Apache rule based on http status and on response status

Question

I want to create an apache rule based on the user agent AND on the http response.

For example, I want a rule that says: if user-agent=test and the status of the request based on this user agent=503, redirect the request to /home

On the documentation page, I found a variable for based on the user agent( HTTP_USER_AGENT ), but nothing for the http status. Is that possible?

Answer 1

You could do something like the following, to define a custom 503 "error document" when a request with the User-Agent "test" is sent:

<If "%{HTTP_USER_AGENT} == 'test'">
    ErrorDocument 503 https://example.com/home
</If>

When an absolute URL is used in the ErrorDocument directive, it will trigger a 302 (temporary) redirect to that URL should the stated HTTP response status be triggered by Apache.

So, the above will issue an external redirect to /home when a request with User-Agent "test" triggers a 503 response in Apache.

This will need to be defined in the main server config (not .htaccess ) to stand a chance of catching an arbitrary 503 generated by the server. Although it is questionable whether this would catch such an "unexpected" error since a 503 - if triggered by the server itself - is a rather serious/fatal error. Ordinarily, a 503 is a controlled response for when the application goes into "maintenance mode". In this scenario, you would arguably handle this differently.

Alternatively, the REDIRECT_STATUS environment variable holds the HTTP response status code so you could do something like the following using mod_rewrite to override the ErrorDocument and trigger a 302 redirect to /home :

RewriteEngine On    

RewriteCond %{ENV:REDIRECT_STATUS} =503
RewriteCond %{HTTP_USER_AGENT} "=test"
RewriteRule ^ /home [R=302,L]

If the 503 is triggered by the application itself (eg. in PHP) then this will not be caught by the above rule(s).

Answer 2

The documentation page mentions the following environment variables:

HTTP_ACCEPT
HTTP_COOKIE
HTTP_FORWARDED
HTTP_HOST
HTTP_PROXY_CONNECTION
HTTP_REFERER
HTTP_USER_AGENT
AUTH_TYPE
CONN_REMOTE_ADDR
CONTEXT_PREFIX
CONTEXT_DOCUMENT_ROOT
IPV6
PATH_INFO
QUERY_STRING
REMOTE_ADDR
REMOTE_HOST
REMOTE_IDENT
REMOTE_PORT
REMOTE_USER
REQUEST_METHOD
SCRIPT_FILENAME
DOCUMENT_ROOT
SCRIPT_GROUP
SCRIPT_USER
SERVER_ADDR
SERVER_ADMIN
SERVER_NAME
SERVER_PORT
SERVER_PROTOCOL
SERVER_SOFTWARE
TIME_YEAR
TIME_MON
TIME_DAY
TIME_HOUR
TIME_MIN
TIME_SEC
TIME_WDAY
TIME
API_VERSION
CONN_REMOTE_ADDR
HTTPS
IS_SUBREQ
REMOTE_ADDR
REQUEST_FILENAME
REQUEST_SCHEME
REQUEST_URI
THE_REQUEST

Sadly, I am unable to find any variables that show the HTTP status.