import io import logging import re from datetime import datetime from functools import partial from typing import Any, AsyncIterable, Callable, Coroutine, Dict, Optional, Union import anyio from starlette.background import BackgroundTask from starlette.concurrency import iterate_in_threadpool from starlette.responses import Response from starlette.types import Receive, Scope, Send _log = logging.getLogger(__name__) # https://stackoverflow.com/questions/58133694/graceful-shutdown-of-uvicorn-starlette-app-with-websockets class AppStatus: """helper for monkey-patching the signal-handler of uvicorn""" should_exit = False should_exit_event: Union[anyio.Event, None] = None @staticmethod def handle_exit(*args, **kwargs): # set bool flag before checking the event to avoid race condition AppStatus.should_exit = True # Check if event has been initialized, if so notify listeners if AppStatus.should_exit_event is not None: AppStatus.should_exit_event.set() original_handler(*args, **kwargs) try: from uvicorn.main import Server original_handler = Server.handle_exit Server.handle_exit = AppStatus.handle_exit # type: ignore def unpatch_uvicorn_signal_handler(): """restores original signal-handler and rolls back monkey-patching. Normally this should not be necessary. """ Server.handle_exit = original_handler except ModuleNotFoundError: _log.debug("Uvicorn not used.") class ServerSentEvent: def __init__( self, data: Optional[Any] = None, *, event: Optional[str] = None, id: Optional[int] = None, retry: Optional[int] = None, comment: Optional[str] = None, sep: Optional[str] = None, ) -> None: """Send data using EventSource protocol :param str data: The data field for the message. :param str id: The event ID to set the EventSource object's last event ID value to. :param str event: The event's type. If this is specified, an event will be dispatched on the browser to the listener for the specified event name; the web site would use addEventListener() to listen for named events. The default event type is "message". :param int retry: The reconnection time to use when attempting to send the event. [What code handles this?] This must be an integer, specifying the reconnection time in milliseconds. If a non-integer value is specified, the field is ignored. :param str comment: A colon as the first character of a line is essence a comment, and is ignored. Usually used as a ping message to keep connecting. If set, this will be a comment message. """ self.data = data self.event = event self.id = id self.retry = retry self.comment = comment self.DEFAULT_SEPARATOR = "\r\n" self.LINE_SEP_EXPR = re.compile(r"\r\n|\r|\n") self._sep = sep if sep is not None else self.DEFAULT_SEPARATOR def encode(self) -> bytes: buffer = io.StringIO() if self.comment is not None: for chunk in self.LINE_SEP_EXPR.split(str(self.comment)): buffer.write(f": {chunk}") buffer.write(self._sep) if self.id is not None: buffer.write(self.LINE_SEP_EXPR.sub("", f"id: {self.id}")) buffer.write(self._sep) if self.event is not None: buffer.write(self.LINE_SEP_EXPR.sub("", f"event: {self.event}")) buffer.write(self._sep) if self.data is not None: for chunk in self.LINE_SEP_EXPR.split(str(self.data)): buffer.write(f"data: {chunk}") buffer.write(self._sep) if self.retry is not None: if not isinstance(self.retry, int): raise TypeError("retry argument must be int") buffer.write(f"retry: {self.retry}") buffer.write(self._sep) buffer.write(self._sep) return buffer.getvalue().encode("utf-8") def ensure_bytes(data: Union[bytes, dict, ServerSentEvent, Any], sep: str) -> bytes: if isinstance(data, bytes): return data elif isinstance(data, ServerSentEvent): return data.encode() elif isinstance(data, dict): data["sep"] = sep return ServerSentEvent(**data).encode() else: return ServerSentEvent(str(data), sep=sep).encode() class EventSourceResponse(Response): """Implements the ServerSentEvent Protocol: https://www.w3.org/TR/2009/WD-eventsource-20090421/ Responses must not be compressed by middleware in order to work. implementation based on Starlette StreamingResponse """ DEFAULT_PING_INTERVAL = 15 # noinspection PyMissingConstructor def __init__( self, content: Any, status_code: int = 200, headers: Optional[Dict] = None, media_type: str = "text/event-stream", background: Optional[BackgroundTask] = None, ping: Optional[int] = None, sep: Optional[str] = None, ping_message_factory: Optional[Callable[[], ServerSentEvent]] = None, data_sender_callable: Optional[ Callable[[], Coroutine[None, None, None]] ] = None, ) -> None: if sep is not None and sep not in ["\r\n", "\r", "\n"]: raise ValueError(f"sep must be one of: \\r\\n, \\r, \\n, got: {sep}") self.sep = sep self.ping_message_factory = ping_message_factory if isinstance(content, AsyncIterable): self.body_iterator = ( content ) # type: AsyncIterable[Union[Any,dict,ServerSentEvent]] else: self.body_iterator = iterate_in_threadpool(content) # type: ignore self.status_code = status_code self.media_type = self.media_type if media_type is None else media_type self.background = background # type: ignore # follows https://github.com/encode/starlette/blob/master/starlette/responses.py self.data_sender_callable = data_sender_callable _headers = {} if headers is not None: # pragma: no cover _headers.update(headers) # mandatory for servers-sent events headers # allow cache control header to be set by user to support fan out proxies # https://www.fastly.com/blog/server-sent-events-fastly _headers.setdefault("Cache-Control", "no-cache") _headers["Connection"] = "keep-alive" _headers["X-Accel-Buffering"] = "no" self.init_headers(_headers) self.ping_interval = self.DEFAULT_PING_INTERVAL if ping is None else ping self.active = True self._ping_task = None self._send_lock = anyio.Lock() @staticmethod async def listen_for_disconnect(receive: Receive) -> None: while True: message = await receive() if message["type"] == "http.disconnect": _log.debug("Got event: http.disconnect. Stop streaming.") break @staticmethod async def listen_for_exit_signal() -> None: # Check if should_exit was set before anybody started waiting if AppStatus.should_exit: return # Setup an Event if AppStatus.should_exit_event is None: AppStatus.should_exit_event = anyio.Event() # Check if should_exit got set while we set up the event if AppStatus.should_exit: return # Await the event await AppStatus.should_exit_event.wait() async def stream_response(self, send) -> None: await send( { "type": "http.response.start", "status": self.status_code, "headers": self.raw_headers, } ) async for data in self.body_iterator: chunk = ensure_bytes(data, self.sep) _log.debug(f"chunk: {chunk.decode()}") await send({"type": "http.response.body", "body": chunk, "more_body": True}) await send({"type": "http.response.body", "body": b"", "more_body": False}) async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None: async def safe_send(message): async with self._send_lock: return await send(message) async with anyio.create_task_group() as task_group: # https://trio.readthedocs.io/en/latest/reference-core.html#custom-supervisors async def wrap(func: Callable[[], Coroutine[None, None, None]]) -> None: await func() # noinspection PyAsyncCall task_group.cancel_scope.cancel() task_group.start_soon(wrap, partial(self.stream_response, safe_send)) task_group.start_soon(wrap, partial(self._ping, safe_send)) task_group.start_soon(wrap, self.listen_for_exit_signal) if self.data_sender_callable: task_group.start_soon(self.data_sender_callable) await wrap(partial(self.listen_for_disconnect, receive)) if self.background is not None: # pragma: no cover, tested in StreamResponse await self.background() def enable_compression(self, force: bool = False) -> None: raise NotImplementedError @property def ping_interval(self) -> Union[int, float]: """Time interval between two ping massages""" return self._ping_interval @ping_interval.setter def ping_interval(self, value: Union[int, float]) -> None: """Setter for ping_interval property. :param int value: interval in sec between two ping values. """ if not isinstance(value, (int, float)): raise TypeError("ping interval must be int") if value < 0: raise ValueError("ping interval must be greater then 0") self._ping_interval = value async def _ping(self, send: Send) -> None: # Legacy proxy servers are known to, in certain cases, drop HTTP connections after a short timeout. # To protect against such proxy servers, authors can send a custom (ping) event # every 15 seconds or so. # Alternatively one can send periodically a comment line # (one starting with a ':' character) while self.active: await anyio.sleep(self._ping_interval) if self.ping_message_factory: assert isinstance(self.ping_message_factory, Callable) # type: ignore # https://github.com/python/mypy/issues/6864 ping = ( ServerSentEvent(comment=f"ping - {datetime.utcnow()}").encode() if self.ping_message_factory is None else ensure_bytes(self.ping_message_factory(), self.sep) ) _log.debug(f"ping: {ping.decode()}") await send({"type": "http.response.body", "body": ping, "more_body": True})