Raise error if EventEmitter used with async callback (#312)

Author: bcherry

livekit-rtc/livekit/rtc/event_emitter.py

@@ -1,4 +1,5 @@
 import inspect
+import asyncio
 from typing import Callable, Dict, Set, Optional, Generic, TypeVar
 
 from .log import logger
@@ -156,6 +157,11 @@ def greet(name):
             ```
         """
         if callback is not None:
+            if asyncio.iscoroutinefunction(callback):
+                raise ValueError(
+                    "Cannot register an async callback with `.on()`. Use `asyncio.create_task` within your synchronous callback instead."
+                )
+
             if event not in self._events:
                 self._events[event] = set()
             self._events[event].add(callback)

livekit-rtc/tests/test_emitter.py

@@ -60,26 +60,27 @@ def on_whatever(first, second, third):
     emitter.emit("whatever", 1, 2, 3)
     emitter.emit("whatever", 1, 2, 3, 4, 5)  # only 3 arguments will be passed
 
-    assert len(calls) == 2
-    assert calls[0] == (1, 2, 3)
-    assert calls[1] == (1, 2, 3)
-
-    calls = []
+    assert calls == [(1, 2, 3), (1, 2, 3)]
 
     with pytest.raises(TypeError):
         emitter.emit("whatever", 1, 2)
 
-    assert len(calls) == 0
+
+def test_varargs():
+    EventTypes = Literal["whatever"]
+
+    emitter = EventEmitter[EventTypes]()
+
+    calls = []
 
     @emitter.on("whatever")
     def on_whatever_varargs(*args):
         calls.append(args)
 
     emitter.emit("whatever", 1, 2, 3, 4, 5)
+    emitter.emit("whatever", 1, 2)
 
-    assert len(calls) == 2
-    assert calls[0] == (1, 2, 3)
-    assert calls[1] == (1, 2, 3, 4, 5)
+    assert calls == [(1, 2, 3, 4, 5), (1, 2)]
 
 
 def test_throw():