How to disable browser caching in php

How to disable browser caching in php: You can disable caching of static pages through meta tags, such as [], expires Used to set the expiration time of web pages.

The method is as follows:

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1. For static pages (set through meta tags)

<!--expires用于设定网页的过期时间,一旦过期就必须从服务器上重新加载.时间必须使用GMT格式-->
<meta http-equiv="expires" content="0" />

or set through pragma no-cache, pragma appears in the http-equiv attribute, and uses the no-cache value of the content attribute to indicate whether to cache the web page (for Improve speed. Some browsers cache pages that viewers have browsed. By definition below, browsers generally do not cache pages, and the browser cannot be browsed offline).

<meta http-equiv="pragma" content="no-cache" />

Cache-Control: Cache control, specifying the caching mechanism followed by requests and responses. Setting Cache-Control in a request message or response message does not modify the caching process during the processing of another message.

The caching instructions in the request include no-cache, no-store, max-age, max-stale, min-fresh, only-if-cached, etc. The instructions in the response message include public, private, no -cache, no-store, no-transform, must-revalidate, proxy-revalidate, max-age.

The meaning of some instructions in each message is as follows:

Public: Indicates that the response can be cached by any cache area.

Private: Indicates that all or part of the response message for a single user cannot be processed by the shared cache. This allows the server to only describe a partial response from a user that is not valid for other users' requests.

no-cache: Indicates that the request or response message cannot be cached

no-store: Used to prevent important information from being released unintentionally. Sending it in the request message will cause both the request and response messages to use caching.

max-age: Indicates that the client can receive responses with a lifetime no greater than the specified time (in seconds).

min-fresh: Indicates that the client can receive responses with a response time less than the current time plus the specified time.

max-stale: Indicates that the client can receive response messages beyond the timeout period. If you specify a value for max-stale messages, the client can receive response messages that exceed the specified value of the timeout period.

Note: The Cache-Control header was added in HTTP1.1 and can achieve more detailed cache control compared to several other methods.

<meta http-equiv="Cache-Control" content="no-cache,no-store, must-revalidate">
header(&#39;Cache-Control: max-age=3600*24&#39;);//缓存1天，表示最大生存期是1天，超过1天浏览器必须去服务器重新读取，这个时间是从用户第一次读取页面时开始计时的

2. For PHP pages:

For dynamic pages, the cached code must be placed before any HTML tag output, otherwise an error will occur.

<?php 
header(&#39;Cache-Control:no-cache,must-revalidate&#39;);   
header(&#39;Pragma:no-cache&#39;);   
header("Expires:0"); 
?>

Last-Modified: The last modification time of the document. Its usage is:

1: If it is a static file, the client will send the time in its cache, and Apache will compare it. If it finds that there is no modification, it will directly return a header with a status code of 304. The number of bytes is very small.

2: If it is a PHP dynamic file, the client sends the comparison time, and PHP will determine whether to modify it. If the modification time is the same, only 1024 bytes will be returned. As for why 1024 is returned, it is unknown. If The file generated by your PHP is very large, and it only returns 1024, so it saves bandwidth. The client will automatically display the file from the cache based on the modification time sent by the server.

Note: If the Last-Modified header is not set, only setting Cache-Control and Expires will also work, but each request must return the actual number of file bytes, not 1024

php Set the Last-Modified header sample code as follows:

header('Last-Modified: '.gmdate('D, d M Y 01:01:01',$time).' GMT');//使用的是格林尼治时间,$time是指文件添加时候的时间戳

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