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romanett 9b034f8291 Enable nullable reference types centrally; migrate all unset and annotations-only projects (#4700) 
# Description

Nullable reference types are now enabled once, in `common.props`, and
every project in the repository builds warning-clean with them.

**Configuration**
- `<Nullable>enable</Nullable>` lives in `common.props`. All per-project
`<Nullable>` settings are removed: 178 project files (enable,
annotations, and the `disable` in the three Aot test projects).
- 419 per-file `#nullable enable`/`restore` directives and the 4
`#nullable disable` directives are removed.
- Kept on purpose:
- The 5 `<auto-generated>` schema files (`UANodeSet.cs`, `UA Type
Dictionary.cs`, `OPCBinarySchema.cs`, `SecuredApplication.cs`,
`PInvokeHelper.cs`) keep `#nullable enable`. The compiler ignores the
project setting in generated code, so the directive is required there.
- `tests/Opc.Ua.Interop.LegacyPeer` keeps `disable`. It builds against
the 1.5.378 packages and does not import the repository props.
- `docs/DeveloperGuide.md` and `.github/copilot-instructions.md` now
describe the central setting.

**Migration** (the 43 unset and 13 annotations-only projects, roughly
10k diagnostics)
- **Production code: annotated at the declarations.** Covers
`tools/Opc.Ua.SourceGeneration.Core`, `src/Opc.Ua.Lds.Server` and the
LDS sample.
- Members, parameters and returns are nullable where null actually
flows.
- Null-check helpers carry `[NotNullWhen]` (`IsNull`, `IsValidXmlName`,
`IsMethodTypeDesign`).
- `CoreUtils.Format`, `Utils.Format`, `ITemplateWriter.WriteLine` take
`params object?[]`. `Template.AddReplacement` takes `string?` (rendering
already skips null replacements).
- `IRegisteredServerStore.RegisterAsync` returns
`Task<RegistrationEntry?>`: it returns null when a registration is
removed.
- Dereferences backed by an invariant (for example, the validated model)
use `!`, so runtime behaviour is unchanged.
- **Behavioural changes in production code** (small, deliberate):
- `NodeSetToModelDesign` throws `InvalidOperationException` when the
file is not a NodeSet. Before, it threw a NullReferenceException on the
next line.
- `ModelDesignValidator` starts its lookup tables empty instead of null.
A redundant `if (m_nodes == null) return;` guard is gone.
- **Test code: minimal annotations.**
  - `?` on values that can be null, `!` where the test asserts non-null.
  - `= null!` for fixture members assigned in SetUp.
- `TryGetStructure<T>(out T? x)` where the inferred `T?` broke the
`IEncodeable` constraint.
- A few redundant `== null` checks on structs (`NodeId`, `ArrayOf<T>`)
folded into the adjacent `IsNull`/`Count` checks.

**Notes for reviewers**
- The diff is large (~1,500 files) but almost entirely mechanical: `?`,
`!` and directive removal. The non-annotation changes are listed above.
- Known follow-up, not done here:
`IModelDesign.Namespaces/TargetNamespace/NamespaceUris` stay
non-nullable even though the validator returns null before it loads a
dictionary. Making them nullable would ripple through every generator
call site.

## Related Issues

- Fixes #4439

## Checklist

- [ ] 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.
- [ ] 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.
- [ ] I fixed **all** failing and flaky tests in the CI pipelines and
**all** CodeQL warnings.
- [ ] I have addressed **all** PR feedback received.

The "no new warnings" box covers net10.0 and net48: full non-incremental
builds of `UA.slnx`, `tools/SourceGeneration.slnx`,
`tools/MigrationAnalyzer.slnx` and the Aot test projects finished with 0
warnings and 0 errors under the repository's warnings-as-errors
settings. net9.0 and net8.0 also had no nullable diagnostics, but they
were not rebuilt after the final fixes. Tests have not been run locally
yet.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-08 08:48:13 +02:00
..
Properties
Bound reconnect cleanup and organize samples by domain (#4276)
2026-08-21 04:35:47 +00:00
MinimalClient.csproj
Enable nullable reference types centrally; migrate all unset and annotations-only projects (#4700)
2026-10-08 08:48:13 +02:00
Program.cs
Add a documentation learning path and fix issues found while verifying it (#4555)
2026-09-28 19:19:39 +00:00
README.md
Add a documentation learning path and fix issues found while verifying it (#4555)
2026-09-28 19:19:39 +00:00

README.md

OPC Foundation UA .NET Standard Minimal Client

Introduction

The minimal console client demonstrates a clean, lightweight OPC UA client implementation using the modern fluent API and dependency injection with HostApplicationBuilder. It is designed as an educational reference and starting point for building OPC UA client applications.

Key Features

  • Fluent DI API: Uses HostApplicationBuilder with fluent .AddOpcUa(), .AddClient(), .AddSubscriptions(), and .AddAlarms() configuration
  • Secure by Default: Discovers a SignAndEncrypt / Basic256Sha256 endpoint unless --insecure is explicitly supplied
  • Managed Sessions: Leverages the modern IManagedSessionFactory for simplified session management
  • Fluent Subscriptions: Creates a V2 subscription and monitored item with AddSubscription() and TryAddMonitoredItem()
  • Dependency Injection: Fully integrated Microsoft.Extensions.DependencyInjection with host-based lifetime management
  • Service-Provided Telemetry: Uses the DI-integrated ITelemetryContext for logging, metrics, and activity tracking
  • Alarms & Conditions: Includes A&C client support via .AddAlarms()
  • Console Logging: Integrated console logging for visibility into client operations
  • Native AOT Compatible: Supports ahead-of-time compilation with .NET

Getting Started

Prerequisites

  • .NET 10.0 SDK or later
  • An OPC UA server accessible at the specified endpoint

Running the Client

To connect to the default MinimalBoilerServer:

dotnet run

The server certificate must already be trusted. For local development only, explicitly opt into automatic trust:

dotnet run -- --auto-accept

To explicitly select an endpoint without message security:

dotnet run -- --insecure

To connect to a different server:

dotnet run -- "opc.tcp://localhost:62542/MinimalCalcServer"

Example Usage

The minimal client demonstrates the following operations:

  1. Host Setup: Creates an application host with Host.CreateApplicationBuilder()
  2. DI Configuration: Configures the application and client services with the fluent API
  3. Endpoint Discovery: Selects the requested secure endpoint through .AddDiscoveryAndConnect(...)
  4. Session Connection: Connects through the DI-provided managed-session factory
  5. Subscriptions: Monitors ServerStatus.CurrentTime with the V2 subscription API
  6. Alarms & Conditions: Resolves AlarmClientFactory and creates an A&C client for the session
  7. Browsing: Browses the server's address space (ObjectsFolder)
  8. Reading: Reads the server's current time from the StandardServer
  9. Notifications: Waits up to 10 seconds for the subscription's first data change notification
  10. Clean Shutdown: Properly closes the subscription, session, and host

Architecture

Program.cs

The application uses top-level statements and demonstrates:

  • Configuring application identity and security directly inside .AddClient(...)
  • Setting up HostApplicationBuilder with OPC UA client services
  • Building and validating the ApplicationConfiguration inside the DI infrastructure
  • Configuring services via fluent API: .AddOpcUa().AddClient(...).AddSubscriptions().AddAlarms()
  • Discovering a secure endpoint and connecting through the DI-provided managed-session delegate
  • Creating a V2 subscription and monitored item with the fluent session extensions
  • Resolving AlarmClientFactory for Part 9 Alarms & Conditions operations
  • Performing basic OPC UA operations (Browse, Read)
  • Proper resource cleanup for the subscription, session, and host

DI Container Integration

The client follows the patterns described in DependencyInjection.md:

  • HostApplicationBuilder: Central entry point for DI and host setup
  • Client Options: OpcUaClientOptions exposes the application identity fields (ApplicationName, ApplicationUri, ProductUri, AutoAcceptUntrustedCertificates, etc.) directly alongside managed-session defaults, so a client-only host can configure everything inside .AddClient(...) without a separate configuration construction step
  • Factory Pattern: IManagedSessionFactory for runtime endpoint selection
  • Fluent API: Chainable .AddXxx() methods on IOpcUaBuilder

Educational Value

This minimal client serves as:

  • A clean reference implementation for building OPC UA clients with dependency injection and HostApplicationBuilder
  • A learning resource for understanding the modern OPC UA client stack and fluent DI patterns
  • A template matching the architecture of MinimalBoilerServer for consistency
  • A starting point for custom client applications

For More Information

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