feat: add support for count tokens endpoint

src/AnthropicClient/AnthropicApiClient.cs

@@ -26,6 +26,13 @@ public interface IAnthropicApiClient
   /// <param name="request">The message request to create.</param>
   /// <returns>An asynchronous enumerable that yields the response event by event.</returns>
   IAsyncEnumerable<AnthropicEvent> CreateMessageAsync(StreamMessageRequest request);
+
+  /// <summary>
+  /// Counts the tokens in a message asynchronously.
+  /// </summary>
+  /// <param name="request">The count message tokens request.</param>
+  /// <returns>A task that represents the asynchronous operation. The task result contains the response as an <see cref="AnthropicResult{T}"/> where T is <see cref="TokenCountResponse"/>.</returns>
+  Task<AnthropicResult<TokenCountResponse>> CountMessageTokensAsync(CountMessageTokensRequest request);
 }
 
 /// <inheritdoc cref="IAnthropicApiClient"/>
@@ -34,6 +41,7 @@ public class AnthropicApiClient : IAnthropicApiClient
   private const string BaseUrl = "https://api.anthropic.com/v1/";
   private const string ApiKeyHeader = "x-api-key";
   private const string MessagesEndpoint = "messages";
+  private const string CountTokensEndpoint = "messages/count_tokens";
   private const string JsonContentType = "application/json";
   private const string EventPrefix = "event:";
   private const string DataPrefix = "data:";
@@ -71,7 +79,7 @@ public class AnthropicApiClient : IAnthropicApiClient
   /// <inheritdoc />
   public async Task<AnthropicResult<MessageResponse>> CreateMessageAsync(MessageRequest request)
   {
-    var response = await SendRequestAsync(request);
+    var response = await SendRequestAsync(MessagesEndpoint, request);
     var anthropicHeaders = new AnthropicHeaders(response.Headers);
     var responseContent = await response.Content.ReadAsStringAsync();
 
@@ -94,7 +102,7 @@ public class AnthropicApiClient : IAnthropicApiClient
   /// <inheritdoc />
   public async IAsyncEnumerable<AnthropicEvent> CreateMessageAsync(StreamMessageRequest request)
   {
-    var response = await SendRequestAsync(request);
+    var response = await SendRequestAsync(MessagesEndpoint, request);
 
     if (response.IsSuccessStatusCode is false)
     {
@@ -274,11 +282,29 @@ public class AnthropicApiClient : IAnthropicApiClient
     return new ToolCall(tool, toolUse);
   }
 
-  private async Task<HttpResponseMessage> SendRequestAsync(BaseMessageRequest request)
+  /// <inheritdoc />
+  public async Task<AnthropicResult<TokenCountResponse>> CountMessageTokensAsync(CountMessageTokensRequest request)
+  {
+    var response = await SendRequestAsync(CountTokensEndpoint, request);
+    var anthropicHeaders = new AnthropicHeaders(response.Headers);
+    var responseContent = await response.Content.ReadAsStringAsync();
+
+    if (response.IsSuccessStatusCode is false)
+    {
+      var error = Deserialize<AnthropicError>(responseContent) ?? new AnthropicError();
+      return AnthropicResult<TokenCountResponse>.Failure(error, anthropicHeaders);
+    }
+
+    var msgResponse = Deserialize<TokenCountResponse>(responseContent) ?? new TokenCountResponse();
+
+    return AnthropicResult<TokenCountResponse>.Success(msgResponse, anthropicHeaders);
+  }
+
+  private async Task<HttpResponseMessage> SendRequestAsync<T>(string endpoint, T request)
   {
     var requestJson = Serialize(request);
     var requestContent = new StringContent(requestJson, Encoding.UTF8, JsonContentType);
-    return await _httpClient.PostAsync(MessagesEndpoint, requestContent);
+    return await _httpClient.PostAsync(endpoint, requestContent);
   }
 
   private string Serialize<T>(T obj) => JsonSerializer.Serialize(obj, JsonSerializationOptions.DefaultOptions);

src/AnthropicClient/Models/AnthropicModels.cs

@@ -69,21 +69,4 @@ public static class AnthropicModels
   /// The Claude 3.5 Haiku model.
   /// </summary>
   public const string Claude35HaikuLatest = "claude-3-5-haiku-latest";
-
-  internal static bool IsValidModel(string modelId) => modelId is
-    Claude3Opus or
-    Claude3Opus20241022 or
-    Claude3OpusLatest or
-
-    Claude3Sonnet or
-    Claude3Sonnet20240229 or
-    Claude35Sonnet or
-    Claude35Sonnet20240620 or
-    Claude35Sonnet20241022 or
-    Claude35SonnetLatest or
-
-    Claude3Haiku or
-    Claude3Haiku20240307 or
-    Claude35Haiku20241022 or
-    Claude35HaikuLatest;
 }

src/AnthropicClient/Models/CountMessageTokensRequest.cs

@@ -0,0 +1,72 @@
+using System.Text.Json.Serialization;
+
+using AnthropicClient.Utils;
+
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents a request to count the number of tokens in a message.
+/// </summary>
+public class CountMessageTokensRequest
+{
+  /// <summary>
+  /// Gets the model ID to be used for the request.
+  /// </summary>
+  public string Model { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Gets the messages to count the number of tokens in.
+  /// </summary>
+  public List<Message> Messages { get; init; } = [];
+
+  /// <summary>
+  /// Gets the tool choice mode to use for the request.
+  /// </summary>
+  [JsonPropertyName("tool_choice")]
+  public ToolChoice? ToolChoice { get; init; } = null;
+
+  /// <summary>
+  /// Gets the tools to use for the request.
+  /// </summary>
+  public List<Tool>? Tools { get; init; } = null;
+
+  /// <summary>
+  /// Gets the system prompt to use for the request.
+  /// </summary>
+  [JsonPropertyName("system")]
+  public List<TextContent>? SystemPrompt { get; init; } = null;
+
+  /// <summary>
+  /// Initializes a new instance of the <see cref="CountMessageTokensRequest"/> class.
+  /// </summary>
+  /// <param name="model">The model ID to use for the request.</param>
+  /// <param name="messages">The messages to count the number of tokens in.</param>
+  /// <param name="toolChoice">The tool choice mode to use for the request.</param>
+  /// <param name="tools">The tools to use for the request.</param>
+  /// <param name="systemPrompt">The system prompt to use for the request.</param>
+  /// <exception cref="ArgumentNullException">Thrown when <paramref name="model"/> or <paramref name="messages"/> is null.</exception>
+  /// <exception cref="ArgumentException">Thrown when <paramref name="messages"/> is empty.</exception>
+  /// <returns>A new instance of the <see cref="CountMessageTokensRequest"/> class.</returns>
+  public CountMessageTokensRequest(
+    string model,
+    List<Message> messages,
+    ToolChoice? toolChoice = null,
+    List<Tool>? tools = null,
+    List<TextContent>? systemPrompt = null
+  )
+  {
+    ArgumentValidator.ThrowIfNull(model, nameof(model));
+    ArgumentValidator.ThrowIfNull(messages, nameof(messages));
+
+    if (messages.Count < 1)
+    {
+      throw new ArgumentException("Messages must contain at least one message");
+    }
+
+    Model = model;
+    Messages = messages;
+    ToolChoice = toolChoice;
+    Tools = tools;
+    SystemPrompt = systemPrompt;
+  }
+}

src/AnthropicClient/Models/TokenCountResponse.cs

@@ -0,0 +1,15 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents a response to a token count request.
+/// </summary>
+public class TokenCountResponse
+{
+  /// <summary>
+  ///  The number of input tokens counted.
+  /// </summary>
+  [JsonPropertyName("input_tokens")]
+  public int InputTokens { get; init; }
+}