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Apache HTTP Server
Custom error responses
- Purpose
- Additional functionality. Allows webmasters to configure the response of Apache to some
error or problem.
Customizable responses can be defined to be activated in the event of a server detected
error or problem.
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).
- Old behavior
- 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.
- New behavior
- The server can be asked to;
- Display some other text, instead of the NCSA hard coded messages, or
- redirect to a local URL, or
- redirect to an external URL.
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.
To achieve this, Apache will define new CGI-like environment variables, e.g.
REDIRECT_HTTP_ACCEPT=*/*, image/gif, image/x-xbitmap, image/jpeg
REDIRECT_HTTP_USER_AGENT=Mozilla/1.1b2 (X11; I; HP-UX A.09.05 9000/712)
REDIRECT_PATH=.:/bin:/usr/local/bin:/etc
REDIRECT_QUERY_STRING=
REDIRECT_REMOTE_ADDR=121.345.78.123
REDIRECT_REMOTE_HOST=ooh.ahhh.com
REDIRECT_SERVER_NAME=crash.bang.edu
REDIRECT_SERVER_PORT=80
REDIRECT_SERVER_SOFTWARE=Apache/0.8.15
REDIRECT_URL=/cgi-bin/buggy.pl
note the REDIRECT_ prefix.
At least REDIRECT_URL and REDIRECT_QUERY_STRING 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. None of these
will be set if your ErrorDocument is an external redirect (i.e.,
anything starting with a scheme name like http:, even if it refers to the
same host as the server).
- Configuration
- Use of "ErrorDocument" is enabled for .htaccess files when the
"FileInfo"
override is allowed.
Here are some examples...
ErrorDocument 500 /cgi-bin/crash-recover
ErrorDocument 500 "Sorry, our script crashed. Oh dear
ErrorDocument 500 http://xxx/
ErrorDocument 404 /Lame_excuses/not_found.html
ErrorDocument 401 /Subscription/how_to_subscribe.html
The syntax is,
ErrorDocument
<3-digit-code> action
where the action can be,
- Text to be displayed. Prefix the text with a quote ("). Whatever follows the
quote is displayed. Note: the (") prefix isn't displayed.
- An external URL to redirect to.
- A local URL to redirect to.
How to cure bad breath permanently. Choosing
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reviews.
Custom error responses and redirects
- Purpose
- Apache's behavior to redirected URLs has been modified so that additional environment
variables are available to a script/server-include.
- Old behavior
- Standard CGI vars were made available to a script which has been redirected to. No
indication of where the redirection came from was provided.
- New behavior
- 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
REDIRECT_. 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
becomes REDIRECT_HTTP_USER_AGENT. In addition to these new variables, Apache
will define REDIRECT_URL and REDIRECT_STATUS to help the script
trace its origin. Both the original URL and the URL being redirected to can be logged in
the access log.
If the ErrorDocument specifies a local redirect to a CGI script, the script should include
a "Status:" 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:
:
print "Content-type: text/html\n";
printf "Status: %s Condition Intercepted\n", $ENV{"REDIRECT_STATUS"};
:
If the script is dedicated to handling a particular error condition, such as 404 Not Found,
it can use the specific code and error text instead.
Apache HTTP Server
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