peter
90567718b2
A /watch link's token is the credential, and it sat in the database as written. Migration 0107 replaces the column with the token's SHA-256 (the lookup) and a Fernet-encrypted copy (so the owner can copy the same link again); every existing address keeps working, and the downgrade decrypts them back. Without a copy this key can read, a link still opens but its address cannot be shown: "Copy link" then takes the newest link that has one or makes a new one, and the Share dialog says so in that row instead of a broken URL. Making, changing and revoking a link are audited, never with its token or password.
137 lines
6.0 KiB
Python
137 lines
6.0 KiB
Python
"""Public "share by link" helpers for the download center.
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A DownloadLink is a capability URL: the unguessable token grants anyone read access to one
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download's file on the login-free `/watch/{token}` page. So the token is never stored as written:
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the link is found by its SHA-256, and the owner's copy is Fernet-encrypted — a database copy alone
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opens nothing. Without that copy (no TOKEN_ENCRYPTION_KEY, or a key since changed) the link still
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opens; only its address cannot be shown again, and the owner makes a new link to share.
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Password-protected links additionally require a short-lived signed **grant** on the file request —
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because a `<video src>` can't send a header, the password is exchanged once at `/unlock` for an HMAC
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grant appended to the file URL, so the raw password never rides in the media URL (or server logs).
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"""
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import hashlib
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import hmac
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import secrets
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from datetime import datetime, timezone
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from sqlalchemy import select
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from sqlalchemy.orm import Session
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from app import security
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from app.config import settings
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from app.models import DownloadLink
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_GRANT_TTL = 6 * 3600 # a watch session's grant is good for 6h, then the viewer re-unlocks
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def new_token() -> str:
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return secrets.token_urlsafe(24) # ~32 chars, 192 bits
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def seal(link: DownloadLink, token: str) -> None:
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"""Store `token` on `link` the only ways it is kept: its hash, and its encrypted copy."""
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link.token_hash = security.hash_token(token)
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link.token_enc = security.encrypt(token) if security.can_encrypt() else None
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def find(db: Session, token: str) -> DownloadLink | None:
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"""The link a `/watch` token names, by its hash."""
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return db.execute(
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select(DownloadLink).where(DownloadLink.token_hash == security.hash_token(token))
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).scalar_one_or_none()
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def recover(link: DownloadLink) -> str | None:
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"""The link's token from its encrypted copy, or None when there is none this key can read."""
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return security.decrypt_optional(link.token_enc)
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def is_expired(link: DownloadLink) -> bool:
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return link.expires_at is not None and link.expires_at <= datetime.now(timezone.utc)
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# --- signed grants (password-protected file access) ----------------------------------------
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def _sign(msg: str) -> str:
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return hmac.new(settings.secret_key.encode(), msg.encode(), hashlib.sha256).hexdigest()[:32]
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def make_grant(token: str, password_version: int, now: float | None = None) -> str:
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"""A short-lived HMAC grant proving the viewer unlocked `token`. Format: `<exp>.<sig>`. The
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link's current `password_version` is folded into the signature, so rotating the password (which
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bumps the version) invalidates every grant minted under the old password at once."""
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exp = int((now if now is not None else datetime.now(timezone.utc).timestamp())) + _GRANT_TTL
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return f"{exp}.{_sign(f'{token}.{exp}.{password_version}')}"
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def check_grant(token: str, grant: str | None, password_version: int) -> bool:
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"""Verify a grant against the link's CURRENT `password_version`; a version bump (password
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rotation) fails the signature check even before the grant's TTL expires."""
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if not grant or "." not in grant:
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return False
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exp_s, sig = grant.split(".", 1)
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try:
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exp = int(exp_s)
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# silent-ok: an untrusted grant that does not parse is simply not a valid grant, and the
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# honest answer to it — a password prompt — is the same as for one that expired.
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except ValueError:
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return False
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if exp < datetime.now(timezone.utc).timestamp():
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return False
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return hmac.compare_digest(sig, _sign(f"{token}.{exp}.{password_version}"))
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# --- serialization -------------------------------------------------------------------------
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def owner_view(link: DownloadLink, base_url: str = "", token: str | None = None) -> dict:
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"""What the file owner sees when managing their links. `token` is the one just made (it is in
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hand even where no copy is kept); else it is read back, and `url` is None when it cannot be."""
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token = token or recover(link)
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return {
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"id": link.id,
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"token": token,
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"url": f"{base_url}/watch/{token}" if token else None,
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"allow_download": link.allow_download,
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"has_password": link.password_hash is not None,
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"expires_at": link.expires_at.isoformat() if link.expires_at else None,
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"view_count": link.view_count,
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"created_at": link.created_at.isoformat() if link.created_at else None,
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}
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def public_meta(
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link: DownloadLink, job, asset, file_url: str, poster_url: str | None = None
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) -> dict:
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"""Metadata for the public watch page (only ever returned once access is authorized).
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Resolves the owner's per-download display overrides (custom title/channel) over the asset's
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auto-extracted values, and surfaces the source + any extra reference links as clickable URLs."""
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from app.downloads import mediakind, service
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source_url = service.reference_url(job, asset)
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# Audio-only assets (mp3 rips, extracted audio) can't play inside a <video> element on WebKit
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# (all iOS browsers), so the watch page renders a native <audio> instead. A generic uploaded
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# file (media_kind='file') has no player at all — the watch page shows file info + a download.
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# Both branches read the stored media_kind (the single source), not a re-derived codec check.
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return {
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"title": (job and job.display_name) or asset.title,
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"uploader": (job and job.display_uploader) or asset.uploader,
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"uploader_url": (job and job.display_uploader_url) or asset.uploader_url,
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"source_url": source_url,
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"extra_links": (job and job.extra_links) or [],
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"duration_s": asset.duration_s,
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"width": asset.width,
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"height": asset.height,
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"audio": asset.media_kind == mediakind.AUDIO,
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"media_kind": asset.media_kind,
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"size_bytes": asset.size_bytes,
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"container": asset.container,
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"allow_download": link.allow_download,
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"file_url": file_url,
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"poster_url": poster_url,
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}
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