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[hotfix][mcp] Fix MCPTool Jackson deserialization by ignoring unknown properties #522

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[hotfix][mcp] Fix MCPTool Jackson deserialization by ignoring unknown properties #522

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2 changes: 2 additions & 0 deletions integrations/mcp/src/main/java/org/apache/flink/agents/integrations/mcp/MCPTool.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.apache.flink.agents.api.tools.Tool;
import org.apache.flink.agents.api.tools.ToolMetadata;
Expand All @@ -38,6 +39,7 @@
* <p>This represents a single tool from an MCP server. It extends the base Tool class and delegates
* actual execution to the MCP server.
*/
@JsonIgnoreProperties(ignoreUnknown = true)
public class MCPTool extends Tool {

private static final String FIELD_MCP_SERVER = "mcpServer";
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21 changes: 21 additions & 0 deletions integrations/mcp/src/test/java/org/apache/flink/agents/integrations/mcp/MCPToolTest.java
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Expand Up @@ -34,6 +34,27 @@ class MCPToolTest {

private static final String DEFAULT_ENDPOINT = "http://localhost:8000/mcp";

@Test
@DisabledOnJre(JRE.JAVA_11)
@DisplayName("JSON deserialization works with default ObjectMapper (no FAIL_ON_UNKNOWN_PROPERTIES override)")
void testJsonDeserializationWithDefaultMapper() throws Exception {
ToolMetadata metadata =
new ToolMetadata("add", "Add two numbers", "{\"type\":\"object\"}");
MCPServer server = new MCPServer(DEFAULT_ENDPOINT);
MCPTool original = new MCPTool(metadata, server);

// Use a default ObjectMapper — this would fail without @JsonIgnoreProperties
// because Tool.getName()/getDescription() are serialized but MCPTool's
// @JsonCreator only accepts metadata + mcpServer.
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(original);
MCPTool deserialized = mapper.readValue(json, MCPTool.class);

assertThat(deserialized.getName()).isEqualTo("add");
assertThat(deserialized.getMetadata()).isEqualTo(metadata);
assertThat(deserialized.getMcpServer()).isEqualTo(server);
}

@Test
@DisabledOnJre(JRE.JAVA_11)
@DisplayName("Create MCPTool with metadata and server")
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