php: Detailed explanation of header() function usage examples

PHP only sends the header of the HTML document to the browser using the HTTP protocol, telling the browser how to process this page. As for the transmitted content, you need to be familiar with the HTTP protocol and has nothing to do with PHP. ,

can refer to header() functionInstructions for use:

1. Function:
~~~~~~~~~
PHP only sends the header of the HTML document to the browser using the HTTP protocol, telling the browser how to process the page. As for the content being transmitted, you need to be familiar with the HTTP protocol. No, it has nothing to do with PHP.
The traditional header must contain one of the following three headers and can only appear once.
Location: xxxx:yyyy/zzzz
Content-Type: xxxx/yyyy
Status: nnn xxxxxx

Second, let’s first understand how the HTTP protocol operates
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The HTTP protocol is based on the request/response paradigm. After a client establishes a connection with the server, it sends a request to the server. The format of the request is a uniform resource identifier, a protocol version number, followed by MIME information including request modifiers, client information and possible content. After receiving the request, the server gives corresponding response information. Its format is a status line including the protocol version number of the information, a success or error code, followed by MIME information including server information, entity information and possibly Content.
It is divided into four processes. In the HTTP protocol, the server refers to the part that provides HTTP services, and the client refers to the browser or download tool you use, etc. During communication, the client issues a request for connection, and the server establishes the connection; then, the client issues an HTTP request (Request), and the server returns response information (Respond), thereby completing an HTTP operation.

3. HTTP protocolStatus codemeans
~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~
1×× Reserved
2×× Indicates that the request was successfully received
3×× In order to complete the request, the customer needs to further refine the request
4×× Customer error
5×× Server error

IV. Operation examples:
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<1> Redirect function , the most common

<?php 
Header("Location: http://www.php.cn"); 
?>

<2> forces users to obtain the latest information every time they visit this page, instead of using the cache stored on the client.

<?php 
//告诉浏览器此页面的过期时间(用格林威治时间表示)，只要是已经过去的日期即可。 
header("Expires: Mon, 26 Jul 1970 05:00:00 GMT"); 
//告诉浏览器此页面的最后更新日期(用格林威治时间表示)也就是当天,目的就是强迫浏览器获取最新资料 
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . "GMT"); 
//告诉客户端浏览器不使用缓存 
header("Cache-Control: no-cache, must-revalidate"); 
//参数（与以前的服务器兼容）,即兼容HTTP1.0协议 
header("Pragma: no-cache"); 
//输出MIME类型 
header("Content-type: application/file"); 
//文件长度 
header("Content-Length: 227685"); 
//接受的范围单位 
header("Accept-Ranges: bytes"); 
//缺省时文件保存对话框中的文件名称 
header("Content－Dis
position: attachment; filename=$filename"); 
?>

<3> Output the status value to the browser, mainly used for access control

<?php 
header(&#39;HTTP/1.1 401 Unauthorized&#39;); 
header(&#39;status: 401 Unauthorized&#39;); 
?>

For example, if you want to restrict a user from accessing the page, you can set the status to 404, as follows Display, so the browser will display that the page does not exist

<?php 
header(&#39;HTTP/1.1 404 Not Found&#39;); 
header("status: 404 Not Found"); 
?>

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