Data Types

Unlang supports a number of data types. These data types are used in dictionaries, 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

Values can be cast from one data type to another. However, this cast only changes the type of the data, it does not change the data’s value. That is, a cast allows you to convert an octets data type to a string, but the resulting string may still contain non-printable characters.