Implement batched messages for Digiline Chests

docs/chest.md

@@ -101,13 +101,24 @@ The message is sent when user takes `<stack>` from `<output slot>` in the chest.
 ```
 The message is sent when user puts `<stack>` to the chest to `<input slot>`
 
+----------------------------
+
+```
+{
+    action = "batch",
+    messages = <messages>
+}
+```
+The message contains an array of other messages (`<messages>`) which were emitted within a very short interval, and for this reason merged into a batch and sent as a single message. This is needed to prevent burning of connected Lua controllers in case of a large amount of messages within a very short time. This can happen in case of using the feature which allows to move all items of the same type between inventories at once by taking one of them, and clicking on another one while holding Shift. Another theoretical scenario - sending a lot of requests to the server associated with inventory operations on a Digiline chest using a hacked client or custom software. The decision whether to include a message into a batch is made based on the interval from the previous message. For this reason, a batch message is always preceded by a single message which wasn't included into the batch because there was enough time from the previous message, and we cannot know in advance when the next message will be sent to include the current one into the batch too. Only messages with the following actions can be included into a batch: "uput", "utake", "uswap", "umove", "empty", "full"; all the other messages are related to tube events. This restriction was added because, when we send a batch, the area might become unloaded, so we need to load it back, and the possibility to include messages of all types into a batch might make a possibility to create mechanisms which keep the area loaded by causing a large amount of events to a Digiline chest. Messages with actions "empty" and "full" are included into a batch only if the batch is already not empty. If the chest tries to send a message which cannot be batched while its current batch is not empty, the batch is sent immediately to preserve the original order of messages.
+
 ### Fields used within the messages
 
 | Field | Description |
 | ----- | ----------- |
 | `<stack>` | A table which contains data about the stack, and corresponds to the format returned by the :to_table() method of ItemStack (check the Minetest API documentation). |
 | `<input slot>`, `<output slot>`, `<slot1>`, `<slot2>` | The index of the corresponding slot starting from 1. |
 | `<side>` | A vector represented as a table of format `{ x = <x>, y = <y>, z = <z> }` which represent the direction from which the tube is connected to the chest. |
+| `<messages>` | An array of messages which are emitted by Digiline chest in the same format. |
 
 ## Additional information
 

inventory.lua

@@ -2,6 +2,65 @@ local S = digilines.S
 
 local pipeworks_enabled = minetest.get_modpath("pipeworks") ~= nil
 
+-- Messages which will be sent in a single batch
+--[[
+Table format:
+{
+	[node pos hash] = {
+		messages = { msg1, msg2, ... }
+		timer = <job table from core.after()>
+	},
+	...
+}
+]]
+local batches = {}
+-- Maximum interval from the previous message to include the current one into batch (in seconds)
+local interval_to_batch = 0.1
+-- Maximum number of messages in batch
+local max_messages_in_batch = 100
+-- Time of the last message for each chest
+local last_message_time_for_chest = {}
+
+-- Messages which can be included into batch
+local can_be_batched = {
+	["empty"] = true, ["full"] = true, ["umove"] = true,
+	["uswap"] = true, ["utake"] = true, ["uput"] = true
+}
+
+-- Messages which shouldn't be included into batch when the batch is empty
+local dont_batch_when_empty = { ["empty"] = true, ["full"] = true }
+
+-- Sends the current batch message of a Digiline chest
+-- pos: the position of the Digilines chest node
+-- channel: the channel to which the message will be sent
+local function send_and_clear_batch(pos, channel)
+	local pos_hash = minetest.hash_node_position(pos)
+	if #batches[pos_hash].messages == 1 then
+		-- If there is only one message is the batch, don't send it in a batch
+		digilines.receptor_send(pos, digilines.rules.default, channel,
+			batches[pos_hash].messages[1])
+	else
+		digilines.receptor_send(pos, digilines.rules.default, channel, {
+			action = "batch",
+			messages = batches[pos_hash].messages
+		})
+	end
+	batches[pos_hash] = nil
+	last_message_time_for_chest[pos_hash] = nil
+end
+
+-- Send all the batched messages on timer expiration for the chest if present
+local function send_batch_on_timer(pos)
+	if not batches[minetest.hash_node_position(pos)] then
+		return
+	end
+	if minetest.get_node(pos).name == "ignore" then
+		minetest.load_area(pos)
+	end
+	local channel = minetest.get_meta(pos):get_string("channel")
+	send_and_clear_batch(pos, channel)
+end
+
 -- Sends a message onto the Digilines network.
 -- pos: the position of the Digilines chest node.
 -- action: the action string indicating what happened.
@@ -11,6 +70,7 @@ local pipeworks_enabled = minetest.get_modpath("pipeworks") ~= nil
 -- side: which side of the chest the action occurred (optional).
 local function send_message(pos, action, stack, from_slot, to_slot, side)
 	local channel = minetest.get_meta(pos):get_string("channel")
+
 	local msg = {
 		action = action,
 		stack = stack and stack:to_table(),
@@ -19,6 +79,33 @@ local function send_message(pos, action, stack, from_slot, to_slot, side)
 		-- Duplicate the vector in case the caller expects it not to change.
 		side = side and vector.new(side)
 	}
+
+	-- Check if we need to include the current message into batch
+	local pos_hash = minetest.hash_node_position(pos)
+	if can_be_batched[msg.action] and (batches[pos_hash] or not dont_batch_when_empty[msg.action]) then
+		local prev_time = last_message_time_for_chest[pos_hash] or 0
+		local cur_time = minetest.get_us_time()
+		last_message_time_for_chest[pos_hash] = cur_time
+		if cur_time - prev_time < 1000000 * interval_to_batch or batches[pos_hash] then
+			batches[pos_hash] = batches[pos_hash] or { messages = {} }
+			table.insert(batches[pos_hash].messages, msg)
+			if #batches[pos_hash].messages >= max_messages_in_batch then
+				-- Send the batch immediately if it's full
+				send_and_clear_batch(pos, channel)
+			elseif not batches[pos_hash].timer then
+				batches[pos_hash].timer = minetest.after(interval_to_batch, send_batch_on_timer, pos)
+			end
+
+			return
+		end
+	else
+		-- If the current message cannot be batched, flush the current batch to preserve order
+		if batches[pos_hash] then
+			batches[pos_hash].timer:cancel()
+			send_and_clear_batch(pos, channel)
+		end
+	end
+
 	digilines.receptor_send(pos, digilines.rules.default, channel, msg)
 end
 
@@ -186,6 +273,16 @@ minetest.register_node("digilines:chest", {
 		local inv = meta:get_inventory()
 		inv:set_size("main", 8*4)
 	end,
+	on_destruct = function(pos)
+		local pos_hash = minetest.hash_node_position(pos)
+		if not batches[pos_hash] then
+			return
+		end
+
+		batches[pos_hash].timer:cancel()
+		local channel = minetest.get_meta(pos):get_string("channel")
+		send_and_clear_batch(pos, channel)
+	end,
 	after_place_node = tubescan,
 	after_dig_node = tubescan,
 	can_dig = function(pos)