fix: Resolve URIs

[denniskawurek]

Motivation and Context

Currently, the URL resolving is broken under different circumstances when adding a base URL to the path.

There are quite a few issues regarding this in this repo, but also in the Spring AI repos. Example: #261

Basically, the main issue is that the resolveUri method works for the message endpoint, but not for the SSE endpoint. So an URL resolver for the SSE endpoint is added.

How Has This Been Tested?

See WebMvcSseCustomPathIntegrationTests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Open questions

This PR is currently WIP, because for now it is a little bit unclear for how to handle the context path.
I guess this is not the same as the baseUrl, but the main path of the servlet to reach? As an example, for SSE we would get:

http://localhost + PORT + CONTEXT_PATH + BASE_URL + SSE

If this is correct, then some additional changes need to be made to support this.

[denniskawurek]

I found some time to dig deeper into it and pushed changes which fix the behaviour for the Webflux and WebMvc transport providers.

One of the main issues is that the sse connection returns the message endpoint to the client. This endpoints needs to be the full path with the context under which the server is running.
The downside is that another parameter is needed in the constructors to take this endpoint.

Unfortunately this can't be part of the baseUrl, because it is not really part of the URL and will break the mapping.

However, I tested running a server with Spring-AI with configurations like:

spring.ai.mcp.server:
  type: ASYNC
  base-url: /mcp
  sse-endpoint: /connect

spring:
  webflux:
    base-path: /v1/api

and instead of spring.webflux for webmvc:

servlet:
 context-path: /v1/api

With this solution I can connect succesfully to such routes after applying small changes in the Spring - AI code.

A big clean up of the code is still needed, though.

Edit: Cleanup done and PR marked as ready for review.