fix: remove global logger MCP-103

[nirinchev]

Proposed changes

This refactoring removes the global logger and instead creates a session-scoped logger for each session, which is then used by the whole server machinery. Additionally, we add a session id attribute once the session is bound to ensure that is included in the log messages.

The way this works is we create a composite logger that includes all configured loggers for the transport manager. Then as we create sessions, for each session we create a new composite logger that includes the transport logger and the MCP logger (if configured). Then all tools and api clients will use the session logger.

Checklist

• I have signed the MongoDB CLA

[kmruiz]

[nit] Not blocking at all, but maybe it would be worth to have the logger at the session level because we have access to the session from almost everywhere?

[Copilot]

Pull Request Overview

This PR refactors the logging system to eliminate the global logger pattern in favor of session-scoped loggers. The changes create a composite logger system where each session has its own logger instance that includes transport-specific and MCP-specific loggers as needed.

Key changes:

• Replaced global logger singleton with session-scoped loggers that are passed down to all components
• Added session ID attributes to loggers for better traceability
• Enhanced logger system with attributes support and buffering for disk logger initialization

Reviewed Changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/common/logger.ts	Enhanced logger classes with attributes support, added DiskLogger buffering, and NullLogger for testing
src/transports/base.ts	Added logger creation logic to transport runners and session setup
src/transports/streamableHttp.ts	Updated to use instance logger instead of global logger
src/transports/stdio.ts	Updated to use instance logger instead of global logger
src/common/session.ts	Modified to accept and use a logger instance
src/common/sessionStore.ts	Updated to store logger per session instead of creating MCP loggers
src/server.ts	Removed global logger setup, now uses session logger
src/index.ts	Updated to use transport runner logger with fallback console logger
tests/unit/telemetry.test.ts	Updated tests to use session logger and NullLogger
tests/unit/logger.test.ts	Added comprehensive tests for new logger functionality
tests/integration/helpers.ts	Added logger to session setup in tests
tests/unit/accessListUtils.test.ts	Added logger to mock API client

[coveralls]

Pull Request Test Coverage Report for Build 16790782045

Details

• 158 of 207 (76.33%) changed or added relevant lines in 17 files are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.07%) to 81.233%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/common/atlas/accessListUtils.ts	3	4	75.0%
src/common/atlas/cluster.ts	1	2	50.0%
src/telemetry/telemetry.ts	7	8	87.5%
src/tools/atlas/atlasTool.ts	1	2	50.0%
src/tools/mongodb/mongodbTool.ts	1	2	50.0%
src/tools/tool.ts	4	5	80.0%
src/common/session.ts	4	6	66.67%
src/common/sessionStore.ts	10	12	83.33%
src/tools/atlas/connect/connectCluster.ts	5	7	71.43%
src/transports/stdio.ts	3	5	60.0%

Files with Coverage Reduction	New Missed Lines	%
src/transports/stdio.ts	1	64.41%
src/common/logger.ts	5	88.8%

Totals
Change from base Build 16783784184:	-0.07%
Covered Lines:	3522
Relevant Lines:	4293

---

💛 - Coveralls