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

Browse source 
Handlers should be able to throw RPC errors and `McpError` is the
right exception for that.

Improve `DefaultMcpStatelessServerHandler` error handler to check if the
exception is `McpError` and, if so, use it to build the RPC error
result instead of re-writing as `INTERNAL_ERROR`.
This commit is contained in:
Jordan Zimmerman 2025-08-07 08:26:07 +01:00 • committed by Christian Tzolov
commit a14ef425d6
2 changed files with 82 additions and 25 deletions
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14
mcp/src/main/java/io/modelcontextprotocol/server/DefaultMcpStatelessServerHandler.java
View file

@ -35,9 +35,17 @@ class DefaultMcpStatelessServerHandler implements McpStatelessServerHandler {
}
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();
}
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

93
mcp/src/test/java/io/modelcontextprotocol/server/HttpServletStatelessIntegrationTests.java
View file

@ -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;
@ -41,7 +21,33 @@ import io.modelcontextprotocol.spec.McpSchema.PromptArgument;
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 {
@ -460,6 +466,49 @@ class HttpServletStatelessIntegrationTests {
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) {