cgi_path.html revision 57d0156f7bbd9ea3a72342cf9912aba61d118702
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>PATH_INFO Changes in the CGI Environment</title>
</head>
<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
vlink="#000080" alink="#FF0000">
<!--#include virtual="header.html" -->
<h1 align="CENTER">PATH_INFO Changes in the CGI
Environment</h1>
<hr />
<h2><a id="over" name="over">Overview</a></h2>
<p>As implemented in Apache 1.1.1 and earlier versions, the
method Apache used to create PATH_INFO in the CGI environment
was counterintuitive, and could result in crashes in certain
cases. In Apache 1.2 and beyond, this behavior has changed.
Although this results in some compatibility problems with
certain legacy CGI applications, the Apache 1.2 behavior is
scripts can be easily modified (<a href="#compat">see
below</a>).</p>
<h2><a id="prob" name="prob">The Problem</a></h2>
<p>Apache 1.1.1 and earlier implemented the PATH_INFO and
SCRIPT_NAME environment variables by looking at the filename,
not the URL. While this resulted in the correct values in many
cases, when the filesystem path was overloaded to contain path
information, it could result in errant behavior. For example,
if the following appeared in a config file:</p>
<pre>
</pre>
"/ralph" is information to be passed onto the CGI. If this
configuration was in place, and a request came for
"<code>/cgi-</code>". Obviously, the latter is incorrect. In
certain cases, this could even cause the server to crash.</p>
<h2><a id="solution" name="solution">The Solution</a></h2>
<p>Apache 1.2 and later now determine SCRIPT_NAME and PATH_INFO
by looking directly at the URL, and determining how much of the
URL is client-modifiable, and setting PATH_INFO to it. To use
the above example, PATH_INFO would be set to
"<code>/script</code>", and SCRIPT_NAME to
"<code>/cgi-ralph</code>". This makes sense and results in no
server behavior problems. It also permits the script to be
guaranteed that
will always be an accessible URL that points to the current
script, something which was not necessarily true with previous
versions of Apache.</p>
<p>However, the "<code>/ralph</code>" information from the
<code>Alias</code> directive is lost. This is unfortunate, but
we feel that using the filesystem to pass along this sort of
information is not a recommended method, and a script making
use of it "deserves" not to work. Apache 1.2b3 and later,
however, do provide <a href="#compat">a workaround.</a></p>
<h2><a id="compat" name="compat">Compatibility with Previous
Servers</a></h2>
<p>It may be necessary for a script that was designed for
earlier versions of Apache or other servers to need the
information that the old PATH_INFO variable provided. For this
purpose, Apache 1.2 (1.2b3 and later) sets an additional
variable, FILEPATH_INFO. This environment variable contains the
value that PATH_INFO would have had with Apache 1.1.1.</p>
<p>A script that wishes to work with both Apache 1.2 and
earlier versions can simply test for the existence of
FILEPATH_INFO, and use it if available. Otherwise, it can use
PATH_INFO. For example, in Perl, one might use:</p>
<pre>
$path_info = $ENV{'FILEPATH_INFO'} || $ENV{'PATH_INFO'};
</pre>
<p>By doing this, a script can work with all servers supporting
Apache.</p>
<!--#include virtual="footer.html" -->
</body>
</html>