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

@@ -207,35 +207,23 @@ public override async Task<CallToolResponse> InvokeAsync(
             },
             TextContent textContent => new()
             {
-                Content = [new() { Text = textContent.Text, Type = "text" }]
+                Content = [textContent.ToContent()]
             },
             DataContent dataContent => new()
             {
-                Content = [new()
-                    {
-                        Data = dataContent.GetBase64Data(),
-                        MimeType = dataContent.MediaType,
-                        Type = dataContent.HasTopLevelMediaType("image") ? "image" : "resource",
-                    }]
+                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 switch
-                        {
-                            TextContent textContent => new Content() { Type = "text", Text = textContent.Text },
-                            DataContent dataContent => new Content()
-                            {
-                                Data = dataContent.GetBase64Data(),
-                                MimeType = dataContent.MediaType,
-                                Type = dataContent.HasTopLevelMediaType("image") ? "image" : "resource",
-                            },
-                            _ => new Content() { Type = "text", Text = item.ToString() ?? string.Empty }
-                        })]
+                Content = [.. contentItems.Select(static item => item.ToContent())]
+            },
+            IEnumerable<Content> contents => new()
+            {
+                Content = [.. contents]
             },
 
             // TODO https://github.com/modelcontextprotocol/csharp-sdk/issues/69:
@@ -250,4 +238,5 @@ public override async Task<CallToolResponse> InvokeAsync(
             },
         };
     }
+
 }