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

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9463ca1
fix(server): exit when MCP client closes stdin pipe
ElliotDrel May 1, 2026
e7d3907
fix(server): also handle stdin end event, fix end test isolation
ElliotDrel May 1, 2026
554a427
chore: add changeset for stdin close fix
ElliotDrel May 1, 2026
a3060eb
fix(lint): apply prettier formatting to stdio server test file
ElliotDrel May 2, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-stdio-stdin-close-exit.md
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.
14 changes: 14 additions & 0 deletions packages/server/src/server/stdio.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
});
};
_onstdinend = () => {
this.close().catch(() => {
// Ignore errors during close — stdin pipe ended
});
};

/**
* Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
this._stdout.on('error', this._onstdouterror);
Comment on lines 68 to 73

CopilotAIMay 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.

Copilot uses AI. Check for mistakes.
}

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
this._stdout.off('error', this._onstdouterror);

Comment on lines 97 to 103

CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.

Copilot uses AI. Check for mistakes.
// Check if we were the only data listener
Expand Down
65 changes: 65 additions & 0 deletions packages/server/test/server/stdio.test.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
// Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
// ensuring the test fails unless an 'end' listener is explicitly registered.
const endOnlyInput = new Readable({
autoDestroy: false,
emitClose: false,
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); // confirms close was NOT emitted
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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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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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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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-stdio-stdin-close-exit.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

Comment on lines

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 to 
73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


Comment on lines

97
 to 
103

CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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fix(server): exit when MCP client closes stdin pipe#2003

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#2003
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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-stdio-stdin-close-exit.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

Comment on lines

68
 to 
73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


Comment on lines

97
 to 
103

CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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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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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-stdio-stdin-close-exit.md

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

Comment on lines

68
 to 
73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


Comment on lines

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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fix(server): exit when MCP client closes stdin pipe#2003

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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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.changeset/fix-stdio-stdin-close-exit.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

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73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


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103

CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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if (location.href !== lastUrl) {
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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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fix(server): exit when MCP client closes stdin pipe#2003

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#2003
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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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.changeset/fix-stdio-stdin-close-exit.md

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

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73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


Comment on lines

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 to 
103

CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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fix(server): exit when MCP client closes stdin pipe#2003

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#2003
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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-stdio-stdin-close-exit.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

Comment on lines

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73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


Comment on lines

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 to 
103

CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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fix(server): exit when MCP client closes stdin pipe by ElliotDrel · Pull Request #2003 · modelcontextprotocol/typescript-sdk · GitHub
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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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9463ca1

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


ElliotDrel May 1, 2026
e7d3907

fix(server): also handle stdin end event, fix end test isolation


ElliotDrel May 1, 2026
554a427

chore: add changeset for stdin close fix


ElliotDrel May 1, 2026
a3060eb

fix(lint): apply prettier formatting to stdio server test file


ElliotDrel May 2, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fix-stdio-stdin-close-exit.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/server": patch
---

Exit server process when MCP client closes stdin pipe. Previously, `StdioServerTransport` failed to detect when a client closed its stdin pipe, causing server processes to accumulate as zombies. This adds `close` and `end` event listeners on stdin that trigger proper transport cleanup.

14 changes: 14 additions & 0 deletions
packages/server/src/server/stdio.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,16 @@ 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
 });
 };
 _onstdinend = () => {
 this.close().catch(() => {
 // Ignore errors during close — stdin pipe ended
 });
 };

 /**
 * Starts listening for messages on `stdin`.
Expand All@@ -58,6 +68,8 @@ 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._stdin.on('end', this._onstdinend);
 this._stdout.on('error', this._onstdouterror);

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73

CopilotAIMay 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.
Copilot uses AI. Check for mistakes.

 }

Expand DownExpand Up@@ -85,6 +97,8 @@ 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._stdin.off('end', this._onstdinend);
 this._stdout.off('error', this._onstdouterror);


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CopilotAIMay 1, 2026

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close() cleans up the newly added stdinclose 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.
Copilot uses AI. Check for mistakes.

 // Check if we were the only data listener
Expand Down

65 changes: 65 additions & 0 deletions
packages/server/test/server/stdio.test.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -179,3 +179,68 @@ 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 () => {
 // Use autoDestroy:false + emitClose:false so push(null) fires 'end' but NOT 'close',
 // ensuring the test fails unless an 'end' listener is explicitly registered.
 const endOnlyInput = new Readable({
 autoDestroy: false,
 emitClose: false,
 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); // confirms close was NOT emitted
 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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