Allow overriding the server_notices user's avatar

probably should have done this in the first place, like @turt2live suggested.

docs/server_notices.md

@@ -44,13 +44,16 @@ section, which should look like this:
 server_notices:
    system_mxid_localpart: server
    system_mxid_display_name: "Server Notices"
+   system_mxid_avatar_url: "mxc://server.com/oumMVlgDnLYFaPVkExemNVVZ"
    room_name: "Server Notices"
 ```
 
 The only compulsory setting is `system_mxid_localpart`, which defines the user
-id of the server notices user, as above. `system_mxid_display_name` and
-`room_name` define the displayname of the system notices user, and of
-the notices room, respectively.
+id of the Server Notices user, as above. `room_name` defines the name of the
+room which will be created.
+
+`system_mxid_display_name` and `system_mxid_avatar_url` can be used to set the
+displayname and avatar of the Server Notices user.
 
 Sending notices
 ---------------

synapse/config/server_notices_config.py

@@ -26,12 +26,13 @@ DEFAULT_CONFIG = """\
 # setting, which defines the id of the user which will be used to send the
 # notices.
 #
-# It's also possible to override the room name, or the display name of the
-# "notices" user.
+# It's also possible to override the room name, the display name of the
+# "notices" user, and the avatar for the user.
 #
 # server_notices:
 #   system_mxid_localpart: notices
 #   system_mxid_display_name: "Server Notices"
+#   system_mxid_avatar_url: "mxc://server.com/oumMVlgDnLYFaPVkExemNVVZ"
 #   room_name: "Server Notices"
 """
 
@@ -48,6 +49,10 @@ class ServerNoticesConfig(Config):
             The display name to use for the server notices user.
             None if server notices are not enabled.
 
+        server_notices_mxid_avatar_url (str|None):
+            The display name to use for the server notices user.
+            None if server notices are not enabled.
+
         server_notices_room_name (str|None):
             The name to use for the server notices room.
             None if server notices are not enabled.
@@ -56,6 +61,7 @@ class ServerNoticesConfig(Config):
         super(ServerNoticesConfig, self).__init__()
         self.server_notices_mxid = None
         self.server_notices_mxid_display_name = None
+        self.server_notices_mxid_avatar_url = None
         self.server_notices_room_name = None
 
     def read_config(self, config):
@@ -68,7 +74,10 @@ class ServerNoticesConfig(Config):
             mxid_localpart, self.server_name,
         ).to_string()
         self.server_notices_mxid_display_name = c.get(
-            'system_mxid_display_name', 'Server Notices',
+            'system_mxid_display_name', None,
+        )
+        self.server_notices_mxid_avatar_url = c.get(
+            'system_mxid_avatar_url', None,
         )
         # todo: i18n
         self.server_notices_room_name = c.get('room_name', "Server Notices")

synapse/server_notices/server_notices_manager.py

@@ -113,6 +113,19 @@ class ServerNoticesManager(object):
         # apparently no existing notice room: create a new one
         logger.info("Creating server notices room for %s", user_id)
 
+        # see if we want to override the profile info for the server user.
+        # note that if we want to override either the display name or the
+        # avatar, we have to use both.
+        join_profile = None
+        if (
+            self._config.server_notices_mxid_display_name is not None or
+            self._config.server_notices_mxid_avatar_url is not None
+        ):
+            join_profile = {
+                "displayname": self._config.server_notices_mxid_display_name,
+                "avatar_url": self._config.server_notices_mxid_avatar_url,
+            }
+
         requester = create_requester(system_mxid)
         info = yield self._room_creation_handler.create_room(
             requester,
@@ -125,9 +138,7 @@ class ServerNoticesManager(object):
                 "invite": (user_id,)
             },
             ratelimit=False,
-            creator_join_profile={
-                "displayname": self._config.server_notices_mxid_display_name,
-            },
+            creator_join_profile=join_profile,
         )
         room_id = info['room_id']