Apache HTTP Server Version 1.3
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.
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 Version 1.3
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