Use a safer implementation of gsub in core.chat_format_message (#9133)

This search-and-replace implementation does not use Lua pattern-matching

diff --git a/builtin/game/chat.lua b/builtin/game/chat.lua
index 37d12c458e9dbcbd5b4749535e39eaeb52b49993..291e72b7033726d10ff3beb05f2e4cb4fedd3c21 100644 (file)
--- a/builtin/game/chat.lua
+++ b/builtin/game/chat.lua
@@ -1,27 +1,41 @@
 -- Minetest: builtin/game/chat.lua
 
+-- Helper function that implements search and replace without pattern matching
+-- Returns the string and a boolean indicating whether or not the string was modified
+local function safe_gsub(s, replace, with)
+       local i1, i2 = s:find(replace, 1, true)
+       if not i1 then
+               return s, false
+       end
+
+       return s:sub(1, i1 - 1) .. with .. s:sub(i2 + 1), true
+end
+
 --
 -- Chat message formatter
 --
 
 -- Implemented in Lua to allow redefinition
 function core.format_chat_message(name, message)
-       local str = core.settings:get("chat_message_format")
        local error_str = "Invalid chat message format - missing %s"
-       local i
+       local str = core.settings:get("chat_message_format")
+       local replaced
 
-       str, i = str:gsub("@name", name, 1)
-       if i == 0 then
+       -- Name
+       str, replaced = safe_gsub(str, "@name", name)
+       if not replaced then
                error(error_str:format("@name"), 2)
        end
 
-       str, i = str:gsub("@message", message, 1)
-       if i == 0 then
+       -- Timestamp
+       str = safe_gsub(str, "@timestamp", os.date("%H:%M:%S", os.time()))
+
+       -- Insert the message into the string only after finishing all other processing
+       str, replaced = safe_gsub(str, "@message", message)
+       if not replaced then
                error(error_str:format("@message"), 2)
        end
 
-       str = str:gsub("@timestamp", os.date("%H:%M:%S", os.time()), 1)
-
        return str
 end