Wolfgang ColsmanandMarc Schier
3c5aa421d3
# Description ## Depends on This pull request depends on #4883 (application-supplied reverse connection sources) and includes its commits. #4884 (ServiceLevel-driven failover, member probing and read statuses) is already merged into master. Current master and the concurrent dependency merges are preserved without rewriting branch history. Review the complete PR diff, not only the last commit. Master's ManagedSession logging event IDs 32-35 are preserved; unused reverse-connection cleanup uses event ID 36. ## Problem With Reverse Connect, each member of a non-transparent redundant Server set opens its own connections to the Client. The existing redundancy path assumed dialed connections for endpoint resolution, ServiceLevel probes and recovery, preventing a Client from using the members' incoming connections consistently. ## Change - `IReverseConnectionAvailability : IReverseConnectionSource` exposes `GetAvailableEndpointUrls(string serverUri)`. `ReverseConnectManager` advertises unaccepted held connections and excludes a connection as soon as it is accepted, including inside the accepting callback. - Optional `ServerRedundancyOptions.MemberConnections` selects the reverse-connect member resolver. Endpoint matching preserves the ServerUri, security mode, security policy and URL scheme checks. - Member probing, failover and subsequent recovery use the member source, including for a custom resolver or explicit target whose endpoint does not set `ReverseConnect.Enabled`. - The initial Server retains its authenticated endpoint and original source, manager or outbound transport. A-to-B-to-A failover uses that original path consistently for resolution, availability, probing and recovery. - Switching to another member waits for at least `PeerDiscoveryTimeout`, including after the previous reconnect budget expires. The reverse-source dependency's cancellation and exhausted-budget handling are preserved. - Without `MemberConnections`, existing dialed member behavior remains unchanged. ## Tests The real reference-server fixture covers source, manager and outbound initial connections, each with marked and unmarked member endpoints. All six combinations exercise member failover, transport closure and member recovery, then handler-selected failback to the initial Server with probing enabled. They assert readable ServiceLevel, fresh member connection requests and no initial-Server waits through the member source. The manager lifecycle regression asserts that a held connection is available before acceptance and unavailable inside the accepting callback. Existing resolver, handler, reactive failover, unavailable-member and reverse-source budget/cancellation tests remain enabled. ## Repair Evidence, 2026-10-23 Local Windows developer checks with .NET SDK 10.0.402, Release/net10.0, before the later concurrent master integration: - Initial-source/member routing: 6 passed. - Combined dependency budgets, routing and accepted availability: 15 passed. - Affected client redundancy, resolver, handler and manager lifecycle suites: 198 passed. - Every listed run completed with 0 build warnings and 0 build errors. - The dependency's WoT retained-input fixture repair passed the original case and both injected-conflict cases (3 tests), plus 15 neighboring retained-input and retry-boundary cases. It checks exactly one correct input per bounded publication attempt and retains the exact-one cold-recovery assertion. No production WoT behavior is changed by that repair. The newly integrated baseline is being checked separately; the PR comments and GitHub checks report its results. These prior results do not claim completion of current-head full CI. ## Earlier Evidence The original PR description recorded these results for historical head `dc471de5d`, not the current head: client builds on net10.0/net9.0/net8.0/net48 with no warnings or errors; affected classes 107/107 on net10.0 and net48; Sessions 80/80 on net10.0; the full Client project 3311 executed and passed out of 3315 total; changed-file whitespace/style/analyzer checks clean. Those historical checks have not been relabeled as current-head evidence. ## Operational Notes ServiceLevel probing consumes member connections. Members must continue opening connections while they are probed and recovered. A previously resolved member remains selectable while its probes obtain connections; a member whose probe cannot obtain a connection and reports none available becomes unavailable. The initial Server's original transport is not subject to the separate member-source availability filter. ## Checklist - [x] I have signed the CLA and read CONTRIBUTING. - [x] Regression tests cover the repaired behavior. - [x] Reverse Connect documentation describes initial-source failback, unmarked endpoints and accepted-connection availability. - [ ] Current-head full solution tests on .NET Framework and .NET 10 have completed successfully. - [ ] All required current-head CI checks and CodeQL checks have passed. - [ ] All review threads have been addressed and reviewed. --------- Co-authored-by: Marc Schier <marcschier@users.noreply.github.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 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; ships Native-AOT-friendly assemblies.
- Conformance regression testing — the reference server is tested with the Compliance Test Tool (CTT) through the CTT regression workflow. These results identify regressions; they do not constitute product certification.
- Companion-spec coverage — Part 9 (Alarms & Conditions), Part 10 (Programs), 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), Part 110 (Asset Management Basics), 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), Part 200 (Industrial Automation), OPC 40001-1/-2/-3/-4/-101 (Machinery with Process Values, Job Management, Energy and Result Transfer), OPC 34100 (Energy Consumption Management), OPC 30081 (PA-DIM), OPC 40010-1 (Robotics), OPC 40100-1/-2 (Machine Vision control and asset management), OPC 40501-1 and OPC 40505 (Machine Tools and independent wireless peripherals), OPC 40210 (Geometric Measurement Systems, with its documented upstream Production-facet exception), OPC 40020-1 (Cranes and Hoists), OPC 40223 (Pumps and Vacuum Pumps), OPC 30010 (AutoID Devices), OPC 40200 (Weighing Technology) with OPC 30050 (PackML).
- Hosting and code generation —
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
To run a first OPC UA client and server, from NuGet packages or from the samples in this repository, follow Getting started. The documentation index then leads from the core concepts to advanced and experimental features.
The recycling operator console demonstrates live browser monitoring, native companion-specification inspection, material genealogy, and authorized controls over the synthetic recycling line.
You need a stable .NET SDK
version 10.0.400 or later to build the repo. global.json selects the
highest installed stable SDK, including newer major versions. 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
bundles a default set of stack packages; see its
package inventory.
Reference PubSub and other optional feature packages separately, or select
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,
which is the only feed they are published to. nuget.org receives a version
only through a manually approved promotion from a release/<major>.<minor>
branch — that is where the 2.0.0-preview.N packages already on nuget.org
came from, via the earlier release/2.0.0 line. To use those, enable
prerelease packages and float with 2.0.0-preview.* until 2.0.0 is
released. The XRegistry, WoT Connectivity, Robotics, CranesHoists,
Redundancy, Positioning, OpenUSD, and AI package families, the Vision.OpenUsd
renderer, and the Robotics MCP extension remain
preview packages when the root version is promoted to a stable version, and
keep their own -preview.N versions on nuget.org. This includes all CranesHoists
model/server/client/MCP packages and their Debug variants.
The Vision, MachineVision, MachineTool (including WMTP), and GMS
model/client/server packages and their MCP packages follow the root version
without a preview-only override;
development builds still inherit the root prerelease version. See
docs/ReleaseProcess.md for how and when stable
versions are released.
Samples
The platform-independent sample applications show how to use the stack's core services and companion models in client/server workflows. More applications, including platform-specific examples, are available in the companion OPC UA .NET Samples repository.
Developer tools
- UaLens — NativeAOT-capable desktop engineering workspace for secure connections, monitoring, alarms, structured values, history, administration, PubSub, continuity diagnostics, and guided companion-model tasks. See build and artifact qualification.
- OPC UA MCP Server — installable .NET tool and container exposing OPC UA client operations to LLMs and Copilot. Embeddable libraries provide Part 4 services, PubSub, diagnostics, Robotics and Vision, plus industrial companion profiles for AMB, Machinery, Scales, Pumps, AutoID, Device Integration, ISA-95 and Positioning. The WoT and xRegistry profiles add asset/registry management and bounded document validation, planning and NodeSet conversion. Stack workflow profiles provide GDS/credential issuance, roles/users, files, alarms, history, schemas, and host-authorized PubSub and live WoT execution.
🔧 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 remaining manual changes. It selects the migration sub-document for each symptom.
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.
- Preview Nuget package feed —
prerelease builds from every successful
masterbuild.