Backend._any_clients(): only pick a healthy client

When selecting a random client for get_profile(), thumbnail(), or
download() requests, ignore those that aren't currently syncing.
Also warn if we still can't find a healthy client after 30s.

src/python/backend.py

@@ -1,7 +1,7 @@
 import asyncio
 import logging as log
 from pathlib import Path
-from typing import Any, DefaultDict, Dict, List, Optional, Tuple
+from typing import Any, Callable, DefaultDict, Dict, List, Optional, Tuple
 
 import hsluv
 
@@ -82,10 +82,11 @@ class Backend:
             backend=self,
             user=user_id, homeserver=homeserver, device_id=device_id,
         )
-        await client.resume(user_id=user_id, token=token, device_id=device_id)
 
-        self.clients[client.user_id]         = client
-        self.models[Account][client.user_id] = Account(client.user_id)
+        self.clients[user_id]         = client
+        self.models[Account][user_id] = Account(user_id)
+
+        await client.resume(user_id=user_id, token=token, device_id=device_id)
 
 
     async def load_saved_accounts(self) -> Tuple[str, ...]:
@@ -169,14 +170,22 @@ class Backend:
 
     # Client functions that don't need authentification
 
-    async def _any_client(self, prefer: str = "") -> MatrixClient:
-        while True:
-            if self.clients:
-                break
-            await asyncio.sleep(0.1)
+    async def _any_client(self, caller: Callable, *args, **kw) -> MatrixClient:
+        failures = 0
 
-        return self.clients.get(prefer) or \
-               next(c for c in self.clients.values())
+        while True:
+            for client in self.clients.values():
+                if client.syncing:
+                    return client
+
+            await asyncio.sleep(0.1)
+            failures += 1
+
+            if failures and failures % 300 == 0:
+                log.warn(
+                    "No syncing client found after %ds of wait for %s %r %r",
+                    failures / 10, caller.__name__, args, kw,
+                )
 
 
     async def get_profile(self, user_id: str) -> nio.ProfileGetResponse:
@@ -184,7 +193,7 @@ class Backend:
             return self.profile_cache[user_id]
 
         async with self.get_profile_locks[user_id]:
-            client   = await self._any_client(prefer=user_id)
+            client   = await self._any_client(self.get_profile, user_id)
             response = await client.get_profile(user_id)
 
             if isinstance(response, nio.ProfileGetError):
@@ -198,8 +207,9 @@ class Backend:
         self, server_name: str, media_id: str, width: int, height: int,
     ) -> nio.ThumbnailResponse:
 
-        client   = await self._any_client()
-        response = await client.thumbnail(server_name, media_id, width, height)
+        args     = (server_name, media_id, width, height)
+        client   = await self._any_client(self.thumbnail, *args)
+        response = await client.thumbnail(*args)
 
         if isinstance(response, nio.ThumbnailError):
             raise MatrixError.from_nio(response)
@@ -211,7 +221,7 @@ class Backend:
         self, server_name: str, media_id: str,
     ) -> nio.DownloadResponse:
 
-        client   = await self._any_client()
+        client   = await self._any_client(self.download, server_name, media_id)
         response = await client.download(server_name, media_id)
 
         if isinstance(response, nio.DownloadError):

src/python/matrix_client.py

@@ -134,9 +134,8 @@ class MatrixClient(nio.AsyncClient):
 
 
     async def resume(self, user_id: str, token: str, device_id: str) -> None:
-        self.user_id      = user_id
-        self.access_token = token
-        self.device_id    = device_id
+        response = nio.LoginResponse(user_id, device_id, token)
+        await self.receive_response(response)
 
         asyncio.ensure_future(self.start())
 
@@ -152,6 +151,14 @@ class MatrixClient(nio.AsyncClient):
         await self.close()
 
 
+    @property
+    def syncing(self) -> bool:
+        if not self.sync_task:
+            return False
+
+        return not self.sync_task.done()
+
+
     async def start(self) -> None:
         def on_profile_response(future) -> None:
             exception = future.exception()