chore: housekeeping

packages/charm-sync/src/server.luau

@@ -0,0 +1,252 @@
+local Players = game:GetService("Players")
+
+local Charm = require(script.Parent.Parent.Charm)
+local interval = require(script.Parent.interval)
+local patch = require(script.Parent.patch)
+local types = require(script.Parent.types)
+
+type AtomMap = types.AtomMap
+type SyncPayload = types.SyncPayload
+
+type ServerOptions = {
+	--- The atoms to synchronize with the client.
+	atoms: AtomMap,
+	--- The interval at which to send patches to the client, in seconds.
+	--- Defaults to `0` (patches are sent up to once per frame). Set to a
+	--- negative value to disable automatic syncing.
+	interval: number?,
+	--- Whether the history of state changes since the client's last update
+	--- should be preserved. This is useful for values that change multiple times
+	--- per frame, where each individual change is important. Defaults to `false`.
+	preserveHistory: boolean?,
+	--- When `true`, Charm will apply validation and serialize unsafe arrays
+	--- to address remote event argument limitations. Defaults to `true`.
+	---
+	--- This option should be disabled if your network library uses a custom
+	--- serialization method (i.e. Zap, ByteNet) to prevent interference.
+	autoSerialize: boolean?,
+}
+
+type ServerSyncer = {
+	--- Sets up a subscription to each atom that schedules a patch to be sent to
+	--- the client whenever the state changes. When a change occurs, the `callback`
+	--- is called with the player and the payload to send.
+	---
+	--- Note that the `payload` object should not be mutated. If you need to
+	--- modify the payload, apply the changes to a copy of the object.
+	---
+	--- @param callback The function to call when the state changes.
+	--- @return A cleanup function that unsubscribes all listeners.
+	connect: (self: ServerSyncer, callback: (player: Player, ...SyncPayload) -> ()) -> () -> (),
+	--- Hydrates the client's state with the server's state. This should be
+	--- called when a player joins the game and requires the server's state.
+	---
+	--- @param player The player to hydrate.
+	hydrate: (self: ServerSyncer, player: Player) -> (),
+	--- @deprecated For internal use only.
+	_sendPatch: (self: ServerSyncer, player: Player) -> (),
+}
+
+--- Creates a `ServerSyncer` object that sends patches to the client and
+--- hydrates the client's state.
+---
+--- @param options The atoms to synchronize with the client.
+--- @return A `ServerSyncer` object.
+local function server(options: ServerOptions): ServerSyncer
+	local atoms = options.atoms
+	local autoSerialize = options.autoSerialize ~= false
+	local preserveHistory = options.preserveHistory
+	local syncRate = options.interval or 0
+
+	local self = {} :: ServerSyncer
+	local sync: (player: Player, payload: SyncPayload) -> ()
+
+	local function createSnapshot()
+		local snapshot = {}
+
+		for key, atom in next, atoms do
+			snapshot[key] = atom()
+		end
+
+		return snapshot
+	end
+
+	-- Send the initial state to a player when they join the server.
+	function self:hydrate(player)
+		assert(sync, "connect() must be called before hydrate()")
+
+		sync(player, {
+			type = "init",
+			data = createSnapshot(),
+		})
+	end
+
+	-- If the history of state changes should be preserved, keep a list of
+	-- previous snapshots and diff-check each one from the last.
+	if preserveHistory then
+		local snapshots = { createSnapshot() }
+		local changed = false
+
+		function self:connect(callback)
+			local subscriptions = {}
+
+			sync = callback
+
+			local function pushSnapshot(key: string | number, current: any, previous: any)
+				local lastSnapshot = snapshots[#snapshots]
+				local previousSnapshot = snapshots[#snapshots - 1]
+
+				-- Optimize snapshots by updating the most recent snapshot if the
+				-- previous and current values are the same, since this allows us
+				-- to group multiple changes into a single snapshot.
+				if previousSnapshot and previousSnapshot[key] == previous and lastSnapshot[key] == previous then
+					lastSnapshot[key] = current
+				else
+					local nextSnapshot = table.clone(lastSnapshot)
+					nextSnapshot[key] = current
+					table.insert(snapshots, nextSnapshot)
+				end
+			end
+
+			-- Populate the snapshot with the initial state of each atom.
+			-- Subscribe to each atom and update the state when it changes.
+			for key, atom in next, atoms do
+				subscriptions[key] = Charm.subscribe(atom, function(current, previous)
+					pushSnapshot(key, current, previous)
+					changed = true
+				end)
+			end
+
+			local disconnect = interval(function()
+				if not changed then
+					return
+				end
+
+				local payloads: { SyncPayload } = {}
+				local lastSnapshot
+
+				for index, snapshot in next, snapshots do
+					lastSnapshot = snapshot
+
+					if index == 1 then
+						continue
+					end
+
+					table.insert(payloads, {
+						type = "patch",
+						data = patch.diff(snapshots[index - 1], snapshot, autoSerialize),
+					})
+				end
+
+				snapshots = { lastSnapshot }
+				changed = false
+
+				for _, player in next, Players:GetPlayers() do
+					callback(player, unpack(payloads))
+				end
+			end, syncRate)
+
+			return function()
+				disconnect()
+
+				for _, unsubscribe in next, subscriptions do
+					unsubscribe()
+				end
+			end
+		end
+
+		function self:_sendPatch(player: Player)
+			assert(sync, "connect() must be called before _sendPatch()")
+
+			if not changed then
+				return
+			end
+
+			local payloads: { SyncPayload } = {}
+
+			for index, snapshot in next, snapshots do
+				if index == 1 then
+					continue
+				end
+
+				table.insert(payloads, {
+					type = "patch",
+					data = patch.diff(snapshots[index - 1], snapshot, autoSerialize),
+				})
+			end
+
+			snapshots = { snapshots[#snapshots] }
+			changed = false
+
+			sync(player, unpack(payloads))
+		end
+
+		return self
+	end
+
+	local previousSnapshot = createSnapshot()
+	local currentSnapshot = table.clone(previousSnapshot)
+	local changed = false
+
+	function self:connect(callback)
+		local subscriptions = {}
+
+		sync = callback
+
+		-- Subscribe to each atom and update the state when one changes.
+		for key, atom in next, atoms do
+			subscriptions[key] = Charm.subscribe(atom, function(state)
+				currentSnapshot[key] = state
+				changed = true
+			end)
+		end
+
+		local disconnect = interval(function()
+			if not changed then
+				return
+			end
+
+			local payload: SyncPayload = {
+				type = "patch",
+				data = patch.diff(previousSnapshot, currentSnapshot, autoSerialize),
+			}
+
+			previousSnapshot = table.clone(currentSnapshot)
+			changed = false
+
+			for _, player in next, Players:GetPlayers() do
+				callback(player, payload)
+			end
+		end, syncRate)
+
+		return function()
+			disconnect()
+
+			for _, unsubscribe in next, subscriptions do
+				unsubscribe()
+			end
+		end
+	end
+
+	function self:_sendPatch(player)
+		assert(sync, "connect() must be called before _sendPatch()")
+
+		if not changed then
+			return
+		end
+
+		local payload: SyncPayload = {
+			type = "patch",
+			data = patch.diff(previousSnapshot, currentSnapshot, autoSerialize),
+		}
+
+		previousSnapshot = table.clone(currentSnapshot)
+		changed = false
+
+		sync(player, payload)
+	end
+
+	return self
+end
+
+return server