fix(server): gracefully handle EPIPE in StdioServerTransport - #1615

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stakeswky:fix/stdio-epipe-crash-1564
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fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom
stakeswky:fix/stdio-epipe-crash-1564

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@stakeswkystakeswky commented Mar 2, 2026

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Summary

Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.

Changes

  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)
    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path
    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths

Tests

Added tests in packages/server/test/server/stdio.test.ts:

  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure

Verified with:

  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts

User added 3 commits February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky requested a review from a team as a code ownerMarch 2, 2026 20:44
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Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

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commit: 99830c7

@felixweinberger

felixweinberger commented Mar 12, 2026

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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.

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Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect

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, 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
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})();
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try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
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stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
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@stakeswky
@stakeswkystakeswky
commented
Mar 2, 2026

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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
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from a team
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Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
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@modelcontextprotocol/server
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@modelcontextprotocol/express
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commit: 99830c7
@felixweinberger
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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


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, 'i');
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Skip to content
fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
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@stakeswkystakeswky
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Mar 2, 2026

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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
requested a review
from a team
as a code ownerMarch 2, 2026 20:44
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⚠️ No Changeset found
Latest commit: 819da20
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1615

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1615

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1615

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1615

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1615

commit: 99830c7
@felixweinberger
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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


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@stakeswky@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
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try {
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Skip to content
fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
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@stakeswky
@stakeswkystakeswky
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Mar 2, 2026

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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
requested a review
from a team
as a code ownerMarch 2, 2026 20:44
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Latest commit: 819da20
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1615

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1615

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1615

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1615

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1615

commit: 99830c7
@felixweinberger
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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


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@stakeswky@felixweinberger

, 'i');
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fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
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from a team
as a code ownerMarch 2, 2026 20:44
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Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
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@modelcontextprotocol/express
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commit: 99830c7
@felixweinberger
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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


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@stakeswky@felixweinberger

, 'i');
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function tryTheater() {
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})();
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
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@stakeswky
@stakeswkystakeswky
commented
Mar 2, 2026

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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
requested a review
from a team
as a code ownerMarch 2, 2026 20:44
@changeset-bot
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⚠️ No Changeset found
Latest commit: 819da20
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1615

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1615

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1615

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1615

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1615

commit: 99830c7
@felixweinberger
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Mar 12, 2026

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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


2 participants

@stakeswky@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
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observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Conversation
@stakeswky
@stakeswkystakeswky
commented
Mar 2, 2026

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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
requested a review
from a team
as a code ownerMarch 2, 2026 20:44
@changeset-bot
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⚠️ No Changeset found
Latest commit: 819da20
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1615

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1615

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1615

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1615

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1615

commit: 99830c7
@felixweinberger
felixweinberger
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Mar 12, 2026

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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Successfully merging this pull request may close these issues.

Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


2 participants

@stakeswky@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
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})();
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Skip to content
fix(server): gracefully handle EPIPE in StdioServerTransport - #1615
Closed
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Closed
fix(server): gracefully handle EPIPE in StdioServerTransport#1615
stakeswky wants to merge 3 commits into
modelcontextprotocol:mainfrom 
stakeswky:fix/stdio-epipe-crash-1564
Conversation
@stakeswky
@stakeswkystakeswky
commented
Mar 2, 2026

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Summary
Fixes#1564 by handling broken pipe (EPIPE) in StdioServerTransport so the process does not crash when the stdio client disconnects.
Changes
  • Add EPIPE-aware handling to stdout error listener (_onstdouterror)

    • On EPIPE, close transport gracefully and emit onclose
    • Keep non-EPIPE behavior routed to onerror
  • Harden send() write path

    • Wrap write in try/catch
    • Handle async write callback/stream errors with one-shot cleanup
    • On EPIPE, resolve send and close transport gracefully instead of rejecting/crashing
  • Make close() idempotent with _closed guard to avoid duplicate close events from concurrent EPIPE paths
Tests
Added tests in packages/server/test/server/stdio.test.ts:
  • should handle EPIPE from stdout error event and close gracefully
  • should resolve send and close on EPIPE write failure
Verified with:
  • pnpm --filter @modelcontextprotocol/server test -- test/server/stdio.test.ts
User
added 3 commits
February 22, 2026 16:12
User
fix: throw ProtocolError as JSON-RPC error for tool not found
65f5f72
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.
Fixesmodelcontextprotocol#1510
User
fix: handle EPIPE errors in StdioServerTransport
af8ccdc
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.
Fixesmodelcontextprotocol#1564
User
fix(server): handle EPIPE in stdio transport send path
819da20
@stakeswky
stakeswky
requested a review
from a team
as a code ownerMarch 2, 2026 20:44
@changeset-bot
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Mar 2, 2026

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⚠️ No Changeset found
Latest commit: 819da20
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1615

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1615

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1615

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1615

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1615

commit: 99830c7
@felixweinberger
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Mar 12, 2026

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Closing in favor of #1568, which addresses the same EPIPE handling and now incorporates the _closed guard and send() cleanup pattern from this PR (without the mcp.ts change, which breaks validation tests). Thanks for the contribution.
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Successfully merging this pull request may close these issues.

Unhandled 'EPIPE' in 'StdioServerTransport' causes fatal process crash on client disconnect


2 participants

@stakeswky@felixweinberger