fix cleanup warning when no process listening on debug port

[lbeziaud]

Summary

The following warning is raised on Linux when using use_persistent_context=True without any existing process listening to the debugging port:

[BROWSER]. ℹ pre-launch cleanup failed: Command '[['lsof', '-t', '-i:9222']]'

Can be seen at line 2 in the Error logs of https://github.com/unclecode/crawl4ai/issues/1138#issue-3077595076

This is caused by lsof returning an error on empty search result, since no process is listening.

List of files changed and why

The fix changes crawl4ai.browser_manager.ManagedBrowser.start to pass -Q to lsof:

-Q ignore failed search terms. […] lsof will return an error if any of the search results are empty. The -Q option will change this behavior so that lsof will instead return a successful exit code

How Has This Been Tested?

Current behavior when no process is listening:

https://github.com/unclecode/crawl4ai/blob/897e0173618d20fea5d8952ccdbcdad0febc0fee/crawl4ai/browser_manager.py#L217-L220

>>> subprocess.check_output(shlex.split("lsof -t -i:1234")).decode().strip().splitlines()
Traceback (most recent call last):
  File "<python-input-5>", line 1, in <module>
    subprocess.check_output(shlex.split("lsof -t -i:1234")).decode().strip().splitlines()
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.13/subprocess.py", line 472, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
           ~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
               **kwargs).stdout
               ^^^^^^^^^
  File "/usr/lib64/python3.13/subprocess.py", line 577, in run
    raise CalledProcessError(retcode, process.args,
                             output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['lsof', '-t', '-i:1234']' returned non-zero exit status 1.

New behavior

>>> subprocess.check_output(shlex.split("lsof -Q -t -i:1234")).decode().strip().splitlines()
[]
>>> subprocess.check_output(shlex.split("lsof -Q -t -i:9222")).decode().strip().splitlines()
['76965', '76973']

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have added/updated unit tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

Summary by CodeRabbit

• Bug Fixes
  • Improved reliability of browser startup cleanup on macOS/Linux systems by updating the process detection command.

[coderabbitai[bot]]

Walkthrough

The update changes the command used to identify processes listening on a specific port during browser startup cleanup. Specifically, it adds the -Q flag to the lsof command on macOS/Linux, altering how process information is retrieved before termination. No other logic or public interfaces are modified.

Changes

File(s)	Change Summary
crawl4ai/browser_manager.py	Updated lsof command to include -Q flag for process lookup.

Poem

A bunny tweaks a single line,
For browsers neat and ports divine.
With -Q in tow, the search is new,
Fewer hiccups, smoother through.
Hopping on with gentle might,
The code is cleaner—oh, what delight!

---

📜 Recent review details

Configuration used: CodeRabbit UI Review profile: CHILL Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 897e0173618d20fea5d8952ccdbcdad0febc0fee and 8013ea8024bfba5db5365a431d076d6b10e786c6.

📒 Files selected for processing (1)

• crawl4ai/browser_manager.py (1 hunks)

🔇 Additional comments (1)

crawl4ai/browser_manager.py (1)

217-217: LGTM! Clean fix for the cleanup warning issue.

The addition of the -Q flag to the lsof command correctly addresses the reported warning when no process is listening on the debug port. This flag instructs lsof to ignore failed search terms and return a successful exit code, which is exactly the desired behavior for cleanup logic.

✨ Finishing Touches

• [ ] 📝 Generate Docstrings

---

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