[Cfengine-develop] ExecResult results interpreted as a list

[Luke A. Kanies]

Hi Mark,

This is the third time I've encountered this, so I'm going to bring it up
this time.

As I mentioned in my previous email, I'm calling an external script within
cfservd.conf and trying to use the results of that script to decide whom
I'm going to allow to connect to cfservd.

For a little background, the reason I'm doing this is to reduce the number
of manual steps involved in building a server.  I already am putting all
of my servers in LDAP, so if I can have cfservd retrieve all IP addresses
from LDAP, that would be very easy.  Otherwise I'm going to have to
dynamically generate a cfengine file with all of the IP addresses and then
import that file.  I can do this, but I've already got a bunch of these
and they're really, really annoying.

So, I want to retrieve a list from LDAP.  Well, call an external script
using ExecResult.  Okay, that's easy.  Problem is, only certain variables
support returning lists, vs. strings.  For instance, if you call
ExecResult within AddClasses, then the result is split based on the '.'
character.  If you call it from within AddInstallables, the result is
split based on '%'.  A very interesting point about both AddInstallables
and AddClasses is that you can use ExecResult to set completely invalid
classes, including classes containing spaces.  Go ahead, try it.  It's
fun.

There are probably a couple other variables that support lists, but these
are sufficient.  We have completely inconsistent behaviour here.  Given
three variables, two of them split based on separate characters and the
third doesn't split at all.

Just getting this far and understanding where everything happens is
relatively complicated, and I'm apparently one of the few people who
encounter this problem.  My guess is actually that many people encounter
it but most just give up.  I guess I'm stubborn.

So, my question is:  Is there any way we can bring some consistency here?
I'm pretty convinced that this inconsistency is a result of how the parser
is built, and making function call behaviour truly consistent would
involve a lot of rewriting, but am I wrong?  Does someone see a good,
simple solution?  Yes, I know that I could just add a wrapper function for
every variable, like AddClasses has, but that's a hack and doesn't solve
the deeper problem.  The section of cfengine (specifically in install.c)
dealing with variables is already in dire need of abstraction.

Frankly, I'd like to solve this problem by making the "variable" settings
in cfengine into what the really are: function calls.

Take the following snippet:

control:
  actionsequence = ( files )
  actionsequence = ( shellcommands )
  variable = ( files )
  variable = ( shellcommands )

The settings for variable result in a warning, but the setting for
actionsequence result in actions being added to a stack.  Nearly all of
cfengine's builtin variables would be better off as functions, from what I
can tell.  I'm seeing if I could somewhat easily modify the parser et al
to allow this, but as I mentioned, I don't think it will be terribly
straightforward.

My main point, though, is:

Do you have any idea how we can relatively easily support using ExecResult
to consistently gather more than one piece of data?  I need to allow every
machine in LDAP access to cfengine, and I don't want to keep that list
manually, and I don't want to have to generate a file that gets imported
by cfservd.  That's a hack, and I hate it.

Luke

-- 
Measure with a micrometer.  Mark with chalk.  Cut with an axe.