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OPC UA .NET Standard stack documentation

Here is a list of available documentation for different topics:

UA Core stack related

  • OPC UA Profiles and Facets - Overview of supported OPC UA profiles, facets, security policies, and transport protocols.
  • Transport Profiles - Developer guide for the wire transports: opc.tcp / HTTPS (binary + JSON + REST) / WSS (binary + JSON), including server hosting and client connect examples.
  • REST Binding (OpenAPI Mapping) - OPC UA Part 6 §G.3 OpenAPI mapping: ASP.NET Core MVC controllers for every spec service, Compact / Verbose encoding negotiation, four pluggable auth modes (Anonymous / Bearer JWT / HTTP Basic / Mutual TLS), and the symmetric IWebApiClient.
  • What's New in 2.0 - Developer-facing tour of the 1.5.378 → 2.0 changes, grouped by theme and layer, with links to deeper feature docs.
  • Migration Guide - How to migrate from a previous version.
  • Sessions, Reconnection, and Subscription Engines - Architectural overview of Session, ManagedSession, SessionReconnectHandler, and the classic / V2 subscription engines, including guidance on which to use.
  • About .NET platform support, Nuget packages and versioning.
  • How X.509 Certificates are used in the certificate stores.
  • Using the Reverse Connect for the UA-TCP and WSS transports.
  • Support for the TransferSubscriptions service set.
  • Diagnostics — logging, telemetry, server audit events, server diagnostics nodes, and packet capture.
  • Performance Benchmarks — BenchmarkDotNet methodology, the 2.0 (master) vs 1.5.378 (master378) comparison, root-cause analysis of the encoder/decoder/session regressions and their real-world impact, the subscription-notification (pooled encodeable) micro-benchmarks, server session scalability (the 500-session capability, sizing and bottlenecks), and planned future work.
  • Server Session Scalability — why a single node tops out at ~2000 concurrent sessions, the establishment vs steady-state boundaries (socket backlog, the BadTcpInternalError retry-storm amplifier, the O(N²) diagnostics rescan, CreateSession crypto-under-lock, the RSA CPU wall, and the held-Publish worker-accounting coupling) with code references, and a prioritized admission-control / rate-limiting roadmap for moving beyond it.
  • Support for WellKnownRoles & RoleBasedUserManagement.
  • Pluggable Identity Providers — interfaces (IClientIdentityProvider, IUserTokenAuthenticator, IAccessTokenProvider, ITokenIssuer, IIdentityClaims) plus the OPC 10000-6 §6.5.2.2 IssuerEndpointUrl JSON parser for OAuth2 / OIDC / Entra / JWT flows.
  • Support for ECC Certificates.
  • Working with ComplexTypes - Custom structures and enumerations.
  • Client-based NodeSet Export - Export server address space to NodeSet2 XML.
  • Source generated [DataTypes] - How to annotate POCO classes and let the source generator generate the IEncodeable implementation.
  • Runtime Schema Generation - Produce XSD, OPC Binary (BSD) and JSON Schema (Part 6 Annex C, compact + verbose) for generated encodeable types and dynamically added complex types via the injectable ISchemaProvider; schemas are built as object models in code (trimmable, NativeAOT compatible).
  • Source generated NodeManagers - Emit an AsyncCustomNodeManager from a model design XML and wire callbacks via the fluent INodeManagerBuilder API; supports NativeAOT single-file servers (samples: MinimalBoilerServer, PumpDeviceIntegrationServer). Covers engineering units, property initialisation, alarms, simulation timers, instance creation, NAMUR-style supervision, multi-model composition, and the fluent state-machine builder on top of any FiniteStateMachineState subclass. Cross-assembly model references are tracked via the ModelDependencyAttribute. Companion-spec packaging — model + server + client library trios — is covered end-to-end by the Device Integration developer guide using the Opc.Ua.Di / Opc.Ua.Di.Server / Opc.Ua.Di.Client trio as the worked example.
  • Device Integration (DI) developer guide - End-to-end documentation for the Opc.Ua.Di* library trio: fluent IDeviceBuilder, device sub-type extensions (AddSoftware, AddBlock, AddConfigurableObject, AddLifetimeIndication, WithSupportInfo), hosting integration (AddOpcUaDi / ConfigureDevicesFor), lock service, software-update package store, and client helpers (DiLockClient, DiTopologyClient, SoftwareUpdateClient). Includes a section enumerating supported OPC 10000-100 features against the spec.
  • Alias Names - Full server + client support for the OPC UA Part 17 alias-name model (AliasNameType, AliasNameCategoryType, FindAlias, FindAliasVerbose, AddAliasesToCategory, DeleteAliasesFromCategory, LastChange).
  • Alarms and Conditions - Full server + client support for OPC UA Part 9. Server-side state types for latched/silenced/out-of-service alarms, alarm groups and suppression engine, alarm rate metrics. Client-side AlarmClient, typed alarm event records, fluent AlarmEventFilterBuilder, IAsyncEnumerable alarm streaming via AlarmStreamExtensions.
  • Historical Access (Part 11) - Server provider model (IHistorianProvider family) and InMemoryHistorianProvider, plus the client HistoryClient (session.Historian()) for raw/modified/at-time/processed reads, annotations, and updates.
  • Aggregates (Part 13) - All 37 standard Part 13 v1.05.07 aggregate functions over historical data: server AggregateManager / calculators, native push-down vs framework fallback, AnnotationCount via the annotation provider, AggregateConfiguration defaults, and the client ReadProcessedAsync helper.
  • Subscriptions and Monitored Items Service Set - V2 subscription engine API. Covers ISubscriptionManager for long-lived callback-based subscriptions, the declarative+imperative SetTriggering API with N:M support and automatic replay on recreate/reconnect, and IStreamingSubscription (IAsyncEnumerable-based) for state-machine waits and short-lived monitoring (ManagedSession.DefaultStreaming, TakeUntilAsync / WithTimeoutAsync helpers).
  • Unbounded Monitored Items - V2 logical-subscription wrapper that transparently splits monitored items across multiple server-side partitions when the per-subscription cap is exceeded (IPartitionedSubscription, MonitoredItemOptions.Affinity, reactive Bad_TooManyMonitoredItems fallback, secondary-partition idle-delete).
  • State Machines - Generic, extensible Part 16 state-machine API. Client side: streaming + read helpers on the source-generated *TypeClient proxies (GetCurrentFiniteStateAsync, ObserveFiniteTransitionsAsync, WaitForStateAsync). Server side: unified fluent StateMachineBuilder with two complementary modes — definition (Create(...) + AddState / AddTransition / OnCause for ad-hoc machines via FluentFiniteStateMachineState) and lifecycle (For(...) / INodeBuilder.AsStateMachine() + OnEnterState / WithCause / WithTimedTransition to attach behavior to stack-shipped or generator-emitted FSMs). Vendor state machines inherit both ends of the API automatically.
  • Model Change Tracking - Client-side address-space change tracking with per-node INodeCache invalidation; server-side ModelChangeAggregator and auto-emitted GeneralModelChangeEvent from CustomNodeManager.CreateNode/DeleteNode.
  • NodeManagement Service Set - Server-side AddNodes / DeleteNodes / AddReferences / DeleteReferences, including the INodeManagementAsyncNodeManager opt-in pattern and per-NodeManager AllowNodeManagement gate.
  • Dependency Injection - The unified services.AddOpcUa() / IOpcUaBuilder surface for hosting OPC UA components in Microsoft.Extensions.DependencyInjection / the .NET Generic Host (servers as IHostedService, options via Action<T> or IConfiguration, AOT-friendly).
  • AuthorizationService - Modern Part 12 StartRequestToken / FinishRequestToken, ITokenIssuer, and GDS token issuance.
  • Fuzz testing - SharpFuzz + afl-fuzz + libFuzzer integration. Three areas: Encoders (Binary/JSON/XML decoders, built-in type readers, parser entry points), Certificates (X509CRL, X509 extension parsers, PEMReader, Pkcs10CertificationRequest, ASN.1 helpers), and Network (UA-SC framing via Opc.Ua.Core.Diagnostics + internal TcpMessageParsers seam on Opc.Ua.Core). The fuzz-tester custom agent drives the whole toolchain autonomously: it detects OS-available engines, runs them in parallel, fixes novel findings per repo guidelines, adds the failing input as a regression asset, and pushes one commit per fix until the user says stop.
  • KeyCredentialService - Pull, Push, and experimental bridge guidance for Part 12 KeyCredential flows.
  • PubSub (Part 14) - Publisher/subscriber support library: architecture, fluent builder, transports (UDP / MQTT 3.1.1 + 5.0 / Ethernet Layer 2), encodings (UADP / JSON), security, and server-side address space.
    • Migration sub-doc - 1.5.378 → 2.0 breaking API, transport, JSON, and field-encoding changes, plus the compatibility matrix.
    • Ethernet transport - Layer 2 PubSub (opc.eth://, EtherType 0xB62C, 802.1Q VLAN) with native AF_PACKET / BPF, SharpPcap, and in-memory backends.
    • External server adapter - Bind PubSub publishers, subscribers, and Action responders to an external OPC UA server through ManagedSession.
    • Dependency Injection extensions - AddPubSub, AddPubSubPublisher, AddPubSubSubscriber, AddPubSubSecurityKeyServiceClient/Server, AddPubSubAddressSpace.
    • Profiles - Datagram-v2, SKS pull / push, AES-128/256-CTR security facets.
    • PubSub Diagnostics - packet capture, dissection and replay of UDP / MQTT PubSub traffic, including decryption of encrypted UADP messages.

Reference application related

  • Reference Client documentation for configuration of the console reference client using parameters.
  • Reference Server documentation for running against CTT.
  • ConsoleReferencePubSubClient documentation for the PubSub reference sample (publisher / subscriber / external-server adapter modes).
  • Provisioning Mode for secure certificate provisioning and initial server configuration.
  • Using the Container support of the Reference Server in Visual Studio 2026 and for local testing.

Starting with version 1.5.375.XX the Windows Forms reference client & reference server were moved to the OPC UA .NET Standard Samples repository.

Global Discovery Server (GDS)

  • GDS Developer Guide — Application registration, certificate management (pull & push models), roles and authorization, provider implementation, end-to-end examples.
  • KeyCredentialService — Credential issuance for non-OPC UA services (MQTT, REST), IKeyCredentialRequestStore provider guide, ISecretStore integration.
  • AuthorizationService — OAuth2-style access token issuance, IAccessTokenProvider implementation guide.
  • Role-Based Security — Part 18 roles and claim-based identity-mapping rules.
  • Identity Providers — server and client identity-provider architecture.
  • Dependency Injection — dependency injection hosting and identity registration extensions.