Asgi recv() on lambda should hang when there are no more events (#93)

This commit fixes a bug when running on AWS lambda. The asgi
wrapper, before this commit, did not 'hang' when there are no
more events to produce. With this commit when there are no more
events we return a pending future.

Author: igalshilman

python/restate/aws_lambda.py

@@ -87,16 +87,19 @@ def request_to_receive(req: RestateLambdaRequest) -> Receive:
         "type": "http.request",
         "body": body,
         "more_body": False
+    },
+    {
+        "type": "http.request",
+        "body": b'',
+        "more_body": False
     }])
 
     async def recv() -> HTTPRequestEvent:
         if len(events) != 0:
-            return events.pop()
-        return {
-            "type": "http.request",
-            "body": b'',
-            "more_body": False
-        }
+            return events.pop(0)
+        # If we are out of events, return a future that will never complete
+        f = asyncio.Future[HTTPRequestEvent]()
+        return await f
 
     return recv