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99 lines
4.2 KiB
Plaintext
99 lines
4.2 KiB
Plaintext
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>PATH_INFO Changes in the CGI Environment</title>
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</head>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
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vlink="#000080" alink="#FF0000">
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<!--#include virtual="header.html" -->
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<h1 align="center">PATH_INFO Changes in the CGI
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Environment</h1>
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<hr />
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<h2><a id="over" name="over">Overview</a></h2>
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<p>As implemented in Apache 1.1.1 and earlier versions, the
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method Apache used to create PATH_INFO in the CGI environment
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was counterintuitive, and could result in crashes in certain
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cases. In Apache 1.2 and beyond, this behavior has changed.
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Although this results in some compatibility problems with
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certain legacy CGI applications, the Apache 1.2 behavior is
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still compatible with the CGI/1.1 specification, and CGI
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scripts can be easily modified (<a href="#compat">see
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below</a>).</p>
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<h2><a id="prob" name="prob">The Problem</a></h2>
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<p>Apache 1.1.1 and earlier implemented the PATH_INFO and
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SCRIPT_NAME environment variables by looking at the filename,
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not the URL. While this resulted in the correct values in many
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cases, when the filesystem path was overloaded to contain path
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information, it could result in errant behavior. For example,
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if the following appeared in a config file:</p>
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<pre>
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Alias /cgi-ralph /usr/local/httpd/cgi-bin/user.cgi/ralph
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</pre>
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<p>In this case, <code>user.cgi</code> is the CGI script, the
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"/ralph" is information to be passed onto the CGI. If this
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configuration was in place, and a request came for
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"<code>/cgi-ralph/script/</code>", the code would set PATH_INFO
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to "<code>/ralph/script</code>", and SCRIPT_NAME to
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"<code>/cgi-</code>". Obviously, the latter is incorrect. In
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certain cases, this could even cause the server to crash.</p>
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<h2><a id="solution" name="solution">The Solution</a></h2>
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<p>Apache 1.2 and later now determine SCRIPT_NAME and PATH_INFO
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by looking directly at the URL, and determining how much of the
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URL is client-modifiable, and setting PATH_INFO to it. To use
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the above example, PATH_INFO would be set to
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"<code>/script</code>", and SCRIPT_NAME to
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"<code>/cgi-ralph</code>". This makes sense and results in no
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server behavior problems. It also permits the script to be
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guaranteed that
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"<code>http://$SERVER_NAME:$SERVER_PORT$SCRIPT_NAME$PATH_INFO</code>"
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will always be an accessible URL that points to the current
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script, something which was not necessarily true with previous
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versions of Apache.</p>
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<p>However, the "<code>/ralph</code>" information from the
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<code>Alias</code> directive is lost. This is unfortunate, but
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we feel that using the filesystem to pass along this sort of
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information is not a recommended method, and a script making
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use of it "deserves" not to work. Apache 1.2b3 and later,
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however, do provide <a href="#compat">a workaround.</a></p>
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<h2><a id="compat" name="compat">Compatibility with Previous
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Servers</a></h2>
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<p>It may be necessary for a script that was designed for
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earlier versions of Apache or other servers to need the
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information that the old PATH_INFO variable provided. For this
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purpose, Apache 1.2 (1.2b3 and later) sets an additional
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variable, FILEPATH_INFO. This environment variable contains the
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value that PATH_INFO would have had with Apache 1.1.1.</p>
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<p>A script that wishes to work with both Apache 1.2 and
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earlier versions can simply test for the existence of
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FILEPATH_INFO, and use it if available. Otherwise, it can use
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PATH_INFO. For example, in Perl, one might use:</p>
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<pre>
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$path_info = $ENV{'FILEPATH_INFO'} || $ENV{'PATH_INFO'};
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</pre>
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<p>By doing this, a script can work with all servers supporting
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the CGI/1.1 specification, including all versions of
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Apache.</p>
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<!--#include virtual="footer.html" -->
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</body>
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</html>
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