secure request for lua-utf8 library

init.lua

@@ -28,7 +28,13 @@
 local S = minetest.get_translator("filter")
 
 filter = { registered_on_violations = {} }
-local utf8 = require 'lua-utf8'
+local ie = core.request_insecure_environment()
+local str = nil
+if ie then
+    str = ie.require("lua-utf8")
+else
+    str = string
+end
 local words = {}
 local muted = {}
 local violations = {}
@@ -66,7 +72,7 @@ end
 
 function filter.check_message(name, message)
 	for _, w in ipairs(words) do
-		if utf8.find(utf8.lower(message), "%f[%a]" .. w .. "%f[%A]") then
+		if str.find(str.lower(message), "%f[%a]" .. w .. "%f[%A]") then
 			return false
 		end
 	end

readme.md

@@ -13,6 +13,8 @@ muted for 1 minute. After that, their `shout` privilege is restored.
 If they leave, their `shout` privilege is still restored, but only after
 the time expires, not before.
 
+Add this mod to `secure.trusted_mods` to allow filtering utf8 lines.
+
 ## API
 
 ### Callbacks