Adding support for returning collections from tools

src/ModelContextProtocol/AIContentExtensions.cs

@@ -1,7 +1,9 @@
 using Microsoft.Extensions.AI;
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Utils;
+using ModelContextProtocol.Utils.Json;
 using System.Runtime.InteropServices;
+using System.Text.Json;
 
 namespace ModelContextProtocol;
 
@@ -101,4 +103,34 @@ internal static string GetBase64Data(this DataContent dataContent)
             Convert.ToBase64String(dataContent.Data.ToArray());
 #endif
     }
+
+    /// <summary>
+    /// Converts different types of <see cref="AIContent"/> into a standardized <see cref="Content"/> object with specific properties based on the
+    /// content type.
+    /// </summary>
+    /// <param name="content"></param>
+    /// <returns>A <see cref="Content"/> object that encapsulates the relevant properties derived from the input content.</returns>
+    public static Content ToContent(this AIContent content) =>
+        content switch
+        {
+            TextContent textContent => new()
+            {
+                Text = textContent.Text,
+                Type = "text",
+            },
+            DataContent dataContent => new()
+            {
+                Data = dataContent.GetBase64Data(),
+                MimeType = dataContent.MediaType,
+                Type =
+                dataContent.HasTopLevelMediaType("image") ? "image" :
+                dataContent.HasTopLevelMediaType("audio") ? "audio" :
+                "resource",
+            },
+            _ => new()
+            {
+                Text = JsonSerializer.Serialize(content, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(object))),
+                Type = "text",
+            }
+        };
 }

src/ModelContextProtocol/Server/AIFunctionMcpServerTool.cs

@@ -22,7 +22,7 @@ internal sealed class AIFunctionMcpServerTool : McpServerTool
     public static new AIFunctionMcpServerTool Create(
         Delegate method,
         string? name,
-        string? description, 
+        string? description,
         IServiceProvider? services)
     {
         Throw.IfNull(method);
@@ -34,7 +34,7 @@ internal sealed class AIFunctionMcpServerTool : McpServerTool
     /// Creates an <see cref="McpServerTool"/> instance for a method, specified via a <see cref="Delegate"/> instance.
     /// </summary>
     public static new AIFunctionMcpServerTool Create(
-        MethodInfo method, 
+        MethodInfo method,
         object? target,
         string? name,
         string? description,
@@ -195,57 +195,48 @@ public override async Task<CallToolResponse> InvokeAsync(
             };
         }
 
-        switch (result)
+        return result switch
         {
-            case null:
-                return new()
-                {
-                    Content = []
-                };
-
-            case string text:
-                return new()
-                {
-                    Content = [new() { Text = text, Type = "text" }]
-                };
-
-            case TextContent textContent:
-                return new()
-                {
-                    Content = [new() { Text = textContent.Text, Type = "text" }]
-                };
-
-            case DataContent dataContent:
-                return new()
-                {
-                    Content = [new()
-                    {
-                        Data = dataContent.GetBase64Data(),
-                        MimeType = dataContent.MediaType,
-                        Type = dataContent.HasTopLevelMediaType("image") ? "image" : "resource",
-                    }]
-                };
-
-            case string[] texts:
-                return new()
-                {
-                    Content = texts
-                        .Select(x => new Content() { Type = "text", Text = x ?? string.Empty })
-                        .ToList()
-                };
+            null => new()
+            {
+                Content = []
+            },
+            string text => new()
+            {
+                Content = [new() { Text = text, Type = "text" }]
+            },
+            TextContent textContent => new()
+            {
+                Content = [textContent.ToContent()]
+            },
+            DataContent dataContent => new()
+            {
+                Content = [dataContent.ToContent()]
+            },
+            string[] texts => new()
+            {
+                Content = [.. texts.Select(x => new Content() { Type = "text", Text = x ?? string.Empty })]
+            },
+            IEnumerable<AIContent> contentItems => new()
+            {
+                Content = [.. contentItems.Select(static item => item.ToContent())]
+            },
+            IEnumerable<Content> contents => new()
+            {
+                Content = [.. contents]
+            },
 
             // TODO https://github.com/modelcontextprotocol/csharp-sdk/issues/69:
             // Add specialization for annotations.
-
-            default:
-                return new()
-                {
-                    Content = [new()
+            _ => new()
+            {
+                Content = [new()
                     {
                         Text = JsonSerializer.Serialize(result, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(object))),
                         Type = "text"
                     }]
-                };
-        }
+            },
+        };
     }
+
 }