"""Stream controller: subscription registry and fan-out for AsyncThreadStream. `StreamController` manages the set of active subscriptions against one shared SSE connection, routing events from the shared stream to per-subscription queues. It is the centralised place for: - subscription registration / teardown - shared-stream lifecycle (open, rotate, close) - dedup of replayed events across rotations - fan-out from the shared stream to subscriber queues """ from __future__ import annotations import asyncio import contextlib import logging import random from collections import OrderedDict from collections.abc import AsyncGenerator, AsyncIterator, Awaitable, Callable from dataclasses import dataclass, field from typing import Any from langchain_protocol import Event, SubscribeParams from langgraph_sdk.stream.transport import AsyncProtocolTransport, EventStreamHandle # --------------------------------------------------------------------------- # Bounded LRU set for event-id dedup # --------------------------------------------------------------------------- class _SeenEventIds: """LRU set of event ids with bounded memory.""" __slots__ = ("_data", "_maxsize") def __init__(self, maxsize: int = 10_000) -> None: self._data: OrderedDict[str, None] = OrderedDict() self._maxsize = maxsize def add(self, event_id: str) -> None: if event_id in self._data: self._data.move_to_end(event_id) return self._data[event_id] = None if len(self._data) > self._maxsize: self._data.popitem(last=False) def __contains__(self, event_id: object) -> bool: return event_id in self._data def __iter__(self): return iter(self._data) # --------------------------------------------------------------------------- # Per-subscription record # --------------------------------------------------------------------------- _logger = logging.getLogger(__name__) @dataclass class _Subscription: """Internal record for one active subscription on a `StreamController`.""" id: int params: SubscribeParams queue: asyncio.Queue = field(default_factory=asyncio.Queue) # Why: asyncio.Queue[Event | None] as a subscript in the field annotation # causes a type error with ty; bare asyncio.Queue is accepted. # --------------------------------------------------------------------------- # Rotation close helper # --------------------------------------------------------------------------- async def _close_after(handle: EventStreamHandle, *, delay: float = 0.0) -> None: """Close a handle, optionally after a brief delay. Used to detach closing the old stream from the synchronous rotation step so the new stream can absorb server-side replayed events first. """ if delay: await asyncio.sleep(delay) await handle.close() # --------------------------------------------------------------------------- # StreamController # --------------------------------------------------------------------------- class StreamController: """Manages subscriptions and fan-out against one shared SSE connection. Responsibilities: - subscription registry (register / unregister) - shared-stream lifecycle (open on first subscribe, rotate on filter widen) - dedup of replayed events via a bounded LRU `_SeenEventIds` - fan-out from the shared stream to per-subscription queues Args: transport: the `AsyncProtocolTransport` bound to this thread session. run_start_gate: zero-argument async callable that resolves once the current `run.start` has committed server-side (no-op when no run is in flight). max_queue_size: per-subscription queue bound (default 1024). seen_event_ids_max: LRU cap for the dedup set (default 10_000). """ def __init__( self, *, transport: AsyncProtocolTransport, run_start_gate: Callable[[], Awaitable[None]] | None = None, # noqa: ARG002 max_queue_size: int = 1024, seen_event_ids_max: int = 10_000, max_reconnect_attempts: int = 5, reconnect_backoff_base: float = 0.1, reconnect_backoff_cap: float = 2.0, ) -> None: self._transport = transport self._max_queue_size = max_queue_size self._seen_event_ids = _SeenEventIds(maxsize=seen_event_ids_max) self._next_subscription_id = 1 self._subscriptions: dict[int, _Subscription] = {} self._shared_stream: EventStreamHandle | None = None self._shared_stream_filter: dict[str, Any] | None = None self._fanout_task: asyncio.Task[None] | None = None self._rotation_close_tasks: set[asyncio.Task[None]] = set() self._closed = False self._cursor: int | None = None self._max_reconnect_attempts = max_reconnect_attempts self._reconnect_backoff_base = reconnect_backoff_base self._reconnect_backoff_cap = reconnect_backoff_cap # ------------------------------------------------------------------ # Public API # ------------------------------------------------------------------ def subscribe( self, channels: list[str], *, namespaces: list[list[str]] | None = None, depth: int | None = None, ) -> AsyncIterator[Event]: """Open a typed subscription against the shared SSE. Returns an async iterator that yields raw `Event` dicts matching the given filter. Multiple concurrent subscribes share one HTTP connection whose union expands or rotates as subscriptions come and go. """ params: SubscribeParams = {"channels": list(channels)} if namespaces is not None: params["namespaces"] = namespaces if depth is not None: params["depth"] = depth return self._subscription_iter(params) async def close(self) -> None: """Tear down the controller, awaiting any pending rotation closes.""" if self._closed: return self._closed = True if self._fanout_task is not None: self._fanout_task.cancel() with contextlib.suppress(Exception, asyncio.CancelledError): await self._fanout_task if self._shared_stream is not None: await self._shared_stream.close() if self._rotation_close_tasks: await asyncio.gather(*self._rotation_close_tasks, return_exceptions=True) # ------------------------------------------------------------------ # Subscription internals # ------------------------------------------------------------------ def _register_subscription(self, params: SubscribeParams) -> _Subscription: """Allocate a subscription id, create a bounded queue, add to registry.""" sub = _Subscription( id=self._next_subscription_id, params=params, queue=asyncio.Queue(maxsize=self._max_queue_size), ) self._next_subscription_id += 1 self._subscriptions[sub.id] = sub return sub def _unregister_subscription(self, subscription_id: int) -> None: """Remove a subscription from the registry. No-op if already absent.""" self._subscriptions.pop(subscription_id, None) # Public aliases used by tests and external callers. register_subscription = _register_subscription unregister_subscription = _unregister_subscription async def _subscription_iter( self, params: SubscribeParams ) -> AsyncGenerator[Event, None]: sub = self._register_subscription(params) try: if self._closed: return await self._reconcile_stream(params) self._ensure_fanout_running() while True: item = await sub.queue.get() if item is None: return yield item finally: self._unregister_subscription(sub.id) # ------------------------------------------------------------------ # Fan-out # ------------------------------------------------------------------ def _ensure_fanout_running(self) -> None: if self._fanout_task is None or self._fanout_task.done(): self._fanout_task = asyncio.create_task(self._fanout()) # Public alias. ensure_fanout_running = _ensure_fanout_running async def _fanout(self) -> None: """Single consumer of the shared SSE; routes events to subscriptions. Why: rotation in `_reconcile_stream` replaces `_shared_stream` mid-loop. Re-read `self._shared_stream` on each outer iteration so we always consume from the current handle. The old handle's iterator exhausts naturally after `_close_after` closes it. On a post-ready transport drop (non-cancelled error in `shared.done`), attempts to reconnect up to `_max_reconnect_attempts` times before giving up and closing subscriber queues. """ from langgraph_sdk.stream.subscription import matches_subscription while not self._closed: shared = self._shared_stream if shared is None: return try: async for event in self._dedup_iter(shared.events): if self._closed: break for sub in list(self._subscriptions.values()): if matches_subscription(event, sub.params): sub.queue.put_nowait(event) except Exception as drop_err: _logger.debug("transport drop in fanout: %r", drop_err) if self._shared_stream is shared: err = await shared.done if ( err is not None and not isinstance(err, asyncio.CancelledError) and not self._closed ): with contextlib.suppress(Exception): await self._shared_stream.close() reconnected = await self._reconnect_shared_stream() if reconnected: continue break # Rotation: loop again to pick up the new _shared_stream. # Terminate consumers cleanly on shutdown / stream-end. for sub in self._subscriptions.values(): sub.queue.put_nowait(None) async def _reconnect_sleep(self, attempt: int) -> None: """Sleep with exponential backoff and jitter for reconnect attempt *attempt*.""" base = self._reconnect_backoff_base cap = self._reconnect_backoff_cap delay = min(cap, base * (2**attempt)) jitter = random.uniform(0, delay * 0.25) await asyncio.sleep(delay + jitter) async def _reconnect_shared_stream(self) -> bool: """Attempt to reopen the shared stream after a transport drop. Returns True if a new stream was successfully opened, False if all reconnect attempts were exhausted or the controller was closed. """ # We intentionally use the *current* shared_stream_filter (the latest # computed union of all live subscriptions), not the filter that was # active when this stream was originally opened. If subscriptions were # added or removed during the drop window, the reconnect picks up the # new shape. base_filter = self._shared_stream_filter if base_filter is None: return False for attempt in range(self._max_reconnect_attempts): if self._closed: return False try: new_stream = self._transport.open_event_stream( self._filter_with_since(base_filter) ) await new_stream.ready except asyncio.CancelledError: raise except Exception: await self._reconnect_sleep(attempt) continue self._shared_stream = new_stream return True return False # ------------------------------------------------------------------ # Stream rotation # ------------------------------------------------------------------ async def _reconcile_stream(self, candidate_filter: SubscribeParams) -> None: """Ensure the shared SSE covers `candidate_filter`. Rotate if not. Open-new-before-close-old: any events buffered server-side between the two opens are replayed on the new SSE, and `_seen_event_ids` dedupes the overlap. Awaits `new_stream.ready` so the HTTP connection is established before returning. """ from langgraph_sdk.stream.subscription import filter_covers if ( self._shared_stream is not None and self._shared_stream_filter is not None and filter_covers(self._shared_stream_filter, dict(candidate_filter)) ): return # Existing stream is sufficient. new_filter = self._compute_current_union(extra=candidate_filter) new_stream = self._transport.open_event_stream( self._filter_with_since(new_filter) ) old_stream = self._shared_stream self._shared_stream = new_stream self._shared_stream_filter = new_filter await new_stream.ready if old_stream is not None: task = asyncio.create_task(_close_after(old_stream)) self._rotation_close_tasks.add(task) task.add_done_callback(self._rotation_close_tasks.discard) async def reconcile_stream(self, candidate_filter: SubscribeParams) -> None: """Public alias for `_reconcile_stream`.""" return await self._reconcile_stream(candidate_filter) def _compute_current_union( self, extra: SubscribeParams | None = None ) -> dict[str, Any]: from langgraph_sdk.stream.subscription import compute_union_filter filters: list[dict[str, Any]] = [ dict(sub.params) for sub in self._subscriptions.values() ] if extra is not None: filters.append(dict(extra)) return compute_union_filter(filters) # ------------------------------------------------------------------ # Cursor tracking # ------------------------------------------------------------------ def observe_applied_through_seq(self, seq: Any) -> None: """Advance the reconnect cursor from a command response meta sequence.""" self._observe_seq(seq) def _observe_event(self, event: Event) -> None: self._observe_seq(event.get("seq")) def _observe_seq(self, seq: Any) -> None: if isinstance(seq, int) and (self._cursor is None or seq > self._cursor): self._cursor = seq def _filter_with_since(self, params: dict[str, Any]) -> dict[str, Any]: out = dict(params) if self._cursor is not None: out["since"] = self._cursor return out # ------------------------------------------------------------------ # Dedup iterator # ------------------------------------------------------------------ async def _dedup_iter(self, source: AsyncIterator[Event]) -> AsyncIterator[Event]: async for event in source: event_id = event.get("event_id") if event_id is not None: if event_id in self._seen_event_ids: continue self._seen_event_ids.add(event_id) self._observe_event(event) yield event