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109 lines
4.1 KiB
HTML
109 lines
4.1 KiB
HTML
<HTML>
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<HEAD>
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<TITLE>Custom error responses</TITLE>
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</HEAD>
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<BODY>
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<!--#include virtual="header.html" -->
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<H1>Custom error responses</H1>
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<DL>
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<DT>Purpose
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<DD>Additional functionality. Allows web-masters to configure the response of
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Apache to some error or problem.<BR>
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<P>Customizable responses can be defined to be activated in the event of a
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server detected error or problem.<BR>
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e.g. if a script crashes and produces a "500 Server Error" response, then
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this response can be replaced with either some friendlier text or by a
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redirection to another URL (local or external).
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<DT>Old behavior
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<DD>NCSA httpd 1.3 would return some boring old error/problem message which
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would often be meaningless to the user, and would provide no means of logging
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the symptoms which caused it.<BR><BR>
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<DT>New behavior
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<DD>The server can be asked to;
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<OL>
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<LI>Display some other text, instead of the NCSA hard coded messages, or
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<LI>redirect to a local URL, or
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<LI>redirect to an external URL.
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</OL>
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<P>Redirecting to another URL can be useful, but only if some information
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can be passed which can then be used to explain and/or log the error/problem
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more clearly.<BR>To achieve this, Apache will define new CGI-like environment
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variables, e.g.
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<blockquote><code>
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REDIRECT_HTTP_ACCEPT=*/*, image/gif, image/x-xbitmap, image/jpeg <br>
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REDIRECT_HTTP_USER_AGENT=Mozilla/1.1b2 (X11; I; HP-UX A.09.05 9000/712) <br>
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REDIRECT_PATH=.:/bin:/usr/local/bin:/etc <br>
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REDIRECT_QUERY_STRING= <br>
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REDIRECT_REMOTE_ADDR=121.345.78.123 <br>
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REDIRECT_REMOTE_HOST=ooh.ahhh.com <br>
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REDIRECT_SERVER_NAME=crash.bang.edu <br>
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REDIRECT_SERVER_PORT=80 <br>
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REDIRECT_SERVER_SOFTWARE=Apache/0.8.15 <br>
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REDIRECT_URL=/cgi-bin/buggy.pl <br>
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</code></blockquote>
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note the <code>REDIRECT_</code> prefix. <p>
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At least <code>REDIRECT_URL</code> and <code>REDIRECT_QUERY_STRING</code> will
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be passed to the new URL (assuming it's a cgi-script or a cgi-include). The
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other variables will exist only if they existed prior to the error/problem.<p>
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<DT>Configuration
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<DD><em>file: </em>server configuration<BR>
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<P>Here are some examples...
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<blockquote><code>
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ErrorDocument 500 /cgi-bin/crash-recover <br>
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ErrorDocument 500 "Sorry, our script crashed because %s. Oh dear<br>
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ErrorDocument 500 http://xxx/ <br>
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ErrorDocument 404 /Lame_excuses/not_found.html <br>
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ErrorDocument 401 /Subscription/how_to_subscribe.html
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</code></blockquote>
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The syntax is, <p>
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<code><A HREF="mod/core.html#errordocument">ErrorDocument</A></code>
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<3-digit-code> action <p>
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where the action can be,
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<OL>
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<LI>Text to be displayed.<BR>Prefix the text with a quote ("). Whatever
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follows the quote is displayed. If the error/problem produced any additional
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information, it can be specified using <code>%s</code>.
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<em>Note: the (") prefix isn't displayed.</em>
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<LI>An external URL to redirect to.
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<LI>A local URL to redirect to.
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</OL>
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<P><code>ErrorDocument</code> definitions are sensitive to a
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<code>SIGHUP</code>, so you can change any of the definitions or add new ones
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prior to sending a <code>SIGHUP</code> (kill -1) signal.
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</DL>
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<P><HR><P>
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<h2>Custom error responses and redirects</H2>
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<DL>
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<DT>Purpose
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<DD>Apache's behavior to redirected URLs has been modified so that additional
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environment variables are available to a script/server-include.<p>
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<DT>Old behavior
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<DD>Standard CGI vars were made available to a script which has been
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redirected to. No indication of where the redirection came from was provided.
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<p>
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<DT>New behavior
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<DD>A new batch of environment variables will be initialized for use by a
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script which has been redirected to.<BR>
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Each new variable will have the prefix <code>REDIRECT_</code>.<BR>
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REDIRECT_ environment variables are created from the CGI environment
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variables which existed prior to the redirect, they are renamed with a
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REDIRECT_ prefix, i.e. HTTP_USER_AGENT -> REDIRECT_HTTP_USER_AGENT.<BR>
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In addition to these new variables, Apache will define
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<code>REDIRECT_URL</code> and <code>REDIRECT_STATUS</code> to help the script
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trace its origin.<BR>
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Logging: both the original URL and the URL being redirected to, will
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now be logged correctly in the access log.<p>
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</DL>
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<!--#include virtual="footer.html" -->
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</BODY>
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</HTML>
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