Aligning the resource data structures with the 2024-11-05 schema

- Introducing separate classes for Text and Blob ResourceContents
- Custom JSON converter to allow those types to be returned, making it easier to follow the type system against the spec
- Updated tests

Author: aaronpowell

src/ModelContextProtocol/AIContentExtensions.cs

@@ -39,11 +39,7 @@ public static AIContent ToAIContent(this Content content)
         }
         else if (content is { Type: "resource" } && content.Resource is { } resourceContents)
         {
-            ac = resourceContents.Blob is not null && resourceContents.MimeType is not null ?
-                new DataContent(Convert.FromBase64String(resourceContents.Blob), resourceContents.MimeType) :
-                new TextContent(resourceContents.Text);
-
-            (ac.AdditionalProperties ??= [])["uri"] = resourceContents.Uri;
+            ac = resourceContents.ToAIContent();
         }
         else
         {
@@ -62,9 +58,12 @@ public static AIContent ToAIContent(this ResourceContents content)
     {
         Throw.IfNull(content);
 
-        AIContent ac = content.Blob is not null && content.MimeType is not null ?
-            new DataContent(Convert.FromBase64String(content.Blob), content.MimeType) :
-            new TextContent(content.Text);
+        AIContent ac = content switch
+        {
+            BlobResourceContents blobResource => new DataContent(Convert.FromBase64String(blobResource.Blob), blobResource.MimeType ?? "application/octet-stream"),
+            TextResourceContents textResource => new TextContent(textResource.Text),
+            _ => throw new NotSupportedException($"Resource type '{content.GetType().Name}' is not supported.")
+        };
 
         (ac.AdditionalProperties ??= [])["uri"] = content.Uri;
         ac.RawRepresentation = content;
@@ -79,7 +78,7 @@ public static IList<AIContent> ToAIContents(this IEnumerable<Content> contents)
     {
         Throw.IfNull(contents);
 
-        return contents.Select(ToAIContent).ToList();
+        return [.. contents.Select(ToAIContent)];
     }
 
     /// <summary>Creates a list of <see cref="AIContent"/> from a sequence of <see cref="ResourceContents"/>.</summary>
@@ -89,7 +88,7 @@ public static IList<AIContent> ToAIContents(this IEnumerable<ResourceContents> c
     {
         Throw.IfNull(contents);
 
-        return contents.Select(ToAIContent).ToList();
+        return [.. contents.Select(ToAIContent)];
     }
 
     /// <summary>Extracts the data from a <see cref="DataContent"/> as a Base64 string.</summary>

src/ModelContextProtocol/Client/McpClientExtensions.cs

@@ -475,17 +475,7 @@ internal static (IList<ChatMessage> Messages, ChatOptions? Options) ToChatClient
             }
             else if (sm.Content is { Type: "resource", Resource: not null })
             {
-                ResourceContents resource = sm.Content.Resource;
-
-                if (resource.Text is not null)
-                {
-                    message.Contents.Add(new TextContent(resource.Text));
-                }
-
-                if (resource.Blob is not null && resource.MimeType is not null)
-                {
-                    message.Contents.Add(new DataContent(Convert.FromBase64String(resource.Blob), resource.MimeType));
-                }
+                message.Contents.Add(sm.Content.Resource.ToAIContent());
             }
 
             messages.Add(message);

src/ModelContextProtocol/ModelContextProtocol.csproj

@@ -14,7 +14,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.AI.Abstractions"/>
+    <PackageReference Include="Microsoft.Extensions.AI.Abstractions" />
     <PackageReference Include="Microsoft.Extensions.AI" />
     <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />

src/ModelContextProtocol/Protocol/Types/ResourceContents.cs

@@ -0,0 +1,16 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Binary contents of a resource.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
+/// </summary>
+public class BlobResourceContents : ResourceContents
+{
+    /// <summary>
+    /// The binary content of the resource.
+    /// </summary>
+    [JsonPropertyName("blob")]
+    public string Blob { get; set; } = default!;
+}