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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 Client
Introduction
The console reference client can be configured using several console parameters. Some of these parameters are explained in more detail below.
To see all available parameters call console reference client with the parameter -h.
Reverse Connect
The OPC UA reverse connect feature allows an OPC UA server to initiate the connection to a client, rather than the traditional model where clients connect to servers. This is particularly useful in scenarios where the server is behind a firewall or NAT, making it difficult for clients to directly connect to it.
How to use Reverse Connect
To enable reverse connect mode, specify the client endpoint URL using the --rc or --reverseconnect parameter:
dotnet ConsoleReferenceClient.dll --rc=opc.tcp://localhost:65300 opc.tcp://localhost:62541/Quickstarts/ReferenceServer
The client will start a reverse connect listener on the specified endpoint (e.g., opc.tcp://localhost:65300) and wait for the server to connect to it.
Example: Client and Server with Reverse Connect
-
Start the client with reverse connect listener on port 65300:
dotnet ConsoleReferenceClient.dll --rc=opc.tcp://localhost:65300 opc.tcp://localhost:62541/Quickstarts/ReferenceServer -
In a separate terminal, start the server with reverse connect to the client:
dotnet ConsoleReferenceServer.dll --rc=opc.tcp://localhost:65300 -a
The server will establish a reverse connection to the client endpoint, and the client will use this connection to communicate with the server.
How to specify User Identity
Username & Password
Specify as console parameters:
-un YourUsername
-up YourPassword
Certificate
Place your user certificate in the TrustedUserCertificatesStore (the path can be found in the client configuration XML). Make sure to include an accessible private key with the certificate.
Specify console parameters:
-uc Thumbprint (of the user certificate to select)
-ucp Password (of the user certificates private key (optional))