.NET: Add serialization support for ContextualFunctionProvider

dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs

@@ -69,6 +69,7 @@ private static JsonSerializerOptions CreateDefaultOptions()
     [JsonSerializable(typeof(ChatClientAgentThread.ThreadState))]
     [JsonSerializable(typeof(TextSearchProvider.TextSearchProviderState))]
     [JsonSerializable(typeof(ChatHistoryMemoryProvider.ChatHistoryMemoryProviderState))]
+    [JsonSerializable(typeof(Functions.ContextualFunctionProvider.ContextualFunctionProviderState))]
 
     [ExcludeFromCodeCoverage]
     internal sealed partial class JsonContext : JsonSerializerContext;

dotnet/src/Microsoft.Agents.AI/Functions/ContextualFunctionProvider.cs

@@ -4,6 +4,7 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Extensions.AI;
@@ -60,6 +61,30 @@ public ContextualFunctionProvider(
         int maxNumberOfFunctions,
         ContextualFunctionProviderOptions? options = null,
         ILoggerFactory? loggerFactory = null)
+        : this(vectorStore, vectorDimensions, functions, maxNumberOfFunctions, default(JsonElement), options, null, loggerFactory)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ContextualFunctionProvider"/> class.
+    /// </summary>
+    /// <param name="vectorStore">An instance of a vector store.</param>
+    /// <param name="vectorDimensions">The number of dimensions to use for the memory embeddings.</param>
+    /// <param name="functions">The functions to vectorize and store for searching related functions.</param>
+    /// <param name="maxNumberOfFunctions">The maximum number of relevant functions to retrieve from the vector store.</param>
+    /// <param name="serializedState">A <see cref="JsonElement"/> representing the serialized provider state.</param>
+    /// <param name="options">Further optional settings for configuring the provider.</param>
+    /// <param name="jsonSerializerOptions">Optional serializer options. If not provided, <see cref="AgentJsonUtilities.DefaultOptions"/> will be used.</param>
+    /// <param name="loggerFactory">The logger factory to use for logging. If not provided, no logging will be performed.</param>
+    public ContextualFunctionProvider(
+        VectorStore vectorStore,
+        int vectorDimensions,
+        IEnumerable<AIFunction> functions,
+        int maxNumberOfFunctions,
+        JsonElement serializedState,
+        ContextualFunctionProviderOptions? options = null,
+        JsonSerializerOptions? jsonSerializerOptions = null,
+        ILoggerFactory? loggerFactory = null)
     {
         Throw.IfNull(vectorStore);
         Throw.IfLessThan(vectorDimensions, 1, "Vector dimensions must be greater than 0");
@@ -81,6 +106,21 @@ public ContextualFunctionProvider(
                 EmbeddingValueProvider = this._options.EmbeddingValueProvider,
             }
          );
+
+        // Restore recent messages from serialized state if provided
+        if (serializedState.ValueKind is not JsonValueKind.Null and not JsonValueKind.Undefined)
+        {
+            JsonSerializerOptions jso = jsonSerializerOptions ?? AgentJsonUtilities.DefaultOptions;
+            ContextualFunctionProviderState? state = serializedState.Deserialize(jso.GetTypeInfo(typeof(ContextualFunctionProviderState))) as ContextualFunctionProviderState;
+            if (state?.RecentMessages is { Count: > 0 })
+            {
+                // Restore recent messages respecting the limit (may truncate if limit changed afterwards).
+                foreach (ChatMessage message in state.RecentMessages.Take(this._options.NumberOfRecentMessagesInContext))
+                {
+                    this._recentMessages.Enqueue(message);
+                }
+            }
+        }
     }
 
     /// <inheritdoc />
@@ -135,6 +175,22 @@ public override ValueTask InvokedAsync(InvokedContext context, CancellationToken
         return default;
     }
 
+    /// <summary>
+    /// Serializes the current provider state to a <see cref="JsonElement"/> containing the recent messages.
+    /// </summary>
+    /// <param name="jsonSerializerOptions">Optional serializer options. This parameter is not used; <see cref="AgentJsonUtilities.DefaultOptions"/> is always used for serialization.</param>
+    /// <returns>A <see cref="JsonElement"/> with the recent messages, or default if there are no recent messages.</returns>
+    public override JsonElement Serialize(JsonSerializerOptions? jsonSerializerOptions = null)
+    {
+        ContextualFunctionProviderState state = new();
+        if (this._options.NumberOfRecentMessagesInContext > 0 && !this._recentMessages.IsEmpty)
+        {
+            state.RecentMessages = this._recentMessages.Take(this._options.NumberOfRecentMessagesInContext).ToList();
+        }
+
+        return JsonSerializer.SerializeToElement(state, AgentJsonUtilities.DefaultOptions.GetTypeInfo(typeof(ContextualFunctionProviderState)));
+    }
+
     /// <summary>
     /// Builds the context from chat messages.
     /// </summary>
@@ -160,4 +216,9 @@ private async Task<string> BuildContextAsync(IEnumerable<ChatMessage> newMessage
                 .Where(m => !string.IsNullOrWhiteSpace(m?.Text))
                 .Select(m => m.Text));
     }
+
+    internal sealed class ContextualFunctionProviderState
+    {
+        public List<ChatMessage>? RecentMessages { get; set; }
+    }
 }

dotnet/tests/Microsoft.Agents.AI.UnitTests/Functions/ContextualFunctionProviderTests.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Agents.AI.Functions;
@@ -304,6 +305,188 @@ public async Task ContextEmbeddingValueProvider_ReceivesRecentAndNewMessages_Asy
         Assert.Equal("msg5", capturedNewMessages.ElementAt(1).Text);
     }
 
+    [Fact]
+    public void Serialize_WithNoRecentMessages_ShouldReturnEmptyState()
+    {
+        // Arrange
+        var functions = new List<AIFunction> { CreateFunction("f1") };
+        var options = new ContextualFunctionProviderOptions
+        {
+            NumberOfRecentMessagesInContext = 3
+        };
+
+        var provider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            options: options);
+
+        // Act
+        JsonElement state = provider.Serialize();
+
+        // Assert
+        Assert.Equal(JsonValueKind.Object, state.ValueKind);
+        Assert.False(state.TryGetProperty("recentMessages", out _));
+    }
+
+    [Fact]
+    public async Task Serialize_WithRecentMessages_ShouldPersistMessagesUpToLimitAsync()
+    {
+        // Arrange
+        var functions = new List<AIFunction> { CreateFunction("f1") };
+        var options = new ContextualFunctionProviderOptions
+        {
+            NumberOfRecentMessagesInContext = 3
+        };
+
+        var provider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            options: options);
+
+        var messages = new[]
+        {
+            new ChatMessage() { Contents = [new TextContent("M1")] },
+            new ChatMessage() { Contents = [new TextContent("M2")] },
+            new ChatMessage() { Contents = [new TextContent("M3")] }
+        };
+
+        // Act
+        await provider.InvokedAsync(new AIContextProvider.InvokedContext(messages, aiContextProviderMessages: null));
+        JsonElement state = provider.Serialize();
+
+        // Assert
+        Assert.True(state.TryGetProperty("recentMessages", out JsonElement recentProperty));
+        Assert.Equal(JsonValueKind.Array, recentProperty.ValueKind);
+        int count = recentProperty.GetArrayLength();
+        Assert.Equal(3, count);
+    }
+
+    [Fact]
+    public async Task SerializeAndDeserialize_RoundtripRestoresMessagesAsync()
+    {
+        // Arrange
+        var functions = new List<AIFunction> { CreateFunction("f1") };
+        var options = new ContextualFunctionProviderOptions
+        {
+            NumberOfRecentMessagesInContext = 4
+        };
+
+        var provider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            options: options);
+
+        var messages = new[]
+        {
+            new ChatMessage() { Contents = [new TextContent("A")] },
+            new ChatMessage() { Contents = [new TextContent("B")] },
+            new ChatMessage() { Contents = [new TextContent("C")] },
+            new ChatMessage() { Contents = [new TextContent("D")] }
+        };
+
+        await provider.InvokedAsync(new AIContextProvider.InvokedContext(messages, aiContextProviderMessages: null));
+
+        // Act
+        JsonElement state = provider.Serialize();
+        var roundTrippedProvider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            serializedState: state,
+            options: new ContextualFunctionProviderOptions
+            {
+                NumberOfRecentMessagesInContext = 4
+            });
+
+        // Trigger search to verify messages are used
+        var invokingContext = new AIContextProvider.InvokingContext(Array.Empty<ChatMessage>());
+        await roundTrippedProvider.InvokingAsync(invokingContext);
+
+        // Assert
+        string expected = string.Join(Environment.NewLine, ["A", "B", "C", "D"]);
+        this._collectionMock.Verify(c => c.SearchAsync(expected, It.IsAny<int>(), null, It.IsAny<CancellationToken>()), Times.Once);
+    }
+
+    [Fact]
+    public async Task Deserialize_WithChangedLowerLimit_ShouldTruncateToNewLimitAsync()
+    {
+        // Arrange
+        var functions = new List<AIFunction> { CreateFunction("f1") };
+        var initialProvider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            options: new ContextualFunctionProviderOptions
+            {
+                NumberOfRecentMessagesInContext = 5
+            });
+
+        var messages = new[]
+        {
+            new ChatMessage() { Contents = [new TextContent("L1")] },
+            new ChatMessage() { Contents = [new TextContent("L2")] },
+            new ChatMessage() { Contents = [new TextContent("L3")] },
+            new ChatMessage() { Contents = [new TextContent("L4")] },
+            new ChatMessage() { Contents = [new TextContent("L5")] }
+        };
+
+        await initialProvider.InvokedAsync(new AIContextProvider.InvokedContext(messages, aiContextProviderMessages: null));
+        JsonElement state = initialProvider.Serialize();
+
+        // Act
+        var restoredProvider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            serializedState: state,
+            options: new ContextualFunctionProviderOptions
+            {
+                NumberOfRecentMessagesInContext = 3 // Lower limit
+            });
+
+        var invokingContext = new AIContextProvider.InvokingContext(Array.Empty<ChatMessage>());
+        await restoredProvider.InvokingAsync(invokingContext);
+
+        // Assert
+        string expected = string.Join(Environment.NewLine, ["L1", "L2", "L3"]);
+        this._collectionMock.Verify(c => c.SearchAsync(expected, It.IsAny<int>(), null, It.IsAny<CancellationToken>()), Times.Once);
+    }
+
+    [Fact]
+    public async Task Deserialize_WithEmptyState_ShouldHaveNoMessagesAsync()
+    {
+        // Arrange
+        var functions = new List<AIFunction> { CreateFunction("f1") };
+        JsonElement emptyState = JsonSerializer.Deserialize("{}", TestJsonSerializerContext.Default.JsonElement);
+
+        // Act
+        var provider = new ContextualFunctionProvider(
+            vectorStore: this._vectorStoreMock.Object,
+            vectorDimensions: 1536,
+            functions: functions,
+            maxNumberOfFunctions: 5,
+            serializedState: emptyState,
+            options: new ContextualFunctionProviderOptions
+            {
+                NumberOfRecentMessagesInContext = 3
+            });
+
+        var invokingContext = new AIContextProvider.InvokingContext(Array.Empty<ChatMessage>());
+        await provider.InvokingAsync(invokingContext);
+
+        // Assert
+        this._collectionMock.Verify(c => c.SearchAsync(string.Empty, It.IsAny<int>(), null, It.IsAny<CancellationToken>()), Times.Once);
+    }
+
     private static AIFunction CreateFunction(string name, string description = "")
     {
         return AIFunctionFactory.Create(() => { }, name, description);