Instructions for using the php header() function_PHP tutorial-PHP Tutorial-php.cn

Instructions for using the php header() function_PHP tutorial

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Release： 2016-07-21 15:51:05

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Instructions for using the header() function:

1. Function:
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PHP only sends the header of the HTML document using the HTTP protocol Go to the browser and tell the browser how to process this page. As for the transmitted content, you need to be familiar with the HTTP protocol. It has nothing to do with PHP. You can refer to http://www.w3.org/Protocols/rfc2616/rfc2616.
Traditional headers 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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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 possible 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 sends a request for connection, and the server establishes the connection; then, the client sends an HTTP request (Request), and the server returns response information (Respond), thus completing an HTTP operation.

3. The meaning of HTTP protocol status code
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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

4. Operation examples:
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<1> Redirect function, this is the most common

Copy code The code is as follows:

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

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

Copy code The code is as follows:

//Tell the browser the expiration time of this page ( Expressed in Greenwich Mean Time), as long as it is a date in the past. 
header("Expires: Mon, 26 Jul 1970 05:00:00 GMT"); 
//Tell the browser the last updated date of this page (expressed in Greenwich Mean Time), which is the current day. The purpose is Force the browser to obtain the latest information 
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . "GMT"); 
//Tell the client browser not to use cache 
header("Cache-Control: no-cache, must-revalidate"); 
//Parameters (compatible with previous servers), that is, compatible with HTTP1.0 protocol
header("Pragma: no- cache"); 
//Output MIME type
header("Content-type: application/file"); 
//File length
header("Content-Length: 227685"); 
//Accepted range units
header("Accept-Ranges: bytes"); 
//The default file name in the file save dialog box
header("Content-Disposition: attachment; filename=$filename"); 
?>

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

Copy code The code is as follows:

header('HTTP/1.1 401 Unauthorized'); 
header('status: 401 Unauthorized'); 
?>

For example, if you want to restrict a user from accessing this page, you can set the status to 404, as shown below, so that the browser will display this page Does not exist

Copy code The code is as follows:

header('HTTP/1.1 404 Not Found'); 
header("status: 404 Not Found"); 
?> 