To list all of the categories that are available for URL filtering, Symantec Protection Engine uses the Attribute-List response body extension in a response to an ICAP OPTIONS request. This extension is formally specified in the ICAP Extensions Internet Draft, section 5.2.
To use this extension, an OPTIONS response must specify the header Encapsulated:opt-body=0. Not all ICAP clients recognize the opt-body encapsulation, so Symantec Protection Engine makes the opt-body and Attribute-List optional. However, they are included by default.
To make it possible to disable their use, the OptBodyAllowed option is included in the configuration settings. If the OptBodyAllowed value is set to true (the default setting), then Attribute-List is included in OPTIONS responses. If the OptBodyAllowed value is set to false, then Attribute-List is not included in OPTIONS responses. If OptBodyAllowed is set to false, an ICAP client that wants to use the URL filtering in audit mode cannot obtain the list of filtering categories that are available.