Adds LanguageModelRateLimitingPlugin. Closes #1309 (#1324)

Co-authored-by: Copilot <[email protected]>

Author: waldekmastykarz

DevProxy.Abstractions/LanguageModel/OpenAIModels.cs

@@ -6,7 +6,7 @@
 
 namespace DevProxy.Abstractions.LanguageModel;
 
-public abstract class OpenAIRequest
+public class OpenAIRequest
 {
     [JsonPropertyName("frequency_penalty")]
     public long? FrequencyPenalty { get; set; }
@@ -22,7 +22,7 @@ public abstract class OpenAIRequest
     public double? TopP { get; set; }
 }
 
-public abstract class OpenAIResponse : ILanguageModelCompletionResponse
+public class OpenAIResponse : ILanguageModelCompletionResponse
 {
     public long Created { get; set; }
     public OpenAIError? Error { get; set; }
@@ -37,12 +37,12 @@ public abstract class OpenAIResponse : ILanguageModelCompletionResponse
     public string? RequestUrl { get; set; }
 
     public string? ErrorMessage => Error?.Message;
-    public abstract string? Response { get; }
+    public virtual string? Response { get; }
 
     public OpenAIResponse ConvertToOpenAIResponse() => this;
 }
 
-public abstract class OpenAIResponse<TChoice> : OpenAIResponse
+public class OpenAIResponse<TChoice> : OpenAIResponse
 {
     public IEnumerable<TChoice>? Choices { get; set; }
 }

DevProxy.Plugins/Behavior/LanguageModelRateLimitingCustomResponseLoader.cs

@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using DevProxy.Abstractions.Utils;
+using DevProxy.Abstractions.Proxy;
+using DevProxy.Abstractions.Plugins;
+using Microsoft.Extensions.Logging;
+using System.Text.Json;
+using DevProxy.Abstractions.Models;
+
+namespace DevProxy.Plugins.Behavior;
+
+internal sealed class LanguageModelRateLimitingCustomResponseLoader(
+    HttpClient httpClient,
+    ILogger<LanguageModelRateLimitingCustomResponseLoader> logger,
+    LanguageModelRateLimitConfiguration configuration,
+    IProxyConfiguration proxyConfiguration) :
+    BaseLoader(httpClient, logger, proxyConfiguration)
+{
+    private readonly LanguageModelRateLimitConfiguration _configuration = configuration;
+
+    protected override string FilePath => _configuration.CustomResponseFile;
+
+    protected override void LoadData(string fileContents)
+    {
+        try
+        {
+            var response = JsonSerializer.Deserialize<MockResponseResponse>(fileContents, ProxyUtils.JsonSerializerOptions);
+            if (response is not null)
+            {
+                _configuration.CustomResponse = response;
+            }
+        }
+        catch (Exception ex)
+        {
+            Logger.LogError(ex, "An error has occurred while reading {ConfigurationFile}:", _configuration.CustomResponseFile);
+        }
+    }
+}