[opennms-devel] New feature added to trunk: "functions" on generic index resource labels

Hello,

I'm curious about whether people think the way these "functions" work is
a good design and if it should be kept this way or changed.  I hacked it
together pretty quickly because it was a small, fun project, but I don't
want to start going down a road that will be painful to support in the
future.

To address an enhancement request, I added support for two "functions"
(kinda) on generic index resource labels:

        http://bugzilla.opennms.org/show_bug.cgi?id=2467

One is of the form "${index:<start>-<end>}" which will select a portion
of an index for a generic resource.  The <start> and <end> parts are
indexes both starting at zero and either can be omitted, but not both. 
A shorthand for "<num>-<num>" where both numbers are the same is just to
specify the number.  In the specific example above, an index is of the
form "0.21.109.80.9.66.4", where the first six octets are a MAC address,
and the last octet is an interface ID.  So, ${index:6} would select the
interface ID (it's the seventh octet, but remember that things are
indexed by zero).

I thought about using the form "subIndex(<sub-symbol>, <start>, <end>),
but it started to get a little confusing about what I should do if I
wanted to omit one or more of the arguments (but I guess I could always
require a start and make the end optional).  It might be good to
restructure it this way to make it like the next feature.

The other feature is of the form "hex(<sub-symbol>)", which assumes that
the evaluation of the sub-symbol is a dotted integer string, and it's
converted to a hex string, perfect for a MAC address.  The sub-symbol is
any other symbol that is recognized as a generic index expression, such
as "index", the new form of "index:6", or whatever.

Together, they can be used with a resource label expression like this:

        "MAC Address ${hex(index:0-5)} on interface ${index:6}"

... to create a resource label for the index "0.21.109.80.9.66.4" of
"MAC Address 00:15:6D:50:09:42 on interface 4".


        What do you think?
        - djg



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