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Update server.go race condition #524

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Merged
merged 1 commit into from
Jul 31, 2025
Merged

Update server.go race condition #524

merged 1 commit into from
Jul 31, 2025

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outofthisworld
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@outofthisworld outofthisworld commented Jul 31, 2025 •
edited by coderabbitai bot
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Description

Fixes potential race condition

Type of Change

  • [ x] Bug fix (non-breaking change that fixes an issue)
  • New feature (non-breaking change that adds functionality)
  • MCP spec compatibility implementation
  • Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • Documentation update
  • Code refactoring (no functional changes)
  • Performance improvement
  • Tests only (no functional changes)
  • Other (please describe):

Checklist

  • My code follows the code style of this project
  • I have performed a self-review of my own code
  • I have added tests that prove my fix is effective or that my feature works
  • I have updated the documentation accordingly

Summary by CodeRabbit

  • Bug Fixes
    • Improved stability when applying middlewares by ensuring they cannot be modified during processing.

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coderabbitai bot commented Jul 31, 2025 •
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Walkthrough

The change updates the locking logic in the handleToolCall method of server/server.go, ensuring the middlewareMu read lock is held throughout the entire middleware application process rather than being released immediately after copying the middleware slice.

Changes

Cohort / File(s) Change Summary
Middleware Locking Update
server/server.go		 Adjusts the scope of the middlewareMu read lock in handleToolCall so that it is held during the entire middleware application loop, preventing concurrent modification during middleware wrapping.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~7 minutes

Possibly related PRs

Suggested reviewers

  • ezynda3

Note

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL
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📥 Commits

Reviewing files that changed from the base of the PR and between 4cca302 and 9deb188.

📒 Files selected for processing (1)
  • server/server.go (1 hunks)
🧰 Additional context used
🧠 Learnings (3)
📓 Common learnings 
Learnt from: ezynda3
PR: mark3labs/mcp-go#461
File: server/sampling.go:22-26
Timestamp: 2025-06-30T07:13:17.052Z
Learning: In the mark3labs/mcp-go project, the MCPServer.capabilities field is a struct value (serverCapabilities), not a pointer, so it cannot be nil and doesn't require nil checking. Only pointer fields within the capabilities struct should be checked for nil.

Learnt from: floatingIce91
PR: mark3labs/mcp-go#401
File: server/server.go:1082-1092
Timestamp: 2025-06-23T11:10:42.948Z
Learning: In Go MCP server, ServerTool.Tool field is only used for tool listing and indexing, not for tool execution or middleware. During handleToolCall, only the Handler field is used, so dynamic tools don't need the Tool field populated.
📚 Learning: in go mcp server, servertool.tool field is only used for tool listing and indexing, not for tool exe... 
Learnt from: floatingIce91
PR: mark3labs/mcp-go#401
File: server/server.go:1082-1092
Timestamp: 2025-06-23T11:10:42.948Z
Learning: In Go MCP server, ServerTool.Tool field is only used for tool listing and indexing, not for tool execution or middleware. During handleToolCall, only the Handler field is used, so dynamic tools don't need the Tool field populated.

Applied to files:

  • server/server.go
📚 Learning: in the mark3labs/mcp-go project, the mcpserver.capabilities field is a struct value (servercapabilit... 
Learnt from: ezynda3
PR: mark3labs/mcp-go#461
File: server/sampling.go:22-26
Timestamp: 2025-06-30T07:13:17.052Z
Learning: In the mark3labs/mcp-go project, the MCPServer.capabilities field is a struct value (serverCapabilities), not a pointer, so it cannot be nil and doesn't require nil checking. Only pointer fields within the capabilities struct should be checked for nil.

Applied to files:

  • server/server.go
🔇 Additional comments (1)
server/server.go (1)

1072-1079: LGTM! Proper fix for the race condition.

Moving the RUnlock() call after the middleware application loop correctly addresses the race condition. Previously, the read lock was released immediately after copying the middleware slice, but the slice was still being accessed during iteration. This could trigger Go's race detector if another goroutine modified toolHandlerMiddlewares concurrently.

The fix ensures the middleware slice remains stable throughout the entire middleware wrapping process.

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@ezynda3 ezynda3 merged commit 96de112 into mark3labs:main Jul 31, 2025
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