Lua script for atomic API rate checking in Redis

rate_check.lua

local current, expected, cur_val, callcount, maxcps
current = redis.call('GET', KEYS[1])
callcount = tonumber(ARGV[1])
maxcps = tonumber(ARGV[2])
cur_val = 0
if current then
    cur_val = tonumber(current)
end
expected = cur_val + callcount
if expected > maxcps then
    return nil
else
    redis.call('incrby', KEYS[1], callcount)
    redis.call('expire', KEYS[1], 10)
    return 1
end