reference/network/functions/header.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://docbook.org/ns/docbook" xml:id="function.header">
 <refnamediv>
  <refname>header</refname>
  <refpurpose>Send a raw HTTP header</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>void</type><methodname>header</methodname>
   <methodparam><type>string</type><parameter>header</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>replace</parameter><initializer>&true;</initializer></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>response_code</parameter><initializer>0</initializer></methodparam>
  </methodsynopsis>
  <para>
   <function>header</function> is used to send a raw <acronym>HTTP</acronym>
   header. See the <link xlink:href="&url.rfc;2616">HTTP/1.1 specification</link>
   for more information on <acronym>HTTP</acronym> headers.
  </para>
  <para>
   Remember that <function>header</function> 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
   <function>include</function>, or <function>require</function>,
   functions, or another file access function, and have spaces or empty
   lines that are output before <function>header</function> is called.
   The same problem exists when using a single PHP/HTML file.
   <informalexample>
    <programlisting role="php">
<![CDATA[
<html>
<?php
/* This will give an error. Note the output
 * above, which is before the header() call */
header('Location: http://www.example.com/');
exit;
?>
]]>
    </programlisting>
   </informalexample>
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>header</parameter></term>
     <listitem>
      <para>
       The header string.
      </para>
      <para>
       There are two special-case header calls.  The first is a header
       that starts with the string "<literal>HTTP/</literal>" (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 <literal>ErrorDocument</literal> directive), you may want to
       make sure that your script generates the proper status code.
      </para>
      <para>
       <informalexample>
        <programlisting role="php">
<![CDATA[
<?php
// This example illustrates the "HTTP/" special case
// Better alternatives in typical use cases include:
// 1. header($_SERVER["SERVER_PROTOCOL"] . " 404 Not Found");
//    (to override http status messages for clients that are still using HTTP/1.0)
// 2. http_response_code(404); (to use the default message)
header("HTTP/1.1 404 Not Found");
?>
]]>
        </programlisting>
       </informalexample>
      </para>
      <para>
       The second special case is the "Location:" header.  Not only does
       it send this header back to the browser, but it also returns a
       <literal>REDIRECT</literal> (302) status code to the browser
       unless the <literal>201</literal> or
       a <literal>3xx</literal> status code has already been set.
      </para>
      <para>
       <informalexample>
        <programlisting role="php">
<![CDATA[
<?php
header("Location: http://www.example.com/"); /* Redirect browser */

/* Make sure that code below does not get executed when we redirect. */
exit;
?>
]]>
        </programlisting>
       </informalexample>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>replace</parameter></term>
     <listitem>
      <para>
       The optional <parameter>replace</parameter> 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:
      </para>
      <para>
       <informalexample>
        <programlisting role="php">
<![CDATA[
<?php
header('WWW-Authenticate: Negotiate');
header('WWW-Authenticate: NTLM', false);
?>
]]>
        </programlisting>
       </informalexample>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>response_code</parameter></term>
     <listitem>
      <para>
       Forces the HTTP response code to the specified value. Note that this
       parameter only has an effect if the <parameter>header</parameter> is
       not empty.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   &return.void;
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   On failure to schedule the header to be sent, <function>header</function>
   issues an <constant>E_WARNING</constant> level error.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Download dialog</title>
    <para>
     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 <link
     xlink:href="&url.rfc;2183">Content-Disposition</link> header to
     supply a recommended filename and force the browser to display the
     save dialog.
    </para>
    <programlisting role="php">
<![CDATA[
<?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');
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>Caching directives</title>
    <para>
     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:
    </para>
    <programlisting role="php">
<![CDATA[
<?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
?>
]]>
    </programlisting>
    <para>
     <note>
      <para>
       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.
      </para>
      <para>
       Additionally, <function>session_cache_limiter</function> and
       the <literal>session.cache_limiter</literal> configuration
       setting can be used to automatically generate the correct
       caching-related headers when sessions are being used.
      </para>
     </note>
    </para>
   </example>
  </para>
  <para>
   <example>
    <title>Setting a cookie</title>
    <para>
     <function>setcookie</function> provides a convenient way to set cookies.
     To set a cookie that includes attributes which <function>setcookie</function>
     doesn't support, <function>header</function> can be used.
    </para>
    <para>
     For example, the following sets a cookie that includes a
     <literal>Partitioned</literal> attribute.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
header('Set-Cookie: name=value; Secure; Path=/; SameSite=None; Partitioned;');
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  &note.network.header.sapi;
  <note>
   <para>
    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
    <function>ob_start</function> and <function>ob_end_flush</function>
    in your script, or setting the <literal>output_buffering</literal>
    configuration directive on in your &php.ini; or
    server configuration files.
   </para>
  </note>
  <note>
   <para>
    The HTTP status header line will always be the first sent
    to the client, regardless of the actual <function>header</function>
    call being the first or not. The status may be overridden
    by calling <function>header</function> with a new status line
    at any time unless the HTTP headers have already been sent.
   </para>
  </note>
  <note>
   <para>
    Most contemporary clients accept relative <acronym>URI</acronym>s as argument to
    <link xlink:href="&spec.http1.1;#section-7.1.2">Location:</link>,
    but some older clients require an absolute URI
    including the scheme, hostname and absolute path. You can usually use
    <varname>$_SERVER['HTTP_HOST']</varname>,
    <varname>$_SERVER['PHP_SELF']</varname>
    and <function>dirname</function> to make an absolute URI from a
    relative one yourself:
    <informalexample>
     <programlisting role="php">
<![CDATA[
<?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;
?>
]]>
     </programlisting>
    </informalexample>
   </para>
  </note>
  <note>
   <para>
    Session ID is not passed with Location header even if <link
    linkend="ini.session.use-trans-sid">session.use_trans_sid</link> is
    enabled. It must by passed manually using <constant>SID</constant>
    constant.
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>headers_sent</function></member>
    <member><function>setcookie</function></member>
    <member><function>http_response_code</function></member>
    <member><function>header_remove</function></member>
    <member><function>headers_list</function></member>
    <member>
     The section on <link linkend="features.http-auth">HTTP
     authentication</link>
    </member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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