http头

Veeooo小于 1 分钟

缓存1

    Expires:GMT时间 
    Pragma:no-cache(唯一值)

缓存2

    Cache-contral:...

缓存时间

    last-modified:GMT时间
    if-modified-since:...

缓存签名

    etag:字符串
    if-none-match:...

跨域

    Access-Control-Allow-Origin:*
    Access-Control-Allow-Credentials:true
    Access-Control-Allow-Methods:GET, POST, OPTIONS
    Access-Control-Allow-Headers:*
    Access-Control-Expose-Headers:*

跨域OPTIONS

    Access-Control-Max-Age:1728000
    Content-Type:text/plain;charset=utf-8
    Content-Length:0