# Description PR #4194 removed the unused `ServerConfiguration.MinMetadataSamplingInterval` and left nothing in its place. As a result there was no way to populate `Server.ServerCapabilities.MinSupportedSampleRate` (`i=2272`) — `ServerInternalData.CreateServerObjectAsync` hardcoded it to `0`. Separately, the only clamp applied when revising a monitored item's sampling interval was the per-node `BaseVariableState.MinimumSamplingInterval`, which defaults to `MinimumSamplingIntervals.Continuous` (`0`), so reference-server nodes accepted any requested interval (e.g. 10 ms) unrevised — exactly what was reported. This adds a configuration entry **in the exact schema slot #4194 vacated** and enforces it as a lower bound. ## Configuration - **`ServerConfiguration.MinSupportedSamplingInterval`** — `double` (milliseconds), default `0`, `[DataTypeField(Order = 17)]`, i.e. between `MaxNotificationsPerPublish` (16) and `AvailableSamplingRates` (18). - `ApplicationConfiguration.xsd` — `<xs:element name="MinSupportedSamplingInterval" type="xs:double" minOccurs="0" />` in the same position the removed element occupied. - Fluent API **`SetMinSupportedSamplingInterval(double)`** on `IApplicationConfigurationBuilderServerOptions`, in the place `SetMinMetadataSamplingInterval` was removed from. - The element is added to the six config XML files #4194 touched (reference / CTT / AOT / GDS use `0`; `test-server-full.xml` uses a distinctive non-zero value for the round-trip test). The address-space Property keeps its OPC UA spec name, so `Server.ServerCapabilities.MinSupportedSampleRate` and `VariableIds.Server_ServerCapabilities_MinSupportedSampleRate` are unchanged. ```xml <MaxNotificationsPerPublish>1000</MaxNotificationsPerPublish> <MinSupportedSamplingInterval>2000</MinSupportedSamplingInterval> <AvailableSamplingRates> ``` ```csharp application.Build(applicationUri, productUri) .AsServer([endpointUrl]) .SetMinSupportedSamplingInterval(2000); ``` ## Behavior - `ServerInternalData` now publishes the configured value to `Server.ServerCapabilities.MinSupportedSampleRate`. - New `SubscriptionManager.CalculateRevisedSamplingInterval(...)` (two overloads, alongside the existing `CalculateRevisedQueueSize`) centralizes the revision rule and replaces the logic that was duplicated across four call sites — the create and modify paths of `AsyncCustomNodeManager` and `CustomNodeManager` — which now expose a `MinSupportedSamplingInterval` property seeded from the configuration (mirroring how `MaxQueueSize` is initialized). The rule: 1. A requested interval below zero resolves to the *default sampling interval*: the **publishing interval of the subscription** on create, and the item's **current sampling interval** on modify. The modify case preserves 1.5.378 behavior, so a `ModifyMonitoredItems` call that leaves the sampling interval unspecified does not silently retune the item. 2. A node declaring `MinimumSamplingIntervals.Continuous` (`0`) for the `Value` Attribute reports **by exception** and is **not** bound by the server-wide minimum — the requested interval is returned unchanged. 3. Every other item is raised to `max(nodeMinimumSamplingInterval, MinSupportedSamplingInterval)`. Attributes other than `Value`, nodes declaring `MinimumSamplingIntervals.Indeterminate` (`-1`), and non-Variable nodes are bound only by `MinSupportedSamplingInterval`. 4. `double.MaxValue` is capped to one year (pre-existing behavior, now in one place). Event monitored items do not sample and are unaffected. **Backward compatible:** with the default of `0` the computation is identical to the previous code for every input, including `Continuous`, `Indeterminate`, positive node minimums, non-`Value` attributes and `NaN`. No existing configuration or deployment changes behavior. Node managers that implement `INodeManager` directly can call the new public helper to apply the same rule. ## Related Issues - Fixes #4191 The issue thread also asked whether `Subscription.MaxNotificationsPerPublish` is revised by the server. It is (`SubscriptionManager.CalculateMaxNotificationsPerPublish`), but it was untested and is not observable from the `CreateSubscription` response, which carries no revised field for that parameter. Four tests were added that assert it through `SubscriptionDiagnostics.MaxNotificationsPerPublish` on a privileged session, covering create and modify, the above-limit, below-limit and `0` (server default) cases. ## Tests - **`SamplingIntervalRevisionTests`** (17 unit tests, `Opc.Ua.Server.Tests`) — the full revision matrix: negative request resolving to the default interval, the `Continuous` bypass, `Indeterminate`, node minimum above *and* below the floor, a floor of `0` being a no-op, non-`Value` attributes, non-Variable and null nodes, and the `double.MaxValue` cap. - **`MinSupportedSamplingIntervalTests`** (10 integration tests, `Opc.Ua.Subscriptions.Tests`) — against a reference server configured with a 500 ms floor: the capabilities node reflects the configuration; a node declaring 100 ms is lifted to 500 ms; `Scalar_Static_Arrays2D_LocalizedText` (1000 ms) wins over the floor; `CurrentTime` (250 ms) is lifted; a `Continuous` node keeps its 10 ms; a non-`Value` attribute is floored; `ModifyMonitoredItems` behaves the same in both directions; event items are unaffected. - Restored the configuration builder and round-trip test coverage that #4194 deleted. - `TestFixture` gained a `protected virtual void ConfigureServer(ApplicationConfiguration)` hook so a derived fixture can vary the server configuration before start. Default implementation is a no-op, so no existing fixture changes behavior. ## Documentation - `docs/Subscriptions.md` — new **Sampling interval revision** section with the input table, the four-step rule (including both negative-interval fallbacks), XML and fluent configuration examples, and guidance for custom node managers. - `docs/migrate/2.0.x/configuration.md` — new section documenting that `MinMetadataSamplingInterval` was removed and `MinSupportedSamplingInterval` added. Verified against `master378`: the old setting defaulted to `1000` but was never read, and `MinSupportedSampleRate` was hardcoded to `0` with no server-wide floor. The guide therefore stresses that these are **two different settings, not a rename** — consumers should drop the old element (a default of `0` reproduces 1.5.378 exactly) and only opt into the new one deliberately, since reusing the old value would silently introduce a sampling floor. ## Validation - `dotnet build UA.slnx` — **0 warnings, 0 errors** across all TFMs. - .NET 10: `Opc.Ua.Server.Tests` 4091 passed, `Opc.Ua.Subscriptions.Tests` 619 passed (full suite including the new fixture), `Opc.Ua.InformationModel.Tests` 1063 passed, `Opc.Ua.Configuration.Tests` 221 passed, `Opc.Ua.Gds.Tests` 119 passed. - .NET Framework 4.8: new unit tests (200 incl. sampling groups), new integration tests (17) and configuration round-trip (135) all passed. - `ConsoleReferenceServer` starts successfully with the updated configuration file. ## 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. - [x] 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. - [x] I have addressed **all** PR feedback received. --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 79f8090c-b2a3-409c-a5bf-56b6d2a35e70
OPC Foundation UA .NET Standard Reference Server
Introduction
The console reference server 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 server 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 ConsoleReferenceServer.dll --rc=opc.tcp://localhost:65300
or
dotnet ConsoleReferenceServer.dll --reverseconnect=opc.tcp://localhost:65300
Example: Server and Client 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.
Additional Options
-aor--autoaccept: Auto accept untrusted certificates (for testing only)-cor--console: Log to console-lor--log: Log app output-tor--timeout: Timeout in seconds to exit application
For the complete list of options, use --help.
X509 user identity certificates
The reference server validates X509 user identity tokens against its trusted-user certificate
store (TrustedUserCertificates, by default %LocalApplicationData%/OPC Foundation/pki/trustedUser).
An untrusted user certificate is rejected with BadIdentityTokenRejected — the --autoaccept option
only auto-accepts the application/channel certificate, never user identity certificates.
To let a trusted client (for example the OPC Foundation Compliance Test Tool) authenticate with an
X509 user token, its user certificate must be present in that store. To make provisioning easy, the
server writes every rejected X509 user certificate to a dedicated review store,
pki/rejectedUser (a sibling of pki/trustedUser). After one failing activation you can move the
legitimate user certificate from pki/rejectedUser/certs into pki/trustedUser/certs (and any
issuing CA into pki/issuerUser/certs) and reconnect. Deliberately-untrusted certificates simply stay
out of the trusted store and continue to be rejected.