Add missing Title and Icons properties to ResourceLinkBlock (#1320)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -90,11 +90,13 @@ public sealed class Converter : JsonConverter<ContentBlock>
             string? type = null;
             string? text = null;
             string? name = null;
+            string? title = null;
             ReadOnlyMemory<byte>? data = null;
             string? mimeType = null;
             string? uri = null;
             string? description = null;
             long? size = null;
+            IList<Icon>? icons = null;
             ResourceContents? resource = null;
             Annotations? annotations = null;
             JsonObject? meta = null;
@@ -130,6 +132,10 @@ public sealed class Converter : JsonConverter<ContentBlock>
                         name = reader.GetString();
                         break;
 
+                    case "title":
+                        title = reader.GetString();
+                        break;
+
                     case "data":
                         data = reader.HasValueSequence ? reader.ValueSequence.ToArray() : reader.ValueSpan.ToArray();
                         break;
@@ -150,6 +156,18 @@ public sealed class Converter : JsonConverter<ContentBlock>
                         size = reader.GetInt64();
                         break;
 
+                    case "icons":
+                        if (reader.TokenType == JsonTokenType.StartArray)
+                        {
+                            icons = [];
+                            while (reader.Read() && reader.TokenType != JsonTokenType.EndArray)
+                            {
+                                icons.Add(JsonSerializer.Deserialize(ref reader, McpJsonUtilities.JsonContext.Default.Icon) ??
+                                    throw new JsonException("Unexpected null item in icons array."));
+                            }
+                        }
+                        break;
+
                     case "resource":
                         resource = JsonSerializer.Deserialize(ref reader, McpJsonUtilities.JsonContext.Default.ResourceContents);
                         break;
@@ -233,9 +251,11 @@ public sealed class Converter : JsonConverter<ContentBlock>
                 {
                     Uri = uri ?? throw new JsonException("URI must be provided for 'resource_link' type."),
                     Name = name ?? throw new JsonException("Name must be provided for 'resource_link' type."),
+                    Title = title,
                     Description = description,
                     MimeType = mimeType,
                     Size = size,
+                    Icons = icons,
                 },
 
                 "tool_use" => new ToolUseContentBlock
@@ -299,6 +319,10 @@ public override void Write(Utf8JsonWriter writer, ContentBlock value, JsonSerial
                 case ResourceLinkBlock resourceLink:
                     writer.WriteString("uri", resourceLink.Uri);
                     writer.WriteString("name", resourceLink.Name);
+                    if (resourceLink.Title is not null)
+                    {
+                        writer.WriteString("title", resourceLink.Title);
+                    }
                     if (resourceLink.Description is not null)
                     {
                         writer.WriteString("description", resourceLink.Description);
@@ -311,6 +335,16 @@ public override void Write(Utf8JsonWriter writer, ContentBlock value, JsonSerial
                     {
                         writer.WriteNumber("size", resourceLink.Size.Value);
                     }
+                    if (resourceLink.Icons is { Count: > 0 })
+                    {
+                        writer.WritePropertyName("icons");
+                        writer.WriteStartArray();
+                        foreach (var icon in resourceLink.Icons)
+                        {
+                            JsonSerializer.Serialize(writer, icon, McpJsonUtilities.JsonContext.Default.Icon);
+                        }
+                        writer.WriteEndArray();
+                    }
                     break;
 
                 case ToolUseContentBlock toolUse:
@@ -595,6 +629,17 @@ public sealed class ResourceLinkBlock : ContentBlock
     [JsonPropertyName("name")]
     public required string Name { get; set; }
 
+    /// <summary>
+    /// Gets or sets a title for this resource.
+    /// </summary>
+    /// <remarks>
+    /// This is intended for UI and end-user contexts. It is optimized to be human-readable and easily understood,
+    /// even by those unfamiliar with domain-specific terminology.
+    /// If not provided, <see cref="Name"/> can be used for display.
+    /// </remarks>
+    [JsonPropertyName("title")]
+    public string? Title { get; set; }
+
     /// <summary>
     /// Gets or sets a description of what this resource represents.
     /// </summary>
@@ -638,6 +683,15 @@ public sealed class ResourceLinkBlock : ContentBlock
     /// </remarks>
     [JsonPropertyName("size")]
     public long? Size { get; set; }
+
+    /// <summary>
+    /// Gets or sets an optional list of icons for this resource.
+    /// </summary>
+    /// <remarks>
+    /// This can be used by clients to display the resource's icon in a user interface.
+    /// </remarks>
+    [JsonPropertyName("icons")]
+    public IList<Icon>? Icons { get; set; }
 }
 
 /// <summary>Represents a request from the assistant to call a tool.</summary>

tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs

@@ -13,9 +13,11 @@ public void ResourceLinkBlock_SerializationRoundTrip_PreservesAllProperties()
         {
             Uri = "https://example.com/resource",
             Name = "Test Resource",
+            Title = "Test Resource Title",
             Description = "A test resource for validation",
             MimeType = "text/plain",
-            Size = 1024
+            Size = 1024,
+            Icons = [new Icon { Source = "https://example.com/icon.png", MimeType = "image/png" }]
         };
 
         // Act - Serialize to JSON
@@ -30,10 +32,15 @@ public void ResourceLinkBlock_SerializationRoundTrip_PreservesAllProperties()
 
         Assert.Equal(original.Uri, resourceLink.Uri);
         Assert.Equal(original.Name, resourceLink.Name);
+        Assert.Equal(original.Title, resourceLink.Title);
         Assert.Equal(original.Description, resourceLink.Description);
         Assert.Equal(original.MimeType, resourceLink.MimeType);
         Assert.Equal(original.Size, resourceLink.Size);
         Assert.Equal("resource_link", resourceLink.Type);
+        Assert.NotNull(resourceLink.Icons);
+        Assert.Single(resourceLink.Icons);
+        Assert.Equal("https://example.com/icon.png", resourceLink.Icons[0].Source);
+        Assert.Equal("image/png", resourceLink.Icons[0].MimeType);
     }
 
     [Fact]
@@ -57,9 +64,11 @@ public void ResourceLinkBlock_DeserializationWithMinimalProperties_Succeeds()
 
         Assert.Equal("https://example.com/minimal", resourceLink.Uri);
         Assert.Equal("Minimal Resource", resourceLink.Name);
+        Assert.Null(resourceLink.Title);
         Assert.Null(resourceLink.Description);
         Assert.Null(resourceLink.MimeType);
         Assert.Null(resourceLink.Size);
+        Assert.Null(resourceLink.Icons);
         Assert.Equal("resource_link", resourceLink.Type);
     }
 
@@ -81,6 +90,44 @@ public void ResourceLinkBlock_DeserializationWithoutName_ThrowsJsonException()
         Assert.Contains("Name must be provided for 'resource_link' type", exception.Message);
     }
 
+    [Fact]
+    public void ResourceLinkBlock_DeserializationWithTitleAndIcons_Succeeds()
+    {
+        // Arrange - JSON with title and icons properties per spec
+        const string Json = """
+            {
+                "type": "resource_link",
+                "uri": "https://example.com/resource",
+                "name": "my-resource",
+                "title": "My Resource",
+                "icons": [
+                    { "src": "https://example.com/icon1.png", "mimeType": "image/png", "sizes": ["48x48"], "theme": "light" },
+                    { "src": "https://example.com/icon2.svg", "mimeType": "image/svg+xml" }
+                ]
+            }
+            """;
+
+        // Act
+        var deserialized = JsonSerializer.Deserialize<ContentBlock>(Json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        var resourceLink = Assert.IsType<ResourceLinkBlock>(deserialized);
+
+        Assert.Equal("https://example.com/resource", resourceLink.Uri);
+        Assert.Equal("my-resource", resourceLink.Name);
+        Assert.Equal("My Resource", resourceLink.Title);
+        Assert.NotNull(resourceLink.Icons);
+        Assert.Equal(2, resourceLink.Icons.Count);
+        Assert.Equal("https://example.com/icon1.png", resourceLink.Icons[0].Source);
+        Assert.Equal("image/png", resourceLink.Icons[0].MimeType);
+        Assert.NotNull(resourceLink.Icons[0].Sizes);
+        Assert.Equal("48x48", resourceLink.Icons[0].Sizes![0]);
+        Assert.Equal("light", resourceLink.Icons[0].Theme);
+        Assert.Equal("https://example.com/icon2.svg", resourceLink.Icons[1].Source);
+        Assert.Equal("image/svg+xml", resourceLink.Icons[1].MimeType);
+    }
+
     [Fact]
     public void Deserialize_IgnoresUnknownArrayProperty()
     {