Add ZeroConnectionsError in bfxapi.websocket.exceptions. Add log if connections = 0 in BfxWebsocketClient::start. Add raise ZeroConnectionError in BfxWebsocketClient::subscribe if connections equals 0.

.pylintrc

@@ -1,6 +1,5 @@
 [MAIN]
 py-version=3.8.0
-ignore=examples
 
 [MESSAGES CONTROL]
 disable=

bfxapi/websocket/client/bfx_websocket_client.py

@@ -13,7 +13,7 @@ from .bfx_websocket_bucket import _HEARTBEAT, F, _require_websocket_connection,
 from .bfx_websocket_inputs import BfxWebsocketInputs
 from ..handlers import PublicChannelsHandler, AuthenticatedChannelsHandler
 from ..exceptions import WebsocketAuthenticationRequired, InvalidAuthenticationCredentials, EventNotSupported, \
-    OutdatedClientVersion
+    ZeroConnectionsError, OutdatedClientVersion
 
 from ...utils.json_encoder import JSONEncoder
 
@@ -85,6 +85,10 @@ class BfxWebsocketClient:
         return asyncio.run(self.start(connections))
 
     async def start(self, connections = 5):
+        if connections == 0:
+            self.logger.info("With connections set to 0 it will not be possible to subscribe to any public channel. " \
+                    "Attempting a subscription will cause a ZeroConnectionsError to be thrown.")
+
         if connections > BfxWebsocketClient.MAXIMUM_CONNECTIONS_AMOUNT:
             self.logger.warning(f"It is not safe to use more than {BfxWebsocketClient.MAXIMUM_CONNECTIONS_AMOUNT} " \
                     f"buckets from the same connection ({connections} in use), the server could momentarily " \
@@ -121,7 +125,8 @@ class BfxWebsocketClient:
 
                 self.websocket, self.authentication = websocket, False
 
-                if await asyncio.gather(*[on_open_event.wait() for on_open_event in self.on_open_events]):
+                if len(self.on_open_events) == 0 or \
+                        (await asyncio.gather(*[on_open_event.wait() for on_open_event in self.on_open_events])):
                     self.event_emitter.emit("open")
 
                 if self.credentials:
@@ -202,6 +207,9 @@ class BfxWebsocketClient:
         await self.websocket.send(json.dumps(data))
 
     async def subscribe(self, channel, **kwargs):
+        if len(self.buckets) == 0:
+            raise ZeroConnectionsError("Unable to subscribe: the number of connections must be greater than 0.")
+
         counters = [ len(bucket.pendings) + len(bucket.subscriptions) for bucket in self.buckets ]
 
         index = counters.index(min(counters))

bfxapi/websocket/exceptions.py

@@ -5,9 +5,11 @@ __all__ = [
 
     "ConnectionNotOpen",
     "TooManySubscriptions",
+    "ZeroConnectionsError",
     "WebsocketAuthenticationRequired",
     "InvalidAuthenticationCredentials",
     "EventNotSupported",
+    "HandlerNotFound",
     "OutdatedClientVersion"
 ]
 
@@ -26,29 +28,33 @@ class TooManySubscriptions(BfxWebsocketException):
     This error indicates a subscription attempt after reaching the limit of simultaneous connections.
     """
 
+class ZeroConnectionsError(BfxWebsocketException):
+    """
+    This error indicates an attempt to subscribe to a public channel while the number of connections is 0.
+    """
+
 class WebsocketAuthenticationRequired(BfxWebsocketException):
     """
     This error indicates an attempt to access a protected resource without logging in first.
     """
 
+class InvalidAuthenticationCredentials(BfxWebsocketException):
+    """
+    This error indicates that the user has provided incorrect credentials (API-KEY and API-SECRET) for authentication.
+    """
+
 class EventNotSupported(BfxWebsocketException):
     """
     This error indicates a failed attempt to subscribe to an event not supported by the BfxWebsocketClient.
     """
 
-class OutdatedClientVersion(BfxWebsocketException):
-    """
-    This error indicates a mismatch between the client version and the server WSS version.
-    """
-
-
-class InvalidAuthenticationCredentials(BfxWebsocketException):
-    """
-    This error indicates that the user has provided incorrect credentials (API-KEY and API-SECRET) for authentication.
-    """
-
 
 class HandlerNotFound(BfxWebsocketException):
     """
     This error indicates that a handler was not found for an incoming message.
     """
+
+class OutdatedClientVersion(BfxWebsocketException):
+    """
+    This error indicates a mismatch between the client version and the server WSS version.
+    """