Avoid mutating global STDOUT & STDERR (#1837)

[MitchLewis930]

PR_051

[greptile-apps]

Greptile Overview

Greptile Summary

Modified Puma::Events#initialize to duplicate stdout/stderr parameters before storing them, preventing mutation of global STDOUT and STDERR constants when setting sync mode.

• Changed @stdout = stdout to @stdout = stdout.dup (and same for stderr) in lib/puma/events.rb:32-33
• Updated tests to verify that duplication works correctly and that global constants remain unaffected
• Added test verifying that setting sync on Events object doesn't mutate the original STDOUT.sync
• Required workaround in test_tcp_logger.rb to re-assign @stdout for test output capture to work

The change prevents side effects where creating a Puma::Events object would permanently modify the global STDOUT and STDERR sync settings, affecting other code in the same process.

Confidence Score: 4/5

• Safe to merge with minor comment typo
• The core change is sound and prevents global state mutation, tests properly verify the new behavior, but there's a typo in a test comment and the workaround pattern in test_tcp_logger.rb suggests potential brittleness in testing approach
• test/test_tcp_logger.rb has a comment typo that should be fixed

Important Files Changed

Filename	Overview
lib/puma/events.rb	Changed to duplicate stdout/stderr before storing to avoid mutating global IO objects
test/test_events.rb	Updated tests to verify duplication behavior and that sync settings don't affect globals
test/test_tcp_logger.rb	Added workaround to ensure test output can be captured after duplication change

Sequence Diagram

sequenceDiagram
    participant App as Application Code
    participant Events as Puma::Events
    participant STDOUT as STDOUT (constant)
    participant StdoutDup as STDOUT.dup
    
    Note over App,STDOUT: Before PR (mutates global)
    App->>Events: new(STDOUT, STDERR)
    Events->>STDOUT: @stdout = STDOUT
    Events->>STDOUT: @stdout.sync = true
    Note over STDOUT: STDOUT.sync mutated globally!
    
    Note over App,StdoutDup: After PR (no mutation)
    App->>Events: new(STDOUT, STDERR)
    Events->>STDOUT: stdout.dup
    STDOUT->>StdoutDup: create duplicate
    Events->>StdoutDup: @stdout = dup
    Events->>StdoutDup: @stdout.sync = true
    Note over STDOUT: STDOUT.sync unchanged
    Note over StdoutDup: Only dup is modified

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[greptile-apps]

_{3 files reviewed, 1 comment}

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[greptile-apps]

typo in comment: 'capture_process_io' should be 'capture_subprocess_io'

Suggested change

	logger.instance_variable_set(:@stdout, $stdout) # ensure capture_process_io has access to the loggers output
	logger.instance_variable_set(:@stdout, $stdout) # ensure capture_subprocess_io has access to the loggers output

Prompt To Fix With AI

This is a comment left during a code review.
Path: test/test_tcp_logger.rb
Line: 21:21

Comment:
typo in comment: 'capture_process_io' should be 'capture_subprocess_io'

```suggestion
    logger.instance_variable_set(:@stdout, $stdout) # ensure capture_subprocess_io has access to the loggers output
```

How can I resolve this? If you propose a fix, please make it concise.