Powerbot: limit size of power levels event in bytes, not count.

Guards against super long usernames or domain names.

diff --git a/misc/infrastructure/powerbot/powerlevels.go b/misc/infrastructure/powerbot/powerlevels.go
index c07855e8d0b51a1a2298f13b70c3292ddab7f4bd..e7838886ec1ae7370ac53cd97da0edc3b6bf9ab3 100644 (file)
--- a/misc/infrastructure/powerbot/powerlevels.go
+++ b/misc/infrastructure/powerbot/powerlevels.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+       "encoding/json"
        "github.com/google/go-cmp/cmp"
        "log"
        "math"
@@ -26,8 +27,8 @@ const (
        maxApplyLevel = 9
        // Expire power level if no event for 1 month. Level comes back on next event, including join.
        powerExpireTime = time.Hour * 24 * 30
-       // Maximum count of ACL entries. Should avoid hitting the 64k limit.
-       maxPowerLevelEntries = 2048
+       // Maximum size of powerlevels message. This is a quarter of the expected Matrix limit.
+       maxPowerLevelBytes = (65535 - 1024) / 4
 )
 
 func logPowerLevelBounds() {
@@ -105,7 +106,7 @@ func syncPowerLevels(client *mautrix.Client, room id.RoomID, roomGroup []Room, s
                        }
                }
        }
-       newRoomLevels := *roomLevels
+       newRoomLevels := makeDefaultsExplicit(roomLevels)
        newRoomLevels.Users = make(map[id.UserID]int)
        for user, level := range roomLevels.Users {
                if level == roomLevels.UsersDefault {
@@ -161,7 +162,15 @@ func syncPowerLevels(client *mautrix.Client, room id.RoomID, roomGroup []Room, s
                }
        }
        clearPowerLevel := minPowerLevel
-       for len(newRoomLevels.Users) > maxPowerLevelEntries && clearPowerLevel <= maxPowerLevel {
+       for clearPowerLevel <= maxPowerLevel {
+               j, err := json.Marshal(newRoomLevels)
+               if err != nil {
+                       log.Printf("could not marshal newRoomLevels: %v", err)
+                       break
+               }
+               if len(j) <= maxPowerLevelBytes {
+                       continue
+               }
                log.Printf("room %v not including power level %d to reduce message size", clearPowerLevel)
                for user, level := range newRoomLevels.Users {
                        if level == clearPowerLevel {
@@ -174,7 +183,7 @@ func syncPowerLevels(client *mautrix.Client, room id.RoomID, roomGroup []Room, s
        if dirty {
                diff := cmp.Diff(roomLevels.Users, newRoomLevels.Users)
                log.Printf("room %v power level update:\n%v", room, diff)
-               _, err := client.SendStateEvent(room, event.StatePowerLevels, "", makeDefaultsExplicit(&newRoomLevels))
+               _, err := client.SendStateEvent(room, event.StatePowerLevels, "", newRoomLevels)
                if err != nil {
                        log.Printf("Failed to update power levels: %v", err)
                }