GH-81881: Raise SpecialFileError for sockets and devices in shutil.copyfile

[savannahostrowski]

The original issue just mentions sockets, but while documenting this I found it very confusing and inconsistent that device files didn't get the same treatment, so I figured I'd fix them all in one go.

• Issue: shutil.copyfile does not raise SpecialFileError for socket files #81881

---

📚 Documentation preview 📚: https://cpython-previews--142693.org.readthedocs.build/

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[orsenthil]

@savannahostrowski , are you interested in pursuing this. Overall this looks good to me.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #33364327 | 📁 Comparing 78695f1 against main (46d1809)

  🔍 Preview build  

14 files changed · ± 14 modified

± Modified

• howto/curses.html
• howto/mro.html
• library/curses.html
• library/dialog.html
• library/hashlib.html
• library/http.client.html
• library/itertools.html
• library/numbers.html
• library/shutil.html
• library/tkinter.html
• and 4 more...

[savannahostrowski]

@orsenthil Yes, but was waiting for someone else to review it!

[orsenthil]

Test failures in test_logging seems unrelated. It should be re-run.

1. Raising for Socket devices is correct. The code raises OSError right now. So raising a specific sub-exception, SpecialFileError is correct.

2. Block devices raise OSError too. So, good here.

For Character Device. This is a legitimate program at the moment and it will stop functioning after this change.

import shutil

shutil.copyfile('noisy_error_log.log', '/dev/null')
shutil.copyfile('/dev/null', 'empty_file.txt')

However, this is not pythonic and correct way piping to character device /dev/null is using subprocess.DEVNULL which uses os.devnull

Empty file is created using open and close call. Or pathlib.Path.touch

It only "works" because '/dev/null' happens to return EOF immediately It's incidental, not designed. Similarly, using /dev/random would be boundless call and an exploit.

So, it okay to raise against the Character Device too.

I did a github search of using shutil with /dev/null and I couldn't find any.

[orsenthil]

LGTM

[orsenthil]

but was waiting for someone else to review it!

Reviewed and approved. Thank you.