Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

MCP server to be able to return custom http codes

Open
#737 1 comment 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
java
Domain
api, backend

Research direction

Start with HttpServletStatelessServerTransport and McpStatelessServerHandler, especially handleRequest and the transport's service method. Trace how exceptions reach responseError and how the current workaround inspects the MCP request method before calling the transport. Done means handler failures can return a caller-selected HTTP status and MCP error message, including session-validation failures.

Written by the indexing model from the issue text.

Description

enhancement feature/session-storage

Please do a quick search on GitHub issues first, the feature you are about to request might have already been requested.

I am writing a custom MCP server. I am using an existing HttpServletStatelessServerTransport but mine is a stateful server with multiple pods. But since I do not have control on the session Id generation & validation & moreover, the validation in stateful transport is based on memory, I have chosen a stateless transport. But now on validating the sessionId in every MCP request, I want to be able to return an 404, if session id is not found or return 500 or other status codes. But I do not have this control now.

I was looking if there is a way in HttpServletStatelessServerTransport by which the MCP Error message can be passed by the McpStatelessServerHandler in the exception thrown by it

Current Behavior
In the below code, we can see that even if handleRequest method of McpStatelessServerHandler throws IllegalArgumentException, a customized error message cannot be returned to the client.

			logger.error("Failed to deserialize message: {}", e.getMessage());
			this.responseError(response, HttpServletResponse.SC_BAD_REQUEST, new McpError("Invalid message format"));
		}
		catch (Exception e) {
			logger.error("Unexpected error handling message: {}", e.getMessage());
			this.responseError(response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
					new McpError("Unexpected error: " + e.getMessage()));
		}```

**Context**

The only work around is to find the MCP request method before calling the transport's service method and return appropriate http code with required message. This is not ideal though
Dominant language
Java
Stars
3.7k
Forks
1.1k
Avg merge
1d 15h
Merged PRs (30d)
9

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from modelcontextprotocol/java-sdk

All issues in modelcontextprotocol/java-sdk

Similar issues

More Java issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.