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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@110250 c90b9560-bf6c-de11-be94-00142212c4b1
262 lines
9.2 KiB
XML
262 lines
9.2 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.11 $ -->
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<!-- splitted from ./en/functions/http.xml, last change in rev 1.2 -->
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<refentry id="function.header">
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<refnamediv>
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<refname>header</refname>
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<refpurpose>Send a raw HTTP header</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<methodsynopsis>
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<type>int</type><methodname>header</methodname>
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<methodparam><type>string</type><parameter>string</parameter></methodparam>
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<methodparam choice="opt"><type>bool</type><parameter>replace</parameter></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>http_reponse_code</parameter></methodparam>
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</methodsynopsis>
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<para>
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<function>header</function> is used to send raw
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<acronym>HTTP</acronym> headers. See the <ulink
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url="&spec.http1.1;">HTTP/1.1 specification</ulink> for more
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information on <acronym>HTTP</acronym> headers.
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</para>
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<para>
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The optional <parameter>replace</parameter> parameter indicates
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whether the header should replace a previous similar header, or
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add a second header of the same type. By default it will replace,
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but if you pass in &false; as the second argument you can force
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multiple headers of the same type. For example:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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header('WWW-Authenticate: Negotiate');
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header('WWW-Authenticate: NTLM', FALSE);
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<para>
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The second optional <parameter>http_response_code</parameter> force the
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HTTP response code to the specified value. (This parameter is available
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in PHP 4.3.0 and higher.)
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</para>
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<para>
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There are two special-case header calls. The first is a header
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that starts with the string "<literal>HTTP/</literal>" (case is not
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significant), which will be used to figure out the HTTP status
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code to send. For example, if you have configured Apache to
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use a PHP script to handle requests for missing files (using
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the <literal>ErrorDocument</literal> directive), you may want to
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make sure that your script generates the proper status code.
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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header("HTTP/1.0 404 Not Found");
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?>
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]]>
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</programlisting>
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</informalexample>
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<note>
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<para>
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The HTTP status header line will always be the first sent
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to the client, regardless of the actual <function>header</function>
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call beeing the first or not. The status may be overridden
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by calling <function>header</function> with a new status line
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at any time unless the HTTP headers have already been sent.
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</para>
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</note>
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<note>
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<para>
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In PHP 3, this only works when PHP is compiled as an Apache
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module. You can achieve the same effect using the
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<literal>Status</literal> header.
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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header("Status: 404 Not Found");
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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</note>
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</para>
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<para>
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The second special case is the "Location:" header. Not only does
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it send this header back to the browser, but it also returns a
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<literal>REDIRECT</literal> (302) status code to the browser unless
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some <literal>3xx</literal> status code has already been set.
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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header("Location: http://www.example.com/"); /* Redirect browser */
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exit; /* Make sure that code below does
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not get executed when we redirect. */
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<note>
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<para>
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HTTP/1.1 requires an absolute <acronym>URI</acronym> as argument to
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<ulink url="&spec.http1.1;-sec14.html#sec14.30">Location:</ulink>
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including the scheme, hostname and absolute path, but
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some clients accept relative URIs. You can usually use
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<literal>$_SERVER['HTTP_HOST']</literal>, <literal>$_SERVER['PHP_SELF']</literal>
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and <function>dirname</function> to make an absolute URI from a
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relative one yourself:
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<informalexample>
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<programlisting>
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<![CDATA[
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<?php
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header("Location: http://".$_SERVER['HTTP_HOST']
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.dirname($_SERVER['PHP_SELF'])
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."/".$relative_url);
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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</note>
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<para>
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PHP scripts often generate dynamic content that must not be cached
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by the client browser or any proxy caches between the server and the
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client browser. Many proxies and clients can be forced to disable
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caching with
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); // Date in the past
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header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
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// always modified
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header("Cache-Control: no-store, no-cache, must-revalidate"); // HTTP/1.1
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header("Cache-Control: post-check=0, pre-check=0", false);
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header("Pragma: no-cache"); // HTTP/1.0
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?>
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]]>
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</programlisting>
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</informalexample>
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<note>
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<para>
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You may find that your pages aren't cached even if you don't
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output all of the headers above. There are a number of options
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that users may be able to set for their browser that change its
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default caching behavior. By sending the headers above, you should
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override any settings that may otherwise cause the output of your
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script to be cached.
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</para>
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<para>
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Additionally, <function>session_cache_limiter</function> and
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the <literal>session.cache_limiter</literal> configuration
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setting can be used to automatically generate the correct
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caching-related headers when sessions are being used.
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</para>
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</note>
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</para>
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<para>
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Remember that <function>header</function> must be
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called before any actual output is sent, either by normal HTML
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tags, blank lines in a file, or from PHP. It is a very common
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error to read code with <function>include</function>, or
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<function>require</function>, functions, or another file access
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function, and have spaces or empty lines that are output before
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<function>header</function> is called. The same problem exists
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when using a single PHP/HTML file.
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<html>
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<?php
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// This will give an error. Note the output
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// above, which is before the header() call
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header('Location: http://www.example.com/');
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?>
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]]>
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</programlisting>
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</informalexample>
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<note>
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<para>
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In PHP 4, you can use output buffering to get around this problem,
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with the overhead of all of your output to the browser being buffered
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in the server until you send it. You can do this by calling
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<function>ob_start</function> and <function>ob_end_flush</function>
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in your script, or setting the <literal>output_buffering</literal>
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configuration directive on in your &php.ini; or
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server configuration files.
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</para>
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</note>
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</para>
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<para>
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If you want the user to be prompted to save the data you are
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sending, such as a generated PDF file, you can use the <ulink
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url="&url.rfc2183;">Content-Disposition</ulink> header to
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supply a recommended filename and force the browser to display the
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save dialog.
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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// We'll be outputting a PDF
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header("Content-type: application/pdf");
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// It will be called downloaded.pdf
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header("Content-Disposition: attachment; filename=downloaded.pdf");
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// The PDF source is in original.pdf
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readfile('original.pdf');
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?>
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]]>
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</programlisting>
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</informalexample>
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<note>
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<para>
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There is a bug in Microsoft Internet Explorer 4.01 that prevents
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this from working. There is no workaround. There is also a bug
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in Microsoft Internet Explorer 5.5 that interferes with this,
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which can be resolved by upgrading to Service Pack 2 or later.
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</para>
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</note>
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</para>
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<note>
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<simpara>
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If <link linkend="ini.safe-mode">safe mode</link> is enabled the
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uid of the script is added to the <literal>realm</literal> part
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of the <literal>WWW-Authenticate</literal> header if you set
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this header (used for HTTP Authentication).
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</simpara>
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</note>
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<para>
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See also <function>headers_sent</function>,
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<function>setcookie</function>, and the section on
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<link linkend="features.http-auth">HTTP authentication</link>.
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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