Citrix Systems Network Router 9.2 User Manual

You can configure various expressions for working with text that flows through 
the NetScaler. Following are some examples of how you can parse text using an 
advanced expression:

•

Determine that a particular HTTP header exists.

For example, you may want to identify HTTP requests that contains a 
particular Accept-Language header for the purpose of directing the request 
to a particular server. 

•

Determine that a particular HTTP URL contains a particular string.

For example, you may want to block requests for particular URLs. Note 
that the string can occur at the beginning, middle, or end of another string.

•

Identify a POST request that is directed to a particular application.

For example, you may want to identify all POST requests that are directed 
to a database application for the purpose of refreshing cached application 
data.

Note that there are specialized tools for viewing the data stream for HTTP 
requests and responses. For example, you can download a Firefox Web browser 
plug-in that displays HTTP request and response headers from the following 
URL:

The following plug-in displays headers, query strings, POST data, and other 
information:

After downloading these plug-ins, they are accessible from the Firefox Tools 
menu. 

A text-based expression consists of at least one prefix to identify an element of 
data and usually (although not always) an operation on that prefix. Text-based 
operations can apply to any part of a request or a response. Basic operations on 
text include various types of string matches. 

For example, the following expression compares a header value with a string:

http.req.header("myHeader").contains("some-text")

Following expressions are examples of matching a file type in a request:

http.req.url.suffix.contains("jpeg") 

http.req.url.suffix.eq("jpeg")