Enhance syntax to support whitelisted resources

[ryancox]

For certain resource types, it would be very useful to specify a white list. e.g. only users 'apache' and 'root' should exist. This whitelist might be the null set. e.g. no ports should be listening.

[aelsabbahy]

Can you give a few examples using the current goss JSON structure on how this would look like.

I'm having a hard time visualizing where this will fit.

[aelsabbahy]

This is possibly dependent on #31

[ryancox]

Syntax is the tricky part. Keeping things clean and backward compatible. Here are some ideas; none of which are particularly great, but perhaps they will spark some inspiration ;)

"port!": {     <--- some sort of operator that specifies only .. very magical
    "tcp6:80": {
        "listening": true
    },
},

"port-whitelist": { <--- '-whitelist' suffix which is a bit more descriptive
    "tcp:80": {
        "listening": false
    },
},

"only-port": { <--- 'only-' prefix which is also a bit more descriptive 
    "tcp6:80": {
        "listening": true
    },
},  

"only-port": {
}, <-- empty section means no ports should be listening

[aelsabbahy]

Hmm, that clarifies a lot, and I think I'll use a similar syntax as the one I take in issue #31. The only magical piece about this is feature is keying off of the attribute that determines Existence, similar to autoadd (ex. File.Exists, Port.Listening, Package.Installed).

All your examples made sense to me except for one:

"port-whitelist": { <--- '-whitelist' suffix which is a bit more descriptive
    "tcp:80": {
        "listening": false
    },
},

I'm not really understanding the expected behavior for this, would that ensure port 80 is NOT listening and all other ports are listening, or is it the same as no ports are listening.

[ryancox]

Oops ... that was a copy/paste error. Should have been "listening": true

[aelsabbahy]

Now that #31 is shipped, I'm wondering if this should be a separate resource all together. Something like:

user:
  nobody:
    exists: true
    uid: 99
    gid: 99
    groups:
    - nobody
    home: /
whitelist:
  users: [nobody, root]
  ports: { have-len: 0 }
  packages: { have-len: 2 }

or

package-whitelist:
  kernel:
    installed: true
  openssh:
    installed: true
port-whitelist: {}
user-whitelist:
  nobody:
    exists: true
    uid: 99
    gid: 99
    groups:
    - nobody
    home: /
  root:
    exists: true

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