modelcontextprotocol/java-sdk
Watch
1
0
Fork
You've already forked java-sdk
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

fix: Skip structured output validation for error tool results

Browse source 
This ensures that when a tool handler returns an error result, the structured
output schema validation is skipped, preventing validation failures on error
responses that don't conform to the expected output schema.

- Add validation bypass when CallToolResult.isError() is true in async/stateless servers
- Fix async tool handler chaining to properly use then() instead of block()
- Add comprehensive tests for structured output with in-handler errors
- Improve error handling to use proper JSON-RPC error codes for unknown tools
- Add findRootCause utility method for better error diagnostics
- Increase test timeouts for stability in StdioMcp client tests. These tests use npx
  to download and run the MCP "everything" server locally. The first
  test execution will download the everything server scripts and cache them locally,
  which can take more than 15 seconds. Subsequent test runs will use the cached version
  and execute faster.

Resolves #538
Related to #422

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>
This commit is contained in:
Christian Tzolov 2025-09-07 01:01:52 +02:00
commit c7736b6ec6
3 changed files with 353 additions and 80 deletions
Download patch file Download diff file Expand all files Collapse all files

13
mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java
View file

@ -29,10 +29,12 @@ import io.modelcontextprotocol.spec.McpClientSession;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCResponse;
import io.modelcontextprotocol.spec.McpSchema.LoggingLevel;
import io.modelcontextprotocol.spec.McpSchema.LoggingMessageNotification;
import io.modelcontextprotocol.spec.McpSchema.ResourceTemplate;
import io.modelcontextprotocol.spec.McpSchema.SetLevelRequest;
import io.modelcontextprotocol.spec.McpSchema.TextContent;
import io.modelcontextprotocol.spec.McpSchema.Tool;
import io.modelcontextprotocol.spec.McpServerSession;
import io.modelcontextprotocol.spec.McpServerTransportProvider;
@ -376,6 +378,11 @@ public class McpAsyncServer {
return this.delegateCallToolResult.apply(exchange, request).map(result -> {
if (Boolean.TRUE.equals(result.isError())) {
// If the tool call resulted in an error, skip further validation
return result;
}
if (outputSchema == null) {
if (result.structuredContent() != null) {
logger.warn(
@ -507,11 +514,11 @@ public class McpAsyncServer {
.findAny();
if (toolSpecification.isEmpty()) {
return Mono.error(new McpError("Tool not found: " + callToolRequest.name()));
return Mono.error(new McpError(new JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INVALID_PARAMS,
"Unknown tool: invalid_tool_name", "Tool not found: " + callToolRequest.name())));
}
return toolSpecification.map(tool -> Mono.defer(() -> tool.callHandler().apply(exchange, callToolRequest)))
.orElse(Mono.error(new McpError("Tool not found: " + callToolRequest.name())));
return toolSpecification.get().callHandler().apply(exchange, callToolRequest);
};
}

13
mcp/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java
View file

@ -11,7 +11,9 @@ import io.modelcontextprotocol.spec.JsonSchemaValidator;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCResponse;
import io.modelcontextprotocol.spec.McpSchema.ResourceTemplate;
import io.modelcontextprotocol.spec.McpSchema.TextContent;
import io.modelcontextprotocol.spec.McpSchema.Tool;
import io.modelcontextprotocol.spec.McpStatelessServerTransport;
import io.modelcontextprotocol.util.Assert;
@ -249,6 +251,11 @@ public class McpStatelessAsyncServer {
return this.delegateHandler.apply(transportContext, request).map(result -> {
if (Boolean.TRUE.equals(result.isError())) {
// If the tool call resulted in an error, skip further validation
return result;
}
if (outputSchema == null) {
if (result.structuredContent() != null) {
logger.warn(
@ -375,11 +382,11 @@ public class McpStatelessAsyncServer {
.findAny();
if (toolSpecification.isEmpty()) {
return Mono.error(new McpError("Tool not found: " + callToolRequest.name()));
return Mono.error(new McpError(new JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INVALID_PARAMS,
"Unknown tool: invalid_tool_name", "Tool not found: " + callToolRequest.name())));
}
return toolSpecification.map(tool -> tool.callHandler().apply(ctx, callToolRequest))
.orElse(Mono.error(new McpError("Tool not found: " + callToolRequest.name())));
return toolSpecification.get().callHandler().apply(ctx, callToolRequest);
};
}

4
mcp/src/main/java/io/modelcontextprotocol/util/Utils.java
View file

@ -4,12 +4,12 @@
package io.modelcontextprotocol.util;
import reactor.util.annotation.Nullable;
import java.net.URI;
import java.util.Collection;
import java.util.Map;
import reactor.util.annotation.Nullable;
/**
* Miscellaneous utility methods.
*