Introduces `IClientChannelManager` as the central registry for client-side
transport channels. Sessions and discovery clients now share ref-counted
managed channels per (endpoint, reverse-connect identity); reconnect is
coalesced and notified to attached participants via a new
`IReconnectParticipant` callback interface; service calls are gated by a
three-state lifecycle (`TransportReconnecting` -> `TransportConnectedSessionReactivating`
-> `Ready`) until reactivation completes.
New types in `Stack/Opc.Ua.Core/Stack/Client/`:
- `ManagedChannelKey`, `ChannelState`, `ChannelStateChange`, `ParticipantReconnectResult`
- `IReconnectParticipant`, `IManagedTransportChannel`, `IClientChannelManager`
- `IChannelReconnectPolicy` + `ExponentialBackoffChannelReconnectPolicy`
- `IRetryBudget` + `RetryBudget` (shared retry deadline across the two layers)
- `ClientChannelManager.Managed/Entry/Lease/Metrics/Diagnostics/CertRotation.cs`
partials with refcount, coalesced reconnect, IMeter instruments, ActivitySource
+ EventSource, and automatic ReconnectAllAsync on certificate rotation.
Session integration (Libraries/Opc.Ua.Client):
- `Session.CreateAsync(IClientChannelManager, ...)` overload constructs a
Session that shares its channel with co-located participants.
- `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; 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.
- 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 to UI / health dashboards.
- `ConnectionStateChangedEventArgs.UnderlyingChannelState` populated when
outer reconnect was triggered by a channel fault.
- Shared `IRetryBudget` propagated to channel-mgr so the two layers
enforce a single max-total-time instead of compounding multiplicatively.
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 (~70 new unit + 4 live-server integration fixtures):
- Core: `ClientChannelManagerManagedTests`, `ClientChannelManagerCertRotationTests`,
`RetryBudgetTests`, `OpcUaHttpClientFactoryTests` (56/56 pass).
- Client: `ManagedSession*Tests` updated (129/129 pass) + back-compat
suites pass with `#pragma warning disable CS0618`.
- Sessions integration: `ChannelManagerSharing/TransparentReconnect/SessionLifecycle/CertRotation`
(6 pass, 2 skipped with documented blockers for faulted-entry reset and
RequiresSessionRecreate end-to-end plumbing).
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 section 4 documents the channel manager,
three-state gating, two-level retry with shared `IRetryBudget`, and
HTTPS resilience layering.
- `Docs/MigrationGuide.md` migration recipes for the four obsoleted API
groups.
- `Docs/DependencyInjection.md` channel-manager and HTTPS factory
registration.
- Add new managed session, wrapping session and providing connection management and failover handling
- Add new Subscription engine that can act as alternative to current engine, but is based on channels with worker tasks
- Add a fluent builder for managed session clients
- Replace NodeCache with LruNodeCache, rename ILruNodeCache and LruNodeCache to INodeCache and NodeCache
- Update migration guide and document new functionality.
Marc Schier