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# -*- text -*-
#
# $Id$
#
# This module is useful only for 'xlat'.
# To use it, add it to the raddb/mods-enabled/ directory.
#
# Two xlat functions are provided by this module:
# - unpack
# - substring
#
# Both are for use on the right-hand side of a variable assignment.
#
# unpack
# ======
#
# ... = "%{unpack:data 1 integer}"
#
# The arguments are three fields:
#
# data
# Either &Attribute-Name
# the name of the attribute to unpack.
# MUST be a "string" or "octets" type.
#
# or 0xabcdef
# e.g. hex data.
#
# 1
# The offset into the string from which
# it starts unpacking. The offset starts
# at zero, for the first attribute.
#
# integer
# the data type to unpack at that offset.
# e.g. integer, ipaddr, byte, short, etc.
#
# e.g. if we have Class = 0x0000000102030405, then
#
# %{unpack:&Class 4 short}
#
# will unpack octets 4 and 5 as a "short", which has
# value 0x0304.
#
# This module is used when vendors put multiple fields
# into one attribute of type "octets".
#
# The module can also be used to unpack substrings, by specifing a
# data type of "string(len)" or "octets(len)". Where "len" is an
# actual number. For example:
#
# %{unpack:&User-Name 1 string(2)}
#
# When given a User-Name of "hello", it will start taking the
# substring at offset 1 (i.e. "e"), and it will take two characters
# from that offset, i.e. "el".
#
# As a special case, you can unpack an entire string by specifying
# the offset, and nothing for the length:
#
# %{unpack:&User-Name 1 string()}
#
# When "octets(len)" is used, the output is printed as hex. e.g. for
# the above example with Class:
#
# %{unpack:&Class 4 octets(4)}
#
# Will return the hex string "02030405"
#
#
# substring
# =========
#
# substring will return a substring of a string or attribute using
# the syntax
#
# %{substring:data start len}
#
# data
# Either an attribute name or string data. String data
# can have leading or trailing spaces. Only a single
# space before "start" is taken as the separator.
#
# start
# the zero based offset for the start of the substring.
# A negative value will count in from the end of the
# string.
#
# len
# the number of characters to return. A Negative value
# will remove that number of characters from the end.
# If len is more than the available number of characters
# then only the available number will be returned.
#
# Examples:
#
# "%{substring:foobar 2 3}" == "oba"
# "%{substring:foobar -3 2}" == "ba"
# "%{substring:foobar 1 -1}" == "ooba"
# if User-Name is "foobar" "%{substring:&User-Name 1 -2}" == "oob"
#
unpack {
}
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