Server-side Stateful Sessions

[headlessButSmart]

During integration of MCP Server capabilities into our platform, we've come across a use case where we need to utilize certain session specific parameters across all RPC calls during the session. We are utilizing our own transport layer and utilizing core functionality only with a different approach to sessions, so this may not be 100% relevant for all, but, two minor changes would open up new capabilities:

1. Adding a generic "Map<String, Object> sessionParameters" variable to McpServerSession
2. Making "session" variable within McpAsyncServerExchange & McpSyncServerExchange accessible

With these two, information such as requestor profile can be passed with an initial request and made accessible in tool calls:

(exchange, arguments) -> {
	McpServerSession session = exchange.getSession();
	Map<String, Object> sessionParameters = session.getSessionParameters();
	//Enriched tool call with arguments & sessionParameters
}

[krzysztof-osiecki]

We have similar case and the proposed solution would be great.

[chemicL]

While leaking the session to the user land is not an option, in my draft PR for Streamable HTTP server implementation I am proposing an extraction mechanism dedicated for each transport that will allow the user to hook into the request processing and fill in such a map for later use inside the MCP processing layer (e.g. tool call handler):

For WebFlux server:

Extractor hook:

Function<ServerRequest, McpTransportContext> contextExtractor;

McpAsyncExchange:

public class McpAsyncServerExchange {
// ...
	public McpTransportContext transportContext() {
		return this.transportContext;
	}
// ...
}

The McpTransportContext draft is the following:

public interface McpTransportContext {

	Object get(String key);

	void put(String key, Object value);

	McpTransportContext copy();

}

Let me know if that'd work for you.

I also understand the session identifier is something desired and will allow keeping track of the session between requests. I wonder if the McpAsyncServerExchange should have a sessionId() method or whether it sohuld be under a well known name in the McpTransportContext. A caveat would be that in the case of session-less servers this entry would be missing.

[chemicL]

Ok, I explored the session ID exposing and concluded that it needs to be passed explicitly to the exchange and can not be extracted from the McpSession object. The reason for it is that not all McpSession objects are actually representative of the concept of session from the MCP specification that introduced session management. The McpSession idea was initially just a coordinator for keeping promises of fulfilling a sent request in the realm of JSON-RPC. While these concepts are somehow similar, they are not necessarily the same thing. E.g. a dedicated SSE stream in Streamable HTTP is represented as an McpSession but it is a child of a larger McpSession item and might consider having its own identifier.

Anyway, here's the commit: cef7aac

[MaxHoecker]

Any mechanism to let me use info from HTTP Request headers in my tool call is sorely needed.

[bharat-avn-14416]

Any mechanism to let me use info from HTTP Request headers in my tool call is sorely needed.

Did you find any way of doing it?

[chemicL]

Mcp(Async|Sync)ServerExchange now exposes

• String sessionId()
• McpTransportContext transportContext()

The sessionId is populated for you, the McpTransportContext can be populated using McpTransportContextExtractor when instantiating the particular transport, e.g. io.modelcontextprotocol.server.transport.HttpServletStatelessServerTransport.Builder#contextExtractor

Is anything missing?