Product Documentation

Migration of Apache mod_rewrite rules to the default syntax

The Apache HTTP Server provides an engine known as mod_rewrite for rewriting HTTP request URLs. If you migrate the mod_rewrite rules from Apache to the Citrix ADC, you boost back-end server performance. In addition, because the Citrix ADC typically load balances multiple (sometimes thousands of) Web servers, after migrating the rules to the Citrix ADC you will have a single point of control for these rules.

Following are examples of mod_rewrite functions, and translations of these functions into Rewrite and Responder policies on the Citrix ADC.

Converting URL variations into canonical URLs

On some Web servers you can have multiple URLs for a resource. Although the canonical URLs should be used and distributed, other URLs can exist as shortcuts or internal URLs. You can make sure that users see the canonical URL regardless of the URL used to make an initial request.

In the following examples, the URL /~user is converted to /u/user.

Apache mod_rewrite solution for converting a URL

RewriteRule ^/~([^/]+)/?(.*) /u/$1/$2[R]

Citrix ADC solution for converting a URL

add responder action act1 redirect '"/u/"+HTTP.REQ.URL.AFTER_STR("/~")' -bypassSafetyCheck yes
add responder policy pol1 'HTTP.REQ.URL.STARTSWITH("/~") && HTTP.REQ.URL.LENGTH.GT(2)' act1
bind responder global pol1 100

Converting Host Name Variations to Canonical Host Names

You can enforce the use of a particular host name for reaching a site. For example, you can enforce the use of www.example.com instead of example.com.

Apache mod_rewrite solution for enforcing a particular host name for sites running on a port other than 80


RewriteCond %{HTTP_HOST}   !^www.example.com
RewriteCond %{HTTP_HOST}   !^$
RewriteCond %{SERVER_PORT} !^80$
RewriteRule ^/(.*)         http://www.example.com:%{SERVER_PORT}/$1 [L,R]

Apache mod_rewrite solution for enforcing a particular host name for sites running on port 80


RewriteCond %{HTTP_HOST}   !^www.example.com
RewriteCond %{HTTP_HOST}   !^$
RewriteRule ^/(.*)         http://www.example.com/$1 [L,R]

Citrix ADC solution for enforcing a particular host name for sites running on a port other than 80


add responder action act1 redirect '"http://www.example.com:"+CLIENT.TCP.DSTPORT+HTTP.REQ.URL' -bypassSafetyCheck yes
add responder policy pol1 '!HTTP.REQ.HOSTNAME.CONTAINS("www.example.com")&&!HTTP.REQ.HOSTNAME.EQ("")&&!HTTP.REQ.HOSTNAME.PORT.EQ(80)&&HTTP.REQ.HOSTNAME.CONTAINS("example.com")' act1
bind responder global pol1 100 END

Citrix ADC solution for enforcing a particular host name for sites running on port 80


add responder action act1 redirect '"http://www.example.com"+HTTP.REQ.URL' -bypassSafetyCheck yes
add responder policy pol1  '!HTTP.REQ.HOSTNAME.CONTAINS("www.example.com")&&!HTTP.REQ.HOSTNAME.EQ("")&&HTTP.REQ.HOSTNAME.PORT.EQ(80)&&HTTP.REQ.HOSTNAME.CONTAINS("example.com")' act1
bind responder global  pol1 100 END

Moving a document root

Usually the document root of a Web server is based on the URL “/”. However, the document root can be any directory. You can redirect traffic to the document root if it changes from the top-level “/” directory to another directory.

In the following examples, you change the document root from / to /e/www. The first two examples simply replace one string with another. The third example is more universal because, along with replacing the root directory, it preserves the rest of the URL (the path and query string), for example, redirecting /example/file.html to /e/www/example/file.html.

Apache mod_rewrite solution for moving the document root


RewriteEngine on
RewriteRule   ^/$  /e/www/  [R]

Citrix ADC solution for moving the document root


add responder action act1 redirect '"/e/www/"' -bypassSafetyCheck yes
add responder policy pol1 'HTTP.REQ.URL.EQ("/")' act1
bind responder global pol1 100

Citrix ADC solution for moving the document root and appending path information to the request


add responder action act1 redirect '"/e/www"+HTTP.REQ.URL' -bypassSafetyCheck yes
add responder policy pol1 '!HTTP.REQ.URL.STARTSWITH("/e/www/")' act1
bind responder global pol1 100 END

Moving home directories to a new web server

You may want to redirect requests that are sent to home directories on a Web server to a different Web server. For example, if a new Web server is replacing an old one over time, as you migrate home directories to the new location you need to redirect requests for the migrated home directories to the new Web server.

In the following examples, the host name for the new Web server is newserver.

Apache mod_rewrite solution for redirecting to another Web server


RewriteRule   ^/(.+)  http://newserver/$1     [R,L]

Citrix ADC solution for redirecting to another Web server (method 1)


add responder  action act1 redirect '"http://newserver"+HTTP.REQ.URL' -bypassSafetyCheck yes
add responder policy pol1 'HTTP.REQ.URL.REGEX_MATCH(re#^/(.+)#)'   act1
bind responder global pol1 100 END

Citrix ADC solution for redirecting to another Web server (method 2)


add responder  action act1 redirect '"http://newserver"+HTTP.REQ.URL' -bypassSafetyCheck yes
add responder policy pol1 'HTTP.REQ.URL.LENGTH.GT(1)' act1
bind responder global pol1 100 END

Working with structured home directories

Typically, a site with thousands of users has a structured home directory layout. For example, each home directory may reside under a subdirectory that is named using the first character of the user name. For example, the home directory for jsmith (/~jsmith/anypath) might be /home/j/smith/.www/anypath, and the home directory for rvalveti (/~rvalveti/anypath) might be /home/r/rvalveti/.www/anypath.

The following examples redirect requests to the home directory.

Apache mod_rewrite solution for structured home directories

RewriteRule   ^/~(([a-z])[a-z0-9]+)(.*)  /home/$2/$1/.www$3

Citrix ADC solution for structured home directories


Citrix ADC solution for structured home directories

add rewrite action act1 replace ‘HTTP.REQ.URL’ ‘“/home/”+ HTTP.REQ.URL.AFTER_STR(“~”).PREFIX(1)+”/”+ HTTP.REQ.URL.AFTER_STR(“~”).BEFORE_STR(“/”)+”/.www”+HTTP.REQ.URL.SKIP('/',1)’ -bypassSafetyCheck yes add rewrite policy pol1 ‘HTTP.REQ.URL.PATH.STARTSWITH(“/~”)’ act1 bind rewrite global pol1 100

## Redirecting invalid URLs to other web servers

If a URL is not valid, it should be redirected to another Web server. For example, you should redirect to another Web server if a file that is named in a URL does not exist on the server that is named in the URL.

On Apache, you can perform this check using mod\_rewrite. On the Citrix ADC, an HTTP callout can check for a file on a server by running a script on the server. In the following Citrix ADC examples, a script named file\_check.cgi processes the URL and uses this information to check for the presence of the target file on the server. The script returns TRUE or FALSE, and the Citrix ADC uses the value that the script returns to validate the policy.

In addition to performing the redirection, the Citrix ADC can add custom headers or, as in the second Citrix ADC example, it can add text in the response body.

## Apache mod_rewrite solution for redirection if a URL is wrong

RewriteCond /your/docroot/%{REQUEST_FILENAME} !-f RewriteRule ^(.+) http://webserverB.com/$1 [R]


## Citrix ADC solution for redirection if a URL is wrong (method 1)

add HTTPCallout Call set policy httpCallout Call -IPAddress 10.102.59.101 -port 80 -hostExpr ‘“10.102.59.101”’ -returnType BOOL -ResultExpr ‘HTTP.RES.BODY(100).CONTAINS(“True”)’ -urlStemExpr ‘“/cgi-bin/file_check.cgi”’ -parameters query=http.req.url.path -headers Name(“ddd”) add responder action act1 redirect ‘“http://webserverB.com”+HTTP.REQ.URL’ -bypassSafetyCheck yes add responder policy pol1 ‘!HTTP.REQ.HEADER(“Name”).EXISTS && !SYS.HTTP_CALLOUT(call)’ act1 bind responder global pol1 100


## Citrix ADC solution for redirection if a URL is wrong (method 2)

add HTTPCallout Call set policy httpCallout Call -IPAddress 10.102.59.101 -port 80 -hostExpr ‘“10.102.59.101”’ -returnType BOOL -ResultExpr ‘HTTP.RES.BODY(100).CONTAINS(“True”)’ -urlStemExpr ‘“/cgi-bin/file_check.cgi”’ -parameters query=http.req.url.path -headers Name(“ddd”) add responder action act1 respondwith ‘“HTTP/1.1 302 Moved Temporarily\r\nLocation: http://webserverB.com”+HTTP.REQ.URL+”\r\n\r\nHTTPCallout Used”’ -bypassSafetyCheck yes add responder policy pol1 ‘!HTTP.REQ.HEADER(“Name”).EXISTS && !SYS.HTTP_CALLOUT(call)’ act1 bind responder global pol1 100


## Rewriting a URL based on time

You can rewrite a URL based on the time. The following examples change a request for example.html to example.day.html or example.night.html, depending on the time of day.

## Apache mod_rewrite solution for rewriting a URL based on the time

RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700 RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900 RewriteRule ^example.html$ example.day.html [L] RewriteRule ^example.html$ example.night.html


## Citrix ADC solution for rewriting a URL based on the time

add rewrite action act1 insert_before ‘HTTP.REQ.URL.PATH.SUFFIX('.',0)’ ‘“day.”’ add rewrite action act2 insert_before ‘HTTP.REQ.URL.PATH.SUFFIX('.',0)’ ‘“night.”’ add rewrite policy pol1 ‘SYS.TIME.WITHIN(LOCAL 07h 00m,LOCAL 18h 59m)’ act1 add rewrite policy pol2 ‘true’ act2 bind rewrite global pol1 101 bind rewrite global pol2 102


## Redirecting to a new file name (Invisible to the User)

If you rename a Web page, you can continue to support the old URL for backward compatibility while preventing users from recognizing that the page was renamed.

In the first two of the following examples, the base directory is /~quux/. The third example accommodates any base directory and the presence of query strings in the URL.

## Apache mod_rewrite solution for managing a file name change in a fixed location

RewriteEngine on RewriteBase /~quux/ RewriteRule ^foo.html$ bar.html


## Citrix ADC solution for managing a file name change in a fixed location

add rewrite action act1 replace ‘HTTP.REQ.URL.AFTER_STR(“/~quux”).SUBSTR(“foo.html”)’ ‘“bar.html”’ add rewrite policy pol1 ‘HTTP.REQ.URL.ENDSWITH(“/~quux/foo.html”)’ act1 bind rewrite global pol1 100


## Citrix ADC solution for managing a file name change regardless of the base directory or query strings in the URL

add rewrite action act1 replace ‘HTTP.REQ.URL.PATH.SUFFIX('/',0)’ ‘“bar.html”’ Add rewrite policy pol1 ‘HTTP.REQ.URL.PATH.CONTAINS(“foo.html”)’ act1 Bind rewrite global pol1 100


## Redirecting to new file name (user-visible URL)

If you rename a Web page, you may want to continue to support the old URL for backward compatibility and allow users to see that the page was renamed by changing the URL that is displayed in the browser.

In the first two of the following examples, redirection occurs when the base directory is /~quux/. The third example accommodates any base directory and the presence of query strings in the URL.

## Apache mod_rewrite solution for changing the file name and the URL displayed in the browser

RewriteEngine on RewriteBase /~quux/ RewriteRule ^old.html$ new.html [R]


## Citrix ADC solution for changing the file name and the URL displayed in the browser

add responder action act1 redirect ‘HTTP.REQ.URL.BEFORE_STR(“foo.html”)+”new.html”’ -bypassSafetyCheck yes add responder policy pol1 ‘HTTP.REQ.URL.ENDSWITH(“/~quux/old.html”)’ act1 bind responder global pol1 100


## Citrix ADC solution for changing the file name and the URL displayed in the browser regardless of the base directory or query strings in the URL

add responder action act1 redirect ‘HTTP.REQ.URL.PATH.BEFORE_STR(“old.html”)+”new.html”+HTTP.REQ.URL.AFTER_STR(“old.html”)’ -bypassSafetyCheck yes add responder policy pol1 ‘HTTP.REQ.URL.PATH.CONTAINS(“old.html”)’ act1 bind responder global pol1 100


## Accommodating browser dependent content

To accommodate browser-specific limitations—at least for important top-level pages—it is sometimes necessary to set restrictions on the browser type and version. For example, you might want to set a maximum version for the latest Netscape variants, a minimum version for Lynx browsers, and an average feature version for all others.

The following examples act on the HTTP header "User-Agent", such that if this header begins with "Mozilla/3", the page MyPage.html is rewritten to MyPage.NS.html. If the browser is "Lynx" or "Mozilla" version 1 or 2, the URL becomes MyPage.20.html. All other browsers receive page MyPage.32.html.

## Apache mod_rewrite solution for browser-specific settings

RewriteCond %{HTTP_USER_AGENT} ^Mozilla/3.* RewriteRule ^MyPage.html$ MyPage.NS.html [L] RewriteCond %{HTTP_USER_AGENT} ^Lynx/.* [OR] RewriteCond %{HTTP_USER_AGENT} ^Mozilla/[12].* RewriteRule ^MyPage.html$ MyPage.20.html [L] RewriteRule ^fMyPage.html$ MyPage.32.html [L] Citrix ADC solution for browser-specific settings add patset pat1 bind patset pat1 Mozilla/1 bind Patset pat1 Mozilla/2 bind patset pat1 Lynx bind Patset pat1 Mozilla/3 add rewrite action act1 insert_before ‘HTTP.REQ.URL.SUFFIX’ ‘“NS.”’ add rewrite action act2 insert_before ‘HTTP.REQ.URL.SUFFIX’ ‘“20.”’ add rewrite action act3 insert_before ‘HTTP.REQ.URL.SUFFIX’ ‘“32.”’ add rewrite policy pol1 ‘HTTP.REQ.HEADER(“User-Agent”).STARTSWITH_INDEX(“pat1”).EQ(4)’ act1 add rewrite policy pol2 ‘HTTP.REQ.HEADER(“User-Agent”).STARTSWITH_INDEX(“pat1”).BETWEEN(1,3)’ act2 add rewrite policy pol3 ‘!HTTP.REQ.HEADER(“User-Agent”).STARTSWITH_ANY(“pat1”)’ act3 bind rewrite global pol1 101 END bind rewrite global pol2 102 END bind rewrite global pol3 103 END


## Blocking access by robots

You can block a robot from retrieving pages from a specific directory or a set of directories to ease up the traffic to and from these directories. You can restrict access based on the specific location or you can block requests based on information in User-Agent HTTP headers.

In the following examples, the Web location to be blocked is /~quux/foo/arc/, the IP addresses to be blocked are 123.45.67.8 and 123.45.67.9, and the robot’s name is NameOfBadRobot.

## Apache mod_rewrite solution for blocking a path and a User-Agent header

RewriteCond %{HTTP_USER_AGENT} ^NameOfBadRobot.* RewriteCond %{REMOTE_ADDR} ^123.45.67.[8-9]$ RewriteRule ^/~quux/foo/arc/.+ - [F]


## Citrix ADC solution for blocking a path and a User-Agent header

add responder action act1 respondwith ‘“HTTP/1.1 403 Forbidden\r\n\r\n”’ add responder policy pol1 ‘HTTP.REQ.HEADER(“User_Agent”).STARTSWITH(“NameOfBadRobot”)&&CLIENT.IP.SRC.EQ(123.45.67.8)&&CLIENT.IP.SRC.EQ(123.45.67.9) && HTTP.REQ.URL.STARTSWITH(“/~quux/foo/arc”)’ act1 bind responder global pol1 100


## Blocking access to inline images

If you find people frequently going to your server to copy inline graphics for their own use (and generating unnecessary traffic), you may want to restrict the browser’s ability to send an HTTP Referer header.

In the following example, the graphics are located in [Example](http://www.quux-corp.de/~quux/).

## Apache mod_rewrite solution for blocking access to an inline image

RewriteCond %{HTTP_REFERER} !^$ RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.$ RewriteRule ..gif$ - [F]


## Citrix ADC solution for blocking access to an inline image

add patset pat1 bind patset pat1 .gif bind patset pat1 .jpeg add responder action act1 respondwith ‘“HTTP/1.1 403 Forbidden\r\n\r\n”’ add responder policy pol1 ‘!HTTP.REQ.HEADER(“Referer”).EQ(“”) && !HTTP.REQ.HEADER(“Referer”).STARTSWITH(“http://www.quux-corp.de/~quux/”)&&HTTP.REQ.URL.ENDSWITH_ANY(“pat1”)’ act1 bind responder global pol1 100


## Creating extensionless links

To prevent users from knowing application or script details on the server side, you can hide file extensions from users. To do this, you may want to support extensionless links. You can achieve this behavior by using rewrite rules to add an extension to all requests, or to selectively add extensions to requests.

The first two of the following examples show adding an extension to all request URLs. In the last example, one of two file extensions is added. Note that in the last example, the mod_rewrite module can easily find the file extension because this module resides on the Web server. In contrast, the Citrix ADC must invoke an HTTP callout to check the extension of the requested file on the Web server. Based on the callout response, the Citrix ADC adds the .html or .php extension to the request URL.

> **Note**
>
> In the second Citrix ADC example, an HTTP callout is used to query a script named
file_check.cgi hosted on the server. This script checks whether the argument that is provided in the callout is a valid file name.

## Apache mod_rewrite solution for adding a .php extension to all requests

RewriteRule ^/?([a-z]+)$ $1.php [L]


## Citrix ADC policy for adding a .php extension to all requests

add rewrite action act1 insert_after ‘HTTP.REQ.URL’ ‘“.php”’ add rewrite policy pol1 ‘HTTP.REQ.URL.PATH.REGEX_MATCH(re#^/([a-z]+)$#)’ act1 bind rewrite global pol1 100


## Apache mod_rewrite solution for adding either .html or .php extensions to requests

RewriteCond %{REQUEST_FILENAME}.php -f RewriteRule ^/?([a-zA-Z0-9]+)$ $1.php [L] RewriteCond %{REQUEST_FILENAME}.html –f RewriteRule ^/?([a-zA-Z0-9]+)$ $1.html [L]


## Citrix ADC policy for adding either .html or .php extensions to requests

add HTTPCallout Call_html add HTTPCallout Call_php set policy httpCallout Call_html -IPAddress 10.102.59.101 -port 80 -hostExpr ‘“10.102.59.101”’ -returnType BOOL -ResultExpr ‘HTTP.RES.BODY(100).CONTAINS(“True”)’ -urlStemExpr ‘“/cgi-bin/file_check.cgi”’ -parameters query=http.req.url+”.html” set policy httpCallout Call_php -IPAddress 10.102.59.101 -port 80 -hostExpr ‘“10.102.59.101”’ -returnType BOOL -ResultExpr ‘HTTP.RES.BODY(100).CONTAINS(“True”)’ -urlStemExpr ‘“/cgi-bin/file_check.cgi”’ -parameters query=http.req.url+”.php” add patset pat1 bind patset pat1 .html bind patset pat1 .php bind patset pat1 .asp bind patset pat1 .cgi add rewrite action act1 insert_after ‘HTTP.REQ.URL.PATH’ ‘“.html”’ add rewrite action act2 insert_after “HTTP.REQ.URL.PATH” ‘“.php”’ add rewrite policy pol1 ‘!HTTP.REQ.URL.CONTAINS_ANY(“pat1”) && SYS.HTTP_CALLOUT(Call_html)’ act1 add rewrite policy pol2 ‘!HTTP.REQ.URL.CONTAINS_ANY(“pat1”) && SYS.HTTP_CALLOUT(Call_php)’ act2 bind rewrite global pol1 100 END bind rewrite global pol2 101 END


## Redirecting a Working URI to a New Format

Suppose that you have a set of working URLs that resemble the following:

/index.php?id=nnnn


To change these URLs to /nnnn and make sure that search engines update their indexes to the new URI format, you need to do the following:

-  Redirect the old URIs to the new ones so that search engines update their indexes.
-  Rewrite the new URI back to the old one so that the index.php script runs correctly.

To accomplish this, you can insert marker code into the query string (making sure that the marker code is not seen by visitors), and then removing the marker code for the index.php script.

The following examples redirect from an old link to a new format only if a marker is not present in the query string. The link that uses the new format is re-written back to the old format, and a marker is added to the query string.

## Apache mod_rewrite solution

RewriteCond %{QUERY_STRING} !marker RewriteCond %{QUERY_STRING} id=([-a-zA-Z0-9+]+) RewriteRule ^/?index.php$ %1? [R,L] RewriteRule ^/?([-a-zA-Z0-9+]+)$ index.php?marker&id=$1 [L] Citrix ADC solution add responder action act_redirect redirect ‘HTTP.REQ.URL.PATH.BEFORE_STR(“index.php”)+HTTP.REQ.URL.QUERY.VALUE(“id”)’ -bypassSafetyCheck yes add responder policy pol_redirect ‘!HTTP.REQ.URL.QUERY.CONTAINS(“marker”)&& HTTP.REQ.URL.QUERY.VALUE(“id”).REGEX_MATCH(re/[-a-zA-Z0-9_+]+/) && HTTP.REQ.URL.PATH.CONTAINS(“index.php”)’ act_redirect bind responder global pol_redirect 100 END add rewrite action act1 replace ‘HTTP.REQ.URL.PATH.SUFFIX('/',0)’ ‘“index.phpmarker&id=”+HTTP.REQ.URL.PATH.SUFFIX('/',0)’ -bypassSafetyCheck yes add rewrite policy pol1 ‘!HTTP.REQ.URL.QUERY.CONTAINS(“marker”)’ act1 bind rewrite global pol1 100 END


## Ensuring That a Secure Server Is Used for Selected Pages

To make sure that only secure servers are used for selected Web pages, you can use the following Apache mod_rewrite code or Citrix ADC Responder policies.

## Apache mod_rewrite solution

RewriteCond %{SERVER_PORT} !^443$ RewriteRule ^/?(page1|page2|page3|page4|page5)$ https://www.example.com/%1 [R,L]


## Citrix ADC solution using regular expressions

add responder action res_redirect redirect ‘“https://www.example.com”+HTTP.REQ.URL’ -bypassSafetyCheck yes add responder policy pol_redirect ‘!CLIENT.TCP.DSTPORT.EQ(443)&&HTTP.REQ.URL.REGEX_MATCH(re/page[1-5]/)’ res_redirect bind responder global pol_redirect 100 END


## Citrix ADC solution using pattern sets

add patset pat1 bind patset pat1 page1 bind patset pat1 page2 bind patset pat1 page3 bind patset pat1 page4 bind patset pat1 page5 add responder action res_redirect redirect ‘“https://www.example.com”+HTTP.REQ.URL’ -bypassSafetyCheck yes add responder policy pol_redirect ‘!CLIENT.TCP.DSTPORT.EQ(443)&&HTTP.REQ.URL.CONTAINS_ANY(“pat1”)’ res_redirect bind responder global pol_redirect 100 END

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