JSON-RPC: retrieve events via long polling

This way is more compatible to JSON-RPC libraries
that do not support receiving notifications from the server
and allows describing event types in the OpenRPC specification.

Event thread converting events to notifications in the FFI
is removed, so it is now possible to construct a dc_jsonrpc_instance_t
while still retrieving events via dc_event_emitter_t.

deltachat-rpc-client/src/deltachat_rpc_client/rpc.py

@@ -23,7 +23,9 @@ class Rpc:
         self.event_queues: Dict[int, asyncio.Queue]
         # Map from request ID to `asyncio.Future` returning the response.
         self.request_events: Dict[int, asyncio.Future]
+        self.closing: bool
         self.reader_task: asyncio.Task
+        self.events_task: asyncio.Task
 
     async def start(self) -> None:
         self.process = await asyncio.create_subprocess_exec(
@@ -35,10 +37,15 @@ class Rpc:
         self.id = 0
         self.event_queues = {}
         self.request_events = {}
+        self.closing = False
         self.reader_task = asyncio.create_task(self.reader_loop())
+        self.events_task = asyncio.create_task(self.events_loop())
 
     async def close(self) -> None:
         """Terminate RPC server process and wait until the reader loop finishes."""
+        self.closing = True
+        await self.stop_io_for_all_accounts()
+        await self.events_task
         self.process.terminate()
         await self.reader_task
 
@@ -58,21 +65,28 @@ class Rpc:
             if "id" in response:
                 fut = self.request_events.pop(response["id"])
                 fut.set_result(response)
-            elif response["method"] == "event":
-                # An event notification.
-                params = response["params"]
-                account_id = params["contextId"]
-                if account_id not in self.event_queues:
-                    self.event_queues[account_id] = asyncio.Queue()
-                await self.event_queues[account_id].put(params["event"])
             else:
                 print(response)
 
+    async def get_queue(self, account_id: int) -> asyncio.Queue:
+        if account_id not in self.event_queues:
+            self.event_queues[account_id] = asyncio.Queue()
+        return self.event_queues[account_id]
+
+    async def events_loop(self) -> None:
+        """Requests new events and distributes them between queues."""
+        while True:
+            if self.closing:
+                return
+            event = await self.get_next_event()
+            account_id = event["context_id"]
+            queue = await self.get_queue(account_id)
+            await queue.put(event["event"])
+
     async def wait_for_event(self, account_id: int) -> Optional[dict]:
         """Waits for the next event from the given account and returns it."""
-        if account_id in self.event_queues:
-            return await self.event_queues[account_id].get()
-        return None
+        queue = await self.get_queue(account_id)
+        return await queue.get()
 
     def __getattr__(self, attr: str):
         async def method(*args, **kwargs) -> Any: