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| <h1 align="CENTER">Custom error responses</h1> |
| |
| <dl> |
| <dt>Purpose</dt> |
| |
| <dd> |
| Additional functionality. Allows webmasters to configure |
| the response of Apache to some error or problem. |
| |
| <p>Customizable responses can be defined to be activated in |
| the event of a server detected error or problem.</p> |
| |
| <p>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).</p> |
| </dd> |
| |
| <dt>Old behavior</dt> |
| |
| <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 /> |
| </dd> |
| |
| <dt>New behavior</dt> |
| |
| <dd> |
| The server can be asked to; |
| |
| <ol> |
| <li>Display some other text, instead of the NCSA hard |
| coded messages, or</li> |
| |
| <li>redirect to a local URL, or</li> |
| |
| <li>redirect to an external URL.</li> |
| </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.</p> |
| |
| <p>To achieve this, Apache will define new CGI-like |
| environment variables, <em>e.g.</em></p> |
| |
| <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> |
| |
| <p>note the <code>REDIRECT_</code> prefix.</p> |
| |
| <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. <strong>None</strong> of these will be |
| set if your ErrorDocument is an <em>external</em> redirect |
| (<em>i.e.</em>, anything starting with a scheme name like |
| <code>http:</code>, even if it refers to the same host as |
| the server).</p> |
| </dd> |
| |
| <dt>Configuration</dt> |
| |
| <dd> |
| Use of "ErrorDocument" is enabled for .htaccess files when |
| the <a href="mod/core.html#allowoverride">"FileInfo" |
| override</a> is allowed. |
| |
| <p>Here are some examples...</p> |
| |
| <blockquote> |
| <code>ErrorDocument 500 /cgi-bin/crash-recover<br /> |
| ErrorDocument 500 "Sorry, our script crashed. 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> |
| |
| <p>The syntax is,</p> |
| |
| <p><code><a |
| href="mod/core.html#errordocument">ErrorDocument</a></code> |
| <3-digit-code> action</p> |
| |
| <p>where the action can be,</p> |
| |
| <ol> |
| <li>Text to be displayed. Prefix the text with a quote |
| ("). Whatever follows the quote is displayed. <em>Note: |
| the (") prefix isn't displayed.</em></li> |
| |
| <li>An external URL to redirect to.</li> |
| |
| <li>A local URL to redirect to.</li> |
| </ol> |
| </dd> |
| </dl> |
| <hr /> |
| |
| <h2>Custom error responses and redirects</h2> |
| |
| <dl> |
| <dt>Purpose</dt> |
| |
| <dd>Apache's behavior to redirected URLs has been modified so |
| that additional environment variables are available to a |
| script/server-include.</dd> |
| |
| <dt>Old behavior</dt> |
| |
| <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.</dd> |
| |
| <dt>New behavior</dt> |
| |
| <dd>A new batch of environment variables will be initialized |
| for use by a script which has been redirected to. Each new |
| variable will have the prefix <code>REDIRECT_</code>. |
| <code>REDIRECT_</code> environment variables are created from |
| the CGI environment variables which existed prior to the |
| redirect, they are renamed with a <code>REDIRECT_</code> |
| prefix, <em>i.e.</em>, <code>HTTP_USER_AGENT</code> becomes |
| <code>REDIRECT_HTTP_USER_AGENT</code>. 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. Both the original URL and the URL being redirected to |
| can be logged in the access log.</dd> |
| </dl> |
| |
| <p>If the ErrorDocument specifies a local redirect to a CGI |
| script, the script should include a "<samp>Status:</samp>" |
| header field in its output in order to ensure the propagation |
| all the way back to the client of the error condition that |
| caused it to be invoked. For instance, a Perl ErrorDocument |
| script might include the following:</p> |
| <pre> |
| : |
| print "Content-type: text/html\n"; |
| printf "Status: %s Condition Intercepted\n", $ENV{"REDIRECT_STATUS"}; |
| : |
| </pre> |
| |
| <p>If the script is dedicated to handling a particular error |
| condition, such as <samp>404 Not Found</samp>, it can |
| use the specific code and error text instead.</p> |
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