fix(transport): single Server instance causes response routing to wrong clients by polaz · Pull Request #141 · structured-world/gitlab-mcp

polaz · 2026-01-23T13:53:05Z

Summary

Replaces single global Server instance with per-session Server instances via new SessionManager class
Each SSE/StreamableHTTP connection gets its own isolated Server, preventing _transport overwrite that caused responses to be routed to wrong clients
Adds automatic session cleanup: idle timeout (30min default) + disconnect-based cleanup for SSE
Fixes ERR_HTTP_HEADERS_SENT by checking res.headersSent before sending error responses
sendToolsListChangedNotification() now broadcasts to all active sessions

Test plan

All 3495 existing unit tests pass
New SessionManager unit tests (19 tests): per-session isolation, cleanup, broadcast, shutdown
Updated server.test.ts (30 tests): verifies session manager integration
Lint clean, build succeeds
Manual testing with concurrent Claude Code agents connecting simultaneously
Verify SSE clients receive responses after another client connects
Verify session cleanup after disconnect (no orphaned sessions)

Closes #138

…routing to wrong clients A single global Server instance caused `_transport` to be overwritten on each new connection, routing responses to the most recently connected client instead of the requesting one. This resulted in clients hanging indefinitely in multi-session deployments. Introduces SessionManager that creates isolated Server instances per session with automatic idle timeout cleanup (30min default), disconnect-based cleanup for SSE, and broadcast notifications across all active sessions. Also fixes ERR_HTTP_HEADERS_SENT by checking res.headersSent before error responses. Closes #138

github-actions · 2026-01-23T13:54:21Z

📊 Test Coverage Report

Overall Coverage: 91.57%

Coverage Details

Metric	Percentage
Statements	91.57%
Branches	83.54%
Functions	81.26%
Lines	91.98%

Coverage Report: View detailed coverage report

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codecov · 2026-01-23T13:55:35Z

Codecov Report

❌ Patch coverage is 97.24771% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/session-manager.ts	97.14%	1 Missing and 1 partial ⚠️
src/server.ts	97.43%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

Copilot

Pull request overview

This pull request fixes a critical bug where a single global MCP Server instance caused response routing failures when multiple clients connected concurrently. The fix replaces the global server with per-session Server instances managed by a new SessionManager class.

Changes:

Introduces SessionManager class to manage per-session Server instances, preventing transport routing conflicts
Adds automatic session cleanup with configurable idle timeout (30 minutes default) and disconnect-based cleanup for SSE
Improves error handling by checking res.headersSent before sending error responses to prevent ERR_HTTP_HEADERS_SENT errors
Updates sendToolsListChangedNotification to broadcast to all active sessions via SessionManager

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/session-manager.ts	New SessionManager class that creates isolated Server instances per session, manages session lifecycle, cleanup, and broadcasts notifications
src/server.ts	Removes global Server instance, integrates SessionManager, adds session cleanup on disconnect, improves error handling with headersSent checks, updates graceful shutdown
tests/unit/session-manager.test.ts	Comprehensive unit tests (19 tests) for SessionManager covering isolation, cleanup, broadcast, and edge cases
tests/unit/server.test.ts	Updated tests (30 tests) to verify SessionManager integration, mocks sessionManager instead of global server

tests/unit/server.test.ts

src/session-manager.ts

src/server.ts

…e-causes-respons

- Pre-generate session ID and await createSession before handleWithContext to prevent race condition in StreamableHTTP - Remove redundant handlersInitialized if-else in SessionManager - Wrap sendToolsListChangedNotification in try/catch to prevent error propagation to callers - Add tests for onsessioninitialized/closed callbacks, OAuth session association, graceful shutdown, SSE disconnect cleanup, and headersSent guards

…e-causes-respons

src/server.ts

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

src/session-manager.ts

src/server.ts

src/session-manager.ts

src/server.ts

…heck - Wrap SSE createSession calls in try/catch with proper error response - Add schemaModeDetected flag to prevent setDetectedSchemaMode race condition - Add duplicate sessionId guard in createSession (warns and closes existing) - Add tests for all new behaviors

github-actions · 2026-01-23T14:47:08Z

Test Coverage Report

Overall Coverage: 93.18%

Metric	Percentage
Statements	92.69%
Branches	84.21%
Functions	82.48%
Lines	93.18%

View detailed coverage report

…t-single-server-instance-causes-respons

… transport cases determineTransportMode() only returns "stdio" or "dual", making the standalone "sse" and "streamable-http" switch cases dead code that cannot be tested. The "dual" mode already provides both transports.

…e-causes-respons

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

src/session-manager.ts

Move the duplicate session guard to the beginning of createSession(), before creating a new Server instance and registering handlers. This avoids wasteful resource allocation when a duplicate is detected.

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

## [6.31.1](v6.31.0...v6.31.1) (2026-01-23) ### Bug Fixes * **transport:** single Server instance causes response routing to wrong clients ([#141](#141)) ([86f5317](86f5317)), closes [#138](#138)

sw-release-bot · 2026-01-23T16:03:23Z

🎉 This PR is included in version 6.31.1 🎉

The release is available on:

Your semantic-release bot 📦🚀

Copilot AI review requested due to automatic review settings January 23, 2026 13:53

Copilot started reviewing on behalf of polaz January 23, 2026 13:53 View session

Copilot AI reviewed Jan 23, 2026

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polaz added 4 commits January 23, 2026 16:12

Merge branch 'main' into feat/#138-fixtransport-single-server-instanc…

de6600a

…e-causes-respons

style(session-manager): condense doc comment

66b2972

Merge branch 'main' into feat/#138-fixtransport-single-server-instanc…

6f9795f

…e-causes-respons

polaz requested a review from Copilot January 23, 2026 14:19

Copilot started reviewing on behalf of polaz January 23, 2026 14:20 View session

github-advanced-security bot found potential problems Jan 23, 2026

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Copilot AI reviewed Jan 23, 2026

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polaz added 3 commits January 23, 2026 17:24

Merge remote-tracking branch 'origin/main' into feat/#138-fixtranspor…

38a74a9

…t-single-server-instance-causes-respons

Merge branch 'main' into feat/#138-fixtransport-single-server-instanc…

950c7b2

…e-causes-respons

polaz requested a review from Copilot January 23, 2026 15:34

Copilot started reviewing on behalf of polaz January 23, 2026 15:36 View session

Copilot AI reviewed Jan 23, 2026

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src/session-manager.ts Show resolved Hide resolved

fix(session): move duplicate sessionId check before resource allocation

a7b0a0d

Move the duplicate session guard to the beginning of createSession(), before creating a new Server instance and registering handlers. This avoids wasteful resource allocation when a duplicate is detected.

polaz requested a review from Copilot January 23, 2026 15:51

Copilot started reviewing on behalf of polaz January 23, 2026 15:52 View session

Copilot AI reviewed Jan 23, 2026

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polaz merged commit 86f5317 into main Jan 23, 2026
21 checks passed

polaz deleted the feat/#138-fixtransport-single-server-instance-causes-respons branch January 23, 2026 15:56

sw-release-bot bot added the released label Jan 23, 2026

sw-release-bot bot mentioned this pull request Mar 29, 2026

chore(main): release gitlab-mcp 7.0.0 #368

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polaz commented Jan 23, 2026

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