utils/security.py

"""
utils/security.py — Security headers and upload hardening.
"""

import re
import secrets
import unicodedata

_FILENAME_SAFE = re.compile(r"[^A-Za-z0-9._-]")


def secure_upload_name(filename: str) -> str:
    """
    Normalize a user-supplied filename to a safe ASCII name with a random
    prefix (prevents traversal, collisions, and overwrites).
    """
    filename = unicodedata.normalize("NFKD", filename or "file")
    filename = filename.rsplit("/", 1)[-1].rsplit("\\", 1)[-1]
    filename = _FILENAME_SAFE.sub("_", filename).strip("._") or "file"
    return f"{secrets.token_hex(8)}_{filename[:120]}"


def apply_security_headers(response):
    """Defensive HTTP headers applied to every response by app.py."""
    response.headers.setdefault("X-Content-Type-Options", "nosniff")
    response.headers.setdefault("X-Frame-Options", "SAMEORIGIN")
    response.headers.setdefault("Referrer-Policy", "strict-origin-when-cross-origin")
    response.headers.setdefault(
        "Permissions-Policy", "camera=(self), geolocation=(self), microphone=(self)"
    )
    return response