+class WSMethod(enum.Enum):
+ """Arvados WebSocket methods
+
+ This enum represents valid values for the `method` field in messages
+ sent to an Arvados WebSocket server.
+ """
+ SUBSCRIBE = 'subscribe'
+ SUB = SUBSCRIBE
+ UNSUBSCRIBE = 'unsubscribe'
+ UNSUB = UNSUBSCRIBE
+
+
+class EventClient(threading.Thread):
+ """Follow Arvados events via WebSocket
+
+ EventClient follows events on Arvados cluster published by the WebSocket
+ server. Users can select the events they want to follow and run their own
+ callback function on each.
+ """
+ _USER_AGENT = 'Python/{}.{}.{} arvados.events/{}'.format(
+ *sys.version_info[:3],
+ __version__,
+ )
+
+ def __init__(
+ self,
+ url: str,
+ filters: Optional[Filter],
+ on_event_cb: EventCallback,
+ last_log_id: Optional[int]=None,
+ *,
+ insecure: Optional[bool]=None,
+ ) -> None:
+ """Initialize a WebSocket client
+
+ Constructor arguments:
+
+ * url: str --- The `wss` URL for an Arvados WebSocket server.
+
+ * filters: arvados.events.Filter | None --- One event filter to
+ subscribe to after connecting to the WebSocket server. If not
+ specified, the client will subscribe to all events.
+
+ * on_event_cb: arvados.events.EventCallback --- When the client
+ receives an event from the WebSocket server, it calls this
+ function with the event object.
+
+ * last_log_id: int | None --- If specified, this will be used as the
+ value for the `last_log_id` field in subscribe messages sent by
+ the client.
+
+ Constructor keyword arguments:
+
+ * insecure: bool | None --- If `True`, the client will not check the
+ validity of the server's TLS certificate. If not specified, uses
+ the value from the user's `ARVADOS_API_HOST_INSECURE` setting.
+ """
+ self.url = url
+ self.filters = [filters or []]
+ self.on_event_cb = on_event_cb
+ self.last_log_id = last_log_id
+ self.is_closed = threading.Event()
+ self._ssl_ctx = ssl.create_default_context(
+ purpose=ssl.Purpose.SERVER_AUTH,
+ cafile=util.ca_certs_path(),
+ )
+ if insecure is None:
+ insecure = config.flag_is_true('ARVADOS_API_HOST_INSECURE')
+ if insecure:
+ self._ssl_ctx.check_hostname = False
+ self._ssl_ctx.verify_mode = ssl.CERT_NONE
+ self._subscribe_lock = threading.Lock()
+ self._connect()
+ super().__init__(daemon=True)
+ self.start()
+
+ def _connect(self) -> None:
+ # There are no locks protecting this method. After the thread starts,
+ # it should only be called from inside.
+ self._client = ws_client.connect(
+ self.url,
+ logger=_logger,
+ ssl_context=self._ssl_ctx,
+ user_agent_header=self._USER_AGENT,
+ )
+ self._client_ok = True
+
+ def _subscribe(self, f: Filter, last_log_id: Optional[int]) -> None:
+ extra = {}
+ if last_log_id is not None:
+ extra['last_log_id'] = last_log_id
+ return self._update_sub(WSMethod.SUBSCRIBE, f, **extra)
+
+ def _update_sub(self, method: WSMethod, f: Filter, **extra: Any) -> None:
+ msg = json.dumps({
+ 'method': method.value,
+ 'filters': f,
+ **extra,
+ })
+ self._client.send(msg)
+
+ def close(self, code: int=1000, reason: str='', timeout: float=0) -> None:
+ """Close the WebSocket connection and stop processing events
+
+ Arguments:
+
+ * code: int --- The WebSocket close code sent to the server when
+ disconnecting. Default 1000.
+
+ * reason: str --- The WebSocket close reason sent to the server when
+ disconnecting. Default is the empty string.
+
+ * timeout: float --- How long to wait for the WebSocket server to
+ acknowledge the disconnection, in seconds. Default 0, which means
+ no timeout.
+ """
+ self.is_closed.set()
+ self._client.close_timeout = timeout or None
+ self._client.close(code, reason)
+
+ def run_forever(self) -> None:
+ """Run the WebSocket client indefinitely
+
+ This method blocks until the `close` method is called (e.g., from
+ another thread) or the client permanently loses its connection.
+ """
+ # Have to poll here to let KeyboardInterrupt get raised.
+ while not self.is_closed.wait(1):
+ pass
+
+ def subscribe(self, f: Filter, last_log_id: Optional[int]=None) -> None:
+ """Subscribe to another set of events from the server
+
+ Arguments:
+
+ * f: arvados.events.Filter | None --- One filter to subscribe to
+ events for.
+
+ * last_log_id: int | None --- If specified, request events starting
+ from this id. If not specified, the server will only send events
+ that occur after processing the subscription.
+ """
+ with self._subscribe_lock:
+ self._subscribe(f, last_log_id)
+ self.filters.append(f)
+
+ def unsubscribe(self, f: Filter) -> None:
+ """Unsubscribe from an event stream
+
+ Arguments:
+
+ * f: arvados.events.Filter | None --- One event filter to stop
+ receiving events for.
+ """
+ with self._subscribe_lock:
+ try:
+ index = self.filters.index(f)
+ except ValueError:
+ raise ValueError(f"filter not subscribed: {f!r}") from None
+ self._update_sub(WSMethod.UNSUBSCRIBE, f)
+ del self.filters[index]
+
+ def on_closed(self) -> None:
+ """Handle disconnection from the WebSocket server
+
+ This method is called when the client loses its connection from
+ receiving events. This implementation tries to establish a new
+ connection if it was not closed client-side.
+ """
+ if self.is_closed.is_set():
+ return
+ _logger.warning("Unexpected close. Reconnecting.")
+ for _ in RetryLoop(num_retries=25, backoff_start=.1, max_wait=15):
+ try:
+ self._connect()
+ except Exception as e:
+ _logger.warning("Error '%s' during websocket reconnect.", e)
+ else:
+ _logger.warning("Reconnect successful.")
+ break