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mcp: keep notifications/cancelled across session Close - #1
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Since modelcontextprotocol#1151, call() retires a cancelled request and sends notifications/cancelled from a goroutine. Closing the session immediately after the call returns marks the jsonrpc2 connection shutting down with no remaining outgoing calls, so Notify rejects the write. On a stateful streamable HTTP server the tool handler then keeps running and ClientSession.Close blocks for closeDeleteTimeout. Reserve the outgoing notification before returning from call() so Close waits for the write and Notify is allowed during shutdown. The caller still returns immediately, and the call is still retired immediately. For modelcontextprotocol#1505 Co-authored-by: Vishal Punjabi <mr.vishalpunjabi@gmail.com>
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Opened by mistake against the fork. Upstream PR: modelcontextprotocol#1508 |
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Summary
Reserve the outgoing
notifications/cancelledbeforecall()returns so a followingClosecannot drop it.Why
Since modelcontextprotocol#1151, cancel retires the call and sends
notifications/cancelledfrom a goroutine. If the session closes right after return, the connection is already shutting down and the call is gone fromoutgoingCalls, soNotifydrops the notification. On stateful streamable HTTP the server handler never sees cancel, andClientSession.Closewaits outcloseDeleteTimeout(5s).What changed
BeginOutgoingNotification) before returning fromcall()notifyCancellationTimeout);Notifyis allowed while the reservation is heldTests
TestCloseAfterCanceledCallCancelsTheServerHandler— 20/20 (~0ms; was 5s Close + handler never cancelled)TestBeginOutgoingNotificationAllowsNotifyDuringClose— 20/20TestCallCancellation_FastReturn,TestCancellationgo test ./...and-raceon the new testsFixes modelcontextprotocol#1505