private: path policy language

[tzaeschke]

This also applies to doc.
While implementing the path policy language for JPAN, I noticed some discrepancies between the language design and the implementation.

Design

• The design talks about a Policy that can contain ACLs, a Sequence, Options, and that "extends" several other Policies. However:
  • In the implementation, the "extends" feature is not in "Policy" but in separate type "ExtPolicy".
  • The extends feature references ExtPolicies, not Policies
  • The implementation only has a method PolicyFromExtPolicy which takes as input an ExtPolicy (input1) and "applies" other ExtPolicies.
    Moreover, it may or may not modify input1 depending on whether input1 has already a Policy. See also private: Policy.PolicyFromExtPolicy modifies existing policy. #4682

• The design says that Options are a "list of anonymous policies"
  • It is unclear why they must be anonymous (e.g. have no name)? Policies are named (though the name may be empty).
  • In the implementation, an Options contains an ExtPolicy (not a Policy)
• The implementation also contains features that are not mentioned in the design, e.g.:
  • LocalISDAS
  • RemoteISDAS
  • FilterOptions
  • JSON import export (only mentioned in the "outdated content" section.
  • YAML import/export for ACLs
• The example for "extends" in the design doc doesn't really make it clear what the purpose / use-case of this feature is and how it can be beneficial.
  Maybe the example can be improved?

Implementation

• The implementation of PolicyFromExtPolicy is confusing, see private: Policy.PolicyFromExtPolicy modifies existing policy. #4682
• Several tests add illegal ACL entries: "0-0#0" followed by denyEntry or similar. Why is that?
  This seems unnecessary, moreover it seems to violate the contract defined in ACL.validateACL()

Question

For me the question is which should I follow?

[oncilla]

IMO, the doc is severely outdated, and FWIW, I don't think it was ever completely implemented.

In the commercial implementation of Anapaya, we only support ACL + Hop pattern:

So far, this has been sufficient. With JPAN, I would aim for the same expressiveness in the beginning.

[tzaeschke]

Thanks. I have already implemented a bit more than that, but for ACL and Sequence, the implementation and the design seem to be mostly consistent. So I'll probably just skip the extensions (and Options?).

It would still be good though to get an updated design document...?