Create a smarter OpenAI chat client that honors model ID

kzu · kzu · commit f01765070824 · 2025-07-02T18:16:15.000-03:00
When using `IChatClient` API, the `ChatOptions.ModelId` is ignored by the built-in OpenAI implementation obtained by invoking `OpenAIClient.GetChatClient("model").AsIChatClient`. This is because the `GetChatClient` stores the model passed in and doesn't respect the options-specified one after initial creation.

We now align our own implementation of `IChatClient` for OpenAI so it behaves like Grok's, allowing more flexible usage while following the natural expectation set by having a writable `ChatOptions.ModelId` in the first place :).
diff --git a/src/AI.Tests/AI.Tests.csproj b/src/AI.Tests/AI.Tests.csproj
@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFramework>net10.0</TargetFramework>
     <NoWarn>OPENAI001;$(NoWarn)</NoWarn>
+    <LangVersion>Preview</LangVersion>
     <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
   </PropertyGroup>
 
diff --git a/src/AI.Tests/Extensions/PipelineTestOutput.cs b/src/AI.Tests/Extensions/PipelineTestOutput.cs
@@ -12,57 +12,86 @@ public static class PipelineTestOutput
     /// </summary>
     /// <typeparam name="TOptions">The options type to configure for HTTP logging.</typeparam>
     /// <param name="pipelineOptions">The options instance to configure.</param>
+    /// <param name="output">The test output helper to write to.</param>
+    /// <param name="onRequest">A callback to process the <see cref="JsonNode"/> that was sent.</param>
+    /// <param name="onResponse">A callback to process the <see cref="JsonNode"/> that was received.</param>
     /// <remarks>
     /// NOTE: this is the lowst-level logging after all chat pipeline processing has been done.
     /// <para>
     /// If the options already provide a transport, it will be wrapped with the console 
     /// logging transport to minimize the impact on existing configurations.
     /// </para>
     /// </remarks>
-    public static TOptions UseTestOutput<TOptions>(this TOptions pipelineOptions, ITestOutputHelper output)
+    public static TOptions WriteTo<TOptions>(this TOptions pipelineOptions, ITestOutputHelper? output = default, Action<JsonNode>? onRequest = default, Action<JsonNode>? onResponse = default)
         where TOptions : ClientPipelineOptions
     {
-        pipelineOptions.Transport = new TestPipelineTransport(pipelineOptions.Transport ?? HttpClientPipelineTransport.Shared, output);
-
+        pipelineOptions.AddPolicy(new TestOutputPolicy(output ?? NullTestOutputHelper.Default, onRequest, onResponse), PipelinePosition.BeforeTransport);
         return pipelineOptions;
     }
-}
 
-public class TestPipelineTransport(PipelineTransport inner, ITestOutputHelper? output = null) : PipelineTransport
-{
-    static readonly JsonSerializerOptions options = new JsonSerializerOptions(JsonSerializerDefaults.General)
+    class NullTestOutputHelper : ITestOutputHelper
     {
-        WriteIndented = true,
-    };
-
-    public List<JsonNode> Requests { get; } = [];
-    public List<JsonNode> Responses { get; } = [];
+        public static ITestOutputHelper Default { get; } = new NullTestOutputHelper();
+        NullTestOutputHelper() { }
+        public void WriteLine(string message) { }
+        public void WriteLine(string format, params object[] args) { }
+    }
 
-    protected override async ValueTask ProcessCoreAsync(PipelineMessage message)
+    class TestOutputPolicy(ITestOutputHelper output, Action<JsonNode>? onRequest = default, Action<JsonNode>? onResponse = default) : PipelinePolicy
     {
-        message.BufferResponse = true;
-        await inner.ProcessAsync(message);
+        static readonly JsonSerializerOptions options = new JsonSerializerOptions(JsonSerializerDefaults.General)
+        {
+            WriteIndented = true,
+        };
 
-        if (message.Request.Content is not null)
+        public override void Process(PipelineMessage message, IReadOnlyList<PipelinePolicy> pipeline, int currentIndex)
         {
-            using var memory = new MemoryStream();
-            message.Request.Content.WriteTo(memory);
-            memory.Position = 0;
-            using var reader = new StreamReader(memory);
-            var content = await reader.ReadToEndAsync();
-            var node = JsonNode.Parse(content);
-            Requests.Add(node!);
-            output?.WriteLine(node!.ToJsonString(options));
+            message.BufferResponse = true;
+            ProcessNext(message, pipeline, currentIndex);
+
+            if (message.Request.Content is not null)
+            {
+                using var memory = new MemoryStream();
+                message.Request.Content.WriteTo(memory);
+                memory.Position = 0;
+                using var reader = new StreamReader(memory);
+                var content = reader.ReadToEnd();
+                var node = JsonNode.Parse(content);
+                onRequest?.Invoke(node!);
+                output?.WriteLine(node!.ToJsonString(options));
+            }
+
+            if (message.Response != null)
+            {
+                var node = JsonNode.Parse(message.Response.Content.ToString());
+                onResponse?.Invoke(node!);
+                output?.WriteLine(node!.ToJsonString(options));
+            }
         }
 
-        if (message.Response != null)
+        public override async ValueTask ProcessAsync(PipelineMessage message, IReadOnlyList<PipelinePolicy> pipeline, int currentIndex)
         {
-            var node = JsonNode.Parse(message.Response.Content.ToString());
-            Responses.Add(node!);
-            output?.WriteLine(node!.ToJsonString(options));
+            message.BufferResponse = true;
+            await ProcessNextAsync(message, pipeline, currentIndex);
+
+            if (message.Request.Content is not null)
+            {
+                using var memory = new MemoryStream();
+                message.Request.Content.WriteTo(memory);
+                memory.Position = 0;
+                using var reader = new StreamReader(memory);
+                var content = await reader.ReadToEndAsync();
+                var node = JsonNode.Parse(content);
+                onRequest?.Invoke(node!);
+                output?.WriteLine(node!.ToJsonString(options));
+            }
+
+            if (message.Response != null)
+            {
+                var node = JsonNode.Parse(message.Response.Content.ToString());
+                onResponse?.Invoke(node!);
+                output?.WriteLine(node!.ToJsonString(options));
+            }
         }
     }
-
-    protected override PipelineMessage CreateMessageCore() => inner.CreateMessage();
-    protected override void ProcessCore(PipelineMessage message) => inner.Process(message);
-}
+}
diff --git a/src/AI.Tests/GrokTests.cs b/src/AI.Tests/GrokTests.cs
@@ -1,5 +1,4 @@
-﻿using System.ClientModel.Primitives;
-using System.Text.Json.Nodes;
+﻿using System.Text.Json.Nodes;
 using Microsoft.Extensions.AI;
 using static ConfigurationExtensions;
 
@@ -49,9 +48,11 @@ public async Task GrokInvokesToolAndSearch()
             { "user", "What's Tesla stock worth today?" },
         };
 
-        var transport = new TestPipelineTransport(HttpClientPipelineTransport.Shared, output);
+        var requests = new List<JsonNode>();
+        var responses = new List<JsonNode>();
 
-        var grok = new GrokChatClient(Configuration["XAI_API_KEY"]!, "grok-3", new OpenAI.OpenAIClientOptions() { Transport = transport })
+        var grok = new GrokChatClient(Configuration["XAI_API_KEY"]!, "grok-3",
+                new OpenAI.OpenAIClientOptions().WriteTo(output, requests.Add, responses.Add))
             .AsBuilder()
             .UseFunctionInvocation()
             .Build();
@@ -69,7 +70,7 @@ public async Task GrokInvokesToolAndSearch()
         // "search_parameters": {
         //      "mode": "on"
         //}
-        Assert.All(transport.Requests, x =>
+        Assert.All(requests, x =>
         {
             var search = Assert.IsType<JsonObject>(x["search_parameters"]);
             Assert.Equal("on", search["mode"]?.GetValue<string>());
@@ -79,7 +80,7 @@ public async Task GrokInvokesToolAndSearch()
         Assert.Contains(response.Messages, x => x.Role == ChatRole.Tool);
 
         // Citations include nasdaq.com at least as a web search source
-        var node = transport.Responses.LastOrDefault();
+        var node = responses.LastOrDefault();
         Assert.NotNull(node);
         var citations = Assert.IsType<JsonArray>(node["citations"], false);
         var yahoo = citations.Where(x => x != null).Any(x => x!.ToString().Contains("https://finance.yahoo.com/quote/TSLA/", StringComparison.Ordinal));
@@ -100,16 +101,18 @@ public async Task GrokInvokesHostedSearchTool()
             { "user", "What's Tesla stock worth today? Search X and the news for latest info." },
         };
 
-        var transport = new TestPipelineTransport(HttpClientPipelineTransport.Shared, output);
+        var requests = new List<JsonNode>();
+        var responses = new List<JsonNode>();
 
-        var chat = new GrokChatClient(Configuration["XAI_API_KEY"]!, "grok-3", new OpenAI.OpenAIClientOptions() { Transport = transport });
+        var grok = new GrokChatClient(Configuration["XAI_API_KEY"]!, "grok-3",
+                new OpenAI.OpenAIClientOptions().WriteTo(output, requests.Add, responses.Add));
 
         var options = new ChatOptions
         {
             Tools = [new HostedWebSearchTool()]
         };
 
-        var response = await chat.GetResponseAsync(messages, options);
+        var response = await grok.GetResponseAsync(messages, options);
         var text = response.Text;
 
         Assert.Contains("TSLA", text);
@@ -118,15 +121,15 @@ public async Task GrokInvokesHostedSearchTool()
         // "search_parameters": {
         //      "mode": "auto"
         //}
-        Assert.All(transport.Requests, x =>
+        Assert.All(requests, x =>
         {
             var search = Assert.IsType<JsonObject>(x["search_parameters"]);
             Assert.Equal("auto", search["mode"]?.GetValue<string>());
         });
 
         // Citations include nasdaq.com at least as a web search source
-        Assert.Single(transport.Responses);
-        var node = transport.Responses[0];
+        Assert.Single(responses);
+        var node = responses[0];
         Assert.NotNull(node);
         var citations = Assert.IsType<JsonArray>(node["citations"], false);
         var yahoo = citations.Where(x => x != null).Any(x => x!.ToString().Contains("https://finance.yahoo.com/quote/TSLA/", StringComparison.Ordinal));
diff --git a/src/AI.Tests/OpenAITests.cs b/src/AI.Tests/OpenAITests.cs
@@ -0,0 +1,67 @@
+﻿using System.Text.Json.Nodes;
+using Microsoft.Extensions.AI;
+using static ConfigurationExtensions;
+
+namespace Devlooped.Extensions.AI;
+
+public class OpenAITests(ITestOutputHelper output)
+{
+    [SecretsFact("OPENAI_API_KEY")]
+    public async Task OpenAISwitchesModel()
+    {
+        var messages = new Chat()
+        {
+            { "user", "What products does Tesla make?" },
+        };
+
+        var chat = new OpenAIChatClient(Configuration["OPENAI_API_KEY"]!, "gpt-4.1-nano", new OpenAI.OpenAIClientOptions().WriteTo(output));
+
+        var options = new ChatOptions
+        {
+            ModelId = "gpt-4.1-mini",
+        };
+
+        var response = await chat.GetResponseAsync(messages, options);
+
+        // NOTE: the chat client was requested as grok-3 but the chat options wanted a 
+        // different model and the grok client honors that choice.
+        Assert.StartsWith("gpt-4.1-mini", response.ModelId);
+    }
+
+    [SecretsFact("OPENAI_API_KEY")]
+    public async Task OpenAIThinks()
+    {
+        var messages = new Chat()
+        {
+            { "system", "You are an intelligent AI assistant that's an expert on financial matters." },
+            { "user", "If you have a debt of 100k and accumulate a compounding 5% debt on top of it every year, how long before you are a negative millonaire? (round up to full integer value)" },
+        };
+
+        var requests = new List<JsonNode>();
+
+        var chat = new OpenAIChatClient(Configuration["OPENAI_API_KEY"]!, "o3-mini", new OpenAI.OpenAIClientOptions()
+            .WriteTo(output, requests.Add));
+
+        var options = new ChatOptions
+        {
+            ModelId = "o4-mini",
+            ReasoningEffort = ReasoningEffort.Medium
+        };
+
+        var response = await chat.GetResponseAsync(messages, options);
+
+        var text = response.Text;
+
+        Assert.Contains("48 years", text);
+        // NOTE: the chat client was requested as grok-3 but the chat options wanted a 
+        // different model and the grok client honors that choice.
+        Assert.StartsWith("o4-mini", response.ModelId);
+
+        // Reasoning should have been set to medium
+        Assert.All(requests, x =>
+        {
+            var search = Assert.IsType<JsonObject>(x["reasoning"]);
+            Assert.Equal("medium", search["effort"]?.GetValue<string>());
+        });
+    }
+}
diff --git a/src/AI/OpenAI/OpenAIChatClient.cs b/src/AI/OpenAI/OpenAIChatClient.cs
@@ -0,0 +1,71 @@
+﻿using System.ClientModel;
+using System.ClientModel.Primitives;
+using System.Collections.Concurrent;
+using Microsoft.Extensions.AI;
+using OpenAI;
+using OpenAI.Responses;
+
+namespace Devlooped.Extensions.AI;
+
+/// <summary>
+/// An <see cref="IChatClient"/> implementation for OpenAI.
+/// </summary>
+public class OpenAIChatClient : IChatClient
+{
+    readonly ConcurrentDictionary<string, IChatClient> clients = new();
+    readonly string modelId;
+    readonly ClientPipeline pipeline;
+    readonly OpenAIClientOptions? options;
+
+    /// <summary>
+    /// Initializes the client with the specified API key, model ID, and optional OpenAI client options.
+    /// </summary>
+    public OpenAIChatClient(string apiKey, string modelId, OpenAIClientOptions? options = default)
+    {
+        this.modelId = modelId;
+        this.options = options;
+
+        // NOTE: by caching the pipeline, we speed up creation of new chat clients per model, 
+        // since the pipeline will be the same for all of them.
+        pipeline = new OpenAIClient(new ApiKeyCredential(apiKey), options).Pipeline;
+    }
+
+    /// <inheritdoc/>
+    public Task<ChatResponse> GetResponseAsync(IEnumerable<ChatMessage> messages, ChatOptions? options = null, CancellationToken cancellation = default)
+            => GetChatClient(options?.ModelId ?? modelId).GetResponseAsync(messages, SetOptions(options), cancellation);
+
+    /// <inheritdoc/>
+    public IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(IEnumerable<ChatMessage> messages, ChatOptions? options = null, CancellationToken cancellation = default)
+            => GetChatClient(options?.ModelId ?? modelId).GetStreamingResponseAsync(messages, SetOptions(options), cancellation);
+
+    IChatClient GetChatClient(string modelId) => clients.GetOrAdd(modelId, model
+        => new PipelineClient(pipeline, options).GetOpenAIResponseClient(modelId).AsIChatClient());
+
+    static ChatOptions? SetOptions(ChatOptions? options)
+    {
+        if (options is null)
+            return null;
+
+        if (options.ReasoningEffort is ReasoningEffort effort)
+        {
+            options.RawRepresentationFactory = _ => new ResponseCreationOptions
+            {
+                ReasoningOptions = new ResponseReasoningOptions(effort switch
+                {
+                    ReasoningEffort.High => ResponseReasoningEffortLevel.High,
+                    ReasoningEffort.Medium => ResponseReasoningEffortLevel.Medium,
+                    _ => ResponseReasoningEffortLevel.Low
+                })
+            };
+        }
+
+        return options;
+    }
+
+    void IDisposable.Dispose() { }
+
+    public object? GetService(Type serviceType, object? serviceKey = null) => null;
+
+    // Allows creating the base OpenAIClient with a pre-created pipeline.
+    class PipelineClient(ClientPipeline pipeline, OpenAIClientOptions? options) : OpenAIClient(pipeline, options) { }
+}
