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| <manualpage metafile="custom-error.xml.meta"> |
| |
| <title>Custom Error Responses</title> |
| |
| <summary> |
| <p>Additional functionality allows webmasters to configure the response |
| of Apache to some error or problem.</p> |
| |
| <p>Customizable responses can be defined to be activated in the event of |
| a server detected error or problem.</p> |
| |
| <p>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> |
| </summary> |
| |
| <section id="behavior"> |
| <title>Behavior</title> |
| |
| <section> |
| <title>Old Behavior</title> |
| |
| <p>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.</p> |
| </section> |
| |
| <section> |
| <title>New Behavior</title> |
| |
| <p>The server can be asked to:</p> |
| |
| <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:</p> |
| |
| <example> |
| 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 |
| </example> |
| |
| <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 <directive module="core">ErrorDocument</directive> is an |
| <em>external</em> redirect (anything starting with a |
| scheme name like <code>http:</code>, even if it refers to the same host |
| as the server).</p> |
| </section> |
| </section> |
| |
| <section id="configuration"> |
| <title>Configuration</title> |
| |
| <p>Use of <directive module="core">ErrorDocument</directive> is enabled |
| for .htaccess files when the |
| <directive module="core">AllowOverride</directive> is set accordingly.</p> |
| |
| <p>Here are some examples...</p> |
| |
| <example> |
| 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 |
| </example> |
| |
| <p>The syntax is,</p> |
| |
| <example> |
| ErrorDocument <3-digit-code> <action> |
| </example> |
| |
| <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> |
| </section> |
| |
| <section id="custom"> |
| <title>Custom Error Responses and Redirects</title> |
| |
| <p>Apache's behavior to redirected URLs has been modified so |
| that additional environment variables are available to a |
| script/server-include.</p> |
| |
| <section> |
| <title>Old behavior</title> |
| |
| <p>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> |
| </section> |
| |
| <section> |
| <title>New behavior</title> |
| |
| <p>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.</p> |
| |
| <p>If the ErrorDocument specifies a local redirect to a CGI |
| script, the script should include a "<code>Status:</code>" |
| 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> |
| |
| <example> |
| ... <br /> |
| print "Content-type: text/html\n"; <br /> |
| printf "Status: %s Condition Intercepted\n", $ENV{"REDIRECT_STATUS"}; <br /> |
| ... |
| </example> |
| |
| <p>If the script is dedicated to handling a particular error |
| condition, such as <code>404 Not Found</code>, it can |
| use the specific code and error text instead.</p> |
| |
| <p>Note that the script <em>must</em> emit an appropriate |
| <code>Status:</code> header (such as <code>302 Found</code>), if the |
| response contains a <code>Location:</code> header (in order to issue a |
| client side redirect). Otherwise the <code>Location:</code> header may |
| have no effect.</p> |
| </section> |
| </section> |
| </manualpage> |