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Expressions for HTTP and cache-control headers

August 20, 2024
Contributed by: 
C C S

One common method of evaluating HTTP traffic is to examine the headers in a request or a response. A header can perform a number of functions, including the following:

  • Provide cookies that contain data about the sender.
  • Identify the type of data that is being transmitted.
  • Identify the route that the data has traveled (the Via header).

Note

If an operation is used to evaluate both header and text data, the header-based operation always overrides the text-based operation. For example, the AFTER_STR operation, when applied to a header, overrides text-based AFTER_STR operations for all instances of the current header type.

Prefixes for HTTP headers

The following table describes expression prefixes that extract HTTP headers.

HTTP Header Prefix Description    
HTTP.REQ.HEADER(“") Returns the contents of the HTTP header specified by the argument. The header name cannot exceed 32 characters. Note that this prefix returns the value from the Host header by default. To use this value as a hostname you need to typecast it as follows: http.req.header("host").typecast_http_hostname_t. For more information on typecasting, see [Typecasting data](/en-us/citrix-adc/12-1/appexpert/policies-and-expressions/ns-typecasting-data-wrapper-con.html).    
HTTP.REQ.FULL_HEADER Returns the contents of the complete set of HTTP header fields including the request line (for example, “GET /brochures/index.html HTTP/1.1”) and the terminating \r\n\r\n sequence.    
HTTP.REQ.DATE Returns the contents of the HTTP Date header. The following date formats are recognized: RFC822. Sun, 06 Jan 1980 8:49:37 GMT, RFC850. Sunday, 06-Jan-80 9:49:37 GMT, ASCII TIME. Sun Jan 6 08:49:37 1980. To evaluate a Date header as a date object, see Default Syntax Expressions: Working with Dates, Times, and Numbers.    
HTTP.REQ.COOKIE (Name/Value List) Returns the contents of the HTTP Cookie header.    
HTTP.REQ.TXID Returns the HTTP transaction ID. The value is a function of an internal transaction number, system boot time and system MAC address.    
HTTP.RES.HEADER(“") Returns the contents of the HTTP header specified by the argument. The header name cannot exceed 32 characters.    
HTTP.RES.FULL_HEADER Returns the contents of the complete set of HTTP header fields including the status line (for example, “HTTP/1.1 200 OK”) and the terminating \r\n\r\n sequence.    
HTTP.RES.SET_COOKIE or HTTP.RES.SET_COOKIE2 Returns the HTTP Set-Cookie header object in a response.    
HTTP.RES.SET_COOKIE() or HTTP.RES.SET_COOKIE2() Returns the cookie of the specified name if it is present. If it is not present, returns a text object of length 0. Returns UNDEF if more than 15 Set-Cookie headers are present and the specified cookie was not found in these headers.    
HTTP.RES.SET_COOKIE().DOMAIN or HTTP.RES.SET_COOKIE2().DOMAIN Returns the value of the first Domain field in the cookie. For example, if the cookie is Set-Cookie : Customer = “ABC”; DOMAIN=”.abc.com”; DOMAIN=.xyz.com, the following expression returns .abc.com: http.res.set_cookie.cookie(“customer”).domain. A string of zero length is returned if the Domain field or its value is absent.    
HTTP.RES.SET_COOKIE.EXISTS() or HTTP.RES.SET_COOKIE2.EXISTS() Returns a Boolean TRUE if a Cookie with the name specified in the argument exists in the Set-Cookie header. This prefix returns UNDEF if more than 15 Set-Cookie headers are present and the named cookie is not in the first 15 headers.    
HTTP.RES.SET_COOKIE.COOKIE().EXPIRES or HTTP.RES.SET_COOKIE2.COOKIE().EXPIRES Returns the Expires field of the cookie. This is a date string that can be evaluated as a number, as a time object, or as text. If multiple Expires fields are present, the first one is returned. If the Expires field is absent, a text object of length zero is returned. To evaluate the returned value as a time object, see Default Syntax Expressions: Working with Dates, Times, and Numbers.    
HTTP.RES.SET_COOKIE.COOKIE().PATH PATH.GET(n)    
o HTTP.RES.SET_COOKIE2.COOKIE().PATH PATH.GET(n) Returns the value of Path field of the cookie as a slash- (“/”) separated list. Multiple instances of a slash are treated as single slash. If multiple Path fields are present, the value of the first instance is returned. For example, the following is a cookie with two path fields:Set-Cookie : Customer = “ABC”; PATH=”/a//b/c”; PATH= “/x/y/z”. The following expression returns /a//b/c from this cookie: http.res.set_cookie.cookie(“Customer”).path. The following expression returns b: http.res.set_cookie.cookie(“Customer”).path.get(2). Quotes are stripped from the returned value. A string of zero length is returned if the Path field or its value is absent.  
HTTP.RES.SET_COOKIE.COOKIE().PATH.IGNORE_EMPTY_ELEMENTS or HTTP.RES.SET_COOKIE2.COOKIE().PATH.IGNORE_EMPTY_ELEMENTS Ignores the empty elements in the list. For example, in the list a=10,b=11, ,c=89, the element delimiter in the list is , and the list has an empty element following a=10. The element following b=11 is not considered an empty element. As another example, in the following expression, if a request contains Cust_Header : 123,,24, ,15 the following expression returns a value of 4: http.req.header(“Cust_Header”).typecast_list_t(’,’).ignore_empty_elements.count. The following expression returns a value of 5: http.req.header(“Cust_Header”).typecast_list_t(’,’).count    
HTTP.RES.SET_COOKIE.COOKIE().PORT or HTTP.RES.SET_COOKIE2.COOKIE().PORT Returns the value of Port field of the cookie. Operate as a comma-separated list. For example, the following expression returns 80. 2580 from Set-Cookie : Customer = “ABC”; PATH=”/a/b/c”; PORT= “80, 2580”: http.res.set_cookie.cookie(“ABC”).port. A string of zero length is returned if the Port field or value is absent.    
HTTP.RES.SET_COOKIE.COOKIE().PORT.IGNORE_EMPTY_ELEMENTS or HTTP.RES.SET_COOKIE2.COOKIE().PORT.IGNORE_EMPTY_ELEMENTS Ignores the empty elements in the list. For example, in the list a=10,b=11, ,c=89, the element delimiter in the list is , and the list has an empty element following a=10. The element following b=11 is not considered an empty element.As another example, in the following expression, if a request contains Cust_Header : 123,,24, ,15 the following expression returns a value of 4: http.req.header(“Cust_Header”).typecast_list_t(’,’).ignore_empty_elements.count. The following expression returns a value of 5: http.req.header(“Cust_Header”).typecast_list_t(’,’).count    
HTTP.RES.SET_COOKIE.COOKIE().VERSION or HTTP.RES.SET_COOKIE2.COOKIE().VERSION Returns the value of the first Version field in the cookie as a decimal integer. For example, the following expression returns 1 from the cookie Set-Cookie : Customer = “ABC”; VERSION = “1”; VERSION = “0”: http.res.set_cookie.cookie(“CUSTOMER”).version. A zero is returned if the Version field or its value is absent or if the value is not a decimal number.    
HTTP.RES.SET_COOKIE.COOKIE(, ) or HTTP.RES.SET_COOKIE2.COOKIE(, ) Returns the nth instance (0-based) of the cookie with the specified name. If the cookie is absent, returns a text object of length 0. Returns UNDEF if more than 15 Set-Cookie headers are present and the cookie is not found.    
HTTP.RES.SET_COOKIE.COOKIE(, ).DOMAIN or HTTP.RES.SET_COOKIE2.COOKIE(, ).DOMAIN Returns the value of the Domain field of the first cookie with the specified name. For example, the following expression returns a value of abc.com from the cookie Set-Cookie : Customer = “ABC”; DOMAIN=”.abc.com”; DOMAIN=.xyz.com: http.res.set_cookie.cookie(“CUSTOMER”).domain. A string of zero length is returned if the Domain field or its value is absent.    
HTTP.RES.SET_COOKIE.COOKIE(, ).EXPIRES or HTTP.RES.SET_COOKIE2.COOKIE(, ).EXPIRES Returns the nth instance (0-based) of the Expires field of the cookie with the specified name as a date string. The value can be operated upon as a time object that supports a number of date formats. If the Expires attribute is absent a string of length zero is returned.    
HTTP.RES.SET_COOKIE.COOKIE(, ).PATH PATH.GET(i) or HTTP.RES.SET_COOKIE2.COOKIE(, ).PATH PATH.GET(i) Returns the value of the Path field of the nth cookie, as a ‘/’ separated list. Multiple /s are treated as a single /. For example, the following expression returns /a//b/c from the cookie Set-Cookie : Customer = “ABC”; PATH=”/a//b/c”; PATH= ”/x/y/z”: http.res.set_cookie.cookie(“CUSTOMER”).path. The following returns b: http.res.set_cookie.cookie(“CUSTOMER”).path.get(2). A string of zero length is returned if the Path field or its value is absent.
HTTP.RES.SET_COOKIE.COOKIE(, ).PATH.IGNORE_EMPTY_ELEMENTS or HTTP.RES.SET_COOKIE2.COOKIE(, ).PATH.IGNORE_EMPTY_ELEMENTS Ignores the empty elements in the list. For example, in the list a=10,b=11, ,c=89, the element delimiter in the list is , and the list has an empty element following a=10. The element following b=11 is not considered an empty element. As another example, in the following expression, if a request contains Cust_Header : 123,,24, ,15 the following expression returns a value of 4: http.req.header(“Cust_Header”).typecast_list_t(’,’).ignore_empty_elements.count. The following expression returns a value of 5: http.req.header(“Cust_Header”).typecast_list_t(’,’).count    
HTTP.RES.SET_COOKIE.COOKIE(, ).PORT or HTTP.RES.SET_COOKIE2.COOKIE(, ).PORT Returns the value or values of the Port field of the named cookie as a ‘,’ separated list. For example, the following expression returns 80, 2580 from the cookie Set-Cookie : Customer = “ABC”; PATH=”/a/b/c”; PORT= “80, 2580”: http.res.set_cookie.cookie(“ABC”).port. A string of zero length is returned if the Port field or its value is absent.    
HTTP.RES.SET_COOKIE.COOKIE(, ).PORT.IGNORE_EMPTY_ELEMENTS or HTTP.RES.SET_COOKIE2.COOKIE(, ).PORT.IGNORE_EMPTY_ELEMENTS Ignores the empty elements in the list. For example, in the list a=10,b=11, ,c=89, the element delimiter in the list is , and the list has an empty element following a=10. The element following b=11 is not considered an empty element. As another example, in the following expression, if a request contains Cust_Header : 123,,24, ,15 the following expression returns a value of 4: http.req.header(“Cust_Header”).typecast_list_t(’,’).ignore_empty_elements.count. The following expression returns a value of 5: http.req.header(“Cust_Header”).typecast_list_t(’,’).count    
HTTP.RES.SET_COOKIE.COOKIE(, ).VERSION or HTTP.RES.SET_COOKIE2.COOKIE(, ).VERSION Returns the value of Version field of the nth cookie as a decimal integer. A string of zero length is returned if the Port field or its value is absent.    
HTTP.RES.TXID Returns the HTTP transaction ID. The value is a function of an internal transaction number, system boot time and system MAC address.    

Operations for HTTP headers

The following table describes operations that you can specify with the prefixes for HTTP headers.

HTTP Header Operation Description
http header .EXISTS Returns a Boolean TRUE if an instance of the specified header type exists. Following is an example: http.req.header(“Cache-Control”).exists
http header.CONTAINS” http header.CONTAINS() Returns a Boolean TRUE if the argument appears in any instance of the header value. Note: This operation overrides any text-based Contains operations on all instances of the current header type.
http header .COUNT Returns the number of headers in a request or response, to a maximum of 15 headers of the same type. The result is undefined if there are more than 15 instances of the header.
http header.AFTER_STR() Extracts the text that follows the first occurrence of the argument. The headers are evaluated from the last instance to the first.
http header.BEFORE_STR() Extracts the text that appears prior to the first occurrence of the input argument. The headers are evaluated from the last instance to the first.
http header.INSTANCE() An HTTP header can occur multiple times in a request or a response. This operation returns the header that occurs of places before the final instance. For example, instance(0) selects the last instance of the current type, instance(1) selects the next-to-last instance, and so on. This prefix cannot be used in bidirectional policies.
http header.SUBSTR() Extracts the text that matches the argument. The headers are evaluated from the last instance to the first.
http header.VALUE() An HTTP header can occur multiple times in a request or a response. VALUE(0) selects the value in the last instance, VALUE(1) selects the value in the next-to-last instance, and so on. The argument cannot exceed 14.

Prefixes for cache-control headers

The following prefixes apply specifically to Cache-Control headers.

HTTP Header Prefix Description
HTTP.REQ.CACHE_CONTROL Returns a Cache-Control header in an HTTP request.
HTTP.RES.CACHE_CONTROL Returns a Cache-Control header in an HTTP response.

Operations for cache-control headers

You can apply any of the operations for HTTP headers to Cache-Control headers. For more information, see Operations for HTTP headers.

In addition, the following operations identify specific types of Cache-Control headers. See RFC 2616 for information about these header types.

HTTP Header Operation Description
Cache-Control header.NAME() Returns as a text value the name of the Cache-Control header that corresponds to the nth component in a name-value list, as specified by . The index of the name-value component is 0-based. If the that is specified by the integer argument is greater than the number of components in the list, a zero-length text object is returned. Following is an example: http.req.cache_control.name(3).contains("some_text")
Cache-Control header.IS_INVALID Returns a Boolean TRUE if the Cache-Control header is not present in the request or response. Following is an example: http.req.cache_control.is_invalid
Cache-Control header.IS_PRIVATE Returns a Boolean TRUE if the Cache-Control header has the value Private. Following is an example: http.req.cache_control.is_private
Cache-Control header.IS_PUBLIC Returns a Boolean TRUE if the Cache-Control header has the value Private. Following is an example: http.req.cache_control.is_public
Cache-Control header.IS_NO_STORE Returns a Boolean TRUE if the Cache-Control header has the value No-Store. Following is an example: http.req.cache_control.is_no_store
Cache-Control header.IS_NO_CACHE Returns a Boolean TRUE if the Cache-Control header has the value No-Cache. Following is an example: http.req.cache_control.is_no_cache
Cache-Control header.IS_MAX_AGE Returns a Boolean TRUE if the Cache-Control header has the value Max-Age. Following is an example: http.req.cache_control.is_max_age
Cache-Control header.IS_MIN_FRESH Returns a Boolean TRUE if the Cache-Control header has the value Min-Fresh. Following is an example: http.req.cache_control.is_min_fresh
Cache-Control header.IS_MAX_STALE Returns a Boolean TRUE if the Cache-Control header has the value Max-Stale. Following is an example: http.req.cache_control.is_max_stale
Cache-Control header.IS_MUST_REVALIDATE Returns a Boolean TRUE if the Cache-Control header has the value Must-Revalidate. Following is an example: http.req.cache_control.is_must_revalidate
Cache-Control header.IS_NO_TRANSFORM Returns a Boolean TRUE if the Cache-Control header has the value No-Transform. Following is an example: http.req.cache_control.is_no_transform
Cache-Control header.IS_ONLY_IF_CACHED Returns a Boolean TRUE if the Cache-Control header has the value Only-If-Cached. Following is an example: http.req.cache_control.is_only_if_cached
Cache-Control header.IS_PROXY_REVALIDATE Returns a Boolean TRUE if the Cache-Control header has the value Proxy-Revalidate. Following is an example: http.req.cache_control.is_proxy_revalidate
Cache-Control header.IS_S_MAXAGE Returns a Boolean TRUE if the Cache-Control header has the value S-Maxage. Following is an example: http.req.cache_control.is_s_maxage
Cache-Control header.IS_UNKNOWN Returns a Boolean TRUE if the Cache-Control header is of an unknown type. Following is an example: http.req.cache_control.is_unknown
Cache-Control header.MAX_AGE Returns the value of the Cache-Control header Max-Age. If this header is absent or invalid, 0 is returned. Following is an example: http.req.cache_control.max_age.le(3)
Cache-Control header.MAX_STALE Returns the value of the Cache-Control header Max-Stale. If this header is absent or invalid, 0 is returned. Following is an example: http.req.cache_control.max_stale.le(3)
Cache-Control header.MIN_FRESH Returns the value of the Cache-Control header Min-Fresh. If this header is absent or invalid, 0 is returned. Following is an example: http.req.cache_control.min_fresh.le(3)
Cache-Control header.S_MAXAGE Returns the value of the Cache-Control header S-Maxage. If this header is absent or invalid, 0 is returned.Following is an example: http.req.cache_control.s_maxage.eq(2)
Expressions for HTTP and cache-control headers
August 20, 2024
Contributed by: 
C C S
August 20, 2024
Contributed by: 
C C S

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