Teknium
406 lines
18 KiB
Python
406 lines
18 KiB
Python
"""Replica store and takeover primitives for hosted Group Chat rooms.
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The authority gateway owns a room's ordered log in ``gateway/hosted_rooms.py``;
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this module gives every OTHER participant gateway a durable local copy plus the
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fenced primitives to continue the room when the authority host dies:
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``ingest_page()`` (idempotent, gap- and epoch-regression-safe replay),
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``promote_replica()`` (resume locally at ``epoch + 1`` with a lineage-proving
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``authority.claimed`` event) and ``demote_room()`` (a returning stale authority
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records ``authority.lost`` when shown proof of a newer epoch).
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Storage primitives only: none decide *when* takeover is safe. The caller must
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establish that the previous owner can no longer commit before promoting.
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"""
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from __future__ import annotations
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import json
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import sqlite3
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import time
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from contextlib import contextmanager
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from pathlib import Path
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from typing import Any, Iterator
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from gateway.hosted_rooms import (
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MAX_ACTOR_ID_CHARS,
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MAX_EVENT_JSON_BYTES,
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MAX_ROOM_ID_CHARS,
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HostedRoomError,
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RoomConflictError,
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_canonical_json,
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_connect,
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_transaction,
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_validate_identifier,
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_validate_members,
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_validate_room_name,
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local_authority_gateway_id,
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)
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from gateway.hosted_rooms_common import positive_int, utf8_len
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MAX_REPLICA_ROOMS = 256
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MAX_REPLICA_EVENT_BYTES = 256 * 1024 * 1024
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_SYSTEM_ACTOR = {"kind": "system", "id": "authority-control"}
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_EVENT_COLUMNS = "(room_id, seq, event_id, kind, actor_json, authority_epoch, payload_json, created_at)"
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_INSERT_ROOM_EVENT = f"INSERT INTO hosted_room_events {_EVENT_COLUMNS} VALUES (?, ?, ?, ?, ?, ?, ?, ?)"
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_INSERT_REPLICA_EVENT = f"INSERT INTO hosted_room_replica_events {_EVENT_COLUMNS} VALUES (?, ?, ?, ?, ?, ?, ?, ?)"
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_SELECT_REPLICA = "SELECT * FROM hosted_room_replicas WHERE room_id=?"
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class ReplicaError(HostedRoomError):
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"""Base class for invalid or conflicting replica operations."""
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class ReplicaGapError(ReplicaError):
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"""A page does not start at the replica's next expected sequence."""
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class ReplicaEpochRegressionError(ReplicaError):
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"""A page or demotion carries an older authority epoch than stored."""
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def _initialize_replica_schema(conn: sqlite3.Connection) -> None:
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conn.execute(
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"""CREATE TABLE IF NOT EXISTS hosted_room_replicas (
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room_id TEXT PRIMARY KEY, name TEXT NOT NULL, members_json TEXT NOT NULL,
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authority_gateway_id TEXT NOT NULL,
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authority_epoch INTEGER NOT NULL CHECK (authority_epoch >= 1),
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last_seq INTEGER NOT NULL DEFAULT 0 CHECK (last_seq >= 0),
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latest_seq INTEGER NOT NULL DEFAULT 0, event_bytes INTEGER NOT NULL DEFAULT 0,
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created_at REAL NOT NULL, updated_at REAL NOT NULL
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)"""
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)
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conn.execute(
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"""CREATE TABLE IF NOT EXISTS hosted_room_replica_events (
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room_id TEXT NOT NULL, seq INTEGER NOT NULL CHECK (seq >= 1), event_id TEXT NOT NULL,
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kind TEXT NOT NULL, actor_json TEXT NOT NULL, authority_epoch INTEGER,
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payload_json TEXT NOT NULL, created_at REAL NOT NULL,
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PRIMARY KEY (room_id, seq)
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)"""
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)
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@contextmanager
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def _replica_transaction(db_path: Path | str) -> Iterator[sqlite3.Connection]:
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"""Ensure the replica schema (own autocommit connection), then open an IMMEDIATE transaction.
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The schema DDL is re-run inside the transaction too; that double init is the
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established statement order and is intentionally preserved.
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"""
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conn = _connect(db_path)
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try:
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with conn:
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_initialize_replica_schema(conn)
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finally:
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conn.close()
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with _transaction(db_path, immediate=True) as conn:
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_initialize_replica_schema(conn)
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yield conn
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def _room_id(value: Any) -> str:
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return _validate_identifier(value, label="room_id", max_chars=MAX_ROOM_ID_CHARS)
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def _positive_int(value: Any, message: str) -> int:
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return positive_int(value, error=ReplicaError, message=message)
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def _control_event_json(payload: dict[str, Any]) -> tuple[str, str]:
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"""Canonical (actor_json, payload_json) for a system authority-control event."""
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return (
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_canonical_json(_SYSTEM_ACTOR, label="actor", max_bytes=4 * 1024),
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_canonical_json(payload, label="payload", max_bytes=MAX_EVENT_JSON_BYTES),
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)
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def _event_bytes(event: dict[str, Any]) -> int:
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return utf8_len(
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str(event["event_id"]), str(event["kind"]),
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json.dumps(event["actor"], ensure_ascii=False, separators=(",", ":")),
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json.dumps(event["payload"], ensure_ascii=False, separators=(",", ":")),
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)
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def _validate_page(page: Any) -> tuple[list[dict[str, Any]], dict[str, Any]]:
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if not isinstance(page, dict):
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raise ReplicaError("page must be an object")
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events = page.get("events")
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authority = page.get("authority")
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if not isinstance(events, list):
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raise ReplicaError("page.events must be a list")
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if not isinstance(authority, dict):
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raise ReplicaError("page.authority is required for replication")
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gateway_id = _validate_identifier(
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authority.get("gateway_id"), label="page.authority.gateway_id", max_chars=MAX_ACTOR_ID_CHARS
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)
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epoch = _positive_int(authority.get("epoch"), "page.authority.epoch must be a positive integer")
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previous_seq: int | None = None
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for event in events:
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if not isinstance(event, dict):
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raise ReplicaError("page events must be objects")
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seq = _positive_int(event.get("seq"), "event.seq must be a positive integer")
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if previous_seq is not None and seq != previous_seq + 1:
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raise ReplicaGapError("page events must be contiguous")
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previous_seq = seq
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for field in ("event_id", "kind"):
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if not isinstance(event.get(field), str) or not event[field]:
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raise ReplicaError(f"event.{field} must be a non-empty string")
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if not isinstance(event.get("actor"), dict):
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raise ReplicaError("event.actor must be an object")
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if "payload" not in event:
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raise ReplicaError("event.payload is required")
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return events, {"gateway_id": gateway_id, "epoch": epoch}
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def _replica_row_state(conn: sqlite3.Connection, room_id: str) -> tuple[sqlite3.Row | None, int, int, int]:
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"""Return (row, stored_epoch, last_seq, stored_bytes); a new room is admitted only under the room cap."""
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row = conn.execute(
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"""SELECT authority_gateway_id, authority_epoch, last_seq, latest_seq, event_bytes
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FROM hosted_room_replicas WHERE room_id=?""",
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(room_id,),
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).fetchone()
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if row is None:
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count = conn.execute("SELECT COUNT(*) FROM hosted_room_replicas").fetchone()[0]
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if int(count) >= MAX_REPLICA_ROOMS:
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raise ReplicaError("replica room capacity exhausted")
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return None, 0, 0, 0
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return row, int(row["authority_epoch"]), int(row["last_seq"]), int(row["event_bytes"])
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def _store_replica(
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conn: sqlite3.Connection, *, is_new: bool, room_id: str, room_name: str, members_json: str,
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authority: dict[str, Any], new_last: int, latest_seq: int, added_bytes: int, now: float,
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) -> None:
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"""INSERT the replica row for a new room, else UPDATE it (event_bytes accumulates)."""
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values = (room_name, members_json, authority["gateway_id"], authority["epoch"], new_last, max(latest_seq, new_last))
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if is_new:
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conn.execute(
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"""INSERT INTO hosted_room_replicas (room_id, name, members_json,
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authority_gateway_id, authority_epoch, last_seq, latest_seq, event_bytes,
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created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)""",
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(room_id, *values, added_bytes, now, now),
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)
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else:
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conn.execute(
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"""UPDATE hosted_room_replicas SET name=?, members_json=?, authority_gateway_id=?,
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authority_epoch=?, last_seq=?, latest_seq=?, event_bytes=event_bytes+?,
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updated_at=? WHERE room_id=?""",
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(*values, added_bytes, now, room_id),
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)
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def ingest_page(
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db_path: Path | str, *, room_id: Any, room_name: Any, members: Any, page: Any, now: float | None = None
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) -> dict[str, Any]:
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"""Persist one replay page idempotently; refuses seq gaps and epoch regressions.
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``page`` is the verbatim ``groups.log`` (``read_events()``) result whose
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``authority`` stamp proves lineage.
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"""
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room_id = _room_id(room_id)
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room_name = _validate_room_name(room_name)
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_, members_json = _validate_members(members)
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events, authority = _validate_page(page)
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now = time.time() if now is None else float(now)
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with _replica_transaction(db_path) as conn:
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row, stored_epoch, last_seq, stored_bytes = _replica_row_state(conn, room_id)
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if authority["epoch"] < stored_epoch:
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raise ReplicaEpochRegressionError("page authority epoch is older than the stored replica epoch")
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new_events = [e for e in events if int(e["seq"]) > last_seq]
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if new_events and int(new_events[0]["seq"]) != last_seq + 1:
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raise ReplicaGapError("page skips sequences the replica has not stored")
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added_bytes = 0
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for event in new_events:
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size = _event_bytes(event)
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if stored_bytes + added_bytes + size > MAX_REPLICA_EVENT_BYTES:
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raise ReplicaError("replica event storage exhausted")
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actor_json = _canonical_json(event["actor"], label="actor", max_bytes=4 * 1024)
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payload_json = _canonical_json(event["payload"], label="payload", max_bytes=MAX_EVENT_JSON_BYTES)
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conn.execute(
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_INSERT_REPLICA_EVENT,
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(
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room_id, int(event["seq"]), event["event_id"], event["kind"], actor_json,
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event.get("authority_epoch"), payload_json, float(event.get("created_at") or now),
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),
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)
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added_bytes += size
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new_last = int(new_events[-1]["seq"]) if new_events else last_seq
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latest_seq = page.get("latest_seq")
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if isinstance(latest_seq, bool) or not isinstance(latest_seq, int):
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latest_seq = new_last
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_store_replica(
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conn, is_new=row is None, room_id=room_id, room_name=room_name, members_json=members_json,
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authority=authority, new_last=new_last, latest_seq=latest_seq, added_bytes=added_bytes, now=now,
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)
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return {
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"room_id": room_id,
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"stored_seq": new_last,
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"ingested": len(new_events),
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"authority": authority,
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"caught_up": new_last >= max(latest_seq, new_last),
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}
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def replica_state(db_path: Path | str, *, room_id: Any) -> dict[str, Any]:
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"""Return the stored replica's coverage and authority lineage."""
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room_id = _room_id(room_id)
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with _replica_transaction(db_path) as conn:
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row = conn.execute(_SELECT_REPLICA, (room_id,)).fetchone()
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if row is None:
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raise ReplicaError("replica not found")
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return {
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"room_id": row["room_id"],
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"name": row["name"],
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"members": json.loads(row["members_json"]),
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"authority": {"gateway_id": row["authority_gateway_id"], "epoch": int(row["authority_epoch"])},
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"last_seq": int(row["last_seq"]),
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"latest_seq": int(row["latest_seq"]),
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"event_bytes": int(row["event_bytes"]),
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"created_at": float(row["created_at"]),
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"updated_at": float(row["updated_at"]),
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}
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def promote_replica(
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db_path: Path | str, *, room_id: Any, reason: Any = "authority-unreachable", now: float | None = None
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) -> dict[str, Any]:
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"""Continue a replicated room on THIS gateway at ``epoch + 1``.
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Copies the replica log into the authoritative store and appends a
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lineage-proving ``authority.claimed`` event; wherever the claim replicates,
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the old epoch is stale and every fenced primitive rejects it. The caller
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decides takeover is safe; this only makes it atomic and provable.
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"""
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room_id = _room_id(room_id)
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if not isinstance(reason, str) or not reason or len(reason) > 200:
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raise ReplicaError("reason must be a non-empty string of at most 200 chars")
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now = time.time() if now is None else float(now)
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local_gateway = local_authority_gateway_id()
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with _replica_transaction(db_path) as conn:
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replica = conn.execute(_SELECT_REPLICA, (room_id,)).fetchone()
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if replica is None:
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raise ReplicaError("replica not found")
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if replica["authority_gateway_id"] == local_gateway:
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raise ReplicaError("this gateway already holds the room authority")
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if conn.execute("SELECT 1 FROM hosted_rooms WHERE room_id=?", (room_id,)).fetchone():
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raise RoomConflictError("room_id already exists in the local authoritative store")
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if conn.execute("SELECT 1 FROM hosted_room_retired_ids WHERE room_id=?", (room_id,)).fetchone():
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raise RoomConflictError("room_id belongs to a disbanded room")
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previous_gateway = str(replica["authority_gateway_id"])
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previous_epoch = int(replica["authority_epoch"])
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target_epoch = previous_epoch + 1
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claim_seq = int(replica["last_seq"]) + 1
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claim_event_id = f"system:authority-claimed:{target_epoch}"
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claim_actor_json, claim_payload_json = _control_event_json({
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"previous_gateway_id": previous_gateway,
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"authority_gateway_id": local_gateway,
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"authority_epoch": target_epoch,
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"promoted_from_replica": True,
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"reason": reason,
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})
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claim_bytes = utf8_len(claim_event_id, "authority.claimed", claim_actor_json, claim_payload_json)
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conn.execute(
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"""INSERT INTO hosted_rooms
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(room_id, name, members_json, authority_gateway_id, authority_epoch, next_seq, event_bytes,
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revision, created_at, updated_at, disbanded_at)
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VALUES (?, ?, ?, ?, ?, ?, ?, 1, ?, ?, NULL)""",
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(
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room_id, replica["name"], replica["members_json"], local_gateway, target_epoch,
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claim_seq + 1, int(replica["event_bytes"]) + claim_bytes, now, now,
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),
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)
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conn.execute(
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f"""INSERT INTO hosted_room_events {_EVENT_COLUMNS}
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SELECT room_id, seq, event_id, kind, actor_json, authority_epoch, payload_json, created_at
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FROM hosted_room_replica_events WHERE room_id=?""",
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(room_id,),
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)
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conn.execute(
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_INSERT_ROOM_EVENT,
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(
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room_id, claim_seq, claim_event_id, "authority.claimed",
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claim_actor_json, target_epoch, claim_payload_json, now,
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),
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)
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conn.execute("DELETE FROM hosted_room_replica_events WHERE room_id=?", (room_id,))
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conn.execute("DELETE FROM hosted_room_replicas WHERE room_id=?", (room_id,))
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return {
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"room_id": room_id,
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"authority_gateway_id": local_gateway,
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"authority_epoch": target_epoch,
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"previous_gateway_id": previous_gateway,
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"previous_epoch": previous_epoch,
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"claim_seq": claim_seq,
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"latest_seq": claim_seq,
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}
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def demote_room(
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db_path: Path | str, *, room_id: Any, observed_gateway_id: Any, observed_epoch: Any, now: float | None = None
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) -> dict[str, Any]:
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"""Fence THIS gateway's stale room authority against a proven newer epoch.
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Called when a returning gateway observes (replicated ``authority.claimed``
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or a transport rejection) that another gateway owns the room at a higher
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epoch. Appends ``authority.lost`` and adopts the observed lineage so no
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local send can commit at the stale epoch. Idempotent per lineage.
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"""
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room_id = _room_id(room_id)
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observed_gateway_id = _validate_identifier(
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observed_gateway_id, label="observed_gateway_id", max_chars=MAX_ACTOR_ID_CHARS
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)
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observed_epoch = _positive_int(observed_epoch, "observed_epoch must be a positive integer")
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now = time.time() if now is None else float(now)
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local_gateway = local_authority_gateway_id()
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with _transaction(db_path, immediate=True) as conn:
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row = conn.execute(
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"""SELECT authority_gateway_id, authority_epoch, next_seq
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FROM hosted_rooms WHERE room_id=? AND disbanded_at IS NULL""",
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(room_id,),
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).fetchone()
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if row is None:
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raise ReplicaError("room not found in the local authoritative store")
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current_gateway = str(row["authority_gateway_id"])
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current_epoch = int(row["authority_epoch"])
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if current_gateway == observed_gateway_id and current_epoch == observed_epoch:
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return {
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"room_id": room_id,
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"authority_gateway_id": current_gateway,
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"authority_epoch": current_epoch,
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"idempotent": True,
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}
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if observed_epoch <= current_epoch:
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raise ReplicaEpochRegressionError("observed epoch does not supersede the stored authority")
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if current_gateway != local_gateway:
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raise ReplicaError("room is not locally authoritative; nothing to demote")
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lost_actor_json, lost_payload_json = _control_event_json({
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"previous_gateway_id": current_gateway,
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"authority_gateway_id": observed_gateway_id,
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"authority_epoch": observed_epoch,
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})
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conn.execute(
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_INSERT_ROOM_EVENT,
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(
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room_id, int(row["next_seq"]), f"system:authority-lost:{observed_epoch}",
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"authority.lost", lost_actor_json, observed_epoch, lost_payload_json, now,
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),
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)
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conn.execute(
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"""UPDATE hosted_rooms
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SET authority_gateway_id=?, authority_epoch=?, next_seq=next_seq+1, revision=revision+1, updated_at=?
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WHERE room_id=?""",
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(observed_gateway_id, observed_epoch, now, room_id),
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)
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return {
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"room_id": room_id,
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"authority_gateway_id": observed_gateway_id,
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"authority_epoch": observed_epoch,
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"idempotent": False,
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}
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