feat(db/rooms): disable banning for last user and conduit user in admins room

src/service/rooms/timeline/mod.rs

@@ -733,6 +733,32 @@ impl Service {
                             ));
                         }
                     }
+
+                    if content.membership == MembershipState::Ban && pdu.state_key().is_some() {
+                        let server_user = format!("@conduit:{}", services().globals.server_name());
+                        if pdu.state_key().as_ref().unwrap() == &server_user {
+                            warn!("Conduit user cannot be banned in admins room");
+                            return Err(Error::BadRequest(
+                                ErrorKind::Forbidden,
+                                "Conduit user cannot be banned in admins room.",
+                            ));
+                        }
+
+                        let count = services()
+                            .rooms
+                            .state_cache
+                            .room_members(room_id)
+                            .filter_map(|m| m.ok())
+                            .filter(|m| m.server_name() == services().globals.server_name())
+                            .count();
+                        if count < 3 {
+                            warn!("Last admin cannot be banned in admins room");
+                            return Err(Error::BadRequest(
+                                ErrorKind::Forbidden,
+                                "Last admin cannot be banned in admins room.",
+                            ));
+                        }
+                    }
                 }
                 _ => {}
             }