.Di.Tests`, `Opc.Ua.Features.Tests`, `Opc.Ua.Robotics.Intent.Tests` and the Boiler AOT tests all pass; `UA.slnx` builds with no new warnings. The .NET Framework legs were not run locally — leaving that checklist box to CI. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
OPC UA .NET Standard Stack
🆕 This is version 2.0 of the OPC UA .NET Standard Stack (current
master).Looking for the supported 1.x release? It lives on the
master378branch (last release:1.5.378). All new feature work happens here onmaster;master378continues to receive security and critical-bug fixes for the 1.x line.
The official OPC Foundation reference implementation of OPC UA for .NET — a certified, cross-platform stack with client, server, PubSub, GDS, complex types, and source-generated tooling. Used in production across industrial control, manufacturing, energy, and IoT systems.
📦 What it is
- A full-stack OPC UA implementation — Core / Client / Server / PubSub / GDS / LDS / Complex Types / Device Integration / Positioning libraries built on .NET, with UA-TCP and HTTPS transports.
- Cross-platform — runs on .NET 10, .NET 9, .NET 8 (LTS), .NET Framework 4.8, and .NET Standard 2.1; ships Native-AOT-friendly assemblies.
- Certified for compliance — the reference server has been certified through an OPC Foundation Certification Test Lab and is continuously verified against the latest Compliance Test Tool (CTT).
- Companion-spec coverage — Part 9 (Alarms & Conditions), Part 11 (Historical Access), Part 13 (Aggregates), Part 16 (State Machines), Part 17 (Alias Names), Part 18 (Role Management), Part 20 (File Transfer), Part 100 (Device Integration), Parts 210/211 (Relative Spatial Location and Global Positioning), OPC-10030 (ISA-95 Common Model) with OPC-10031-4 Job Control V1/V2, OPC 30270 / OPC UA for Asset Administration Shell V2 and V3, OPC 10100-1 (WoT Connectivity), OPC 40001-1 (Industrial Automation), OPC 40010-1 (Robotics).
- Modern developer surface — first-class
Microsoft.Extensions.DependencyInjectionhosting (services.AddOpcUa()), fluent server + client builders, source-generated NodeManagers and DataTypes, and an MCP server so LLMs / Copilot can drive an OPC UA client.
For the full feature breakdown see OPC UA Profiles and Facets and the What's New in 2.0 tour.
🚀 Getting started
You need the .NET 10 SDK to build the repo. From the repository root:
dotnet restore UA.slnx
dotnet build UA.slnx
For the supported target frameworks and platform notes see
the Developer Guide. The official NuGet packages
are published to nuget.org under the OPCFoundation.NetStandard
prefix — the meta package
OPCFoundation.NetStandard.Opc.Ua
pulls in everything, or reference individual packages directly, e.g.
OPCFoundation.NetStandard.Opc.Ua.Client for clients or
OPCFoundation.NetStandard.Opc.Ua.Server for servers. Preview builds from
every successful master build are available from the
GitHub Packages NuGet feed.
Official public 2.0 preview releases are also on nuget.org. Enable prerelease
packages and use 2.0.0-preview.* to float to the latest published
2.0.0-preview.N release.
Sample applications
Each sample has its own README.md with build and run instructions.
Reference applications
- Console Reference Server — the certified reference server (with Quickstarts, CTT, and Mono configs). Also ships as a Docker container.
- Console Reference Client — cross-platform reference client demonstrating sessions, subscriptions, browsing, and method calls.
- Console LDS Server — a standalone
Local Discovery Server built on
Opc.Ua.Lds.Server.
PubSub samples
- Console Reference PubSub Client —
one executable with
publisher,subscriber, andexternal(external-server adapter) modes across the supported transport profiles.
Minimal / Device-Integration samples
- Minimal Calc Server — minimal server built on the source-generated NodeManager pipeline (Calc model).
- Minimal Boiler Server — minimal Boiler-model server with the fluent state-machine builder; Native-AOT publishable.
- Pump Device Integration Server —
minimal Device Integration (Part 100) server using
Opc.Ua.Di.Server's fluent builder. - Minimal Robot Server — OPC 40010 Robotics with independently configurable RSL/GPOS motion and live OpenUSD transforms.
- Intent Enabled Robot — one collaborative arm exposing the Robot Intent command surface: task-level motion verbs tracked on a Part 10 program lifecycle, with missions, command authority and safety-aware refusal.
- Intent Viewer Client — click a target in an OpenUSD viewport and watch the arm execute the resulting intent; also runs headless.
- Bin Picking Cell — Robot Intent, Vision, an eye-in-hand camera, and an in-address-space OpenUSD scene in one reference cell.
- Bin Picking Client — closes the Vision-to-Robot-Intent loop, with optional MCP hosting and an OpenUSD viewport.
- Visual Inspection Cell — hosts Vision, AI Model Management, ISA-95 Job Control V2, and an operator dialog for deterministic machined-bracket inspection.
- Visual Inspection Agent — drives
the inspection loop with typed clients, routes inference through deployment
Invoke, applies recipe verdicts, schedules allowlisted jobs, and records operator ground truth. - AI Model Management sample —
ModelManagementServerpublishes the draft AI Model Management catalogue and routes inference;ModelManagementClientdiscovers deployments and exercises the Methods. - Minimal ISA-95 Server — minimal server hosting the OPC-10030 ISA-95 Common Model together with OPC-10031-4 Job Control V1 and V2, using the typed common-model builder and the in-memory Job Control provider.
More sample projects are maintained in the companion OPC UA .NET Samples repository.
Developer tools
- OPC UA MCP Server — installable .NET tool and container that exposes OPC UA client operations as MCP tools for LLMs and Copilot. The tools also ship as libraries (
…Opc.Ua.Mcp.Core,.PubSub,.Diagnostics,.PubSub.Diagnostics) so an application can embed them next to its own MCP tools.
🔧 Migrating from 1.5.378 to 2.0
The 2.0 release introduces breaking API changes, and comes with a full prescriptive migration guide that links to per-area documentation for the migration sub-topics.
Most of the mechanical migration work is automated:
OPCFoundation.NetStandard.Opc.Ua.MigrationAnalyzerNuGet — install it in your project to get 26 analyzer rules throughUA0030(excludingUA0013,UA0016,UA0017, and the shim-onlyUA0029) plus one-click code fixes for the patterns in the guide. Setup steps are in the package's NugetREADME.md.- Migration agent skill — the
opcua-v20-migrationskill walks Copilot / Claude / any coding agent through installing the NuGet, runningdotnet format analyzersto apply auto-fixes, and handling the small residual manual patterns. The skill knows which sub-doc to load for each symptom so it stays context-efficient.
Copilot CLI discovers the skill automatically inside a clone. To install it for use in any repository:
copilot plugin marketplace add OPCFoundation/UA-.NETStandard
copilot plugin install opcua-v20-migration@opcua-dotnet
If you are still on 1.x and not ready to upgrade, stay on the
master378
branch — it continues to receive security and critical-bug fixes.
🤝 Contributing and license
Community contributions are welcome. Fork the repository, make your changes on a branch, and open a pull request; see CONTRIBUTING.md for the contribution workflow.
Contributors must sign the OPC Foundation Contributor License Agreement (CLA). The CLA "I AGREE" gate is presented automatically on your first PR.
The project is licensed under the OPC Foundation MIT License. Report security vulnerabilities via the process documented in SECURITY.md.
📚 Further reading
- Documentation index — every per-feature doc with a one-line description.
- What's New in 2.0 — narrative tour of the 1.5.378 → 2.0 changes grouped by theme and layer.
- OPC UA Profiles and Facets — facets / transports / security policies the stack implements.
- Migration Guide — prescriptive
per-version migration reference (links to
docs/migrate/2.0.x/). - OPC UA Online Reference — the official OPC 10000 series specification index.
- OPC UA .NET Samples — companion repository with more sample applications.
- Preview Nuget package feed —
prerelease builds from every successful
masterbuild.