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If a handler throws McpError, use its values for the RPC error #465

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Merged
merged 1 commit into from
Aug 8, 2025
Merged

If a handler throws McpError, use its values for the RPC error #465

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14 changes: 11 additions & 3 deletions mcp/src/main/java/io/modelcontextprotocol/server/DefaultMcpStatelessServerHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,9 +35,17 @@ public Mono<McpSchema.JSONRPCResponse> handleRequest(McpTransportContext transpo
}
return requestHandler.handle(transportContext, request.params())
.map(result -> new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(), result, null))
.onErrorResume(t -> Mono.just(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(), null,
new McpSchema.JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INTERNAL_ERROR, t.getMessage(),
null))));
.onErrorResume(t -> {
McpSchema.JSONRPCResponse.JSONRPCError error;
if (t instanceof McpError mcpError && mcpError.getJsonRpcError() != null) {
error = mcpError.getJsonRpcError();
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Until we remove the McpError(Object) constructor we need to check that the getJsonRpcError() is not null otherwise create new JSONRCPError.

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done

}
else {
error = new McpSchema.JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INTERNAL_ERROR,
t.getMessage(), null);
}
return Mono.just(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(), null, error));
});
}

@Override
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93 changes: 71 additions & 22 deletions mcp/src/test/java/io/modelcontextprotocol/server/HttpServletStatelessIntegrationTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,33 +4,13 @@

package io.modelcontextprotocol.server;

import static net.javacrumbs.jsonunit.assertj.JsonAssertions.assertThatJson;
import static net.javacrumbs.jsonunit.assertj.JsonAssertions.json;
import static org.assertj.core.api.Assertions.assertThat;
import static org.awaitility.Awaitility.await;

import java.time.Duration;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiFunction;

import org.apache.catalina.LifecycleException;
import org.apache.catalina.LifecycleState;
import org.apache.catalina.startup.Tomcat;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import org.springframework.web.client.RestClient;

import com.fasterxml.jackson.databind.ObjectMapper;

import io.modelcontextprotocol.client.McpClient;
import io.modelcontextprotocol.client.transport.HttpClientStreamableHttpTransport;
import io.modelcontextprotocol.server.transport.HttpServletStatelessServerTransport;
import io.modelcontextprotocol.server.transport.TomcatTestUtil;
import io.modelcontextprotocol.spec.HttpHeaders;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.CompleteRequest;
Expand All @@ -41,7 +21,33 @@
import io.modelcontextprotocol.spec.McpSchema.PromptReference;
import io.modelcontextprotocol.spec.McpSchema.ServerCapabilities;
import io.modelcontextprotocol.spec.McpSchema.Tool;
import io.modelcontextprotocol.spec.ProtocolVersions;
import net.javacrumbs.jsonunit.core.Option;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.LifecycleState;
import org.apache.catalina.startup.Tomcat;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.client.RestClient;

import java.time.Duration;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiFunction;

import static io.modelcontextprotocol.server.transport.HttpServletStatelessServerTransport.APPLICATION_JSON;
import static io.modelcontextprotocol.server.transport.HttpServletStatelessServerTransport.TEXT_EVENT_STREAM;
import static net.javacrumbs.jsonunit.assertj.JsonAssertions.assertThatJson;
import static net.javacrumbs.jsonunit.assertj.JsonAssertions.json;
import static org.assertj.core.api.Assertions.assertThat;
import static org.awaitility.Awaitility.await;

class HttpServletStatelessIntegrationTests {

Expand Down Expand Up @@ -460,6 +466,49 @@ void testStructuredOutputRuntimeToolAddition(String clientType) {
mcpServer.close();
}

@Test
void testThrownMcpError() throws Exception {
var mcpServer = McpServer.sync(mcpStatelessServerTransport)
.serverInfo("test-server", "1.0.0")
.capabilities(ServerCapabilities.builder().tools(true).build())
.build();

Tool testTool = Tool.builder().name("test").description("test").build();

McpStatelessServerFeatures.SyncToolSpecification toolSpec = new McpStatelessServerFeatures.SyncToolSpecification(
testTool, (transportContext, request) -> {
throw new McpError(new McpSchema.JSONRPCResponse.JSONRPCError(12345, "testing", Map.of("a", "b")));
});

mcpServer.addTool(toolSpec);

McpSchema.CallToolRequest callToolRequest = new McpSchema.CallToolRequest("test", Map.of());
McpSchema.JSONRPCRequest jsonrpcRequest = new McpSchema.JSONRPCRequest(McpSchema.JSONRPC_VERSION,
McpSchema.METHOD_TOOLS_CALL, "test", callToolRequest);

MockHttpServletRequest request = new MockHttpServletRequest("POST", CUSTOM_MESSAGE_ENDPOINT);
MockHttpServletResponse response = new MockHttpServletResponse();

byte[] content = new ObjectMapper().writeValueAsBytes(jsonrpcRequest);
request.setContent(content);
request.addHeader("Content-Type", "application/json");
request.addHeader("Content-Length", Integer.toString(content.length));
request.addHeader("Content-Length", Integer.toString(content.length));
request.addHeader("Accept", APPLICATION_JSON + ", " + TEXT_EVENT_STREAM);
request.addHeader("Content-Type", APPLICATION_JSON);
request.addHeader("Cache-Control", "no-cache");
request.addHeader(HttpHeaders.PROTOCOL_VERSION, ProtocolVersions.MCP_2025_03_26);
mcpStatelessServerTransport.service(request, response);

McpSchema.JSONRPCResponse jsonrpcResponse = new ObjectMapper().readValue(response.getContentAsByteArray(),
McpSchema.JSONRPCResponse.class);

assertThat(jsonrpcResponse.error())
.isEqualTo(new McpSchema.JSONRPCResponse.JSONRPCError(12345, "testing", Map.of("a", "b")));

mcpServer.close();
}

private double evaluateExpression(String expression) {
// Simple expression evaluator for testing
return switch (expression) {
Expand Down