feat(core): Associate resource/tool/prompt invocations with request span instead of response span #16126
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…pan instead of response span
Lms24
approved these changes
Apr 25, 2025
dev-packages/e2e-tests/test-applications/node-express/tests/mcp.test.ts
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Co-authored-by: Lukas Stracke <[email protected]>
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This PR adds a best effor mechanism to associate handler spans for
resource,toolandpromptwith the incoming message requests instead of the outgoing SSE response.The work is based on the upstream PR which exposes the request id on the handler metadata: modelcontextprotocol/typescript-sdk#358
This PR actually also fixes a bug where we were instrumenting the registering of the handler instead of the actual handler 🤦♂️.
One thing to note in this PR is that it has a risk of being slightly memory leaky. We are storing away spans by session and request id and cleaning them up when they are used. In the case of long lived sessions the span will not be garbage collected for a long time. There is unfortunately no way of doing a weak reference because session id and request ids are primitives and the framework doesn't give us any identity objects to cross-reference stuff with.