Lua消息分发：映射表驱动的协议路由

-- 错误：大 if 分支堆叠，漏分支静默失踪
function onMsg(msgId, body)
    if msgId == 1001 then
        refreshBag(body)
    elseif msgId == 1002 then
        refreshMail(body)
    end
end

local HANDLERS = {}
local function register(msgId, fn)
    HANDLERS[msgId] = fn
end
local function dispatch(msgId, body)
    local fn = HANDLERS[msgId]
    if fn == nil then
        logMiss(msgId)
        return
    end
    fn(body)
end
register(1001, function(body)
    refreshBag(body)
end)