From 3544b143b1a1272931377c47bf7e17b94ee5360b Mon Sep 17 00:00:00 2001 From: Christophe Besson Date: Thu, 24 Sep 2026 02:41:02 +0200 Subject: refactor(node): move per-account blobs and key bundles out of webrtc_server BlobsMixin in transport/webrtc/blobs.py, with the blob caps and the kind pattern. Co-Authored-By: Claude Opus 5.5 --- .../src/meshbay_node/transport/webrtc/blobs.py | 255 +++++++++++++++++++++ 1 file changed, 255 insertions(+) create mode 100644 packages/meshbay-node/src/meshbay_node/transport/webrtc/blobs.py (limited to 'packages/meshbay-node/src/meshbay_node/transport/webrtc') diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/blobs.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/blobs.py new file mode 100644 index 0000000..5e67a42 --- /dev/null +++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/blobs.py @@ -0,0 +1,255 @@ +"""What a member stores on the node for themselves: per-account blobs +(playlists), and the key bundles that carry their keys between devices.""" + +import logging +import re + +from meshbay_common import MNP_VERSION +from meshbay_common.protocol import MNP + +log = logging.getLogger("meshbay_node.transport.webrtc_server") + + +# Per-account blobs (docs/playlists.md §4.3). These are an unbounded write +# primitive pointed at somebody else's disk, so every one of them is checked — +# and every check **refuses**, never truncates. A truncating cap silently loses +# tracks, which is the one failure the whole playlist design exists to prevent. +# +# The numbers are sized against the measured shape: ~300 bytes per track before +# compression, deflate worth about three on a payload this repetitive. A 1 MB +# body is therefore roughly ten thousand tracks in one playlist, and the +# manifest holds names and revisions only. +USER_BLOB_MANIFEST_MAX = 64 * 1024 +USER_BLOB_BODY_MAX = 1024 * 1024 +USER_BLOB_ACCOUNT_MAX = 8 * 1024 * 1024 + + +# "playlists" is the manifest; "playlist:" is one playlist's tracks. A +# pattern rather than a set, because the ids are client-generated — but a +# pattern, not anything at all, or the table becomes a key/value store for +# whatever a client feels like writing. +# +# The character class is deliberately wider than a UUID: the reserved id is the +# word "favorites" (docs/playlists.md §5.1), so a hex-only pattern refuses the +# one playlist every account has. It stays narrow enough to carry no structure +# of its own — no "/", no ".", no second ":" — so a kind can never be read as a +# path or as anything but one name in one namespace. +_USER_BLOB_KIND_RE = re.compile( + r"^(playlists|playlist:[A-Za-z0-9_-]{1,64})$") + + +class BlobsMixin: + async def _do_gek_bundle_fetch(self) -> None: + """Serve the caller's wrapped GEK bundle during the handshake window.""" + bundle_store = self._ctx.get("bundle_store") + if not bundle_store: + self._send({"type": MNP.GEK_BUNDLE_RESP, "v": MNP_VERSION, "found": False}) + return + + group_id = getattr(self, "_pending_group", "") + user_id = getattr(self, "_pending_sub", "") + if not group_id or not user_id: + self._send({"type": "error", "detail": "No pending handshake"}) + return + + bundle = await bundle_store.fetch(group_id, user_id) + if bundle: + self._send({ + "type": MNP.GEK_BUNDLE_RESP, + "v": MNP_VERSION, + "found": True, + "pk_eph_b64": bundle["pk_eph_b64"], + "nonce_b64": bundle["nonce_b64"], + "wrapped_b64": bundle["wrapped_b64"], + }) + else: + self._send({"type": MNP.GEK_BUNDLE_RESP, "v": MNP_VERSION, "found": False}) + + async def _do_keypair_bundle_fetch(self) -> None: + """Serve the caller's encrypted keypair bundle during the handshake window.""" + bundle_store = self._ctx.get("bundle_store") + if not bundle_store: + self._send({"type": MNP.KEYPAIR_BUNDLE_RESP, "v": MNP_VERSION, "found": False}) + return + + user_id = getattr(self, "_pending_sub", "") + if not user_id: + self._send({"type": "error", "detail": "No pending handshake"}) + return + + kp = await bundle_store.fetch_keypair(user_id) + if kp and kp.get("bundle_enc"): + resp = { + "type": MNP.KEYPAIR_BUNDLE_RESP, + "v": MNP_VERSION, + "found": True, + "bundle_enc": kp["bundle_enc"], + } + # The recovery-wrapped copy (MNP 0.14) rides along when present, so a + # client holding the recovery key can re-wrap it under a new + # passphrase — docs/MESHBAY_DESIGN.md §3.6. + if kp.get("bundle_enc_recovery"): + resp["bundle_enc_recovery"] = kp["bundle_enc_recovery"] + self._send(resp) + else: + self._send({"type": MNP.KEYPAIR_BUNDLE_RESP, "v": MNP_VERSION, "found": False}) + + async def _do_keypair_bundle_store(self, msg: dict) -> None: + """Store an encrypted keypair bundle (user backs up their own keys on node).""" + bundle_store = self._ctx.get("bundle_store") + if not bundle_store: + self._send({"type": "error", "detail": "Bundle store not available"}) + return + + bundle_enc = msg.get("bundle_enc", "") + if not bundle_enc: + self._send({"type": "error", "detail": "Missing bundle_enc"}) + return + + # Optional second copy wrapped under the recovery key (MNP 0.14). Omitted + # by an older client and by a plain re-backup; the store keeps any + # existing recovery copy when this is absent. + recovery = msg.get("bundle_enc_recovery") or None + + await bundle_store.store_keypair(self._user_id, bundle_enc, recovery) + log.info("Keypair bundle stored for user=%s (recovery=%s)", + self._user_id[:8], bool(recovery)) + self._audit("keypair_bundle_store") + self._send({ + "type": "ack", "v": MNP_VERSION, + "detail": "keypair_bundle_stored", + }) + + def _user_blob_refuse(self, detail: str, kind: str = "") -> None: + """ + Refuse, and say so in the audit log. + + A refusal used to be invisible here: the audit line was written only + after a store *succeeded*, so a client whose writes were all being + turned away looked exactly like a client that never wrote — which is + how a wedged sync went unnoticed for two hours. + """ + self._audit("user_blob_refused", f"{kind} {detail}".strip()) + self._send({"type": "error", "detail": detail}) + + def _user_blob_kind(self, msg: dict) -> str | None: + """The validated `kind`, or None having already refused.""" + kind = msg.get("kind") + if not isinstance(kind, str) or not _USER_BLOB_KIND_RE.match(kind): + self._user_blob_refuse("Unknown blob kind", str(kind)[:40]) + return None + return kind + + def _user_blob_store_ok(self): + store = self._ctx.get("bundle_store") + if not store: + self._send({"type": "error", "detail": "Bundle store not available"}) + return None + if not self._user_id: + self._send({"type": "error", "detail": "Not authenticated"}) + return None + return store + + async def _do_user_blob_store(self, msg: dict) -> None: + store = self._user_blob_store_ok() + if not store: + return + kind = self._user_blob_kind(msg) + if not kind: + return + + blob = msg.get("blob_enc") + if not isinstance(blob, (bytes, bytearray)) or not blob: + self._user_blob_refuse("Missing blob_enc", kind) + return + blob = bytes(blob) + + rev = msg.get("rev") + if not isinstance(rev, int) or rev < 0: + self._user_blob_refuse("Missing rev", kind) + return + + limit = (USER_BLOB_MANIFEST_MAX if kind == "playlists" + else USER_BLOB_BODY_MAX) + if len(blob) > limit: + # A stated reason, not a bare error: the client turns this into a + # sentence the reader can act on ("this playlist is too large"), + # and a refusal nobody can read is a support case. + self._user_blob_refuse(f"Blob too large ({len(blob)} > {limit})", kind) + return + + # What the account already uses, minus whatever this call replaces. + used = await store.user_blob_total_bytes(self._user_id) + existing = await store.fetch_user_blob(self._user_id, kind) + if existing: + used -= len(existing["blob_enc"]) + if used + len(blob) > USER_BLOB_ACCOUNT_MAX: + self._user_blob_refuse( + f"Account blob quota exceeded " + f"({used + len(blob)} > {USER_BLOB_ACCOUNT_MAX})", kind) + return + + await store.store_user_blob(self._user_id, kind, rev, blob) + self._audit("user_blob_store", f"{kind} rev={rev} bytes={len(blob)}") + self._send({"type": "ack", "v": MNP_VERSION, "detail": "user_blob_stored"}) + + async def _do_user_blob_fetch(self, msg: dict) -> None: + store = self._user_blob_store_ok() + if not store: + return + kind = self._user_blob_kind(msg) + if not kind: + return + row = await store.fetch_user_blob(self._user_id, kind) + self._audit("user_blob_fetch", kind) + self._send({ + "type": MNP.USER_BLOB_RESP, "v": MNP_VERSION, "kind": kind, + # A kind this account has never written is `null`, not an error: + # "no playlist here yet" is the ordinary state of a fresh node and + # the client must not read it as a failure. + "rev": row["rev"] if row else None, + "blob_enc": row["blob_enc"] if row else None, + }) + + async def _do_user_blob_list(self) -> None: + store = self._user_blob_store_ok() + if not store: + return + blobs = await store.list_user_blobs(self._user_id) + self._audit("user_blob_list", f"{len(blobs)} blobs") + self._send({"type": MNP.USER_BLOB_LIST_RESP, "v": MNP_VERSION, + "blobs": blobs}) + + async def _do_user_blob_delete(self, msg: dict) -> None: + store = self._user_blob_store_ok() + if not store: + return + kind = self._user_blob_kind(msg) + if not kind: + return + removed = await store.delete_user_blob(self._user_id, kind) + self._audit("user_blob_delete", kind) + self._send({"type": "ack", "v": MNP_VERSION, + "detail": "user_blob_deleted" if removed else "user_blob_absent"}) + + async def _do_keypair_bundle_delete(self) -> None: + """ + Withdraw our own key backup from this node. + + Only ever our own: the user_id comes from the authenticated session, never + from the message. Someone who does not want a second browser should not be + leaving a PBKDF2-protected blob on every node they have ever joined (C4), + and turning the setting off has to remove what is already there — not just + stop adding to it. + """ + bundle_store = self._ctx.get("bundle_store") + if not bundle_store: + self._send({"type": "error", "detail": "Bundle store not available"}) + return + + removed = await bundle_store.delete_keypair(self._user_id) + if removed: + log.info("Keypair bundle withdrawn by user=%s", self._user_id[:8]) + self._audit("keypair_bundle_delete") + self._send({"type": "ack", "v": MNP_VERSION, + "detail": "keypair_bundle_deleted", "removed": removed}) -- cgit v1.2.3