The caller Statement

Syntax

caller <protocol> {
    [ statements ]
}

The caller keyword checks the parent request to see if it matches a particular protocol. If so, it executes the given [statements], If the parent does not exist, or the parent protocol does not match, the statements are ignored.

<protocol>: The name of the protocol used by the virtual server which called this policy.
[ statements ]: If the protocol matches, the [statements] from inside of the caller section will be executed. These statements will still be executed in the context of the current request. The calling request can be accessed by using parent in attribute references.

That is, the caller keyword is a way to conditionally execute a subrequest. It is largely equivalent to something like:

if (parent && parent dictionary is RADIUS) {
    ... statements ...
}

However, for various internal reasons, that syntax is difficult to implement. For now, the caller keyword is the best approach.

A virtual server may the the target of multiple call keywords, each of which uses a different protocol. For example, a policy which handles RADIUS Access-Request packets may create a DHCP Discover packet in order to perform IP address allocation. The DHCP Discover packet will typically be processed through DHCPv4 virtual server. However, that virtual server may need to handle requests differently based on whether the original packet was RADIUS, or DHCPv4.

The caller keyword allows a virtual server to check where it is called from, and to apply different policies based on that information. The caller keywords is in some senses the counter-part to the call keyword.

It may have been possible to use if conditions to perform this check. However, doing so would involve creating additional syntax which would not have been as clear as using caller.

Example

This example copies the Client-Identifer from the parent DHCPv4 request to the current RADIUS reply packet, as the contents of the Filter-Id attribute.

caller dhcpv4 {
    &reply += {
        &Filter-Id = &parent.request.Client-Identifier
    }
}