LittleDemon WebShell

from __future__ import annotations

import os
import stat


def raise_on_exist_ro_file(filename: str) -> None:
    try:
        file_stat = os.stat(filename)  # use stat to do exists + can write to check without race condition
    except OSError:
        return None  # swallow does not exist or other errors

    if file_stat.st_mtime != 0:  # if os.stat returns but modification is zero that's an invalid os.stat - ignore it
        if not (file_stat.st_mode & stat.S_IWUSR):
            raise PermissionError(f"Permission denied: {filename!r}")


__all__ = [
    "raise_on_exist_ro_file",
]