fix: allow additional properties by default per JSON Schema spec (#617)

- Remove automatic additionalProperties: false injection (JSON Schema spec compliance)
- Support String input for structuredContent in validate() method
- Move tests to mcp-json-jackson2 module with proper dependencies
- Replace wildcard imports with explicit imports

Complies with JSON Schema Test Suite:
https://github.com/json-schema-org/JSON-Schema-Test-Suite/blob/15e4505/tests/draft2020-12/additionalProperties.json\#L112

Fixes #584

BREAKING CHANGE: Additional properties now allowed by default when not explicitly specified.

Signed-off-by: Christian Tzolov <[email protected]>

Author: tzolov

mcp-core/src/test/java/io/modelcontextprotocol/spec/JSONRPCRequestMcpValidationTest.java

@@ -5,7 +5,10 @@
 package io.modelcontextprotocol.spec;
 
 import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * Tests for MCP-specific validation of JSONRPCRequest ID requirements.

mcp-core/src/test/java/io/modelcontextprotocol/spec/McpErrorTest.java

@@ -4,7 +4,8 @@
 
 import java.util.Map;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class McpErrorTest {
 

mcp-core/src/test/java/io/modelcontextprotocol/spec/PromptReferenceEqualsTest.java

@@ -7,7 +7,9 @@
 import io.modelcontextprotocol.spec.McpSchema.PromptReference;
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 /**
  * Test class to verify the equals method implementation for PromptReference.

mcp-core/src/test/java/io/modelcontextprotocol/spec/json/gson/GsonMcpJsonMapperTests.java

@@ -8,7 +8,10 @@
 import java.util.List;
 import java.util.Map;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 
 class GsonMcpJsonMapperTests {
 

mcp-core/src/test/java/io/modelcontextprotocol/util/AssertTests.java

@@ -8,7 +8,9 @@
 
 import java.util.List;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 
 class AssertTests {
 

mcp-json-jackson2/pom.xml

@@ -49,5 +49,31 @@
             <artifactId>json-schema-validator</artifactId>
             <version>${json-schema-validator.version}</version>
         </dependency>
+
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<version>${assert4j.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-api</artifactId>
+			<version>${junit.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-params</artifactId>
+			<version>${junit.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.mockito</groupId>
+			<artifactId>mockito-core</artifactId>
+			<version>${mockito.version}</version>
+			<scope>test</scope>
+		</dependency>
+
 	</dependencies>
 </project>

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/schema/jackson/DefaultJsonSchemaValidator.java

@@ -7,18 +7,16 @@
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
-import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.networknt.schema.JsonSchema;
 import com.networknt.schema.JsonSchemaFactory;
 import com.networknt.schema.SpecVersion;
 import com.networknt.schema.ValidationMessage;
+import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Default implementation of the {@link JsonSchemaValidator} interface. This class
@@ -60,7 +58,9 @@ public ValidationResponse validate(Map<String, Object> schema, Object structured
 
 		try {
 
-			JsonNode jsonStructuredOutput = this.objectMapper.valueToTree(structuredContent);
+			JsonNode jsonStructuredOutput = (structuredContent instanceof String)
+					? this.objectMapper.readTree((String) structuredContent)
+					: this.objectMapper.valueToTree(structuredContent);
 
 			Set<ValidationMessage> validationResult = this.getOrCreateJsonSchema(schema).validate(jsonStructuredOutput);
 
@@ -125,17 +125,6 @@ private JsonSchema createJsonSchema(Map<String, Object> schema) throws JsonProce
 			};
 		}
 
-		// Handle additionalProperties setting
-		if (schemaNode.isObject()) {
-			ObjectNode objectSchemaNode = (ObjectNode) schemaNode;
-			if (!objectSchemaNode.has("additionalProperties")) {
-				// Clone the node before modification to avoid mutating the original
-				objectSchemaNode = objectSchemaNode.deepCopy();
-				objectSchemaNode.put("additionalProperties", false);
-				schemaNode = objectSchemaNode;
-			}
-		}
-
 		return this.schemaFactory.getSchema(schemaNode);
 	}
 

mcp-core/src/test/java/io/modelcontextprotocol/spec/DefaultJsonSchemaValidatorTests.java renamed to mcp-json-jackson2/src/test/java/io/modelcontextprotocol/json/DefaultJsonSchemaValidatorTests.java

@@ -2,7 +2,7 @@
  * Copyright 2024-2024 the original author or authors.
  */
 
-package io.modelcontextprotocol.spec;
+package io.modelcontextprotocol.json;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -13,6 +13,7 @@
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.when;
 
+import java.util.List;
 import java.util.Map;
 import java.util.stream.Stream;
 
@@ -64,6 +65,16 @@ private Map<String, Object> toMap(String json) {
 		}
 	}
 
+	private List<Map<String, Object>> toListMap(String json) {
+		try {
+			return objectMapper.readValue(json, new TypeReference<List<Map<String, Object>>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
 	@Test
 	void testDefaultConstructor() {
 		DefaultJsonSchemaValidator defaultValidator = new DefaultJsonSchemaValidator();
@@ -198,6 +209,74 @@ void testValidateWithValidArraySchema() {
 		assertNull(response.errorMessage());
 	}
 
+	@Test
+	void testValidateWithValidArraySchemaTopLevelArray() {
+		String schemaJson = """
+				{
+					"$schema" : "https://json-schema.org/draft/2020-12/schema",
+					"type" : "array",
+					"items" : {
+						"type" : "object",
+						"properties" : {
+						"city" : {
+							"type" : "string"
+						},
+						"summary" : {
+							"type" : "string"
+						},
+						"temperatureC" : {
+							"type" : "number",
+							"format" : "float"
+						}
+						},
+						"required" : [ "city", "summary", "temperatureC" ]
+					},
+					"additionalProperties" : false
+				}
+					""";
+
+		String contentJson = """
+				[
+					{
+						"city": "London",
+						"summary": "Generally mild with frequent rainfall. Winters are cool and damp, summers are warm but rarely hot. Cloudy conditions are common throughout the year.",
+						"temperatureC": 11.3
+					},
+					{
+						"city": "New York",
+						"summary": "Four distinct seasons with hot and humid summers, cold winters with snow, and mild springs and autumns. Precipitation is fairly evenly distributed throughout the year.",
+						"temperatureC": 12.8
+					},
+					{
+						"city": "San Francisco",
+						"summary": "Mild year-round with a distinctive Mediterranean climate. Famous for summer fog, mild winters, and little temperature variation throughout the year. Very little rainfall in summer months.",
+						"temperatureC": 14.6
+					},
+					{
+						"city": "Tokyo",
+						"summary": "Humid subtropical climate with hot, wet summers and mild winters. Experiences a rainy season in early summer and occasional typhoons in late summer to early autumn.",
+						"temperatureC": 15.4
+					}
+				]
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+
+		// Validate as JSON string
+		ValidationResponse response = validator.validate(schema, contentJson);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+
+		List<Map<String, Object>> structuredContent = toListMap(contentJson);
+
+		// Validate as List<Map<String, Object>>
+		response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
 	@Test
 	void testValidateWithInvalidTypeSchema() {
 		String schemaJson = """
@@ -266,7 +345,8 @@ void testValidateWithAdditionalPropertiesNotAllowed() {
 					"properties": {
 						"name": {"type": "string"}
 					},
-					"required": ["name"]
+					"required": ["name"],
+					"additionalProperties": false
 				}
 				""";
 
@@ -316,6 +396,35 @@ void testValidateWithAdditionalPropertiesExplicitlyAllowed() {
 		assertNull(response.errorMessage());
 	}
 
+	@Test
+	void testValidateWithDefaultAdditionalProperties() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
 	@Test
 	void testValidateWithAdditionalPropertiesExplicitlyDisallowed() {
 		String schemaJson = """