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Marc Schier
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# Description Introduces a central `IClientChannelManager` that owns client-side transport channels with reference counting, sharing, coalesced reconnect, and asynchronous participant notification. Sessions, discovery clients, and registration clients targeting the same `ConfiguredEndpoint` (with the same reverse-connect identity) now share a single underlying `ITransportChannel`; reconnect is transparent to callers; and the previous `AttachChannel`/`DetachChannel` + `SessionReconnectHandler` patterns are obsoleted. ## What lands ### Core types (`Stack/Opc.Ua.Core/Stack/Client/`) - `ManagedChannelKey`, `ChannelState`, `ChannelStateChange`, `ParticipantReconnectResult` - `IReconnectParticipant`, `IManagedTransportChannel`, `IClientChannelManager` - `IChannelReconnectPolicy` + `ExponentialBackoffChannelReconnectPolicy` (default mirrors historical `SessionReconnectHandler`: 500 ms → 30 s exponential) - `IRetryBudget` + `RetryBudget` — shared retry deadline so the two-level retry no longer compounds multiplicatively - `ClientChannelManager` — single non-partial sealed class with SOLID-extracted internal types under `Stack/Opc.Ua.Core/Stack/Client/Channels/Internal/`: `ChannelEntry` (behind `IChannelEntryHost`), `ManagedTransportChannelLease`, `ClientChannel`, `ClientChannelManagerMetrics` (IMeter), `ClientChannelManagerCertRotation` (auto `ReconnectAllAsync` on `CertificateManager` rotation), `ClientChannelManagerDiagnostics` (ActivitySource + EventSource). Refcount, coalesced reconnect, and transparent faulted-entry recovery via `SwapFaultedEntryAsync` (swaps a lease's underlying entry on subsequent `ReconnectAsync` when the prior cycle Faulted/Closed, preserves participant, back-off via policy `GetDelay(SwapCount)`) ### Three-state lifecycle gate `Disconnected` → `TransportConnecting` / `TransportReconnecting` → `TransportConnectedSessionReactivating` → `Ready` (or `Faulted` / `Closed`). Only `Ready` releases the service-call gate; the manager bypasses the gate internally for participant `ActivateSession` traffic during reactivation via an `AsyncLocal` scope. ### Session integration (`Libraries/Opc.Ua.Client/Session/`) - New `Session.CreateAsync(IClientChannelManager, …)` overload - `Session` implements `IReconnectParticipant`; reactivation handler distinguishes `Reactivated` / `RequiresSessionRecreate` / `TransientFailure` / `FatalForParticipant` / `FatalForChannel` - `Session.ReconnectAsync(ct)` automatically delegates to the channel manager when wired - `Session.RecreateInPlaceAsync` swaps managed-channel leases for failover-to-different-endpoint via a new atomic `IClientChannelManager.GetAsync(endpoint, participantFactory, …)` overload; same-key recreates delegate to manager reconnect; explicit-channel/connection callers retain legacy behavior - KA failure routes through `IClientChannelManager.ReconnectAsync(channel)` ### ManagedSession integration - `WithChannelManager(...)` builder + ctor param; DI-resolved automatically - Two-level retry: channel-mgr handles transparent reconnect; outer `ConnectionStateMachine` + `IReconnectPolicy` only triggers on terminal channel `Faulted`. Outer-state churn suppressed during channel-mgr cycles via `_channelReconnectInProgress` flag wired through `IManagedTransportChannel.StateChanged` - New `ManagedSession.ChannelStateChanged` event surfaces transparent reconnects - `ConnectionStateChangedEventArgs.UnderlyingChannelState` populated when outer reconnect was triggered by a channel fault - Shared `IRetryBudget` propagated so the layers enforce a single max-total-time ### Discovery / Registration / GDS Channel-manager-aware `CreateAsync` overloads on `DiscoveryClient`, `RegistrationClient`, `ServerPushConfigurationClient`, `LocalDiscoveryServerClient`, `GlobalDiscoveryServerClient`. Each registers a minimal `IReconnectParticipant`; co-located sessions and discovery probes targeting the same endpoint share a channel. ### HTTPS transport (`Stack/Opc.Ua.Bindings.Https/`) - New `IOpcUaHttpClientFactory` abstraction - HTTPS / OPC-HTTPS channels migrated to `IHttpClientFactory` + `Microsoft.Extensions.Http.Resilience` (10.6.0; AOT-compatible on net10 via source generators; legacy direct-HTTP path retained for older TFMs / no-DI consumers) ### DI `AddOpcUa().AddClient(...)` registers `IClientChannelManager` and the named HTTPS `HttpClient` + standard resilience handler automatically. `ManagedSessionBuilder` resolves the manager from DI when present. ### Obsoletions (functional, `[Obsolete]` with guidance) - `IClientBase.AttachChannel` / `DetachChannel` - `SessionReconnectHandler` - `SessionExtensions.ReconnectAsync(connection, ct)` and `(channel, ct)` legacy overloads ### Tests - Core: `ClientChannelManagerManagedTests`, `ClientChannelManagerCertRotationTests`, `RetryBudgetTests`, `OpcUaHttpClientFactoryTests` — **56 / 56 pass** - Client: `ManagedSession*Tests` updated; legacy `SessionReconnectHandlerTests` + `SessionExtensionsTests` preserved with `#pragma warning disable CS0618` — **129 / 129 pass** - Sessions integration: `ChannelManagerSharing` / `TransparentReconnect` / `SessionLifecycle` / `CertRotation` — **7 pass, 1 skipped** (`ChannelManagerExhaustionEscalatesAndRecoversWhenServerReturns` un-`[Ignore]`d and implemented in this PR via `SwapFaultedEntryAsync`; remaining skip is end-to-end `RequiresSessionRecreate` plumbing — carry-forward) - Stress (consolidated `Tests/Opc.Ua.Stress.Tests/Subscriptions/` + `Channels/`): chaos / contract / soak / lifecycle / leak-accuracy / gap / participant-result-aggregation tests merged from the previously-separate `Opc.Ua.Channels.Stress.Tests` project; nightly run via `.github/workflows/stress-test.yml` Builds clean (0 warnings / 0 errors) across all six TFMs: `net472`, `net48`, `netstandard2.1`, `net8.0`, `net9.0`, `net10.0`. ### Docs - `Docs/Sessions.md` new § 4 documents the channel manager, three-state gating, two-level retry with shared `IRetryBudget`, HTTPS resilience layering - `Docs/MigrationGuide.md` migration recipes for the four obsoleted API groups - `Docs/DependencyInjection.md` channel-manager and HTTPS factory registration ## Carry-forward (separate PRs) - End-to-end `ParticipantReconnectResult.RequiresSessionRecreate` → `Session.RecreateAsync` lifecycle wiring (currently incomplete — flagged in the 1 remaining skipped integration test) ## Related Issues - Fixes #3288 - Builds on #3282 (PR that introduced the initial `ITransportChannelManager` skeleton) ## 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. *(Channel-manager-specific tests + ManagedSession/client tests verified across all 6 TFMs; full UA.slnx run is pending CI.)* - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received.
OPC Foundation UA .NET Standard Reference Server
Introduction
This document is referring to the CTT version 1.04.9.398.
This OPC Server is designed to be the default OPC UA Server when opening the OPC UA Compliance Test Tool and it uses an address-space that matches the design of the UACTT and the requirements for OPC UA compliance testing.
It uses the OPC Foundation UA .NET Standard Library. Therefore it supports both the opc.tcp and https transports. There is a .NET framework based server with UI and a .NET Core console version of the server which runs on any OS supporting .NET Standard 2.1 or .NET 8.0 and later.
How to build and run the Windows OPC UA Reference Server with UACTT
- Open the solution UA.slnx with Visual Studio 2026.
- Choose the project
Reference Serverin the Solution Explorer and set it with a right click asStartup Project. - Hit
F5to build and execute the sample.
How to build and run the console OPC UA Reference Server on Windows, Linux and iOS
This section describes how to run the ConsoleReferenceServer.
Please follow instructions in this article to setup the dotnet command line environment for your platform.
Start the server
- Open a command prompt.
- Navigate to the folder Applications/ConsoleReferenceServer.
- To run the server sample type
dotnet run --project ConsoleReferenceServer.csproj. The server is now running and waiting for the connection of the UACTT.
UACTT test certificates
The reference server always rejects new client certificates and requires that the UACTT certificates are in appropriate folders.
- The console server certificates are stored in %LocalApplicationData%/OPC Foundation/pki.
- The Windows .NET framework server stores the certificates in %CommonApplicationData%\OPC Foundation\pki.
- %CommonApplicationData% maps to the path set by the environment variable ProgramData on Windows.
- %LocalApplicationData% maps to a hidden location in the user home folder and depends on the target platform. See Certificates for more information.
Certificate stores
Under pki, the following stores contain certificates under certs, CRLs under crl or private keys under private.
- own contains the reference server public certificate and private key.
- rejected contains the rejected client certificates. To trust a client certificate, copy the rejected certificate to the trusted/certs folder.
- trusted contains trusted client and CAs certificates and CRLs.
- issuer contains CAs certificates and CRLs needed for validation.
- trustedUser contains trusted user and user CA certificates and CRLs.
- issuerUser contains user CA certificates and CRLs needed for validation of the certificate chains.
Placing the UACTT certificates
CTT creates a PKI folder in a new project. There is a subfolder copyToServer which contains the application and user identity certificates. Copy the ApplicationInstance_PKI certificates for testing with the UACTT to the following stores:
- trusted/certs: trusted certificates
- trusted/crl: revocation lists of trusted certificates
- issuer/certs: issuer certificates
- issuer/crl: revocation lists of issuer certificates
Copy the X509UserIdentity_PKI certificates for testing with the UACTT to the following stores:
- trustedUser/certs: trusted user certificates
- trustedUser/crl: revocation lists of trusted user certificates
- issuerUser/certs: user issuer certificates
- issuerUser/crl: revocation lists of user issuer certificates
UACTT Testing
Download and install the OPC UA Compliance Test Tool.
Note: Access to the UACTT is granted to OPC Foundation Corporate Members.
UACTT sample configuration
A sample configuration for the UACTT Version 1.04.9.398 can be found in UAReferenceServer.ctt.xml. Originally the reference server was certified only against the Standard UA Server profile, the Method Server Facet and the DataAccess Server Facet, in addition to all security related profiles. During release testing all Conformance Units should be enabled / checked.
Enabling Alarms & Conditions
The address space for Alarms contains a Start method which needs to be called to produce alarms for CTT testing. The method is called from a connected client.
The ConsoleReferenceServer has also a command line option -ctt which starts the Alarms when the server is started. The following Alarm instances are available for monitoring:
AlarmConditionTypeDiscrepancyAlarmTypeLimitAlarmTypeExclusiveLimitAlarmTypeExclusiveDeviationAlarmTypeExclusiveRateOfChangeAlarmTypeNonExclusiveLimitAlarmTypeNonExclusiveDeviationAlarmTypeNonExclusiveRateOfChangeAlarmTypeDiscreteAlarmTypeSystemOffNormalAlarmTypeExclusiveLevelAlarmTypeNonExclusiveLevelAlarmTypeOffNormalAlarmType
Known missing Tests and Issues
Depending on the setup in the provided project configuration, unsupported profiles should be skipped. At the time of writing (1.4.368) the following tests, profiles or facets are not yet covered or not configured due to issues:
- no support for events, historian and only a few basic Alarms & Conditions.
- Decimal type causes crash of CTT (needs investigation)
- no Image / Enumeration scalar test cases
- Arrays may not include Variant (needs investigation)
- no ArrayItemType implemented
- multiple hierarchical references test node missing
- deprecated security profiles support for SHA1/1k RSA keys implemented not according to certification. SHA1/1k keys can only be turned on/off for all profiles, not just for the deprecated profiles.
- Monitored Items with array are failing a few test cases.
It is recommended to run the server as retail build with disabled logging, to avoid side effects due to timing artifacts when log entries are written to a disk drive.
Running the CTT against a Docker container
Please refer to the Docker container of the Reference Server documentation page. Once setup to map the certificate store and the configuration to a local folder, follow the instructions above to copy the certificates to the PKI and get started.
Finding the Address Space Configuration Code
- Project: Reference Server
- File: ReferenceNodeManager.cs
- Method: CreateAddressSpace
Finding the UA Services
- Project: Opc.Ua.Server
- File: StandardServer.cs