feat: initial pass at citations in request and response

src/AnthropicClient/Json/CitationConverter.cs

@@ -0,0 +1,28 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using AnthropicClient.Models;
+
+namespace AnthropicClient.Json;
+
+class CitationConverter : JsonConverter<Citation>
+{
+  public override Citation Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+  {
+    using var jsonDocument = JsonDocument.ParseValue(ref reader);
+    var root = jsonDocument.RootElement;
+    var type = root.GetProperty("type").GetString();
+    return type switch
+    {
+      CitationType.CharacterLocation => JsonSerializer.Deserialize<CharacterLocationCitation>(root.GetRawText(), options)!,
+      CitationType.PageLocation => JsonSerializer.Deserialize<PageLocationCitation>(root.GetRawText(), options)!,
+      CitationType.ContentBlockLocation => JsonSerializer.Deserialize<ContentBlockLocationCitation>(root.GetRawText(), options)!,
+      _ => throw new JsonException($"Unknown content type: {type}")
+    };
+  }
+
+  public override void Write(Utf8JsonWriter writer, Citation value, JsonSerializerOptions options)
+  {
+    JsonSerializer.Serialize(writer, value, value.GetType(), options);
+  }
+}

src/AnthropicClient/Json/JsonSerializationOptions.cs

@@ -18,6 +18,7 @@ static class JsonSerializationOptions
       new ContentDeltaConverter(),
       new JsonStringEnumConverter(),
       new MessageBatchResultConverter(),
+      new CitationConverter(),
     },
     DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
   };

src/AnthropicClient/Models/CitationType.cs

@@ -0,0 +1,8 @@
+namespace AnthropicClient.Models;
+
+public static class CitationType
+{
+  public const string CharacterLocation = "char_location";
+  public const string PageLocation = "page_location";
+  public const string ContentBlockLocation = "content_block_location";
+}

src/AnthropicClient/Models/DocumentContent.cs

@@ -14,6 +14,12 @@ public class DocumentContent : Content
   /// </summary>
   public DocumentSource Source { get; init; } = new();
 
+  public string Title { get; init; } = string.Empty;
+
+  public string Context { get; init; } = string.Empty;
+
+  public CitationOption Citations { get; init; } = new CitationOption();
+
   [JsonConstructor]
   internal DocumentContent()
   {
@@ -53,4 +59,24 @@ public class DocumentContent : Content
 
     Source = new(mediaType, data);
   }
+
+  public DocumentContent(DocumentSource source) : base(ContentType.Document)
+  {
+    ArgumentValidator.ThrowIfNull(source, nameof(source));
+
+    Source = source;
+  }
+
+  public DocumentContent(DocumentSource source, CacheControl cacheControl) : base(ContentType.Document, cacheControl)
+  {
+    ArgumentValidator.ThrowIfNull(source, nameof(source));
+
+    Source = source;
+  }
+}
+
+
+public class CitationOption
+{
+  public bool Enabled { get; init; }
 }

src/AnthropicClient/Models/TextContent.cs

@@ -14,6 +14,8 @@ public class TextContent : Content
   /// </summary>
   public string Text { get; init; } = string.Empty;
 
+  public Citation[] Citations { get; init; } = [];
+
   [JsonConstructor]
   internal TextContent() : base(ContentType.Text)
   {
@@ -50,4 +52,45 @@ public class TextContent : Content
 
     Text = text;
   }
+}
+
+public abstract class Citation
+{
+  public string Type { get; init; } = string.Empty;
+
+  [JsonPropertyName("cited_text")]
+  public string CitedText { get; init; } = string.Empty;
+
+  [JsonPropertyName("document_index")]
+  public int DocumentIndex { get; init; }
+
+  [JsonPropertyName("document_title")]
+  public string DocumentTitle { get; init; } = string.Empty;
+}
+
+public class CharacterLocationCitation : Citation
+{
+  [JsonPropertyName("start_char_index")]
+  public int StartCharIndex { get; init; }
+
+  [JsonPropertyName("end_char_index")]
+  public int EndCharIndex { get; init; }
+}
+
+public class PageLocationCitation : Citation
+{
+  [JsonPropertyName("start_page_number")]
+  public int StartPageNumber { get; init; }
+
+  [JsonPropertyName("end_page_number")]
+  public int EndPageNumber { get; init; }
+}
+
+public class ContentBlockLocationCitation : Citation
+{
+  [JsonPropertyName("start_block_index")]
+  public int StartBlockIndex { get; init; }
+
+  [JsonPropertyName("end_block_index")]
+  public int EndBlockIndex { get; init; }
 }

src/AnthropicClient/Models/TextDocumentSource.cs

@@ -0,0 +1,11 @@
+namespace AnthropicClient.Models;
+
+public class TextDocumentSource : DocumentSource
+{
+  public TextDocumentSource(string data) : base("text/plain", data)
+  {
+    Type = "text";
+  }
+}
+
+

tests/AnthropicClient.Tests/EndToEnd/AnthropicApiClientTests.cs

@@ -286,6 +286,35 @@ public class AnthropicApiClientTests(ConfigurationFixture configFixture) : EndTo
     resultTwo.Value.Usage.CacheReadInputTokens.Should().BeGreaterThan(0);
   }
 
+  [Fact]
+  public async Task CreateMessageAsync_WhenCitationsAreEnabled_ItShouldReturnCitationsInResponse()
+  {
+    var request = new MessageRequest(
+      model: AnthropicModels.Claude3Haiku,
+      messages: [
+        new(
+          MessageRole.User,
+          [
+            new DocumentContent(
+              new TextDocumentSource("The grass is green. The sky is blue.")
+            )
+            {
+              Title = "My Document",
+              Context = "This is a trustworthy document.",
+              Citations = new() { Enabled = true }
+            },
+            new TextContent("What color is the grass and sky?"),
+          ]
+        )
+      ]
+    );
+
+    var result = await _client.CreateMessageAsync(request);
+
+    result.IsSuccess.Should().BeTrue();
+    result.Value.Content.OfType<TextContent>().SelectMany(c => c.Citations).Should().NotBeEmpty();
+  }
+
   [Fact]
   public async Task CountMessageTokensAsync_WhenCalled_ItShouldReturnResponse()
   {