Server Cooldowns

Lesson 7 of 20 in Coddy's Roblox Game: Battlegrounds course.

An exploiter controls their own device, so they can fire Remotes.Ability a hundred times a second, with any name. A cooldown in the LocalScript would stop only honest players: the server has to enforce it.

The server keeps, for each player and ability, when it is ready again, as an attribute of the player (the next lesson shows it on screen). workspace:GetServerTimeNow() is a clock the server and every client agree on:

local now = workspace:GetServerTimeNow()
if now < (player:GetAttribute(name .. "ReadyAt") or 0) then
	return
end
player:SetAttribute(name .. "ReadyAt", now + Settings.Cooldowns[name])

And it checks what it was sent: a string naming a real ability, from a player who is alive.

Challenge

Medium

In the Ability handler, before running the ability, return when:

the name is not a string naming an ability,
the player has no character root, or their Humanoid's health is 0,
GetServerTimeNow() is before the player's ready time for that ability, the attribute name .. "ReadyAt".

Otherwise set that attribute to now plus Settings.Cooldowns[name], then run it. Press Play, then Check: the checks fire the remote as an exploiter would.

Try it yourself

local Players = game:GetService("Players")
local ServerStorage = game:GetService("ServerStorage")
local Settings = require(game.ReplicatedStorage.Settings)

local remotes = game.ReplicatedStorage.Remotes
local lastSwing = {} -- player -> when they last swung

-- Roblox's own sword animations
local slash = Instance.new("Animation")
slash.AnimationId = "rbxassetid://522635514"

print("Swords deal " .. Settings.SwordDamage .. " damage")

-- A swing: the animation, then everyone in the box in front of you is hit
local function swing(player)
	local character = player.Character
	local root = character and character:FindFirstChild("HumanoidRootPart")
	if not root or character.Humanoid.Health <= 0 then
		return
	end
	local now = time()
	if lastSwing[player] and now - lastSwing[player] < Settings.SwingCooldown then
		return
	end
	lastSwing[player] = now
	character.Humanoid.Animator:LoadAnimation(slash):Play()
	-- the box in front of you, never your own body
	local params = OverlapParams.new()
	params.FilterDescendantsInstances = { character }
	local box = root.CFrame * CFrame.new(0, 0, -3)
	local hit = {} -- each humanoid once per swing
	for _, part in workspace:GetPartBoundsInBox(box, Settings.HitboxSize, params) do
		local humanoid = part.Parent:FindFirstChildOfClass("Humanoid")
		if humanoid and not hit[humanoid] then
			hit[humanoid] = true
			humanoid:TakeDamage(Settings.SwordDamage)
		end
	end
end

-- The abilities, by name: what each one does
local abilities = {}

function abilities.Dash(player, character, root)
	root.AssemblyLinearVelocity = root.CFrame.LookVector * Settings.DashSpeed + Vector3.new(0, 15, 0)
end

-- The client asks for an ability by name; the server does it
remotes.Ability.OnServerEvent:Connect(function(player, name)
	local character = player.Character
	local root = character and character:FindFirstChild("HumanoidRootPart")
	if abilities[name] and root then
		abilities[name](player, character, root)
	end
end)

-- Every player gets Kills on the leaderboard, and a sword every life
Players.PlayerAdded:Connect(function(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player

	local kills = Instance.new("IntValue")
	kills.Name = "Kills"
	kills.Parent = leaderstats

	player.CharacterAdded:Connect(function()
		local sword = ServerStorage.Sword:Clone()
		sword.Parent = player.Backpack
		sword.Activated:Connect(function()
			swing(player)
		end)
	end)
end)

-- The training dummy: its health bar follows its health, and a beaten
-- dummy comes back after a moment, a fresh copy in the same place
local function setupDummy(dummy)
	local humanoid = dummy.Humanoid
	humanoid.HealthChanged:Connect(function(health)
		dummy.HealthBar.Back.Fill.Size = UDim2.fromScale(health / humanoid.MaxHealth, 1)
	end)
	humanoid.Died:Connect(function()
		local spot = dummy:GetPivot()
		task.wait(0.5)
		dummy:Destroy()
		task.wait(Settings.DummyRespawn)
		local fresh = ServerStorage.Dummy:Clone()
		fresh:PivotTo(spot)
		fresh.Parent = workspace
		setupDummy(fresh)
	end)
end
setupDummy(workspace.Dummy)