HEADERS_SENT(3) 1 HEADERS_SENT(3)headers_sent - Checks if or where headers have been sentSYNOPSIS
bool headers_sent ([string &$file], [int &$line])
DESCRIPTION
Checks if or where headers have been sent.
You can't add any more header lines using the header(3) function once the header block has already been sent. Using this function you can
at least prevent getting HTTP header related error messages. Another option is to use Output Buffering.
PARAMETERS
o $file
- If the optional $file and $line parameters are set, headers_sent(3) will put the PHP source file name and line number where out-
put started in the $file and $line variables.
o $line
- The line number where the output started.
RETURN VALUES headers_sent(3) will return FALSE if no HTTP headers have already been sent or TRUE otherwise.
EXAMPLES
Example #1
Examples using headers_sent(3)
<?php
// If no headers are sent, send one
if (!headers_sent()) {
header('Location: http://www.example.com/');
exit;
}
// An example using the optional file and line parameters, as of PHP 4.3.0
// Note that $filename and $linenum are passed in for later use.
// Do not assign them values beforehand.
if (!headers_sent($filename, $linenum)) {
header('Location: http://www.example.com/');
exit;
// You would most likely trigger an error here.
} else {
echo "Headers already sent in $filename on line $linenum
" .
"Cannot redirect, for now please click this <a " .
"href="http://www.example.com">link</a> instead
";
exit;
}
?>
NOTES
Note
Headers will only be accessible and output when a SAPI that supports them is in use.
SEE ALSO ob_start(3), trigger_error(3), headers_list(3), header(3) for a more detailed discussion of the matters involved. .
PHP Documentation Group HEADERS_SENT(3)
Check Out this Related Man Page
HEADER(3) 1 HEADER(3)header - Send a raw HTTP headerSYNOPSIS
void header (string $string, [bool $replace = true], [int $http_response_code])
DESCRIPTION header(3) is used to send a raw HTTP header. See the HTTP/1.1 specification for more information on HTTP headers.
Remember that header(3) must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP.
It is a very common error to read code with include(3), or require(3), functions, or another file access function, and have spaces or empty
lines that are output before header(3) is called. The same problem exists when using a single PHP/HTML file.
<html>
<?php
/* This will give an error. Note the output
* above, which is before the header() call */
header('Location: http://www.example.com/');
exit;
?>
PARAMETERS
o $string
- The header string. There are two special-case header calls. The first is a header that starts with the string " HTTP/" (case is
not significant), which will be used to figure out the HTTP status code to send. For example, if you have configured Apache to use
a PHP script to handle requests for missing files (using the ErrorDocument directive), you may want to make sure that your script
generates the proper status code.
<?php
header("HTTP/1.0 404 Not Found");
?>
REDIRECT (302) status code to the browser unless the 201 or a 3xx status code has already been set.
<?php
header("Location: http://www.example.com/"); /* Redirect browser */
/* Make sure that code below does not get executed when we redirect. */
exit;
?>
o $replace
- The optional $replace parameter indicates whether the header should replace a previous similar header, or add a second header of
the same type. By default it will replace, but if you pass in FALSE as the second argument you can force multiple headers of the
same type. For example:
<?php
header('WWW-Authenticate: Negotiate');
header('WWW-Authenticate: NTLM', false);
?>
o $http_response_code
- Forces the HTTP response code to the specified value. Note that this parameter only has an effect if the $string is not empty.
RETURN VALUES
No value is returned.
CHANGELOG
+--------+---------------------------------------------------+
|Version | |
| | |
| | Description |
| | |
+--------+---------------------------------------------------+
| 5.1.2 | |
| | |
| | This function now prevents more than one header |
| | to be sent at once as a protection against header |
| | injection attacks. |
| | |
+--------+---------------------------------------------------+
EXAMPLES
Example #1
Download dialog
If you want the user to be prompted to save the data you are sending, such as a generated PDF file, you can use the Content-Dispo-
sition header to supply a recommended filename and force the browser to display the save dialog.
<?php
// We'll be outputting a PDF
header('Content-Type: application/pdf');
// It will be called downloaded.pdf
header('Content-Disposition: attachment; filename="downloaded.pdf"');
// The PDF source is in original.pdf
readfile('original.pdf');
?>
Example #2
Caching directives
PHP scripts often generate dynamic content that must not be cached by the client browser or any proxy caches between the server and
the client browser. Many proxies and clients can be forced to disable caching with:
<?php
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
?>
Note
You may find that your pages aren't cached even if you don't output all of the headers above. There are a number of options
that users may be able to set for their browser that change its default caching behavior. By sending the headers above, you
should override any settings that may otherwise cause the output of your script to be cached.
Additionally, session_cache_limiter(3) and the session.cache_limiter configuration setting can be used to automatically gen-
erate the correct caching-related headers when sessions are being used.
NOTES
Note
Headers will only be accessible and output when a SAPI that supports them is in use.
Note
You can use output buffering to get around this problem, with the overhead of all of your output to the browser being buffered in
the server until you send it. You can do this by calling ob_start(3) and ob_end_flush(3) in your script, or setting the out-
put_buffering configuration directive on in your php.ini or server configuration files.
Note
The HTTP status header line will always be the first sent to the client, regardless of the actual header(3) call being the first or
not. The status may be overridden by calling header(3) with a new status line at any time unless the HTTP headers have already been
sent.
Note
There is a bug in Microsoft Internet Explorer 4.01 that prevents this from working. There is no workaround. There is also a bug in
Microsoft Internet Explorer 5.5 that interferes with this, which can be resolved by upgrading to Service Pack 2 or later.
Note
If safe mode is enabled the uid of the script is added to the realm part of the WWW-Authenticate header if you set this header
(used for HTTP Authentication).
Note
HTTP/1.1 requires an absolute URI as argument to Location: including the scheme, hostname and absolute path, but some clients
accept relative URIs. You can usually use $_SERVER['HTTP_HOST'], $_SERVER['PHP_SELF'] and dirname(3) to make an absolute URI from a
relative one yourself:
<?php
/* Redirect to a different page in the current directory that was requested */
$host = $_SERVER['HTTP_HOST'];
$uri = rtrim(dirname($_SERVER['PHP_SELF']), '/\');
$extra = 'mypage.php';
header("Location: http://$host$uri/$extra");
exit;
?>
Note
Session ID is not passed with Location header even if session.use_trans_sid is enabled. It must by passed manually using SID con-
stant.
SEE ALSO headers_sent(3), setcookie(3), http_response_code(3), The section on HTTP authentication.
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