jimw Wed Oct 31 17:27:31 2001 EDT
Modified files:
/phpdoc/en/functions http.xml
Log:
cleaned up header(), incorporated all notes.
Index: phpdoc/en/functions/http.xml
diff -u phpdoc/en/functions/http.xml:1.29 phpdoc/en/functions/http.xml:1.30
--- phpdoc/en/functions/http.xml:1.29 Tue Oct 30 13:41:26 2001
+++ phpdoc/en/functions/http.xml Wed Oct 31 17:27:31 2001
@@ -1,5 +1,5 @@
<?xml encoding="iso-8859-1"?>
-<!-- $Revision: 1.29 $ -->
+<!-- $Revision: 1.30 $ -->
<reference id="ref.http">
<title>HTTP functions</title>
<titleabbrev>HTTP</titleabbrev>
@@ -26,34 +26,32 @@
</funcprototype>
</funcsynopsis>
<para>
- The <function>header</function> function is used at the top of an
- <acronym>HTML</acronym> file to send raw <acronym>HTTP</acronym>
- header strings. See the <ulink url="&spec.http1.1;">HTTP 1.1
- Specification</ulink> for more information on raw http headers.
+ <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:
+ 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">
-header('www-authenticate: Negociate');
-header('www-authenticate: NTLM',false);
+header('WWW-Authenticate: Negotiate');
+header('WWW-Authenticate: NTLM',false);
</programlisting>
</informalexample>
</para>
<para>
There are two special-case header calls. The first is the
- "Location" header. Not only does it send this header
- back to the browser, it also returns a REDIRECT status code to
- Apache. From a script writer's point of view this should not be
- important, but for people who understand Apache internals it is
- important to understand.
+ "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.
<informalexample>
<programlisting role="php">
-header ("Location: http://www.php.net/";); /* Redirect browser
+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. */
@@ -62,71 +60,138 @@
</para>
<note>
<para>
- HTTP 1.1 requires an absolute URI as argument to
+ HTTP/1.1 requires an absolute <acronym>URI</acronym> as argument to
<ulink url="&spec.http1.1;-sec14.html#sec14.30">Location:</ulink>
- including protocol, hostname and absolute path. Some clients
- might accept relative URIs but you definetly should not rely on
- it. 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:
+ including the scheme, hostname and absolute path, but
+ some clients accept relative URIs. You can usually use
+ $HTTP_SERVER_VARS['HTTP_HOST'], $HTTP_SERVER_VARS['PHP_SELF']
+ and <function>dirname</function> to make an absolute URI from a
+ relative one yourself:
<informalexample>
<programlisting>
-header ("Location: http://".$HTTP_SERVER_VARS['HTTP_HOST']
- ."/".dirname($HTTP_SERVER_VARS['PHP_SELF'])
- ."/".$relative_url);
+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, "HTTP/" (case is not significant). For
- example, if you have your ErrorDocument 404 Apache directive
- pointed to a PHP script, it would be a good idea to make sure
- that your PHP script is actually generating a 404. The first
- thing you do in your script should then be:
+ The second special case is any 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.
<informalexample>
<programlisting role="php">
-header ("HTTP/1.0 404 Not Found");
+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">
+header("Status: 404 Not Found");
+ </programlisting>
+ </informalexample>
+ </para>
+ </note>
</para>
<para>
- PHP scripts often generate dynamic HTML that must not be cached
+ 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">
-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-cache, must-revalidate"); // HTTP/1.1
-header ("Pragma: no-cache"); // HTTP/1.0
+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 the <function>header</function> function must be
+ 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 will output before
+ 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">
-<?php require("user_logging.inc") ?>
+<?php require("user_logging.inc") ?>
-<?php header ("Content-Type: audio/x-pn-realaudio"); ?>
+<?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>
- See also <function>headers_sent</function>
+ 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.rfc1806;">Content-Disposition</ulink> header to
+ supply a recommended filename and force the browser to display the
+ save dialog.
+ <informalexample>
+ <programlisting role="php">
+<?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>
