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from __future__ import annotations
from collections.abc import Awaitable, Mapping
from contextlib import AsyncExitStack
from functools import partial
from typing import TYPE_CHECKING, Any, Callable, cast
import asyncpg
import attrs
from anyio import (
TASK_STATUS_IGNORED,
EndOfStream,
create_memory_object_stream,
move_on_after,
)
from anyio.streams.memory import MemoryObjectSendStream
from asyncpg import Connection, InterfaceError
from .._events import Event
from .._exceptions import SerializationError
from .base import BaseExternalEventBroker
if TYPE_CHECKING:
from sqlalchemy.ext.asyncio import AsyncEngine
@attrs.define(eq=False)
class AsyncpgEventBroker(BaseExternalEventBroker):
"""
An asynchronous, asyncpg_ based event broker that uses a PostgreSQL server to
broadcast events using its ``NOTIFY`` mechanism.
.. _asyncpg: https://pypi.org/project/asyncpg/
:param connection_factory: a callable that creates an asyncpg connection
:param channel: the ``NOTIFY`` channel to use
:param max_idle_time: maximum time to let the connection go idle, before sending a
``SELECT 1`` query to prevent a connection timeout
"""
connection_factory: Callable[[], Awaitable[Connection]]
channel: str = attrs.field(kw_only=True, default="apscheduler")
max_idle_time: float = attrs.field(kw_only=True, default=10)
_send: MemoryObjectSendStream[str] = attrs.field(init=False)
@classmethod
def from_dsn(
cls, dsn: str, options: Mapping[str, Any] | None = None, **kwargs: Any
) -> AsyncpgEventBroker:
"""
Create a new asyncpg event broker from an existing asyncpg connection pool.
:param dsn: data source name, passed as first positional argument to
:func:`asyncpg.connect`
:param options: keyword arguments passed to :func:`asyncpg.connect`
:param kwargs: keyword arguments to pass to the initializer of this class
:return: the newly created event broker
"""
factory = partial(asyncpg.connect, dsn, **(options or {}))
return cls(factory, **kwargs)
@classmethod
def from_async_sqla_engine(
cls,
engine: AsyncEngine,
options: Mapping[str, Any] | None = None,
**kwargs: Any,
) -> AsyncpgEventBroker:
"""
Create a new asyncpg event broker from an SQLAlchemy engine.
The engine will only be used to create the appropriate options for
:func:`asyncpg.connect`.
:param engine: an asynchronous SQLAlchemy engine using asyncpg as the driver
:type engine: ~sqlalchemy.ext.asyncio.AsyncEngine
:param options: extra keyword arguments passed to :func:`asyncpg.connect` (will
override any automatically generated arguments based on the engine)
:param kwargs: keyword arguments to pass to the initializer of this class
:return: the newly created event broker
"""
if engine.dialect.driver != "asyncpg":
raise ValueError(
f'The driver in the engine must be "asyncpg" (current: '
f"{engine.dialect.driver})"
)
connect_args = dict(engine.url.query)
for optname in ("host", "port", "database", "username", "password"):
value = getattr(engine.url, optname)
if value is not None:
if optname == "username":
optname = "user"
connect_args[optname] = value
if options:
connect_args |= options
factory = partial(asyncpg.connect, **connect_args)
return cls(factory, **kwargs)
@property
def _temporary_failure_exceptions(self) -> tuple[type[Exception]]:
return OSError, InterfaceError
async def start(self, exit_stack: AsyncExitStack) -> None:
await super().start(exit_stack)
self._send = cast(
MemoryObjectSendStream[str],
await self._task_group.start(self._listen_notifications),
)
await exit_stack.enter_async_context(self._send)
async def _listen_notifications(self, *, task_status=TASK_STATUS_IGNORED) -> None:
conn: Connection
def listen_callback(
connection: Connection, pid: int, channel: str, payload: str
) -> None:
event = self.reconstitute_event_str(payload)
if event is not None:
self._task_group.start_soon(self.publish_local, event)
async def close_connection() -> None:
if not conn.is_closed():
with move_on_after(3, shield=True):
await conn.close()
async def unsubscribe() -> None:
if not conn.is_closed():
with move_on_after(3, shield=True):
await conn.remove_listener(self.channel, listen_callback)
task_started_sent = False
send, receive = create_memory_object_stream(100, str)
while True:
async with AsyncExitStack() as exit_stack:
async for attempt in self._retry():
with attempt:
conn = await self.connection_factory()
exit_stack.push_async_callback(close_connection)
self._logger.info("Connection established")
try:
await conn.add_listener(self.channel, listen_callback)
exit_stack.push_async_callback(unsubscribe)
if not task_started_sent:
task_status.started(send)
task_started_sent = True
while True:
notification: str | None = None
with move_on_after(self.max_idle_time):
try:
notification = await receive.receive()
except EndOfStream:
self._logger.info("Stream finished")
return
if notification:
await conn.execute(
"SELECT pg_notify($1, $2)", self.channel, notification
)
else:
await conn.execute("SELECT 1")
except InterfaceError as exc:
self._logger.error("Connection error: %s", exc)
async def publish(self, event: Event) -> None:
notification = self.generate_notification_str(event)
if len(notification) > 7999:
raise SerializationError(
"Serialized event object exceeds 7999 bytes in size"
)
await self._send.send(notification)
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