190 Citrix NetScaler Policy Configuration and Reference Guide
Note: If a request or response that you configure in an HTTP callout (-fullReqExpr or -resultExpr) contains the expression SYS.HTTP_CALLOUT, the callout can recursively generate additional callouts. You should avoid this. Also, be sure that the HTTP callout configuration is complete. For example, if the callout contains a rule but not a server where the callout is to be sent, it can return a value of “undefined.”
To configure a callout policy using the configuration utility
1. In the left navigation pane, expand AppExpert, and then click HTTP Callouts.
Expression-based
request to send to the
server
(fullReqExpr)
Exact HTTP request that the NetScaler is to send as an advanced
expression to 8191 characters.
If you specify this parameter, you must omit the httpMethod,
hostExpr, urlStemExpr, headers, and parameters
arguments.
The request expression is constrained by the feature where the
callout is used. For example, an HTTP.RES expression cannot be
used in a request-time policy bank or in a TCP content switching
policy bank.
The NetScaler does not check the validity of this request. You
must manually validate the request.
Return type
(returnType)
Type of data that the target application returns in the response to
the callout. Valid values:
•TEXT: Treat the returned value as a text string.
•NUM: Treat the returned value as a number.
•BOOL: Treat the returned value as a Boolean value.
Note: You cannot change the return type after it is set.
Expression to extract
data from the
response
(resultExpr)
Advanced expression that extracts HTTP.RES objects from the
response to the HTTP callout. The maximum length is 8191.
The operations in this expression must match the return type. For
example, if you configure a return type of text, the result
expression must be a text-based expression. If the return type is
num, the result expression (resultExpr) must return a
numeric value similar to the following:
"http.res.body(10000).length"
Note: In some cases, if you set a return type of TEXT and the
result sent from the server exceeds 16 KB, the result expression
can return NULL. For example, this can happen when the result is
a concatenated string that exceeds 16 KB.
Elements in an HTTP Callout Policy
Parameter Specifies