fix McpSchema deserialization issues with Jackson3 while keeping Jackson2 behavior unchanged #978

Author: iuliiasobolevska

mcp-core/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -377,6 +377,7 @@ public record InitializeRequest( // @formatter:off
 		@JsonProperty("clientInfo") Implementation clientInfo,
 		@JsonProperty("_meta") Map<String, Object> meta) implements Request { // @formatter:on
 
+		@JsonCreator(mode = JsonCreator.Mode.DISABLED)
 		public InitializeRequest {
 			Assert.notNull(protocolVersion, "protocolVersion must not be null");
 			Assert.notNull(capabilities, "capabilities must not be null");
@@ -1743,6 +1744,7 @@ public record ReadResourceRequest( // @formatter:off
 		@JsonProperty("uri") String uri,
 		@JsonProperty("_meta") Map<String, Object> meta) implements Request { // @formatter:on
 
+		@JsonCreator(mode = JsonCreator.Mode.DISABLED)
 		public ReadResourceRequest {
 			Assert.notNull(uri, "uri must not be null");
 		}
@@ -2481,6 +2483,7 @@ public record GetPromptRequest( // @formatter:off
 		@JsonProperty("arguments") Map<String, Object> arguments,
 		@JsonProperty("_meta") Map<String, Object> meta) implements Request { // @formatter:on
 
+		@JsonCreator(mode = JsonCreator.Mode.DISABLED)
 		public GetPromptRequest {
 			Assert.notNull(name, "name must not be null");
 		}
@@ -3076,6 +3079,7 @@ public record CallToolRequest( // @formatter:off
 		@JsonProperty("arguments") Map<String, Object> arguments,
 		@JsonProperty("_meta") Map<String, Object> meta) implements Request { // @formatter:on
 
+		@JsonCreator(mode = JsonCreator.Mode.DISABLED)
 		public CallToolRequest {
 			Assert.notNull(name, "name must not be null");
 		}

mcp-json-jackson2/src/test/java/io/modelcontextprotocol/json/jackson2/McpSchemaRequestCreatorTests.java

@@ -0,0 +1,136 @@
+/*
+ * Copyright 2026 - 2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson2;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Map;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.spec.McpSchema;
+import io.modelcontextprotocol.spec.McpSchema.CallToolRequest;
+import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
+import io.modelcontextprotocol.spec.McpSchema.GetPromptRequest;
+import io.modelcontextprotocol.spec.McpSchema.Implementation;
+import io.modelcontextprotocol.spec.McpSchema.InitializeRequest;
+import io.modelcontextprotocol.spec.McpSchema.ReadResourceRequest;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Parity tests for the Jackson 2 mapper, confirming that the canonical-constructor
+ * {@code @JsonCreator} fix in {@link McpSchema} preserves the previous Jackson 2 behavior
+ * (the {@code fromJson} static factory used to handle this path). With the fix, the
+ * canonical constructor is the single creator and both mappers must produce the same
+ * results.
+ */
+class McpSchemaRequestCreatorTests {
+
+	private final McpJsonMapper mapper = new JacksonMcpJsonMapper(new ObjectMapper());
+
+	@Test
+	void callToolRequest_allFieldsPresent_bindsName() throws Exception {
+		CallToolRequest req = mapper.readValue("""
+				{"name": "search_tool", "arguments": {"q": "foo"}, "_meta": {"trace": "abc"}}
+				""", CallToolRequest.class);
+
+		assertThat(req.name()).isEqualTo("search_tool");
+		assertThat(req.arguments()).containsEntry("q", "foo");
+		assertThat(req.meta()).containsEntry("trace", "abc");
+	}
+
+	@Test
+	void callToolRequest_missingName_defaultsToEmptyString() throws Exception {
+		CallToolRequest req = mapper.readValue("""
+				{"arguments": {"q": "foo"}}
+				""", CallToolRequest.class);
+
+		assertThat(req.name()).isEqualTo("");
+	}
+
+	@Test
+	void callToolRequest_roundTrip_preservesAllFields() throws Exception {
+		CallToolRequest original = new CallToolRequest("search_tool", Map.of("q", "foo"), Map.of("trace", "abc"));
+
+		String json = mapper.writeValueAsString(original);
+		CallToolRequest roundTripped = mapper.readValue(json, CallToolRequest.class);
+
+		assertThat(roundTripped).isEqualTo(original);
+	}
+
+	@Test
+	void initializeRequest_allFieldsPresent_bindsAllRequired() throws Exception {
+		InitializeRequest req = mapper.readValue("""
+				{
+				  "protocolVersion": "2025-06-18",
+				  "capabilities": {},
+				  "clientInfo": {"name": "test-client", "version": "1.0"}
+				}
+				""", InitializeRequest.class);
+
+		assertThat(req.protocolVersion()).isEqualTo("2025-06-18");
+		assertThat(req.clientInfo().name()).isEqualTo("test-client");
+	}
+
+	@Test
+	void initializeRequest_allRequiredMissing_defaultsAll() throws Exception {
+		InitializeRequest req = mapper.readValue("{}", InitializeRequest.class);
+
+		assertThat(req.protocolVersion()).isEqualTo("");
+		assertThat(req.capabilities()).isNotNull();
+		assertThat(req.clientInfo()).isNotNull();
+		assertThat(req.clientInfo().name()).isEqualTo("");
+	}
+
+	@Test
+	void initializeRequest_roundTrip_preservesAllFields() throws Exception {
+		InitializeRequest original = new InitializeRequest("2025-06-18", new ClientCapabilities(null, null, null, null),
+				new Implementation("test-client", "1.0"), Map.of("k", "v"));
+
+		String json = mapper.writeValueAsString(original);
+		InitializeRequest roundTripped = mapper.readValue(json, InitializeRequest.class);
+
+		assertThat(roundTripped.protocolVersion()).isEqualTo(original.protocolVersion());
+		assertThat(roundTripped.clientInfo()).isEqualTo(original.clientInfo());
+	}
+
+	@Test
+	void getPromptRequest_allFieldsPresent_bindsName() throws Exception {
+		GetPromptRequest req = mapper.readValue("""
+				{"name": "prompt-a", "arguments": {"x": 1}, "_meta": {"k": "v"}}
+				""", GetPromptRequest.class);
+
+		assertThat(req.name()).isEqualTo("prompt-a");
+	}
+
+	@Test
+	void getPromptRequest_missingName_defaultsToEmptyString() throws Exception {
+		GetPromptRequest req = mapper.readValue("""
+				{"arguments": {"x": 1}}
+				""", GetPromptRequest.class);
+
+		assertThat(req.name()).isEqualTo("");
+	}
+
+	@Test
+	void readResourceRequest_allFieldsPresent_bindsUri() throws Exception {
+		ReadResourceRequest req = mapper.readValue("""
+				{"uri": "resource://faults/123", "_meta": {"k": "v"}}
+				""", ReadResourceRequest.class);
+
+		assertThat(req.uri()).isEqualTo("resource://faults/123");
+		assertThat(req.meta()).containsEntry("k", "v");
+	}
+
+	@Test
+	void readResourceRequest_missingUri_defaultsToEmptyString() throws Exception {
+		ReadResourceRequest req = mapper.readValue("{}", ReadResourceRequest.class);
+
+		assertThat(req.uri()).isEqualTo("");
+	}
+
+}