Header type Request header Forbidden header name no 语法 代码语言:javascript 复制 If-Modified-Since:<day-name>,<day><month><year><hour>:<minute>:<second>GMT 指令 <day-name> “星期一”,“星期二”,“星期三”,“星期四”,“星期五”,“星期六”或“星期日”之一(区分大小写),例: “04”或...
复制 z2=requests.head(url,headers=headers)ifz1.headers['Last-Modified']==last_modified:print u'网页没有更新'#这种方法也可以知道网页是否有更新 总结 那么假如我要每天爬取苹果应该商店的app,那么我会在第一次请求的时候吧每个网页的上次修改时间存到数据库(也就是If-Modified-Since) 然后在我第二次爬...
Entity HEAD requests allow for the requester to optionally pass the “If-Modified-Since” HTTP header in the request. This is only permitted for retrieve style requests when querying for a specific resource by id in the URL. The header’s value is the ta
1)浏览器再次访问,请求的Header携带了If-Modified-Since,其值为上次响应的Last-Modified的时间。2)此文件没有修改过,服务器返回响应状态码为304,响应的Body为空。 本地有缓存,文档在服务器有修改 1)在服务器修改文件。2)浏览器的请求的Header携带If-Modified-Since。3)由于文件已修改并且比If-Modified-Since的时...
I checked the request header sent by UV, and it appears as follows: if-modified-since: Wed, 17 Jul 2024 03:39:18 -0000.According to the MDN documentation, HTTP dates should always be expressed in GMT, not in local time.Therefore, uv should adjust the header value to something like: ...
在HTTP 协议中,请求头If-Match、If-None-Match、If-Modified-Since、If-Unmodified-Since、If-Range主要是为了解决浏览器缓存数据而定义的请求头标准,按照协议规范正确的判断和使用这几个请求头,可以更精准的处理浏览器缓存,从而达到提高系统性能和减少系统带宽的占用的目的。
Understanding the Last-Modified Header The Last-Modified header plays a pivotal role in web communication, acting as a timestamp indicating the last date and time a resource was modified before it was requested. This header is closely related to the If-Modified-Since header, working in tandem ...
TheIf-Modified-SinceHTTP header indicates the time for which a browser first downloaded a resource from the server. This helps determine whether or not the resource has changed since the last time it was accessed. If the HTTP status of a particular resource is304 Not Modified, this means that...
浏览器收到304的响应后,就会从缓存中加载资源。 如果协商缓存没有命中,浏览器直接从服务器加载资源时,Last-Modified Header在重新加载的时候会被更新,下次请求时,If-Modified-Since会启用上次返回的Last-Modified值。
Last-Modified和If-Modified-Since 当浏览器GET请求的时候,如果有If-Modified-Since,则会与当前服务器上相关资源最后一次修改时间进行对比,如果相同则返回304(资源可访问,但没修改),否则加载最新数据,浏览器再缓存起来。这样减少网络数据传输和服务器压力。