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fix(test/stdio): address io:read/write on closed pipe error #360

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Merged
merged 1 commit into from
Jun 4, 2025

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cryo-zd
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@cryo-zd cryo-zd commented Jun 3, 2025

Description

Fixes a potential io: read/write on closed pipe error that could occur in certain shutdown scenarios when testing StdioServer.
Problem
When the context is canceled, readNextLine returns an empty string and nil error. This empty string is then passed into processMessage, which:

  1. Fails to unmarshal the input (as it’s invalid JSON).
  2. Triggers an error response write via writeResponse.
  3. By this time, the stdoutWriter might already be closed, leading to write on closed pipe.

Fix

  1. Close stdoutWriter at the sender side after Listen exits:
    Previously, the test explicitly closed stdoutWriter from the test function, which could race with in-flight writes from the server and cause write on closed pipe errors. We now move the stdoutWriter.Close() call to the end of the goroutine that runs stdioServer.Listen, ensuring that the writer is only closed after all server writes have completed.
  2. Added guard for empty input in processMessage:
    If readNextLine() returns an empty string (due to context.Cancel()), we now skip processing in processMessage. This ensures we don't try to decode or respond to invalid input, and allows context.Done() to exit gracefully without triggering unintended writes.

Proof
may1st
code
证明3
final fix

Type of Change

  • 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

MCP Spec Compliance

  • This PR implements a feature defined in the MCP specification
  • Link to relevant spec section: Link text
  • Implementation follows the specification exactly

Additional Information

Summary by CodeRabbit

  • Bug Fixes

    • Improved handling of empty input lines to prevent unnecessary processing and error responses.
  • Tests

    • Updated test cleanup procedures to ensure proper resource management after server operations.

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coderabbitai bot commented Jun 3, 2025

Walkthrough

The processMessage method in the server was updated to immediately return when given an empty input line, preventing unnecessary processing. Corresponding tests were adjusted so that the closing of stdoutWriter now occurs within the server listener goroutine rather than in the main test cleanup, aligning resource management with the new server logic.

Changes

Files Change Summary
server/stdio.go Added early return in processMessage to skip processing when input line is empty.
server/stdio_test.go Moved stdoutWriter.Close() calls to the listener goroutine; removed redundant cleanup calls.

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (1.64.8)

Error: you are using a configuration file for golangci-lint v2 with golangci-lint v1: please use golangci-lint v2
Failed executing command with error: you are using a configuration file for golangci-lint v2 with golangci-lint v1: please use golangci-lint v2


📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 2cbaebf and e09e9a1.

📒 Files selected for processing (2)
  • server/stdio.go (1 hunks)
  • server/stdio_test.go (2 hunks)
🔇 Additional comments (3)
server/stdio.go (1)

247-250: LGTM! Effective fix for the race condition.

This guard clause correctly addresses the core issue described in the PR. When the context is cancelled, readNextLine returns an empty string, and attempting to process it would lead to JSON unmarshaling errors and unnecessary error responses that could trigger "write on closed pipe" errors if the writer is already closed. The early return prevents this cascade of issues.

server/stdio_test.go (2)

53-53: Excellent fix for the race condition in test cleanup.

Moving stdoutWriter.Close() into the server listener goroutine eliminates the race condition where the main test goroutine could close the writer while the server was still attempting to write responses. This ensures proper ordering: all server writes complete before the writer is closed.


165-165: Consistent application of the race condition fix.

Same improvement as in the first test case - moving stdoutWriter.Close() into the server goroutine ensures proper resource cleanup timing and prevents "write on closed pipe" errors.

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@ezynda3 ezynda3 merged commit 9557d0a into mark3labs:main Jun 4, 2025
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3 participants