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Marc Schier 889572472f Convert DataValue from class to readonly struct for further GC relief (#3796)
Convert `DataValue` from a mutable reference type (`class`) to a `readonly struct` to eliminate per-allocation GC pressure on every attribute read, subscription publish, and history sample.

### Key API changes (user-visible)

| Before | After | Pattern |
|---|---|---|
| `class DataValue` | `readonly struct DataValue : INullable` | Foundation |
| `Equals(DataValue?)` / `operator ==(DataValue?, DataValue?)` | `Equals(DataValue)` / `operator ==(DataValue, DataValue)` | Value semantics |
| `IEncoder.WriteDataValue(string?, DataValue?)` | `IEncoder.WriteDataValue(string?, DataValue)` | Non-nullable wire API |
| `IDecoder.ReadDataValue(...) -> DataValue?` | `IDecoder.ReadDataValue(...) -> DataValue` | Same |
| `IDataChangeMonitoredItemQueue.PeekLast/Oldest()` | `TryPeekLastValue/Oldest(out DataValue)` | TryGet pattern |
| `IAggregateCalculator.GetProcessedValue(bool)` | `TryGetProcessedValue(bool, out DataValue)` | Same |
| `IUaPubSubDataStore.ReadPublishedDataItem(...)` | `TryReadPublishedDataItem(NodeId, uint, out DataValue)` | Same |
| `Dictionary<uint, DataValue?>` (NodeCacheContext) | `Dictionary<uint, DataValue>` | Default + IsNull |
| `IHistoryDataSource.FirstRaw/NextRaw` | `TryFirstRaw/TryNextRaw(out DataValue)` | TryGet pattern |
| `NodeState.ReadAttribute(... DataValue)` | `NodeState.ReadAttribute(... ref DataValue)` | Sync mutation via ref |
| `NodeState.ReadAttributeAsync(... DataValue)` | `NodeState.ReadAttributeAsync(...) -> ValueTask<(ServiceResult, DataValue)>` | Async return tuple |
| `obj as DataValue` (heterogeneous Dictionary<string, object>) | `obj is DataValue dv ? dv : default(DataValue)` | Safe struct cast |
| `Assert.That(dv, Is.Not.Null)` (tests) | `Assert.That(dv.IsNull, Is.False)` | Struct test pattern |
| `[Obsolete] Value` setter, all property setters | Removed; use ctor or `With*()` | Immutability |
| `[DataContract]` + `[DataMember]` | Removed; surrogate via `SerializableDataValue` + `DataValueSurrogateProvider` | Serialization |

### Wire format

Wire format is **byte-identical** to the previous class-based implementation across binary / JSON / XML encoders. Default DataValue (`.IsNull == true`) is treated as the equivalent of the old null reference (writes JSON `null`, binary `byte 0`, XML omitted element).

### Why TryGet pattern (instead of leaving `DataValue?`)

For methods that previously returned `DataValue?` to signal "no value available" (queue peek, aggregate result, data store lookup, history navigation), the conversion to `bool TryGet(out DataValue)` matches BCL conventions (`Dictionary.TryGetValue`, `Queue.TryPeek`, `Int32.TryParse`) and gives the caller an explicit "may be absent" affordance without `Nullable<DataValue>` overhead.

### Breaking changes summary

- `DataValue` is now a `readonly struct` - boxing/unboxing semantics change for callers using `object`-typed APIs.
- `IEncoder.WriteDataValue` / `IDecoder.ReadDataValue` / `ReadDataValueArray` interface signatures lose the `Nullable` wrapper.
- `IDataChangeMonitoredItemQueue.PeekLastValue` / `PeekOldestValue` -> `TryPeekLastValue` / `TryPeekOldestValue` (out parameter).
- `IAggregateCalculator.GetProcessedValue` -> `TryGetProcessedValue` (out parameter).
- `IUaPubSubDataStore.ReadPublishedDataItem` -> `TryReadPublishedDataItem` (out parameter).
- `NodeState.ReadAttribute` takes `ref DataValue`; `ReadAttributeAsync` returns `ValueTask<(ServiceResult, DataValue)>`.
- `DataValue` property setters removed (use constructor + `With*` mutators).
2026-05-23 11:38:49 +02:00

140 lines
5.8 KiB
C#

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using System;
namespace Opc.Ua.Fuzzing
{
#pragma warning disable IDE0079 // Remove unnecessary suppression
#pragma warning disable RCS1043
public static partial class Testcases
#pragma warning restore RCS1043, IDE0079
{
public delegate void MessageEncoder(IEncoder encoder);
public static readonly MessageEncoder[] MessageEncoders = [ReadRequest, ReadResponse];
public static void ReadRequest(IEncoder encoder)
{
var nodeId = new NodeId(1000);
var readRequest = new ReadRequest
{
RequestHeader = new RequestHeader
{
Timestamp = DateTime.UtcNow,
RequestHandle = 42,
AdditionalHeader = new ExtensionObject()
},
NodesToRead =
[
new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Description },
new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Value },
new ReadValueId { NodeId = nodeId, AttributeId = Attributes.DisplayName },
new ReadValueId { NodeId = nodeId, AttributeId = Attributes.AccessLevel },
new ReadValueId { NodeId = nodeId, AttributeId = Attributes.RolePermissions }
]
};
encoder.EncodeMessage(readRequest);
}
public static void ReadResponse(IEncoder encoder)
{
DateTimeUtc now = DateTimeUtc.Now;
var readRequest = new ReadResponse
{
Results =
[
new DataValue(
Variant.From("Hello World"),
StatusCodes.Good,
now.AddMilliseconds(60000),
now,
10,
100),
new DataValue(
Variant.From((uint)12345678),
StatusCodes.BadDataLost,
now.AddMilliseconds(60000),
now),
new DataValue(
Variant.From(ByteString.From([0, 1, 2, 3, 4, 5, 6])),
StatusCodes.Good,
now.AddMilliseconds(60000),
now),
new DataValue(
Variant.From((byte)42),
StatusCodes.Good,
now)
],
DiagnosticInfos =
[
new DiagnosticInfo
{
AdditionalInfo = "Hello World",
InnerStatusCode = StatusCodes.BadCertificateHostNameInvalid,
InnerDiagnosticInfo = new DiagnosticInfo
{
AdditionalInfo = "Hello World",
InnerStatusCode = StatusCodes.BadNodeIdUnknown
}
}
],
ResponseHeader = new ResponseHeader
{
Timestamp = DateTime.UtcNow,
RequestHandle = 42,
ServiceResult = StatusCodes.Good,
ServiceDiagnostics = new DiagnosticInfo
{
AdditionalInfo = "NodeId not found",
InnerStatusCode = StatusCodes.BadNodeIdExists,
InnerDiagnosticInfo = new DiagnosticInfo
{
AdditionalInfo = "Hello World",
InnerStatusCode = StatusCodes.BadNodeIdUnknown,
InnerDiagnosticInfo = new DiagnosticInfo
{
AdditionalInfo = "Hello World",
InnerStatusCode = StatusCodes.BadNodeIdUnknown,
InnerDiagnosticInfo = new DiagnosticInfo
{
AdditionalInfo = "Hello World",
InnerStatusCode = StatusCodes.BadNodeIdUnknown
}
}
}
}
}
};
encoder.EncodeMessage(readRequest);
}
}
}