.Net: Example of retry logic using Filters

dotnet/samples/Concepts/Filtering/RetryWithFilters.cs

@@ -0,0 +1,72 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Net;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Connectors.OpenAI;
+
+namespace Filtering;
+
+/// <summary>
+/// This example shows how to perform retry with filter and switch to another model as a fallback.
+/// </summary>
+public class RetryWithFilters(ITestOutputHelper output) : BaseTest(output)
+{
+    [Fact]
+    public async Task ChangeModelAndRetryAsync()
+    {
+        // Default and fallback models for demonstration purposes
+        const string DefaultModelId = "gpt-4";
+        const string FallbackModelId = "gpt-3.5-turbo-1106";
+
+        var builder = Kernel.CreateBuilder();
+
+        // Add OpenAI chat completion service with invalid API key to force a 401 Unauthorized response
+        builder.AddOpenAIChatCompletion(modelId: DefaultModelId, apiKey: "invalid_key");
+
+        // Add OpenAI chat completion service with valid configuration as a fallback
+        builder.AddOpenAIChatCompletion(modelId: FallbackModelId, apiKey: TestConfiguration.OpenAI.ApiKey);
+
+        // Add retry filter
+        builder.Services.AddSingleton<IFunctionInvocationFilter>(new RetryFilter(FallbackModelId));
+
+        // Build kernel
+        var kernel = builder.Build();
+
+        // Initially, use "gpt-4" with invalid API key to simulate exception
+        var executionSettings = new OpenAIPromptExecutionSettings { ModelId = DefaultModelId, MaxTokens = 20 };
+
+        var result = await kernel.InvokePromptAsync("Hi, can you help me today?", new(executionSettings));
+
+        Console.WriteLine(result);
+
+        // Output: Of course! I'll do my best to help you. What do you need assistance with?
+    }
+
+    /// <summary>
+    /// Filter to change the model and perform retry in case of exception.
+    /// </summary>
+    private sealed class RetryFilter(string fallbackModelId) : IFunctionInvocationFilter
+    {
+        public async Task OnFunctionInvocationAsync(FunctionInvocationContext context, Func<FunctionInvocationContext, Task> next)
+        {
+            try
+            {
+                // Try to invoke function
+                await next(context);
+            }
+            // Catch specific exception
+            catch (HttpOperationException exception) when (exception.StatusCode == HttpStatusCode.Unauthorized)
+            {
+                // Get current execution settings
+                PromptExecutionSettings executionSettings = context.Arguments.ExecutionSettings![PromptExecutionSettings.DefaultServiceId];
+
+                // Override settings with fallback model id
+                executionSettings.ModelId = fallbackModelId;
+
+                // Try to invoke function again
+                await next(context);
+            }
+        }
+    }
+}

dotnet/samples/Concepts/README.md

@@ -59,6 +59,7 @@ Down below you can find the code snippets that demonstrate the usage of many Sem
 - [FunctionInvocationFiltering](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/FunctionInvocationFiltering.cs)
 - [Legacy_KernelHooks](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/Legacy_KernelHooks.cs)
 - [PromptRenderFiltering](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/PromptRenderFiltering.cs)
+- [RetryWithFilters](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Filtering/RetryWithFilters.cs)
 
 ## Functions - Invoking [`Method`](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Core/Functions/KernelFunctionFromMethod.cs) or [`Prompt`](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Core/Functions/KernelFunctionFromPrompt.cs) functions with [`Kernel`](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Abstractions/Kernel.cs)