PHP header () function details (301, 404 and other error settings) _php Tutorial

If you have just started to learn PHP, there may be many functions need to study, today we will learn how to use the PHP Header (), more instructions, please refer to the PHP Chinese manual, the following is a detailed use of the header function instructions

Regardless of how many headers the page has, it executes the last one, but conditionally, for example:

Header (' location:http://www.bkjia.com ');
Header (' location:http://www.g.cn ');
Header (' location:http://www.baidu.com ');

This will jump to Baidu

The header (' location:http://www.bkjia.com '); Echo's home for the guests;
Header (' location:http://www.g.cn ');
Header (' location:http://www.baidu.com ');

This will jump to Google
The following is a detailed description of the use of the header function
First, the role:
~~~~~~~~~
PHP only in the HTTP protocol to the HTML document header to the browser, tell the browser how to handle this page, as for the content of the transfer will need to familiarize yourself with the HTTP protocol, not related to PHP
The traditional header must contain one of the following three headers and can only occur once.

Location:xxxx:yyyy/zzzz
Content-type:xxxx/yyyy
status:nnn xxxxxx

Second, first to understand how the HTTP protocol works
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The HTTP protocol is based on the request/response paradigm. After a client establishes a connection to the server, it sends a request to the server in the form of a Uniform Resource Identifier, protocol version number, followed by MIME information including the request modifier, client information, and possible content. After the server receives the request, it gives the corresponding response information in the form of a status line that includes the protocol version number of the information, a successful or incorrect 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 is the part that provides the HTTP service, the client refers to the browser you use or download tools and so on. In the communication, the client makes a request connection, the server establishes the connection, and then the client makes an HTTP request (request) and the server returns the response information (Respond), thus completing an HTTP operation.

HTTP Status Detection (HTTP Header):http://www.bkjia.com/tools/http_header.php

Third, the meaning of the HTTP protocol status Code representation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1XX reserved
2XX indicates that the request was successfully received by
3XX request further refinement of requests for completion of customer requests
4XX Customer Error
5XX Server Error

Four, the operation example:
~~~~~~~~~~~~~
<1> redirection features, the most common

Header ("location:http://www.bkjia.com/");
?>

<2> forces users to get the latest information each time they access the page, rather than using a cache that exists on the client.

Code
Tell the browser how long this page will expire (in Greenwich Mean Time), as long as the date has passed.
Header ("Expires:mon, Jul 1970 05:00:00 GMT");
Tells the browser that the last update date of this page (in Greenwich Mean Time) is the same day, the purpose is to force the browser to get the latest information
Header ("last-modified:".) Gmdate ("D, D M Y h:i:s"). "GMT");
Tell the client browser not to use the cache
Header ("Cache-control:no-cache, must-revalidate");
Parameters (compatible with previous servers), which is compatible with the 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");
File name in the File Save dialog box by default
Header ("content-disposition:attachment; Filename= $filename ");
?>

<3> output status value to the browser, mainly for access rights control

Header (' http/1.1 401 Unauthorized ');
Header (' status:401 unauthorized ');
?>

For example, to restrict a user from accessing the page, you can set the status to 404, as shown below, so that the browser is displayed as if the page does not exist

Header (' http/1.1 404 Not Found ');
Header ("status:404 not Found");
?>

Note: The traditional header must contain one of the following three headers and can only occur once. CONTENT-TYPE:XXXX/YYYY location:xxxx:yyyy/zzzz status:nnn xxxxxx can appear more than two times in the new multi-header specification (Multipart MIME).
Usage examples
Example one: This example redirects the browser to the official PHP website.

Header ("location:http://www.bkjia.com/"); Exit

Example two: Users can get the latest information each time, rather than Proxy or cache data, you can use the following headers

Header ("Expires:mon, Jul 1997 05:00:00 GMT");
Header ("last-modified:".) Gmdate ("D, D M Y h:i:s"). "GMT"); Header ("Cache-control:no-cache, must-revalidate");
Header ("Pragma:no-cache");

Example three: Let the user's browser appear unable to find the file information.

Header ("status:404 not Found");

Example four: Let the user download the file.

Header ("Content-type:application/x-gzip");
Header ("content-disposition:attachment; Filename= file name ");
Header ("Content-description:php3 Generated Data");

Header--Sends an original HTTP header description

void header (String string [, bool replace [, int http_response_code]])

The header () function is used to send an original HTTP header. See the http/1.1 specification for more information about HTTP headers.
The optional parameter, replace, indicates whether to replace the previous similar header or to add a header of the same type. The default is replace, but if you set it to FALSE, you can force multiple, homogeneous headers to be sent. For example:

　 Header (' www-authenticate:negotiate ');
Header (' WWW-AUTHENTICATE:NTLM ', false);
?>

The Second optional parameter, Http_response_code, forces the HTTP response code to be set to the specified value (this parameter is a new addition to PHP 4.3.0).
There are two special types of header calls. The first is that the header begins with the string "http/" (not important in case) and can be used to determine the HTTP status code to send. For example, if Apache is configured with PHP to handle error-handling requests that cannot find files (using the ErrorDocument Directive), you need to make sure that the script produces the correct status code.

Header ("http/1.0 404 Not Found")
?>

Note: The HTTP status code header line is always the first to be sent to the client, and does not control whether the actual header () call is the first one. Unless the HTTP header has been sent, you can overwrite the original by invoking the header () function with the new state line at any time.

　　HTTP Status Detection (HTTP Header):http://www.bkjia.com/tools/http_header.php

The second special case is the "location:" header. It does not just send the label back to the browser, it also returns a REDIRECT (302) status code to the browser, unless a 3XX status code has been issued before.

　 Header ("location:http://www.example.com/"); /* Redirect Browser */
/* Ensure that subsequent code is not executed after redirection */
Exit
?>

Note: The http/1.1 standard requires an absolute address URI as the location: parameter, but there are some clients that support relative URIs. You can usually use $_server[' http_host ', $_server[' php_self '] and the dirname () function to generate an absolute URI from a relative URI:

　 Header ("location:http://%22.$_server[' http_host '/]
. RTrim (dirname ($_server[' php_self '), '/\\ ')
." /". $relative _url);
?>

Note: Even if the session.use_trans_sid,session ID is enabled, it will not be passed along with the location header information. Must be passed manually with SID constants.
　　
PHP scripts often produce dynamic content that must not be cached by the browser or proxy server. Many proxy servers and browsers can be disabled by the following methods:

　 Header ("Cache-control:no-cache, must-revalidate"); http/1.1
Header ("Expires:mon, Jul 1997 05:00:00 GMT"); The past time
?>

Note: You may find that even if you do not output all of the above code, the page is not buffered. There are many options that users can set to change the browser's default caching behavior. By sending the above header, you should be able to overwrite any settings that could cause the script page to be cached.
　　
In addition, when a session is used, the Session_cache_limiter () function and the Session.cache_limiter option can be used to automatically generate the correct cache-related headers.
　　
Remember that the header () must be called before any actual output, whether it's from a normal HTML tag, a blank line, or PHP. One common mistake is that when reading code through include (), require (), or some other file access class function, some spaces or blank lines are sent before the header () is called. This error is also common in a separate php/html file.

　　
　　 /* This will produce an error because the header ()
* I've been outputting something before * *
Header (' location:http://www.example.com/');
?>

Note: Since PHP 4, some output buffering functions can be used to solve this problem. The price is to keep all the output from the browser on the server until the next command sends them. You can use Ob_start () and Ob_end_flush () in your code to implement such functionality, either by modifying the output_buffering configuration options in php.ini, or by modifying the server configuration file.

Header () Two common uses:

To set the page encoding:
Header (' content-type:text/html;charset=gb2312 ');
Adjustment page:
Header (' location:http://www.baidu.com ');

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