Discuss the detailed usage of header in php_PHP tutorial-PHP Tutorial-php.cn

Discuss the detailed usage of header in php_PHP tutorial

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Release： 2016-07-21 15:08:09

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header() is used to send raw HTTP headers. See the HTTP/1.1 specification for more information on HTTP headers.

Example 1:

Copy code The code is as follows:

Header("Location : http://www.jb51.net";); 
exit;//"exit" must be added after each redirection to avoid continuing execution after an error occurs. 
?>

Copy code The code is as follows:

header("refresh:2;url=http://www.jb51.net");
echo "Loading, please wait...
Automatically jump toBaidu...";
?>

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Example 2: Disable page caching in IE
Enable the viewer to get the latest information every time, instead of the information in the Proxy or cache:

Copy the code The code is as follows:

header( 'Expires: Fri, 4 Dec 2009 09:00:00 GMT' );
header( 'Last-Modified: ' . gmdate( 'D , d M Y H:i:s' ) . ' GMT' );
header( 'Cache-Control: no-store, no-cache, must-revalidate' );
header( 'Cache-Control: post -check=0, pre-check=0', false );
header( 'Pragma: no-cache' ); //Compatible with http1.0 and https
?>

CacheControl = no-cache Pragma=no-cache Expires = -1
If the web pages on the server change frequently, set Expires to -1, indicating immediate expiration. If a web page is updated at 1 am every day, you can set Expires to 1 am the next day. When the HTTP1.1 server specifies CacheControl = no-cache, the browser will not cache the web page.
Legacy HTTP 1.0 servers cannot use the Cache-Control header. So for backward compatibility with HTTP 1.0 servers, IE provides special support for HTTP using the Pragma:no-cache header. If the client communicates with the server over a secure connection (https://) and the server returns the Pragma:no-cache header in the response, Internet Explorer does not cache the response.
Note: Pragma:no-cache only prevents caching when used in a secure connection. If used in a non-secure page, the processing method is the same as Expires:-1. The page will be cached but marked as immediate. Expired.
http-equiv meta tag:
You can use http-equiv meta to mark the specified http message header in the html page. Older versions of IE may not support html meta tags, so it's best to use http message headers to disable caching.
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Example 3: Let the user's browser appear Unable to find file information.
A lot of information on the Internet says this: PHP's function header() can send a Status header to the browser,
such as header("Status: 404 Not Found"). But in fact the response returned by the browser is:

Copy code The code is as follows:

HTTP/1.x 200 OK 
Date: Thu, 03 Aug 2006 07:49:11 GMT
Server: Apache/2.0.55 (Win32) PHP/5.0.5
X-Powered-By: PHP/5.0.5
Status: 404 Not Found
Content-Length: 0
Keep-Alive: timeout=15, max=98
Connection: Keep-Alive
Content-Type: text/html

After checking some information, the correct way to write it is:
header("http/1.1 404 Not Found");
The first part is the HTTP protocol version (HTTP-Version); the second part is Status code (Status); the third part is the reason phrase (Reason-Phrase).
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Example 4: Let users download files (hidden files (location)
html tag can realize ordinary file downloading. If you want to keep the file confidential and you cannot tell others the file link, you can use the header function to download the file.

Copy code The code is as follows:

header("Content-type: application/x- gzip"); 
header("Content-Disposition: attachment; filename=filename/"); 
header("Content-Description: PHP3 Generated Data"); 
?>

Example 4: Input content before the header function
Generally speaking, html content cannot be output before the header function. Similarly, there are setcookie() and session functions. These functions need to be in the output stream. Add message header information. If there are statements such as echo before header() is executed, when header() is encountered later, a "Warning: Cannot modify header information - headers already sent by ...." error will be reported. That is to say, there cannot be any text, blank lines, carriage returns, etc. in front of these functions, and it is best to add the exit() function after the header() function. For example, in the following incorrect writing, there is a blank line between the two PHP code snippets:

Copy the code The code is as follows:

//Some code here
?>
//This should be a blank line
header("http/1.1 403 Forbidden");
exit();
?> 

The reason is: When the PHP script starts executing, it can send http message header (title) information and body information at the same time. http message header (from the header() or SetCookie() function) is not sent immediately, instead, it is saved to a list. This allows you to modify the header information, including the default header (such as the Content-Type header). However, , once the script sends any non-header output (for example, using HTML or a print() call), then PHP must first send all Headers, then terminate the HTTP header. Then continue to send the body data. From this point on, any Attempts to add or modify header information are not allowed and one of the above error messages will be sent.
Solution:
Modify php.ini to turn on caching (output_buffering), or use the caching functions ob_start(), ob_end_flush(), etc. in the program. The principle is: when output_buffering is enabled, PHP does not send HTTP headers when the script sends output. Instead, it pipes this output into a dynamically growing cache (only available in PHP 4.0, which has a centralized output mechanism). You can still modify/add headers, or set cookies, because headers are not actually sent. When all scripts terminate, PHP will automatically send HTTP headers to the browser, and then send the contents of the output buffer.
================================================== ==================
PHP Manual Example Application
1: You can use the heder command to force the browser to use Fresh content (no caching).
You can also add a unique number to the URL so that it can read new content every time and avoid caching.
example:

Copy code The code is as follows:

print "

"; //Usually the cache file is read
?>
print "

"; //A unique number is added to make the browser re-request
w//print "

";
?>

2: The following is a good function that sends images to the browser for display.

Copy code The code is as follows:

function PE_img_by_path($PE_imgpath = "" )
{
 if (file_exists($PE_imgpath)) {
 $PE_imgarray = pathinfo($PE_imgpath);
 $iconcontent = file_get_contents($PE_imgpath);
 header("Content-type : image/" . $PE_imgarray["extension"]);
 header('Content-length: ' . strlen($iconcontent));
 echo $iconcontent;
 die(0);
 }
 return false;
} 
?>

More examples:

Copy the code The code is as follows:

// ok
header('HTTP/1.1 200 OK');
//Set a 404 header:
header('HTTP/1.1 404 Not Found');
//Set the address to be permanently redirected
header('HTTP/1.1 301 Moved Permanently');
//Go to a new address
header('Location: http://www.baidu.com');
//File delayed redirection:
header('Refresh: 10; url=http://www.example.org/');
print 'You will be redirected in 10 seconds';
//Of course, you can also use html syntax
// header('Content-Transfer-Encoding: binary');
// load the file to send:
readfile('example.zip');
// Disable caching for the current document
 header('Cache-Control: no-cache, no-store, max-age=0, must-revalidate');
header('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); / / Date in the past
header('Pragma: no-cache');
//Set content type:
header('Content-Type: text/html; charset=iso-8859-1' );
header('Content-Type: text/html; charset=utf-8');
header('Content-Type: text/plain'); //Plain text format
header( 'Content-Type: image/jpeg'); //JPG image
header('Content-Type: application/zip'); // ZIP file
header('Content-Type: application/pdf') ; // PDF file
header('Content-Type: audio/mpeg'); // Audio file
header('Content-Type: application/x-shockwave-flash'); //Flash animation
//Show login dialog box
header('HTTP/1.1 401 Unauthorized');
header('WWW-Authenticate: Basic realm="Top Secret"');
print 'Text that will be displayed if the user hits cancel or ';
print 'enters wrong login data';
?>