Ignore unexpected properties when deserializing a ContentBlock (#956)

* Ignore unexpected properties when deserializing a ContentBlock

* Fix deserialization of Reference.Title and more bugs for unknown props

* Remove comments about skipping additional properties

Author: jeffhandley

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -141,6 +141,7 @@ public class Converter : JsonConverter<ContentBlock>
                         break;
 
                     default:
+                        reader.Skip();
                         break;
                 }
             }

src/ModelContextProtocol.Core/Protocol/ElicitRequestParams.cs

@@ -188,6 +188,7 @@ public class Converter : JsonConverter<PrimitiveSchemaDefinition>
                             break;
 
                         default:
+                            reader.Skip();
                             break;
                     }
                 }

src/ModelContextProtocol.Core/Protocol/ProgressNotificationParams.cs

@@ -81,6 +81,10 @@ public sealed class Converter : JsonConverter<ProgressNotificationParams>
                         case "_meta":
                             meta = JsonSerializer.Deserialize(ref reader, McpJsonUtilities.JsonContext.Default.JsonObject);
                             break;
+
+                        default:
+                            reader.Skip();
+                            break;
                     }
                 }
             }

src/ModelContextProtocol.Core/Protocol/Reference.cs

@@ -81,11 +81,16 @@ public sealed class Converter : JsonConverter<Reference>
                         name = reader.GetString();
                         break;
 
+                    case "title":
+                        title = reader.GetString();
+                        break;
+
                     case "uri":
                         uri = reader.GetString();
                         break;
 
                     default:
+                        reader.Skip();
                         break;
                 }
             }

src/ModelContextProtocol.Core/Protocol/ResourceContents.cs

@@ -116,6 +116,7 @@ public class Converter : JsonConverter<ResourceContents>
                         break;
 
                     default:
+                        reader.Skip();
                         break;
                 }
             }

tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs

@@ -1,5 +1,6 @@
-using System.Text.Json;
+using Microsoft.Extensions.AI;
 using ModelContextProtocol.Protocol;
+using System.Text.Json;
 
 namespace ModelContextProtocol.Tests.Protocol;
 
@@ -80,4 +81,48 @@ public void ResourceLinkBlock_DeserializationWithoutName_ThrowsJsonException()
 
         Assert.Contains("Name must be provided for 'resource_link' type", exception.Message);
     }
+
+    [Fact]
+    public void Deserialize_IgnoresUnknownArrayProperty()
+    {
+        // This is a regression test where a server returned an unexpected response with
+        // `structuredContent` as an array nested inside a content block. This should be
+        // permitted with the `structuredContent` gracefully ignored in that location.
+        string responseJson = @"{
+            ""type"": ""text"",
+            ""text"": ""[\n  {\n    \""Data\"": \""1234567890\""\n  }\n]"",
+            ""structuredContent"": [
+                {
+                    ""Data"": ""1234567890""
+                }
+            ]
+        }";
+
+        var contentBlock = JsonSerializer.Deserialize<ContentBlock>(responseJson, McpJsonUtilities.DefaultOptions);
+        Assert.NotNull(contentBlock);
+
+        var textBlock = Assert.IsType<TextContentBlock>(contentBlock);
+        Assert.Contains("1234567890", textBlock.Text);
+    }
+
+    [Fact]
+    public void Deserialize_IgnoresUnknownObjectProperties()
+    {
+        string responseJson = @"{
+            ""type"": ""text"",
+            ""text"": ""Sample text"",
+            ""unknownObject"": {
+                ""nestedProp1"": ""value1"",
+                ""nestedProp2"": {
+                    ""deeplyNested"": true
+                }
+            }
+        }";
+
+        var contentBlock = JsonSerializer.Deserialize<ContentBlock>(responseJson, McpJsonUtilities.DefaultOptions);
+        Assert.NotNull(contentBlock);
+
+        var textBlock = Assert.IsType<TextContentBlock>(contentBlock);
+        Assert.Contains("Sample text", textBlock.Text);
+    }
 }