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romanett
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# Description Reduces the server subscription API surface per the measurements from issue #4185. ## ISubscription: 42 → 30 members (#4185) A call-site census of the 11 "publish-pipeline protocol" members plus `Publish` (all 68 `src/` projects, samples, tools, fuzzing, tests) found **zero callers outside `Opc.Ua.Server`** and split the members three ways: - **Deleted (4):** `ItemReadyToPublish` and `ItemNotificationsAvailable` were dead — zero callers repo-wide and implementation bodies commented out since before 1.5.378 — the obsolete parameterless `SessionClosed()` had zero callers, and `TransferSessionAsync` (the one-shot direct transfer, which bypassed the reservation protecting a transfer against a concurrently closing source session) lost its last caller once the manager always uses the claim/prepare/commit protocol. - **Internalized (8):** `PublishTimerExpired`, `Acknowledge`, `PublishTimeout`, `SubscriptionTransferred`, `AvailableSequenceNumbersForRetransmission`, `QueueOverflowHandler`, `SessionClosed(ISession)` and `Publish` move to `internal interface ISubscriptionPublishPipeline : ISubscription`, implemented **explicitly** by `Subscription` (the `ISubscriptionMonitoredItemLifecycle` shape) so they are unreachable through the public concrete class too. `Publish` goes with them deliberately — it is the same hazard class (consumes notifications, advances sequence numbers) with the same single production caller. - **Kept public (1):** `ResendData` drops out of the issue's list — its only caller is the `Server_ResendData` UA-method handler in `DiagnosticsNodeManager`, resolving via `TryGetSubscription` like `GetMonitoredItems` does. It is service-facing, not pipeline. ## The pipeline contract is complete: SessionPublishQueue traffics only in it `SessionPublishQueue` becomes `internal sealed` (zero consumers outside the assembly; `SentMessageQueue` already was) and works **solely with `ISubscriptionPublishPipeline`** — no `ISubscription` and no concrete `Subscription` anywhere in the file. To get there, the internal transfer-claim protocol (`TryBeginTransfer`, `PrepareSessionTransferAsync`, `CompleteTransfer`, `AbortTransfer`, `TryRestoreSessionAfterFailedTransfer`) moved from `internal` methods on the concrete class onto the internal interface, implemented explicitly. That completes the contract, so `TransferSubscriptionsAsync` loses its two-tier shape: the ~6 `subscription as Subscription` null-guard branches and the degraded `TransferSessionAsync` fallback for non-`Subscription` implementations are gone — one code path, always the claim/prepare/commit/rollback protocol, and `ISubscription.TransferSessionAsync` is deleted with it. Subscription creation fails with `Bad_InternalError` when a `CreateSubscription` override returns a type not derived from `Subscription`, instead of publishing partially — such implementations were already second-class (transfer required the concrete type before this change). This is the headline behavior change for exotic extenders and is documented prominently in `docs/migrate/2.0.x/sessions-subscriptions.md`. The durable-subscription open question in the issue is answered **no**: `Subscription/Persistence/` never references `ISubscription` (the store deals in `IStoredSubscription` DTOs; restore constructs the concrete type via `Subscription.RestoreAsync` inside the manager), so the internalization cannot break a store implementer. ## #4186: measured, prototyped, and deliberately kept as-is Body inspection showed only 4 of the 10 `ISubscriptionManager` wrappers are pure lookup-and-delegate (`Republish`, `SetTriggering`, `ModifyMonitoredItemsAsync`, `SetMonitoringModeAsync` — one caller each); the other 6 carry logic with no `ISubscription` substitute. A collapse of the four was implemented and then reverted on this branch: it traded ten uniform id-addressed members for a mixed dispatch shape in `StandardServer` without reducing what a reader must understand. **Every subscription service keeps going through `ISubscriptionManager`**; the wrapper bodies now resolve against the pipeline-typed registry. The decision is recorded in `plans/ServerRuntimeAnalysis.md` (open question 5). ## Compatibility treatment Removals are outright, per the documented no-`[Obsolete]`-shim policy for these interfaces (`docs/MigrationGuide.md` — re-adding an interface member would break every implementer; net48/netstandard2.0 have no default interface methods). In its place: - Migration analyzer **UA0030** (pipeline members + `SessionPublishQueue`, distinguishing deleted no-ops from internalized protocol), with tests, following the UA0024 syntax-based pattern. The transfer-claim members were never public in 1.5.378, so they need no migration story. - `docs/MigrationGuide.md#ua0030` section with before/after code; the `docs/migrate/2.0.x/sessions-subscriptions.md` section that told implementers to *add* `SessionClosed(ISession)` is replaced with the derive-from-`Subscription` story; the 2.0.x README symptom table routes the rule. - All 11 removed/internalized members existed in 1.5.378 (verified against `master378`), so each is documented as a 2.0 break. ## Tests Converted, not deleted. `Mock<ISubscription>` setups of pipeline members become `Mock<ISubscriptionPublishPipeline>` — Moq proxies the internal interface via a new `InternalsVisibleTo("DynamicProxyGenAssembly2")` (keyless; the SDK appends `$(PublicKey)` under `SignAssembly`, and signed pipelines do not run tests, matching the existing `Opc.Ua.Redundancy.Kubernetes` precedent). A test-side extension shim forwards the original member names (pipeline + transfer protocol) so the direct call sites on concrete `Subscription` instances compile unchanged. The transfer-race tests' typed reflection probes into `m_abandonedSubscriptions` follow the field's new type. - `Opc.Ua.Server.Tests` (net10.0): 4795 tests, 0 failures - `Opc.Ua.Subscriptions.Tests`, `Opc.Ua.Subscriptions.Durable.Tests`, `Opc.Ua.Subscriptions.Classic.Tests` (net10.0): green - `Opc.Ua.MigrationAnalyzer.Tests`: green incl. the new UA0030 tests - net48 gate: solution build green; subscription-area fixtures green (the known pre-existing local hosting-test environment failures reproduce identically on unmodified master) ## Related Issues - Fixes #4185 - #4186 was measured and prototyped on this branch and deliberately **not** taken (see the section above); the decision is recorded in `plans/ServerRuntimeAnalysis.md`. ## 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. _(net10 suites fully green locally; net48 build green and subscription-area fixtures green — the remaining net48 hosting-test failures on my machine reproduce identically on unmodified master.)_ - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Fable 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 pick the split
OPCFoundation.NetStandard.Opc.Ua.Core / .Client / .Server /
.Bindings.Https packages directly. Preview builds for every successful
master build are available in the
Azure DevOps opcua-preview feed.
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 covering telemetry, packages, source generation, types, encoders, node states, identity, certificates, configuration, sessions / subscriptions, alarms / model change, and TimeProvider.
Most of the mechanical migration work is automated:
OPCFoundation.NetStandard.Opc.Ua.MigrationAnalyzerNuGet — install it in your project to get analyzer warnings (UA0001–UA0022)- 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.
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 for Asset Administration Shell — OPC 30270 / AAS V2 ingestion-only metamodel support and the AAS V3 metamodel, registry, document round-trip, packages, federation and conformance matrices.
- 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 feed — prerelease builds from Azure DevOps.