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sse.py
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sse.py
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import io
import logging
import re
from datetime import datetime, timezone
from functools import partial
from typing import (
Any,
AsyncIterable,
Awaitable,
Callable,
Coroutine,
Iterator,
Mapping,
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__)
class SendTimeoutError(TimeoutError):
pass
# 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[str] = 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: Instruct the client to try reconnecting after *at least* the
given number of milliseconds has passed in case of connection loss. Setting
to 0 does not prevent reconnect attempts, a clean disconnect must be
implemented on top of the SSE protocol if required (eg. as a special event
type). The spec requires client to not attempt reconnecting if it receives a
HTTP 204 No Content response. 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()
Content = Union[str, bytes, dict, ServerSentEvent]
SyncContentStream = Iterator[Content]
AsyncContentStream = AsyncIterable[Content]
ContentStream = Union[AsyncContentStream, SyncContentStream]
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
"""
body_iterator: AsyncContentStream
DEFAULT_PING_INTERVAL = 15
# noinspection PyMissingConstructor
def __init__(
self,
content: ContentStream,
status_code: int = 200,
headers: Optional[Mapping[str, str]] = 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,
send_timeout: Optional[float] = 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.DEFAULT_SEPARATOR = "\r\n"
self.sep = sep if sep is not None else self.DEFAULT_SEPARATOR
self.ping_message_factory = ping_message_factory
if isinstance(content, AsyncIterable):
self.body_iterator = content
else:
self.body_iterator = iterate_in_threadpool(content)
self.status_code = status_code
self.media_type = self.media_type if media_type is None else media_type
self.background = background
self.data_sender_callable = data_sender_callable
self.send_timeout = send_timeout
_headers: dict[str, str] = {}
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
# https://github.com/sysid/sse-starlette/pull/55#issuecomment-1732374113
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: 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("chunk: %s", chunk)
with anyio.move_on_after(self.send_timeout) as timeout:
await send(
{"type": "http.response.body", "body": chunk, "more_body": True}
)
if timeout.cancel_called:
if hasattr(self.body_iterator, "aclose"):
await self.body_iterator.aclose()
raise SendTimeoutError()
async with self._send_lock:
self.active = False
await send({"type": "http.response.body", "body": b"", "more_body": False})
async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
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[[], Awaitable[None]]) -> None:
await func()
# noinspection PyAsyncCall
task_group.cancel_scope.cancel()
task_group.start_soon(wrap, partial(self.stream_response, send))
task_group.start_soon(wrap, partial(self._ping, 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.now(timezone.utc)}", sep=self.sep
).encode()
if self.ping_message_factory is None
else ensure_bytes(self.ping_message_factory(), self.sep)
)
_log.debug("ping: %s", ping)
async with self._send_lock:
if self.active:
await send(
{"type": "http.response.body", "body": ping, "more_body": True}
)