daemon: Ask the homeserver about unknown access tokens.

This patch changes the way clients register to pantalaimon. If there is
already a pan client running for a given user ID clients can now avoid
logging in.

Pantalaimon checks with the homeserver if the access token
is valid and for a user that we already have a pan client running.

This also removes the need to remember access tokens that don't belong
to a pan client.

This partially fixes #14.

pantalaimon/daemon.py

@@ -12,7 +12,8 @@ import keyring
 from aiohttp import ClientSession, web
 from aiohttp.client_exceptions import ClientConnectionError, ContentTypeError
 from multidict import CIMultiDict
-from nio import EncryptionError, LoginResponse, SendRetryError, OlmTrustError
+from nio import (EncryptionError, LoginResponse, SendRetryError, OlmTrustError,
+                 Api)
 
 from pantalaimon.client import PanClient
 from pantalaimon.log import logger
@@ -61,8 +62,6 @@ class ProxyDaemon:
         self.store = PanStore(self.data_dir)
         accounts = self.store.load_users(self.name)
 
-        self.client_info = self.store.load_clients(self.name)
-
         for user_id, device_id in accounts:
             token = keyring.get_password(
                 "pantalaimon",
@@ -92,6 +91,50 @@ class ProxyDaemon:
 
             pan_client.start_loop()
 
+    async def _find_client(self, access_token):
+        client_info = self.client_info.get(access_token, None)
+
+        if not client_info:
+            async with aiohttp.ClientSession() as session:
+                try:
+                    method, path = Api.whoami(access_token)
+                    resp = await session.request(
+                        method,
+                        self.homeserver_url + path,
+                        proxy=self.proxy,
+                        ssl=self.ssl
+                    )
+                except ClientConnectionError:
+                    return None
+
+                if resp.status != 200:
+                    return None
+
+                try:
+                    body = await resp.json()
+                except (JSONDecodeError, ContentTypeError):
+                    return None
+
+                try:
+                    user_id = body["user_id"]
+                except KeyError:
+                    return None
+
+                if user_id not in self.pan_clients:
+                    logger.warn(f"User {user_id} doesn't have a matching pan "
+                                f"client.")
+                    return None
+
+                logger.info(f"Homeserver confirmed valid access token "
+                            f"for user {user_id}, caching info.")
+
+                client_info = ClientInfo(user_id, access_token)
+                self.client_info[access_token] = client_info
+
+        client = self.pan_clients.get(client_info.user_id, None)
+
+        return client
+
     async def _verify_device(self, message_id, client, device):
         ret = client.verify_device(device)
 
@@ -424,7 +467,6 @@ class ProxyDaemon:
     async def start_pan_client(self, access_token, user, user_id, password):
         client = ClientInfo(user_id, access_token)
         self.client_info[access_token] = client
-        self.store.save_client(self.name, client)
         self.store.save_server_user(self.name, user_id)
 
         if user_id in self.pan_clients:
@@ -578,10 +620,8 @@ class ProxyDaemon:
         if not access_token:
             return self._missing_token
 
-        try:
-            client_info = self.client_info[access_token]
-            client = self.pan_clients[client_info.user_id]
-        except KeyError:
+        client = await self._find_client(access_token)
+        if not client:
             return self._unknown_token
 
         sync_filter = request.query.get("filter", None)
@@ -631,10 +671,8 @@ class ProxyDaemon:
         if not access_token:
             return self._missing_token
 
-        try:
-            client_info = self.client_info[access_token]
-            client = self.pan_clients[client_info.user_id]
-        except KeyError:
+        client = await self._find_client(access_token)
+        if not client:
             return self._unknown_token
 
         try:
@@ -670,10 +708,8 @@ class ProxyDaemon:
         if not access_token:
             return self._missing_token
 
-        try:
-            client_info = self.client_info[access_token]
-            client = self.pan_clients[client_info.user_id]
-        except KeyError:
+        client = await self._find_client(access_token)
+        if not client:
             return self._unknown_token
 
         room_id = request.match_info["room_id"]