【高级技巧】负缓存：空结果的穿透防护

local cache = {}
local MISS_TTL = 3
local missAt = {}
local function getItemCached(itemName)
    local hit = cache[itemName]
    if hit ~= nil then
        return hit
    end
    local mAt = missAt[itemName]
    if mAt ~= nil and os.time() - mAt < MISS_TTL then
        return nil, true
    end
    local info = getstditeminfo(itemName, 0)
    if info == 0 or info == "" then
        missAt[itemName] = os.time()
        return nil, true
    end
    cache[itemName] = info
    return info
end

local function queryItem(actor, itemName)
    actor = getplayerbyname(actor)
    local info, isMiss = getItemCached(itemName)
    if info == nil then
        if isMiss then
            sendmsg(actor, 1, "查询无此物品（已限流）。")
        else
            sendmsg(actor, 1, "无此物品。")
        end
        return
    end
    sendmsg(actor, 1, itemName .. " 查询完成。")
end