Execute players for illegal dimension hopping

mods/CORE/mcl_worlds/init.lua

@@ -113,7 +113,7 @@ local last_dimension = {}
 -- * dimension: New dimension ("overworld", "nether", "end", "void")
 function mcl_worlds.dimension_change(player, dimension)
 	for i=1, #mcl_worlds.registered_on_dimension_change do
-		mcl_worlds.registered_on_dimension_change[i](player, dimension)
+		mcl_worlds.registered_on_dimension_change[i](player, dimension, last_dimension[player:get_player_name()])
 		last_dimension[player:get_player_name()] = dimension
 	end
 end

mods/MISC/mcl_anti_dimension_hopping/init.lua

@@ -0,0 +1,196 @@
+local S = minetest.get_translator("mcl_anti_dimension_hopping")
+
+local storage = minetest.get_mod_storage()
+
+local MAX_DISTANCE = 40
+
+local dimension_change_is_legal = function(
+	player_name,		-- string
+	dimension,		-- "end"|"nether"|"overworld"|"void"
+	last_dimension,		-- "end"|"nether"|"overworld"|"void"
+	last_last_dimension	-- "end"|"nether"|"overworld"|"void"|nil
+)
+	local player = minetest.get_player_by_name(player_name)
+	if nil == player then
+		return false
+	end
+	local player_position = player:get_pos()
+	if "end" == dimension then
+		assert( player_position.y > mcl_vars.mg_end_min )
+		assert( player_position.y < mcl_vars.mg_end_max )
+		-- Going to the End through a portal is allowed, but a
+		-- player must appear at End spawn for it to be legal.
+		-- The Nether as the last dimension is included here
+		-- because an End portal in the nether sends players
+		-- to End spawn, but cheaters can not teleport down
+		-- from the Nether, as the Nether is below the End.
+		if (
+			"overworld" == last_dimension or
+			   "nether" == last_dimension
+		) then
+			if vector.distance(
+				player_position,
+				mcl_vars.mg_end_platform_pos
+			) < MAX_DISTANCE then
+				return true
+			end
+		end
+		-- Going to the End via the Void is allowed only if
+		-- the player entered the Void from the End … nil has
+		-- to be handled here for players who were in the Void
+		-- when this mod was activated.
+		if "void" == last_dimension then
+			if (
+				"end" == last_last_dimension or
+				  nil == last_last_dimension
+			) then
+				return true
+			end
+		end
+	end
+	if "nether" == dimension then
+		assert( player_position.y > mcl_vars.mg_nether_min )
+		assert( player_position.y < mcl_vars.mg_nether_max )
+		-- Going to the Nether through a portal is allowed.
+		if "overworld" == last_dimension then
+			if nil ~= minetest.find_node_near(
+				player_position,
+				MAX_DISTANCE,
+				"mcl_portals:portal"
+			) then
+				-- TODO: check for portal in Overworld
+				return true
+			end
+		end
+		-- Going to the Nether via the Void is allowed only if
+		-- the player entered the Void from the Nether … nil
+		-- has to be handled here for players who were in the
+		-- Void when this mod was activated.
+		if "void" == last_dimension then
+			if (
+				"nether" == last_last_dimension or
+				     nil == last_last_dimension
+			) then
+				return true
+			end
+		end
+	end
+	if "overworld" == dimension then
+		assert( player_position.y > mcl_vars.mg_overworld_min )
+		assert( player_position.y < mcl_vars.mg_overworld_max )
+		-- Going to the Overworld from the Nether through a
+		-- portal is allowed.
+		if "nether" == last_dimension then
+			if nil ~= minetest.find_node_near(
+				player_position,
+				MAX_DISTANCE,
+				"mcl_portals:portal"
+			) then
+				-- TODO: check for portal in Nether
+				return true
+			end
+			return true
+		end
+		-- Going to the Overworld via the Void is allowed only
+		-- if the player entered the Void from the Overworld …
+		-- nil has to be handled here for players who were in
+		-- the Void when this mod was activated.
+		if "void" == last_dimension then
+			if (
+				"overworld" == last_last_dimension or
+				        nil == last_last_dimension
+			) then
+				return true
+			end
+		end
+		-- Going to the Overworld via the End (or any other
+		-- way) is allowed only if the player appears at their
+		-- respawn location, either because they used a portal
+		-- in the End or because they died.
+		local player_spawn_position = (
+			mcl_spawn.get_player_spawn_pos(player) or
+			mcl_spawn.get_world_spawn_pos(player)
+		)
+		if vector.distance(
+			player_position,
+			player_spawn_position
+		) < MAX_DISTANCE then
+			return true
+		end
+	end
+	if "void" == dimension then
+		-- Going to the Void is always legal – a player who
+		-- enters the Void and then goes anywhere else than
+		-- where they came from is already handled above.
+		return true
+	end
+	return false
+end
+
+local kill_player_for_dimensional_trespassing = function(
+	player_name,
+	dimension,
+	last_dimension,
+	last_last_dimension
+)
+	local player = minetest.get_player_by_name(player_name)
+	if nil == player then
+		return
+	end
+	-- If the player holds a totem of undying, destroy it before
+	-- killing, so it doesn't rescue the player.
+	local wield = player:get_wielded_item()
+	if wield:get_name() == "mobs_mc:totem" then
+		player:set_wielded_item("")
+	end
+	local death_message = S(
+		"@1 was executed for dimensional trespassing.",
+		player_name
+	)
+	mcl_death_messages.player_damage(
+		player,
+		death_message
+	)
+	player:set_hp(0)
+	local log_message = string.format(
+		"%s was executed for dimensional trespassing: %s → %s → %s",
+		tostring(player_name),
+		tostring(last_last_dimension),
+		tostring(last_dimension),
+		tostring(dimension)
+	)
+	minetest.log(
+		"action",
+		log_message
+	)
+end
+
+mcl_worlds.register_on_dimension_change(
+	function(player, dimension, last_dimension)
+		local player_name = player:get_player_name()
+		local last_last_dimension = storage:get_string(
+			player_name .. ":dimension_previous_previous"
+		)
+		if not dimension_change_is_legal(
+			player_name,
+			dimension,
+			last_dimension,
+			last_last_dimension
+		) then
+			kill_player_for_dimensional_trespassing(
+				player_name,
+				dimension,
+				last_dimension,
+				last_last_dimension
+			)
+		end
+		storage:set_string(
+			player_name .. ":dimension_previous_previous",
+			last_dimension
+		)
+		storage:set_string(
+			player_name .. ":dimension_previous",
+			dimension
+		)
+	end
+)

mods/MISC/mcl_anti_dimension_hopping/mod.conf

@@ -0,0 +1,2 @@
+name = mcl_anti_dimension_hopping
+depends = mcl_init, mcl_death_messages, mcl_portals, mcl_spawn, mcl_worlds