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153 lines
4.6 KiB
Plaintext
153 lines
4.6 KiB
Plaintext
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<TITLE>Custom error responses</TITLE>
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</HEAD>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<BODY
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#000080"
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ALINK="#FF0000"
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>
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<!--#include virtual="header.html" -->
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<H1 ALIGN="CENTER">Custom error responses</H1>
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<DL>
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<DT>Purpose
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<DD>Additional functionality. Allows webmasters to configure the response of
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Apache to some error or problem.
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<P>Customizable responses can be defined to be activated in the
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event of a server detected error or problem.
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<P>e.g. if a script crashes and produces a "500 Server Error"
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response, then this response can be replaced with either some
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friendlier text or by a redirection to another URL (local or
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external).
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<P>
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<DT>Old behavior
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<DD>NCSA httpd 1.3 would return some boring old error/problem message
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which would often be meaningless to the user, and would provide no
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means of logging the symptoms which caused it.<BR>
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<P>
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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.
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<P>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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<P>note the <CODE>REDIRECT_</CODE> prefix.
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<P>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.
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<STRONG>None</STRONG> of these will be set if your ErrorDocument is an
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<EM>external</EM> redirect (i.e. anything starting with a protocol name
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like <CODE>http:</CODE>, even if it refers to the same host as the
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server).<P>
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<DT>Configuration
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<DD> Use of "ErrorDocument" is enabled for .htaccess files when the
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<A HREF="mod/core.html#allowoverride">"FileInfo" override</A> is allowed.
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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. 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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<P>The syntax is,
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<P><CODE><A HREF="mod/core.html#errordocument">ErrorDocument</A></CODE>
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<3-digit-code> action
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<P>where the action can be,
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<OL>
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<LI>Text to be displayed. Prefix the text with a quote ("). Whatever
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follows the quote is displayed. <EM>Note: the (") prefix isn't
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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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</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>
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A new batch of environment variables will be initialized for use by a
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script which has been redirected to. Each new variable will have the
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prefix <CODE>REDIRECT_</CODE>. <CODE>REDIRECT_</CODE> environment
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variables are created from the CGI environment variables which existed
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prior to the redirect, they are renamed with a <CODE>REDIRECT_</CODE>
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prefix, i.e. <CODE>HTTP_USER_AGENT</CODE> becomes
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<CODE>REDIRECT_HTTP_USER_AGENT</CODE>. In addition to these new
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variables, Apache will define <CODE>REDIRECT_URL</CODE> and
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<CODE>REDIRECT_STATUS</CODE> to help the script trace its origin.
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Both the original URL and the URL being redirected to can be logged in
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the access log.
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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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