Server crashes if generated chat message is too long

[gpcf]

Minetest version

Minetest 5.2.0-dev-03e1f23a (Linux)

OS / Hardware

Operating system: Debian 10 CPU: Intel(R) Xeon(R) Gold 6140 CPU @ 2.30GHz

Summary

Server crashes if a generated chat message is too long with the following output:

2020-01-19 21:22:47: ERROR[Main]: ServerError: AsyncErr: ServerThread::run Lua: Runtime error from mod '' in callback on_chat_message(): String too long
2020-01-19 21:22:47: ERROR[Main]: stack traceback:
2020-01-19 21:22:47: ERROR[Main]:       [C]: in function 'chat_send_player'
2020-01-19 21:22:47: ERROR[Main]:       /usr/share/games/minetest/builtin/game/chat.lua:71: in function </usr/share/games/minetest/builtin/game/chat.lua:48>
2020-01-19 21:22:47: ERROR[Main]:       /usr/share/games/minetest/builtin/game/register.lua:429: in function </usr/share/games/minetest/builtin/game/register.lua:413>

In this case, it was caused by /list_areas from the areas mod, on a server with 10k+ areas. Given the number of mods that might take user input, this could be a serious security risk.

Steps to reproduce

call minetest.chat_send_player with an extremely long chat message.

[sfan5]

Should probably raise a warning + stack trace instead.

[ronoaldo]

I'm interested into contributing a fix for this issue. Would it make sense to split the chat message into multiple messages and send one by one, or it is wise to cap at the maximum byte size and log a warning?

[Zughy]

How about putting some ellipsis and log a warning? The limit is around 66 000 characters, that's definitely more than annoying already to see in chat. It should be up to the modder to split their output in pages, such as /list_areas 2, /list_areas 3 etc

[fluxionary]

in case anyone wants some lua code to patch their server to keep /profiler print from crashing their server, here's some:

local old_chat_send_player = minetest.chat_send_player

function minetest.chat_send_player(name, text)
	while #text > 65000 do
		local found_newline = false
		for i = 65000, 1, -1 do
			if text:sub(i, i) == "\n" then
				old_chat_send_player(name, text:sub(1, i - 1))
				text = text:sub(i + 1)
				found_newline = true
				break
			end
		end

		if not found_newline then
			old_chat_send_player(name, text:sub(1, 65000))
			text = text:sub(65000 + 1)
		end
	end

	old_chat_send_player(name, text)
end