header-register-callback.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->

<refentry xml:id="function.header-register-callback" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>header_register_callback</refname>
  <refpurpose>Call a header function</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>header_register_callback</methodname>
   <methodparam><type>callable</type><parameter>callback</parameter></methodparam>
  </methodsynopsis>
  <para>
   Registers a function that will be called when PHP starts sending output.
  </para>
  <para>
   The <parameter>callback</parameter> is executed just after PHP prepares all
   headers to be sent, and before any other output is sent, creating a window
   to manipulate the outgoing headers before being sent.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>callback</parameter></term>
    <listitem>
     <para>
      Function called just before the headers are sent. It gets no parameters
      and the return value is ignored.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   &return.success;
  </para>
 </refsect1>
 
 <refsect1 role="examples">
  &reftitle.examples;
  <example xml:id="header-register-callback.example.basic">
   <title><function>header_register_callback</function> example</title>
   <programlisting role="php">
<![CDATA[
<?php

header('Content-Type: text/plain');
header('X-Test: foo');

function foo() {
 foreach (headers_list() as $header) {
   if (strpos($header, 'X-Powered-By:') !== false) {
     header_remove('X-Powered-By');
   }
   header_remove('X-Test');
 }
}

$result = header_register_callback('foo');
echo "a";
?>
]]>
   </programlisting>
   &example.outputs.similar;
   <screen>
<![CDATA[
Content-Type: text/plain

a
]]>
   </screen>
  </example>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <para>
   <function>header_register_callback</function> is executed just as the
   headers are about to be sent out, so any output from this function can
   break output.
  </para>
  &note.network.header.sapi;
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <simplelist>
   <member><function>headers_list</function></member>
   <member><function>header_remove</function></member>
   <member><function>header</function></member>
  </simplelist>
 </refsect1>

</refentry>

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