mcp: prune completed listen request IDs from the session - #1190
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guglielmo-san merged 4 commits intoAug 25, 2026
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ServerSession tracks the request IDs of in-flight subscriptions/listen streams so Close can cancel the parked handlers and avoid the jsonrpc2 drain deadlock. The ID is appended when the listen starts but never removed when the handler returns, so every completed listen (peer cancel, unsubscribe, stream break) leaks one entry for the life of the session; a client that repeatedly subscribes and unsubscribes leaks one entry per cycle. Close's Cancel on a stale ID is a no-op today, but the slice grows without bound. Remove the ID when the listen handler returns.
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can you add these tests to mcp_test.go? TestServerSessionCloseWithActiveListen is accessing the same listenIDs, and getSession can be deduplicated
Consolidate the tests with the existing session test infrastructure: reuse basicClientServerConnection instead of a bespoke helper, share a listenIDsCount accessor with TestServerSessionCloseWithActiveListen, and drop the separate file.
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Done. Moved the three tests into mcp_test.go next to TestServerSessionCloseWithActiveListen, reusing basicClientServerConnection for setup and a shared listenIDsCount accessor (the old test's inline lock block now uses it too), and removed listenleak_test.go. Verified the tests still fail with the server.go fix reverted and pass with it. |
guglielmo-san
approved these changes
Aug 25, 2026
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@latent-9 thank you for the contribution! |
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Problem
ServerSessiontracks the request IDs of in-flightsubscriptions/listenstreams soClosecan cancel the parked handlers and avoid the jsonrpc2 drain deadlock. The ID is appended when the listen starts, but it is never removed when the listen handler returns.Every completed listen stream (peer cancel, unsubscribe, stream break) therefore leaves one stale entry in the session for its entire lifetime. On a long-lived session where a client repeatedly subscribes and unsubscribes, the slice grows without bound: one leaked entry per cycle.
Closecallsjsonrpc2.Connection.Cancelon each recorded ID, and a stale ID is a no-op there today, but the bookkeeping is meant to hold only in-flight listens and currently never shrinks.Change
Drop the request ID from the session's bookkeeping when the listen handler returns, matching the lifecycle of the in-flight handler that owns it.
Tests
Three tests reproduce the leak, failing on
mainand passing here:TestListenPrunedAfterSingleCompletionTestListenIDsDoNotAccumulateTestListenIDsLeakViaPublicSubscribeUnsubscribeThe third exercises the leak through the public
Subscribe/UnsubscribeAPI.go test ./mcp/passes.