sampling/createMessage hangs

[besmiralia]

Describe the bug
I have an streamablehttp MCP server which exposes a tool. When that tool is called, it sends a sampling request to the client to get some data before proceeding further. This call does not complete and the message only makes it to the client when the sampling context times out.(Verified with inspector).

It could me a lock/mutex or something else.

To Reproduce

Create a simple mcp server with a tool(hello example). Before returning the response, add a sampling request and return it's response.

[findleyr]

Hi @besmiralia, what client are you using where you observe this? Were you using the sdk at the main branch? Are you making the sampling call using the tool handler context, or a detached context like context.Background() (this affects the routing of messages).

I added a test in #289 that tries (and fails) to reproduce this bug.

I suspect that this is something like where the client you are using does not issue the hanging GET request, and so there's nowhere to deliver the sampling request, but the Go SDK naively waits for you to connect so that it can eventually deliver the message...

[besmiralia]

@findleyr I appreciate the feedback and the test case.
I am using the main branch sdk.
As a client, I tried using both my IDE (copilot/cursor) and the mcp inspector from @modelcontextprotocol/inspector

I will investigate the context and compare the server setup against your example and get back

[findleyr]

Hi @besmiralia thanks for the additional information.
I was able to reproduce this using the inspector. I'll investigate and fix.