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 <noreply@anthropic.com>

1 files changed, 255 insertions, 0 deletions

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:<id>" 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})