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| <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 |
| still compatible with the CGI/1.1 specification, and CGI |
| 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> |
| Alias /cgi-ralph /usr/local/httpd/cgi-bin/user.cgi/ralph |
| </pre> |
| |
| <p>In this case, <code>user.cgi</code> is the CGI script, the |
| "/ralph" is information to be passed onto the CGI. If this |
| configuration was in place, and a request came for |
| "<code>/cgi-ralph/script/</code>", the code would set PATH_INFO |
| to "<code>/ralph/script</code>", and SCRIPT_NAME to |
| "<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 |
| "<code>http://$SERVER_NAME:$SERVER_PORT$SCRIPT_NAME$PATH_INFO</code>" |
| 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 |
| the CGI/1.1 specification, including all versions of |
| Apache.</p> |
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