[Client] Fix two bugs in MonitoredItem

Libraries/Opc.Ua.Client/Subscription/MonitoredItem.cs

@@ -138,6 +138,7 @@ public virtual void Restore(MonitoredItemState state)
             ServerId = state.ServerId;
             TriggeringItemId = state.TriggeringItemId;
             TriggeredItems = state.TriggeredItems != null ? new UInt32Collection(state.TriggeredItems) : null;
+            CacheQueueSize = state.CacheQueueSize < 1 ? 1 : state.CacheQueueSize;
         }
 
         /// <inheritdoc/>
@@ -148,7 +149,8 @@ public virtual void Snapshot(out MonitoredItemState state)
                 ServerId = Status.Id,
                 ClientId = ClientHandle,
                 TriggeringItemId = TriggeringItemId,
-                TriggeredItems = TriggeredItems != null ? new UInt32Collection(TriggeredItems) : null
+                TriggeredItems = TriggeredItems != null ? new UInt32Collection(TriggeredItems) : null,
+                CacheQueueSize = CacheQueueSize
             };
         }
 
@@ -401,7 +403,7 @@ public NodeId ResolvedNodeId
         /// <summary>
         /// Returns the queue size used by the cache.
         /// </summary>
-        public int CacheQueueSize
+        public uint CacheQueueSize
         {
             get
             {
@@ -1122,7 +1124,7 @@ public class MonitoredItemDataCache
         /// <summary>
         /// Constructs a cache for a monitored item.
         /// </summary>
-        public MonitoredItemDataCache(ITelemetryContext? telemetry, int queueSize = 1)
+        public MonitoredItemDataCache(ITelemetryContext? telemetry, uint queueSize = 1)
         {
             QueueSize = queueSize;
             m_logger = telemetry.CreateLogger<MonitoredItemDataCache>();
@@ -1139,7 +1141,7 @@ public MonitoredItemDataCache(ITelemetryContext? telemetry, int queueSize = 1)
         /// <summary>
         /// The size of the queue to maintain.
         /// </summary>
-        public int QueueSize { get; private set; }
+        public uint QueueSize { get; private set; }
 
         /// <summary>
         /// The last value received from the server.
@@ -1155,12 +1157,8 @@ public IList<DataValue> Publish()
             if (m_values != null)
             {
                 values = new List<DataValue>(m_values.Count);
-                for (int ii = 0; ii < values.Count; ii++)
+                while (m_values.TryDequeue(out DataValue? dequeued))
                 {
-                    if (!m_values.TryDequeue(out DataValue? dequeued))
-                    {
-                        break;
-                    }
                     values.Add(dequeued);
                 }
             }
@@ -1222,7 +1220,7 @@ public void OnNotification(MonitoredItemNotification notification)
         /// <summary>
         /// Changes the queue size.
         /// </summary>
-        public void SetQueueSize(int queueSize)
+        public void SetQueueSize(uint queueSize)
         {
             if (queueSize == QueueSize)
             {
@@ -1270,7 +1268,7 @@ public class MonitoredItemEventCache
         /// <summary>
         /// Constructs a cache for a monitored item.
         /// </summary>
-        public MonitoredItemEventCache(int queueSize)
+        public MonitoredItemEventCache(uint queueSize)
         {
             QueueSize = queueSize;
             m_events = new Queue<EventFieldList>();
@@ -1279,7 +1277,7 @@ public MonitoredItemEventCache(int queueSize)
         /// <summary>
         /// The size of the queue to maintain.
         /// </summary>
-        public int QueueSize { get; private set; }
+        public uint QueueSize { get; private set; }
 
         /// <summary>
         /// The last event received.
@@ -1318,7 +1316,7 @@ public void OnNotification(EventFieldList notification)
         /// <summary>
         /// Changes the queue size.
         /// </summary>
-        public void SetQueueSize(int queueSize)
+        public void SetQueueSize(uint queueSize)
         {
             if (queueSize == QueueSize)
             {

Libraries/Opc.Ua.Client/Subscription/MonitoredItemState.cs

@@ -95,6 +95,12 @@ public MonitoredItemState(MonitoredItemOptions options)
         /// </summary>
         [DataMember(Order = 17)]
         public UInt32Collection? TriggeredItems { get; init; }
+
+        /// <summary>
+        /// The queue size used by the client-side cache.
+        /// </summary>
+        [DataMember(Order = 18)]
+        public uint CacheQueueSize { get; init; }
     }
 
     /// <summary>

Tests/Opc.Ua.Client.Tests/MonitoredItemTests.cs

@@ -0,0 +1,188 @@
+/* ========================================================================
+ * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
+ *
+ * OPC Foundation MIT License 1.00
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * The complete license agreement can be found here:
+ * http://opcfoundation.org/License/MIT/1.00/
+ * ======================================================================*/
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using NUnit.Framework;
+using Opc.Ua.Tests;
+
+namespace Opc.Ua.Client.Tests
+{
+    [TestFixture]
+    [Category("Client")]
+    [Category("MonitoredItem")]
+    [SetCulture("en-us")]
+    [SetUICulture("en-us")]
+    public sealed class MonitoredItemTests
+    {
+        [Test]
+        public void SaveValueInCacheShouldOverwriteWithQueueSizeOne()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+            var monitoredItem = new MonitoredItem(telemetry) { CacheQueueSize = 1 };
+
+            var notification1 = new MonitoredItemNotification
+            {
+                ClientHandle = monitoredItem.ClientHandle,
+                Value = new DataValue(new Variant(100), StatusCodes.Good, DateTime.UtcNow)
+            };
+            monitoredItem.SaveValueInCache(notification1);
+
+            var notification2 = new MonitoredItemNotification
+            {
+                ClientHandle = monitoredItem.ClientHandle,
+                Value = new DataValue(new Variant(200), StatusCodes.Good, DateTime.UtcNow)
+            };
+            monitoredItem.SaveValueInCache(notification2);
+
+            IList<DataValue> result = monitoredItem.DequeueValues();
+
+            Assert.That(result.Count, Is.EqualTo(1));
+            Assert.That(result[0].Value, Is.EqualTo(200));
+        }
+
+        [Test]
+        public void DequeueValuesShouldReturnAllQueuedValues()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+            var monitoredItem = new MonitoredItem(telemetry) { CacheQueueSize = 5 };
+
+            List<int> expectedValues = [1, 2, 3, 4, 5];
+            List<MonitoredItemNotification> notifications = expectedValues
+                .ConvertAll(value => new MonitoredItemNotification
+                {
+                    ClientHandle = monitoredItem.ClientHandle,
+                    Value = new DataValue(new Variant(value), StatusCodes.Good, DateTime.UtcNow)
+                });
+
+            foreach (MonitoredItemNotification notification in notifications)
+            {
+                monitoredItem.SaveValueInCache(notification);
+            }
+
+            IList<DataValue> result = monitoredItem.DequeueValues();
+
+            Assert.That(result.Count, Is.EqualTo(expectedValues.Count));
+            Assert.That(result.Select(x => x.Value), Is.EquivalentTo(expectedValues));
+
+            // Ensure the cache is empty after dequeue
+            IList<DataValue> emptyResult = monitoredItem.DequeueValues();
+            Assert.That(emptyResult, Is.Empty);
+        }
+
+        [Test]
+        public void SaveValueInCacheShouldOverwriteOldestValues()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+            const int kQueueSize = 5;
+            var monitoredItem = new MonitoredItem(telemetry) { CacheQueueSize = kQueueSize };
+
+            List<int> values = [1, 2, 3, 4, 5, 6, 7];
+            List<MonitoredItemNotification> notifications = values
+                .ConvertAll(value => new MonitoredItemNotification
+                {
+                    ClientHandle = monitoredItem.ClientHandle,
+                    Value = new DataValue(new Variant(value), StatusCodes.Good, DateTime.UtcNow)
+                });
+
+            foreach (MonitoredItemNotification notification in notifications)
+            {
+                monitoredItem.SaveValueInCache(notification);
+            }
+
+            IList<DataValue> result = monitoredItem.DequeueValues();
+
+            Assert.That(result.Count, Is.EqualTo(kQueueSize));
+            Assert.That(result.Select(x => x.Value), Is.EquivalentTo(values.Skip(2)));
+        }
+
+        [Test]
+        public void SerializeDeserializeShouldHaveSameProperties()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+
+            var originalSession = SessionMock.Create();
+            var originalSubscription = new TestableSubscription(telemetry);
+
+            var monitoredItems = new List<MonitoredItem>
+            {
+                new(telemetry)
+                {
+                    DisplayName = "MonitoredItem1", QueueSize = 10, CacheQueueSize = 1, SamplingInterval = 500
+                },
+                new(telemetry)
+                {
+                    DisplayName = "MonitoredItem2", QueueSize = 25, CacheQueueSize = 50, SamplingInterval = 500
+                },
+                new(telemetry)
+                {
+                    DisplayName = "MonitoredItem3", QueueSize = 0, CacheQueueSize = 0, SamplingInterval = 500
+                }
+            };
+
+            // CacheQueueSize of 0 is invalid and should be set to 1 internally
+            Assert.That(monitoredItems[^1].CacheQueueSize, Is.EqualTo(1));
+
+            originalSubscription.AddItems(monitoredItems);
+            originalSession.AddSubscription(originalSubscription);
+
+            using var stream = new MemoryStream();
+            originalSession.Save(stream, [originalSubscription]);
+            stream.Position = 0;
+
+            var loadedSession = SessionMock.Create();
+            loadedSession.Load(stream);
+            Assert.That(loadedSession.Subscriptions.Count(), Is.EqualTo(1));
+            Assert.That(loadedSession.Subscriptions.First().MonitoredItems.Count(), Is.EqualTo(monitoredItems.Count));
+
+            List<MonitoredItemState> originalStates = monitoredItems
+                .ConvertAll(item =>
+                {
+                    item.Snapshot(out MonitoredItemState state);
+                    return state;
+                });
+
+            var loadedItems = loadedSession.Subscriptions.First().MonitoredItems.ToList();
+            List<MonitoredItemState> loadedStates = loadedItems
+                .ConvertAll(item =>
+                {
+                    item.Snapshot(out MonitoredItemState state);
+                    return state;
+                });
+
+            for (int i = 0; i < monitoredItems.Count; i++)
+            {
+                Assert.That(loadedStates[i] with { Timestamp = default },
+                    Is.EqualTo(originalStates[i] with { Timestamp = default }));
+            }
+        }
+    }
+}