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 <reference id="ref.http">
  <title>HTTP functions</title>
  <titleabbrev>HTTP</titleabbrev>

  <partintro>
   <simpara>
    These functions let you manipulate the output sent back to the
    remote browser right down to the HTTP protocol level.
   </simpara>
  </partintro>

  <refentry id="function.header">
   <refnamediv>
    <refname>header</refname>
    <refpurpose>Send a raw HTTP header</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>int</type><methodname>header</methodname>
      <methodparam><type>string</type><parameter>string</parameter></methodparam>
      <methodparam choice="opt"><type>bool</type><parameter>replace</parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>header</function> is used to send raw
     <acronym>HTTP</acronym> headers.  See the <ulink
     url="&spec.http1.1;">HTTP/1.1 specification</ulink> for more
     information on <acronym>HTTP</acronym> headers.
    </para>
    <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:
     <informalexample>
      <programlisting role="php">
<![CDATA[
header('WWW-Authenticate: Negotiate');
header('WWW-Authenticate: NTLM',false);
]]>
      </programlisting>
     </informalexample>
    </para>
    <para>
     There are two special-case header calls.  The first is the
     &quot;Location&quot; 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.
     <informalexample>
      <programlisting role="php">
<![CDATA[
header("Location: http://www.php.net/"); /* Redirect browser 
                                            to PHP web site */
exit;                 /* Make sure that code below does 
                         not get executed when we redirect. */
]]>
      </programlisting>
     </informalexample>
    </para>
    <note>
     <para>
      HTTP/1.1 requires an absolute <acronym>URI</acronym> as argument to
      <ulink url="&spec.http1.1;-sec14.html#sec14.30">Location:</ulink>
      including the scheme, hostname and absolute path, but
      some clients accept relative URIs. You can usually use
      $HTTP_SERVER_VARS['HTTP_HOST'], $HTTP_SERVER_VARS['PHP_SELF']
      and <function>dirname</function> to make an absolute URI from a
      relative one yourself:
      <informalexample>
       <programlisting>
<![CDATA[
header("Location: http://".$HTTP_SERVER_VARS['HTTP_HOST']
                      ."/".dirname($HTTP_SERVER_VARS['PHP_SELF'])
                      ."/".$relative_url);
]]>
       </programlisting>
      </informalexample>
     </para>
    </note>
    <para>
     The second special case is any header that starts with the
     string, &quot;<literal>HTTP/</literal>&quot; (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.
     <informalexample>
      <programlisting role="php">
<![CDATA[
header("HTTP/1.0 404 Not Found");
]]>
      </programlisting>
     </informalexample>
     <note>
      <para>
       In PHP 3, this only works when PHP is compiled as an Apache
       module. You can achieve the same effect using the
       <literal>Status</literal> header.
       <informalexample>
        <programlisting role="php">
<![CDATA[
header("Status: 404 Not Found");
]]>
        </programlisting>
       </informalexample>
      </para>
     </note>
    </para>
    <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
     <informalexample>
      <programlisting role="php">
<![CDATA[
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");    // Date in the past
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); 
                                                     // always modified
header("Cache-Control: no-store, no-cache, must-revalidate");  // HTTP/1.1
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");                          // HTTP/1.0
]]>
      </programlisting>
     </informalexample>
     <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>
    <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[
<?php require("user_logging.inc") ?>


<?php header ("Content-type: audio/x-pn-realaudio"); ?>
// Broken, Note the blank lines above
]]>
      </programlisting>
     </informalexample>
     <note>
      <para>
       In PHP 4, 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 <filename>php.ini</filename> or
       server configuration files.
      </para>
     </note>
    </para>    
    <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 <ulink
     url="&url.rfc2183;">Content-Disposition</ulink> header to
     supply a recommended filename and force the browser to display the
     save dialog.
     <informalexample>
      <programlisting role="php">
<![CDATA[
<?php
header("Content-type: application/pdf");
header("Content-Disposition: attachment; filename=downloaded.pdf");

/* ... output pdf file ... */
]]>
      </programlisting>
     </informalexample>
     <note>
      <para>
       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.
      </para>
     </note>
    </para>
    <para>
     See also <function>headers_sent</function>,
     <function>setcookie</function>, and the section on 
     <link linkend="features.http-auth">HTTP authentication</link>.
    </para>
   </refsect1>
  </refentry>

  <refentry id="function.headers-sent">
   <refnamediv>
    <refname>headers_sent</refname>
    <refpurpose>Returns &true; if headers have been sent</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>bool</type><methodname>headers_sent</methodname>
      <void/>
     </methodsynopsis>
    <para>
     This function returns &true; if the HTTP headers have already been
     sent, &false; otherwise.
    </para>
    <para>
     See also <function>header</function>
    </para>
   </refsect1>
  </refentry>

  <refentry id="function.setcookie">
   <refnamediv>
    <refname>setcookie</refname>
    <refpurpose>Send a cookie</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>int</type><methodname>setcookie</methodname>
      <methodparam><type>string</type><parameter>name</parameter></methodparam>
      <methodparam choice="opt"><type>string</type><parameter>value</parameter></methodparam>
      <methodparam choice="opt"><type>int</type><parameter>expire</parameter></methodparam>
      <methodparam choice="opt"><type>string</type><parameter>path</parameter></methodparam>
      <methodparam choice="opt"><type>string</type><parameter>domain</parameter></methodparam>
      <methodparam choice="opt"><type>int</type><parameter>secure</parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>setcookie</function> defines a cookie to be sent along
     with the rest of the header information.  Cookies must be sent
     <emphasis>before</emphasis> any other headers are sent (this is a
     restriction of cookies, not PHP). This requires you to place
     calls to this function before any <literal>&lt;html></literal> or
     <literal>&lt;head></literal> tags.
    </para>
    <para>
     All the arguments except the <parameter>name</parameter> argument
     are optional.  If only the name argument is present, the cookie
     by that name will be deleted from the remote client.  You may
     also replace any argument with an empty string
     (<emphasis>&quot;&quot;</emphasis>) in order to skip that
     argument.  The <parameter>expire</parameter> and
     <parameter>secure</parameter> arguments are integers and cannot
     be skipped with an empty string.  Use a zero
     (<emphasis>0</emphasis>) instead.  The
     <parameter>expire</parameter> argument is a regular Unix time
     integer as returned by the <function>time</function> or
     <function>mktime</function> functions.  The
     <parameter>secure</parameter> indicates that the cookie should
     only be transmitted over a secure HTTPS connection.
    </para>
    <para>
     Common Pitfalls:
     <itemizedlist>
      <listitem>
       <simpara>
        Cookies will not become visible until the next loading of a page that 
        the cookie should be visible for.
       </simpara>
      </listitem>
      <listitem>
       <simpara>
        Cookies must be deleted with the same parameters as they were set with.
       </simpara>
      </listitem>
     </itemizedlist>
    </para>
    <simpara>
     In PHP 3, multiple calls to <function>setcookie</function> in the same
     script will be performed in reverse order. If you are trying to
     delete one cookie before inserting another you should put the
     insert before the delete. In PHP 4, multiple calls to
     <function>setcookie</function> are performed in the order called.
    </simpara>
    <para>
     Some examples follow how to send cookies:
     <example>
      <title><function>setcookie</function> send examples</title>
      <programlisting role="php">
<![CDATA[
setcookie ("TestCookie", $value);
setcookie ("TestCookie", $value,time()+3600);  /* expire in 1 hour */
setcookie ("TestCookie", $value,time()+3600, "/~rasmus/", ".utoronto.ca", 1);
]]>
      </programlisting>
     </example>
    </para>
    <para>
     When deleting a cookie you should assure that the expiration date
     is in the past, to trigger the removal mechanism in your browser.
     Examples follow how to delete cookies send in previous example:
     <example>
      <title><function>setcookie</function> delete examples</title>
      <programlisting role="php">
<![CDATA[
// set the expiration date to one hour ago
setcookie ("TestCookie", "", time() - 3600);
setcookie ("TestCookie", "", time() - 3600, "/~rasmus/", ".utoronto.ca", 1);
]]>
      </programlisting>
     </example>
    </para>
    <para>
     Note that the value portion of the cookie will automatically be
     urlencoded when you send the cookie, and when it is received, it
     is automatically decoded and assigned to a variable by the same
     name as the cookie name.  To see the contents of our test
     cookie in a script, simply use one of the following examples:
     <informalexample>
      <programlisting role="php">
<![CDATA[
echo $TestCookie;
echo $HTTP_COOKIE_VARS["TestCookie"];
]]>
      </programlisting>
     </informalexample>
    </para>
    <para>
     You may also set array cookies by using array notation in the
     cookie name. This has the effect of setting as many cookies as
     you have array elements, but when the cookie is received by your
     script, the values are all placed in an array with the cookie's
     name:
     <informalexample>
      <programlisting role="php">
<![CDATA[
setcookie ("cookie[three]", "cookiethree");
setcookie ("cookie[two]", "cookietwo");
setcookie ("cookie[one]", "cookieone");
if (isset ($cookie)) {
    while (list ($name, $value) = each ($cookie)) {
        echo "$name == $value<br>\n";
    }
}
]]>
      </programlisting>
     </informalexample>
    </para>
    <para>
     For more information on cookies, see Netscape's cookie
     specification at <ulink
     url="&spec.cookies;">&spec.cookies;</ulink>.
    </para>
    <simpara>
     Microsoft Internet Explorer 4 with Service Pack 1 applied does
     not correctly deal with cookies that have their path parameter
     set.
    </simpara>
    <simpara>
     Netscape Communicator 4.05 and Microsoft Internet Explorer 3.x
     appear to handle cookies incorrectly when the path and time
     are not set.
    </simpara>
   </refsect1>
  </refentry>

 </reference>

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