fix(server): gracefully handle EPIPE in StdioServerTransport#1615
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stakeswky wants to merge 3 commits intomodelcontextprotocol:mainfrom
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fix(server): gracefully handle EPIPE in StdioServerTransport#1615stakeswky wants to merge 3 commits intomodelcontextprotocol:mainfrom
stakeswky wants to merge 3 commits intomodelcontextprotocol:mainfrom
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added 3 commits
February 22, 2026 16:12
Per MCP spec, calling a nonexistent tool should return a JSON-RPC Error (code -32602), not a JSON-RPC Result with isError: true. Previously, only UrlElicitationRequired errors were re-thrown; all other ProtocolErrors (including tool/disabled checks) were swallowed and wrapped in a CallToolResult. Now all ProtocolErrors propagate as JSON-RPC errors, which is the correct behavior per the specification. Fixes modelcontextprotocol#1510
Add error handling for stdout write failures to prevent uncaught EPIPE exceptions when clients disconnect unexpectedly. Changes: - Add stdout error listener in start() to catch EPIPE and other errors - Trigger graceful close when stdout errors occur - Handle write errors in send() by rejecting the promise - Clean up stdout error listener in close() This prevents the Node.js process from crashing when a client disconnects while the server is writing to stdout. Fixes modelcontextprotocol#1564
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@modelcontextprotocol/client
@modelcontextprotocol/server
@modelcontextprotocol/express
@modelcontextprotocol/hono
@modelcontextprotocol/node
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Summary
Fixes #1564 by handling broken pipe (
EPIPE) inStdioServerTransportso the process does not crash when the stdio client disconnects.Changes
errorlistener (_onstdouterror)EPIPE, close transport gracefully and emitoncloseonerrorsend()write pathtry/catchEPIPE, resolve send and close transport gracefully instead of rejecting/crashingclose()idempotent with_closedguard to avoid duplicate close events from concurrent EPIPE pathsTests
Added tests in
packages/server/test/server/stdio.test.ts:should handle EPIPE from stdout error event and close gracefullyshould resolve send and close on EPIPE write failureVerified with:
pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts