feat(websocket): expose heartbeat events with improved implementation

Exposes WebSocket heartbeat events to allow users to monitor connection health
for both public and authenticated channels.

Changes:
- Add 'heartbeat' event to BfxEventEmitter as a valid event type
- Emit heartbeat events in WebSocket client and bucket instead of silently discarding
- Consistent handler signature: receives Optional[Subscription] parameter
  - Public channels: subscription details
  - Authenticated (channel 0): None
- Add comprehensive example with proper type hints and error handling
- Update README with clear documentation and usage examples

The handler signature is consistent across all subscription-based events,
always passing the subscription as first parameter (None for authenticated).

Lines of code: +101 insertions, -4 deletions (+97 net)

Author: 0xferit

README.md

@@ -238,6 +238,33 @@ The same can be done without using decorators:
 bfx.wss.on("candles_update", callback=on_candles_update)
 ```
 
+### Heartbeat events
+
+The WebSocket server sends periodic heartbeat messages to keep connections alive. 
+These are now exposed as `heartbeat` events that you can listen to:
+
+```python
+from typing import Optional
+from bfxapi.websocket.subscriptions import Subscription
+
+@bfx.wss.on("heartbeat")
+def on_heartbeat(subscription: Optional[Subscription]) -> None:
+    if subscription:
+        # Heartbeat for a specific subscription (public channels)
+        channel = subscription["channel"]
+        symbol = subscription.get("symbol", "N/A")
+        print(f"Heartbeat for {channel}: {symbol}")
+    else:
+        # Heartbeat for authenticated connection (channel 0)
+        print("Heartbeat on authenticated connection")
+```
+
+**Note:** The heartbeat handler receives:
+- `subscription` parameter containing subscription details for public channel heartbeats
+- `None` for authenticated connection heartbeats (channel 0)
+
+---
+
 # Advanced features
 
 ## Using custom notifications

bfxapi/websocket/_client/bfx_websocket_bucket.py

@@ -66,9 +66,11 @@ async def start(self) -> None:
                     if (
                         (chan_id := cast(int, message[0]))
                         and (subscription := self.__subscriptions.get(chan_id))
-                        and (message[1] != Connection._HEARTBEAT)
                     ):
-                        self.__handler.handle(subscription, message[1:])
+                        if message[1] == Connection._HEARTBEAT:
+                            self.__event_emitter.emit("heartbeat", subscription)
+                        else:
+                            self.__handler.handle(subscription, message[1:])
 
     def __on_subscribed(self, message: Dict[str, Any]) -> None:
         chan_id = cast(int, message["chan_id"])

bfxapi/websocket/_client/bfx_websocket_client.py

@@ -266,9 +266,11 @@ async def __connect(self) -> None:
                 if (
                     isinstance(message, list)
                     and message[0] == 0
-                    and message[1] != Connection._HEARTBEAT
                 ):
-                    self.__handler.handle(message[1], message[2])
+                    if message[1] == Connection._HEARTBEAT:
+                        self.__event_emitter.emit("heartbeat", None)
+                    else:
+                        self.__handler.handle(message[1], message[2])
 
     async def __new_bucket(self) -> BfxWebSocketBucket:
         bucket = BfxWebSocketBucket(self._host, self.__event_emitter)

bfxapi/websocket/_event_emitter/bfx_event_emitter.py

@@ -32,6 +32,7 @@
 
 _COMMON = [
     "disconnected",
+    "heartbeat",
     "t_ticker_update",
     "f_ticker_update",
     "t_trade_execution",

examples/websocket/heartbeat.py

@@ -0,0 +1,65 @@
+"""
+Demonstrates heartbeat event handling for both public and authenticated WebSocket connections.
+
+Usage:
+    python examples/websocket/heartbeat.py
+
+If BFX_API_KEY and BFX_API_SECRET environment variables are set, the client will
+authenticate and display heartbeats on the authenticated connection (channel 0).
+Otherwise, only public channel heartbeats are shown.
+"""
+
+import os
+from typing import Any, Dict, Optional
+
+from bfxapi import Client
+from bfxapi.websocket.subscriptions import Subscription
+
+
+# Initialize client with optional authentication
+api_key = os.getenv("BFX_API_KEY")
+api_secret = os.getenv("BFX_API_SECRET")
+
+if api_key and api_secret:
+    print("Initializing authenticated client...")
+    bfx = Client(api_key=api_key, api_secret=api_secret)
+else:
+    print("Initializing public client (set BFX_API_KEY and BFX_API_SECRET for auth)...")
+    bfx = Client()
+
+
+@bfx.wss.on("heartbeat")
+def on_heartbeat(subscription: Optional[Subscription]) -> None:
+    """Handle heartbeat events from both public and authenticated channels."""
+    if subscription:
+        channel = subscription["channel"]
+        label = subscription.get("symbol", subscription.get("key", "unknown"))
+        print(f"Heartbeat for {channel}: {label}")
+    else:
+        print("Heartbeat on authenticated connection (channel 0)")
+
+
+@bfx.wss.on("authenticated")
+async def on_authenticated(event: Dict[str, Any]) -> None:
+    """Handle authentication confirmation."""
+    user_id = event.get("userId", "unknown")
+    print(f"Successfully authenticated with userId: {user_id}")
+
+
+@bfx.wss.on("open")
+async def on_open() -> None:
+    """Subscribe to public channels when connection opens."""
+    print("WebSocket connection opened")
+    # Subscribe to a public channel to observe subscription heartbeats
+    await bfx.wss.subscribe("ticker", symbol="tBTCUSD")
+    print("Subscribed to ticker channel for tBTCUSD")
+
+
+if __name__ == "__main__":
+    print("Starting WebSocket client... Press Ctrl+C to stop.")
+    try:
+        bfx.wss.run()
+    except KeyboardInterrupt:
+        print("\nShutting down gracefully...")
+    except Exception as e:
+        print(f"Error: {e}")