obtain.lua

-- obtain.lua: arguments => [value, tokenLen, ttl]
-- Obtain.lua try to set provided keys's with value and ttl if they do not exists.
-- Keys can be overriden if they already exists and the correct value+tokenLen is provided. 

local function pexpire(ttl)
	-- Update keys ttls.
	for _, key in ipairs(KEYS) do
		redis.call("pexpire", key, ttl)
	end
end

-- canOverrideLock check either or not the provided token match
-- previously set lock's tokens.
local function canOverrideKeys() 
	local offset = tonumber(ARGV[2])

	for _, key in ipairs(KEYS) do
		if redis.call("getrange", key, 0, offset-1) ~= string.sub(ARGV[1], 1, offset) then
			return false
		end
	end
	return true
end

-- Prepare mset arguments.
local setArgs = {}
for _, key in ipairs(KEYS) do
	table.insert(setArgs, key)
	table.insert(setArgs, ARGV[1])
end

if redis.call("msetnx", unpack(setArgs)) ~= 1 then
	if canOverrideKeys() == false then
		return false
	end
	redis.call("mset", unpack(setArgs))
end

pexpire(ARGV[3])
return redis.status_reply("OK")