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