BUG: The expiration time may not take effect

lrucache:set(key, value, ttl, flags)
os.execute("sleep " .. tonumber(ttl+2))
local data, stale_data, flags = lrucache:get(key)
data is not nil

lruchache' get method
if node.expire >= 0 and node.expire < ngx_now() then
return nil, val, node.user_flags
end

ngx_now() Returns a floating-point number for the elapsed time in seconds (including milliseconds as the decimal part) from the epoch for the current time stamp from the Nginx cached time (no syscall involved unlike Lua's date library). https://github.com/openresty/lua-nginx-module#ngxnow

Is it better to add an ngx.update_time()？

Start with lrucache's get method and the reported expiration check using ngx_now(). Reproduce the set/get sequence with os.execute("sleep " .. tonumber(ttl+2)), then verify whether the cached time is refreshed before expiration is evaluated; done means the entry is stale and data is nil after the TTL has elapsed.