fix: handle SSE transport send errors in stdio stderr handler#1129
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MumuTW wants to merge 1 commit intomodelcontextprotocol:mainfrom
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fix: handle SSE transport send errors in stdio stderr handler#1129MumuTW wants to merge 1 commit intomodelcontextprotocol:mainfrom
MumuTW wants to merge 1 commit intomodelcontextprotocol:mainfrom
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…ontextprotocol#1014) When the SSE connection is closed (e.g. client disconnects during rapid reconnection), webAppTransport.send() rejects with "Not connected". The stderr handler was calling send() without awaiting or catching the returned promise, causing unhandled rejections that crash the server. Add .catch() to both send() call sites in the stderr data handler so that errors from a closed SSE connection are silently ignored instead of crashing the process. Also move the cleanup logic in the MODULE_NOT_FOUND branch into .finally() so transports are cleaned up regardless of whether the notification send succeeded.
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Summary
Fixes #1014
When multiple STDIO connection requests are made in quick succession (e.g. an MCP server mounting ~20 proxied servers), the SSE connection can close before stderr data finishes being forwarded. The
webAppTransport.send()calls in the stderr handler were not catching the returned promise, so a "Not connected" rejection fromSSEServerTransport.send()would crash the server as an unhandled promise rejection..catch()to bothsend()call sites in the stderrdatahandler to silently ignore errors from a closed SSE connectionMODULE_NOT_FOUNDbranch into.finally()so resources are released regardless of whether the notification send succeededTest plan
npm run build-serverpassesnpx prettier --check server/src/index.ts)