Data Types

Unlang supports a number of data types. These data types are used in conditional expressions or when assigning a value to an attribute.

Using Data Types

The server support a wide range of data types, as given in the list of data types page. The choice of which data type applies is determined by the context in which that data type is used. This context is usually taken from an attribute which is being assigned a value.

The unlang interpreter uses pre-defined attributes which are defined in dictionaries. The dictionaries define both a name, and a data type for the attributes. In the interpreter, then, attributes can be assigned a value or compared to a value, without specifying the data type. The interpreter knows how to parse the value by using the data type assigned to the attribute.

The result is that in most cases, it is not necessary to know the name of the data types. It is possible to write values in the format you expect, and he server will do "the right thing" when interpreting the values.

Attributes with Different Data Types

Framed-IP-Address = 192.0.2.1
Framed-IPv6-Address = 2001:db8::
Reply-Message = "This is a reply"
Port-Limit = 5
Boolean = true
Octets-Thing = 0xabcdef0102030405
MAC-Address = 00:01:02:03:04:05

Parsing Data Types

The interpreter is flexible when parsing data types. So long as the value can be parsed as the given data type without error, the value will be accepted.

For example, a particular attribute may be of data type ipaddr in order to store IPv4 addresses. The interpreter will then accept the following strings as valid IPv4 addresses:

192.168.0.2: Unquoted text, interpreted as the data type
'192.168.0.2': Single-quoted string, the contents of the string are parsed as the data type.

The single-quoted string form is most useful when the data type contains special characters that may otherwise confuse the parser.
"192.168.0.2": Double-quoted string.

The contents of the string are dynamically expanded as described in the dynamic expansion page. The resulting output is then interpreted as the given data type.
`/bin/echo 192.168.0.2`: backtick-quoted string. Run a script, and parse the resulting string as the data type.

Similar processing rules are applied when parsing assignments and comparisons, for all attributes and data types.

Casting Data Types

In some cases, it is necessary to parse values which do not refer to attributes. This situation usually occurs when two values need to be compared, as in the following example:

if ("%{sql:SELECT ipaddress FROM table WHERE user=%{User-Name}}" == 192.0.2.1) }
    ....
}

Since there is no attribute on either side of the == operator, the interpreter has no way of knowing that the string 192.0.2.1 is an IP address. There is unfortunately no way of automatically parsing strings in order to determine the data type to use. Any such automatic parsing would work most of the time, but it would have error cases where the parsing was incorrect.

The solution is to resolve these ambiguities by allowing the values to be cast to a particular type. Casting a value to a type tells the interpreter how that value should be parsed. Casting is done by prefixing a value with the type name, surrounded by angle brackets; <…>.

Syntax

<...>value

We can add a cast to the above example, as follows:

if ("%{sql:SELECT ipaddress FROM table WHERE user=%{User-Name}}" == <ipaddr>192.0.2.1) }
    ....
}

In this example, we prefix the IP address with the string <ipaddr>. The interpreter then knows that the value 192.0.2. should be interpreted as the data type ipaddr, and not as the literal string "192.0.2.".

For a full list of data types which can be used in a cast, please see the list of data types page, and the "Basic Type Types" section.