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fix(server): exit when MCP client closes stdin pipe #2003

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fix(server): exit when MCP client closes stdin pipe #2003

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9378f8b
fix(server): exit when MCP client closes stdin pipe
ElliotDrel May 1, 2026
a3a4e04
fix(server): also handle stdin end event, fix end test isolation
ElliotDrel May 1, 2026
7e70ca3
chore: add changeset for stdin close fix
ElliotDrel May 1, 2026
27f0874
fix(lint): apply prettier formatting to stdio server test file
ElliotDrel May 2, 2026
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7 changes: 7 additions & 0 deletions packages/server/src/server/stdio.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,11 @@ export class StdioServerTransport implements Transport {
// Ignore errors during close — we're already in an error path
});
};
_onstdinclose = () => {
this.close().catch(() => {
// Ignore errors during close — stdin pipe ended
});
};

/**
* Starts listening for messages on `stdin`.
Expand All @@ -58,6 +63,7 @@ export class StdioServerTransport implements Transport {
this._started = true;
this._stdin.on('data', this._ondata);
this._stdin.on('error', this._onerror);
this._stdin.on('close', this._onstdinclose);
this._stdout.on('error', this._onstdouterror);
Comment on lines 68 to 73
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Copilot AI May 1, 2026

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start() only listens for stdin's close event, but a disconnected pipe commonly emits end (and close is not guaranteed for all Readable streams). To reliably shut down on client disconnect, also listen for stdin's end event and remove that listener in close() alongside the existing close cleanup.

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}

Expand Down Expand Up @@ -85,6 +91,7 @@ export class StdioServerTransport implements Transport {
// Remove our event listeners first
this._stdin.off('data', this._ondata);
this._stdin.off('error', this._onerror);
this._stdin.off('close', this._onstdinclose);
this._stdout.off('error', this._onstdouterror);

Comment on lines 97 to 103
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Copilot AI May 1, 2026

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close() cleans up the newly added stdin close handler, but if you add an end handler for stdin (needed for reliable pipe-disconnect detection), it should also be removed here to avoid leaking listeners across start/close cycles.

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// Check if we were the only data listener
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43 changes: 43 additions & 0 deletions packages/server/test/server/stdio.test.ts
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Expand Up @@ -179,3 +179,46 @@ test('should fire onerror before onclose on stdout error', async () => {

expect(events).toEqual(['error', 'close']);
});

test('should fire onclose when stdin emits close', async () => {
const server = new StdioServerTransport(input, output);
server.onerror = error => { throw error; };

let closeCount = 0;
server.onclose = () => { closeCount++; };

await server.start();
input.emit('close');

expect(closeCount).toBe(1);
});

test('should fire onclose when stdin emits end', async () => {
const server = new StdioServerTransport(input, output);
server.onerror = error => { throw error; };

let closeCount = 0;
server.onclose = () => { closeCount++; };

await server.start();
input.push(null); // signals end-of-stream

// Allow microtasks to flush
await new Promise(resolve => setTimeout(resolve, 0));

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Copilot AI May 1, 2026

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This test claims to validate behavior on stdin end, but input.push(null) may also trigger a close event depending on stream settings, so it can pass even if the transport doesn't handle end at all. Make the test explicitly verify the end path (e.g., emit end without close, or construct a Readable where emitClose/autoDestroy won't emit close on end) so it fails unless an end listener is implemented.

Suggested change
const server = new StdioServerTransport(input, output);
server.onerror = error => { throw error; };
let closeCount = 0;
server.onclose = () => { closeCount++; };
await server.start();
input.push(null); // signals end-of-stream
// Allow microtasks to flush
await new Promise(resolve => setTimeout(resolve, 0));
const endOnlyInput = new Readable({
autoDestroy: false,
emitClose: false,
// We'll use endOnlyInput.push() instead.
read: () => {}
});
const server = new StdioServerTransport(endOnlyInput, output);
server.onerror = error => { throw error; };
let closeCount = 0;
let inputCloseCount = 0;
server.onclose = () => { closeCount++; };
endOnlyInput.on('close', () => { inputCloseCount++; });
await server.start();
endOnlyInput.push(null); // signals end-of-stream without emitting close
// Allow microtasks to flush
await new Promise(resolve => setTimeout(resolve, 0));
expect(inputCloseCount).toBe(0);

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expect(closeCount).toBe(1);
});

test('should not fire onclose twice when close() called after stdin close', async () => {
const server = new StdioServerTransport(input, output);
server.onerror = () => {};

let closeCount = 0;
server.onclose = () => { closeCount++; };

await server.start();
input.emit('close');
await server.close();

expect(closeCount).toBe(1);
});
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