feat: adds strict mode support

dotnet/src/Agents/OpenAI/Internal/AssistantThreadActions.cs

@@ -178,7 +178,7 @@ public static async IAsyncEnumerable<ChatMessageContent> GetMessagesAsync(Assist
 
         FunctionCallsProcessor functionProcessor = new(logger);
         // This matches current behavior.  Will be configurable upon integrating with `FunctionChoice` (#6795/#5200)
-        FunctionChoiceBehaviorOptions functionOptions = new() { AllowConcurrentInvocation = true, AllowParallelCalls = true };
+        FunctionChoiceBehaviorOptions functionOptions = new() { AllowConcurrentInvocation = true, AllowParallelCalls = true, AllowStrictSchemaAdherence = true };
 
         // Evaluate status and process steps and messages, as encountered.
         HashSet<string> processedStepIds = [];
@@ -412,7 +412,7 @@ public static async IAsyncEnumerable<StreamingChatMessageContent> InvokeStreamin
 
         FunctionCallsProcessor functionProcessor = new(logger);
         // This matches current behavior.  Will be configurable upon integrating with `FunctionChoice` (#6795/#5200)
-        FunctionChoiceBehaviorOptions functionOptions = new() { AllowConcurrentInvocation = true, AllowParallelCalls = true };
+        FunctionChoiceBehaviorOptions functionOptions = new() { AllowConcurrentInvocation = true, AllowParallelCalls = true, AllowStrictSchemaAdherence = true };
 
         IAsyncEnumerable<StreamingUpdate> asyncUpdates = client.CreateRunStreamingAsync(threadId, agent.Id, options, cancellationToken);
         do

dotnet/src/Connectors/Connectors.OpenAI.UnitTests/Core/OpenAIFunctionTests.cs

@@ -59,17 +59,50 @@ public void ItCanConvertToFunctionDefinitionWithNoPluginName()
         Assert.Equal(sut.Description, result.FunctionDescription);
     }
 
-    [Fact]
-    public void ItCanConvertToFunctionDefinitionWithNullParameters()
+    [InlineData(true)]
+    [InlineData(false)]
+    [Theory]
+    public void ItCanConvertToFunctionDefinitionWithNullParameters(bool strict)
     {
-        // Arrange 
+        // Arrange
         OpenAIFunction sut = new("plugin", "function", "description", null, null);
 
         // Act
-        var result = sut.ToFunctionDefinition();
+        var result = sut.ToFunctionDefinition(strict);
 
         // Assert
-        Assert.Equal("{\"type\":\"object\",\"required\":[],\"properties\":{}}", result.FunctionParameters.ToString());
+        if (strict)
+        {
+            Assert.Equal("{\"type\":\"object\",\"required\":[],\"properties\":{},\"additionalProperties\":false}", result.FunctionParameters.ToString());
+        }
+        else
+        {
+            Assert.Equal("{\"type\":\"object\",\"required\":[],\"properties\":{}}", result.FunctionParameters.ToString());
+        }
+    }
+
+    [InlineData(false)]
+    [InlineData(true)]
+    [Theory]
+    public void SetsParametersToRequiredWhenStrict(bool strict)
+    {
+        var parameters = new List<OpenAIFunctionParameter>
+        {
+            new ("foo", "bar", false, typeof(string), null),
+        };
+        OpenAIFunction sut = new("plugin", "function", "description", parameters, null);
+
+        var result = sut.ToFunctionDefinition(strict);
+
+        Assert.Equal(strict, result.FunctionSchemaIsStrict);
+        if (strict)
+        {
+            Assert.Equal("""{"type":"object","required":["foo"],"properties":{"foo":{"description":"bar","type":["string","null"]}},"additionalProperties":false}""", result.FunctionParameters.ToString());
+        }
+        else
+        {
+            Assert.Equal("""{"type":"object","required":[],"properties":{"foo":{"description":"bar","type":"string"}}}""", result.FunctionParameters.ToString());
+        }
     }
 
     [Fact]

dotnet/src/Connectors/Connectors.OpenAI/Core/ClientCore.ChatCompletion.cs

@@ -370,7 +370,7 @@ internal async IAsyncEnumerable<OpenAIStreamingChatMessageContent> GetStreamingC
 
             // Process function calls by invoking the functions and adding the results to the chat history.
             // Each function call will trigger auto-function-invocation filters, which can terminate the process.
-            // In such cases, we'll return the last message in the chat history.  
+            // In such cases, we'll return the last message in the chat history.
             var lastMessage = await this.FunctionCallsProcessor.ProcessFunctionCallsAsync(
                 chatMessageContent,
                 chatHistory,
@@ -679,8 +679,8 @@ private static List<ChatMessage> CreateRequestMessages(ChatMessageContent messag
         {
             var toolCalls = new List<ChatToolCall>();
 
-            // Handling function calls supplied via either:  
-            // ChatCompletionsToolCall.ToolCalls collection items or  
+            // Handling function calls supplied via either:
+            // ChatCompletionsToolCall.ToolCalls collection items or
             // ChatMessageContent.Metadata collection item with 'ChatResponseMessage.FunctionToolCalls' key.
             IEnumerable<ChatToolCall>? tools = (message as OpenAIChatMessageContent)?.ToolCalls;
             if (tools is null && message.Metadata?.TryGetValue(OpenAIChatMessageContent.FunctionToolCallsProperty, out object? toolCallsObject) is true)
@@ -734,7 +734,7 @@ private static List<ChatMessage> CreateRequestMessages(ChatMessageContent messag
             }
 
             // This check is necessary to prevent an exception that will be thrown if the toolCalls collection is empty.
-            // HTTP 400 (invalid_request_error:) [] should be non-empty - 'messages.3.tool_calls'  
+            // HTTP 400 (invalid_request_error:) [] should be non-empty - 'messages.3.tool_calls'
             if (toolCalls.Count == 0)
             {
                 return [new AssistantChatMessage(message.Content) { ParticipantName = message.AuthorName }];
@@ -1011,7 +1011,7 @@ private ToolCallingConfig GetFunctionCallingConfiguration(Kernel? kernel, OpenAI
 
             foreach (var function in functions)
             {
-                tools.Add(function.Metadata.ToOpenAIFunction().ToFunctionDefinition());
+                tools.Add(function.Metadata.ToOpenAIFunction().ToFunctionDefinition(config?.Options?.AllowStrictSchemaAdherence ?? false));
             }
         }
 

dotnet/src/Connectors/Connectors.OpenAI/Core/OpenAIFunction.cs

@@ -2,6 +2,10 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 namespace Microsoft.SemanticKernel.Connectors.OpenAI;
@@ -72,9 +76,17 @@ public sealed class OpenAIFunction
     /// </remarks>
     private static readonly BinaryData s_zeroFunctionParametersSchema = new("""{"type":"object","required":[],"properties":{}}""");
     /// <summary>
+    /// Same as above, but with additionalProperties: false for strict mode.
+    /// </summary>
+    private static readonly BinaryData s_zeroFunctionParametersSchema_strict = new("""{"type":"object","required":[],"properties":{},"additionalProperties":false}""");
+    /// <summary>
     /// Cached schema for a descriptionless string.
     /// </summary>
     private static readonly KernelJsonSchema s_stringNoDescriptionSchema = KernelJsonSchema.Parse("""{"type":"string"}""");
+    /// <summary>
+    /// Cached schema for a descriptionless string that's nullable.
+    /// </summary>
+    private static readonly KernelJsonSchema s_stringNoDescriptionSchemaAndNull = KernelJsonSchema.Parse("""{"type":["string","null"]}""");
 
     /// <summary>Initializes the OpenAIFunction.</summary>
     internal OpenAIFunction(
@@ -127,52 +139,143 @@ internal OpenAIFunction(
     /// <see cref="ChatTool"/> representation.
     /// </summary>
     /// <returns>A <see cref="ChatTool"/> containing all the function information.</returns>
-    public ChatTool ToFunctionDefinition()
+    public ChatTool ToFunctionDefinition(bool allowStrictSchemaAdherence = false)
     {
-        BinaryData resultParameters = s_zeroFunctionParametersSchema;
+        BinaryData resultParameters = allowStrictSchemaAdherence ? s_zeroFunctionParametersSchema_strict : s_zeroFunctionParametersSchema;
 
         IReadOnlyList<OpenAIFunctionParameter>? parameters = this.Parameters;
         if (parameters is { Count: > 0 })
         {
             var properties = new Dictionary<string, KernelJsonSchema>();
             var required = new List<string>();
 
-            for (int i = 0; i < parameters.Count; i++)
+            foreach (var parameter in parameters)
             {
-                var parameter = parameters[i];
-                properties.Add(parameter.Name, parameter.Schema ?? GetDefaultSchemaForTypelessParameter(parameter.Description));
-                if (parameter.IsRequired)
+                properties.Add(parameter.Name, GetSanitizedSchemaForStrictMode(parameter.Schema, !parameter.IsRequired && allowStrictSchemaAdherence) ?? GetDefaultSchemaForTypelessParameter(parameter.Description, allowStrictSchemaAdherence));
+                if (parameter.IsRequired || allowStrictSchemaAdherence)
                 {
                     required.Add(parameter.Name);
                 }
             }
 
-            resultParameters = BinaryData.FromObjectAsJson(new
-            {
-                type = "object",
-                required,
-                properties,
-            });
+            resultParameters = allowStrictSchemaAdherence
+                ? BinaryData.FromObjectAsJson(new
+                {
+                    type = "object",
+                    required,
+                    properties,
+                    additionalProperties = false
+                })
+                : BinaryData.FromObjectAsJson(new
+                {
+                    type = "object",
+                    required,
+                    properties,
+                });
         }
 
         return ChatTool.CreateFunctionTool
         (
             functionName: this.FullyQualifiedName,
             functionDescription: this.Description,
-            functionParameters: resultParameters
+            functionParameters: resultParameters,
+            functionSchemaIsStrict: allowStrictSchemaAdherence
         );
     }
 
     /// <summary>Gets a <see cref="KernelJsonSchema"/> for a typeless parameter with the specified description, defaulting to typeof(string)</summary>
-    private static KernelJsonSchema GetDefaultSchemaForTypelessParameter(string? description)
+    private static KernelJsonSchema GetDefaultSchemaForTypelessParameter(string? description, bool allowStrictSchemaAdherence)
     {
         // If there's a description, incorporate it.
         if (!string.IsNullOrWhiteSpace(description))
         {
-            return KernelJsonSchemaBuilder.Build(typeof(string), description);
+            return allowStrictSchemaAdherence ?
+                GetOptionalStringSchemaWithDescription(description!) :
+                KernelJsonSchemaBuilder.Build(typeof(string), description, AIJsonSchemaCreateOptions.Default);
         }
 
         // Otherwise, we can use a cached schema for a string with no description.
-        return s_stringNoDescriptionSchema;
+        return allowStrictSchemaAdherence ? s_stringNoDescriptionSchemaAndNull : s_stringNoDescriptionSchema;
+    }
+
+    private static KernelJsonSchema GetOptionalStringSchemaWithDescription(string description)
+    {
+        var jObject = new JsonObject
+        {
+            { "description", description },
+            { "type", new JsonArray { "string", "null" } },
+        };
+        return KernelJsonSchema.Parse(jObject.ToString());
+    }
+    private static KernelJsonSchema? GetSanitizedSchemaForStrictMode(KernelJsonSchema? schema, bool insertNullType)
+    {
+        if (schema is null)
+        {
+            return null;
+        }
+        var forbiddenPropertyNames = s_forbiddenKeywords.Where(k => schema.RootElement.TryGetProperty(k, out _)).ToArray();
+
+        if (forbiddenPropertyNames.Length > 0 || insertNullType && schema.RootElement.TryGetProperty(TypeKey, out var typeElement) &&
+            (typeElement.ValueKind == JsonValueKind.Array && !typeElement.EnumerateArray().Any(static t => NullType.Equals(t.GetString(), StringComparison.OrdinalIgnoreCase)) ||
+            typeElement.ValueKind == JsonValueKind.String && typeElement.GetString() != NullType))
+        {
+            var originalSchema = JsonSerializer.Serialize(schema.RootElement);
+            var parsedJson = JsonNode.Parse(originalSchema);
+
+            if (parsedJson is null)
+            {
+                return schema;
+            }
+
+            var jsonObject = parsedJson.AsObject();
+            foreach (var forbiddenPropertyName in forbiddenPropertyNames)
+            {
+                jsonObject.Remove(forbiddenPropertyName);
+            }
+
+            InsertNullTypeIfRequired(insertNullType, jsonObject);
+
+            return KernelJsonSchema.Parse(jsonObject.ToString());
+        }
+        return schema;
+    }
+    // https://platform.openai.com/docs/guides/structured-outputs#some-type-specific-keywords-are-not-yet-supported
+    private static void InsertNullTypeIfRequired(bool insertNullType, JsonObject jsonObject)
+    {
+        if (insertNullType && jsonObject.TryGetPropertyValue(TypeKey, out var typeValue))
+        {
+            if (typeValue is JsonArray jsonArray && !jsonArray.Contains(NullType))
+            {
+                jsonArray.Add(NullType);
+            }
+            else if (typeValue is JsonValue jsonValue && jsonValue.GetValueKind() == JsonValueKind.String)
+            {
+                jsonObject[TypeKey] = new JsonArray { typeValue.GetValue<string>(), NullType };
+            }
+        }
     }
+    private const string NullType = "null";
+    private const string TypeKey = "type";
+    // https://platform.openai.com/docs/guides/structured-outputs#some-type-specific-keywords-are-not-yet-supported
+    private static readonly string[] s_forbiddenKeywords = [
+        "contains",
+        "format",
+        "maxContains",
+        "maximum",
+        "maxItems",
+        "maxLength",
+        "maxProperties",
+        "minContains",
+        "minimum",
+        "minItems",
+        "minLength",
+        "minProperties",
+        "multipleOf",
+        "pattern",
+        "patternProperties",
+        "propertyNames",
+        "unevaluatedItems",
+        "unevaluatedProperties",
+        "uniqueItems",
+    ];
 }

dotnet/src/Functions/Functions.UnitTests/Yaml/PromptExecutionSettingsTypeConverterTests.cs

@@ -304,6 +304,7 @@ public void ItShouldDeserializeAutoFunctionChoiceBehaviorFromJsonWithOptions()
               options:
                 allow_parallel_calls: true
                 allow_concurrent_invocation: true
+                allow_strict_schema_adherence: true
         """;
 
         var executionSettings = this._deserializer.Deserialize<PromptExecutionSettings>(yaml);
@@ -314,6 +315,7 @@ public void ItShouldDeserializeAutoFunctionChoiceBehaviorFromJsonWithOptions()
         // Assert
         Assert.True(config.Options.AllowParallelCalls);
         Assert.True(config.Options.AllowConcurrentInvocation);
+        Assert.True(config.Options.AllowStrictSchemaAdherence);
     }
 
     [Fact]
@@ -326,6 +328,7 @@ public void ItShouldDeserializeRequiredFunctionChoiceBehaviorFromJsonWithOptions
               options:
                 allow_parallel_calls: true
                 allow_concurrent_invocation: true
+                allow_strict_schema_adherence: true
         """;
 
         var executionSettings = this._deserializer.Deserialize<PromptExecutionSettings>(yaml);
@@ -336,6 +339,7 @@ public void ItShouldDeserializeRequiredFunctionChoiceBehaviorFromJsonWithOptions
         // Assert
         Assert.True(config.Options.AllowParallelCalls);
         Assert.True(config.Options.AllowConcurrentInvocation);
+        Assert.True(config.Options.AllowStrictSchemaAdherence);
     }
 
     private readonly string _yaml = """

dotnet/src/InternalUtilities/src/Schema/KernelJsonSchemaBuilder.cs

@@ -24,7 +24,7 @@ namespace Microsoft.SemanticKernel;
 internal static class KernelJsonSchemaBuilder
 {
     private static JsonSerializerOptions? s_options;
-    private static readonly AIJsonSchemaCreateOptions s_schemaOptions = new()
+    internal static readonly AIJsonSchemaCreateOptions s_schemaOptions = new()
     {
         IncludeSchemaKeyword = false,
         IncludeTypeInEnumSchemas = true,

dotnet/src/SemanticKernel.Abstractions/AI/FunctionChoiceBehaviors/FunctionChoiceBehaviorOptions.cs

@@ -26,4 +26,13 @@ public sealed class FunctionChoiceBehaviorOptions
     /// </remarks>
     [JsonPropertyName("allow_concurrent_invocation")]
     public bool AllowConcurrentInvocation { get; set; } = false;
+
+    /// <summary>
+    /// Gets or sets whether the AI model should strictly adhere to the function schema.
+    /// </summary>
+    /// <remarks>
+    /// The default value is set to false. If set to true, the AI model will strictly adhere to the function schema.
+    /// </remarks>
+    [JsonPropertyName("allow_strict_schema_adherence")]
+    public bool AllowStrictSchemaAdherence { get; set; } = false;
 }

dotnet/src/SemanticKernel.UnitTests/AI/FunctionChoiceBehaviors/AutoFunctionChoiceBehaviorTests.cs

@@ -280,6 +280,24 @@ public void ItShouldPropagateAllowConcurrentInvocationOptionToConfiguration()
         Assert.True(configuration.Options.AllowConcurrentInvocation);
     }
 
+    [Fact]
+    public void ItShouldPropagateAllowStrictSchemaAdherenceOptionToConfiguration()
+    {
+        // Arrange
+        var options = new FunctionChoiceBehaviorOptions
+        {
+            AllowStrictSchemaAdherence = true
+        };
+
+        // Act
+        var choiceBehavior = new AutoFunctionChoiceBehavior(autoInvoke: false, options: options);
+
+        // Assert
+        var configuration = choiceBehavior.GetConfiguration(new FunctionChoiceBehaviorConfigurationContext(chatHistory: []));
+
+        Assert.True(configuration.Options.AllowStrictSchemaAdherence);
+    }
+
     private static KernelPlugin GetTestPlugin()
     {
         var function1 = KernelFunctionFactory.CreateFromMethod(() => { }, "Function1");