Synthetic reverse/forward records

Current state of things.

Working: ✅ Configuration options (reverse|forward) <prefix> <zone> <ttl> <subnet> ✅ Basic reverse record query matching ✅ Basic forward record query matching ✅ Loadable query processing modules ✅ Functional tests ✅ Documentation - not sure where to place configuration string/doc for the modules yet. 8f6e091f

Not working: 😰 Denial of existence proof 😅 Online signing 🔴 Code cleanup

Problems and bugs:

• Query for given name but wrong type yields NXDOMAIN while it should be NODATA
• IPv4 CIDR queries like 129.128/26.2.0.192.in-addr.arpa. are not recognized because 129.128/26.2.0.192 is not exactly a valid address string, this could be worked around but is it needed?

Thoughts:

• Maybe we could make some generic API for internet query processing that could alter the default query plan, like it could replace ANSWER section processing and then rest of the flow would be the same, or it could provide an alternative query plan altogether (list of callback steps). 3c745f
• NSEC is tricky because the synthetic records are not in the zone yet and if have for example following: recordA, <synthetic_start...synthetic_end>, recordB then the NSEC for recordA would point to recordB before it reaches the synthetic rule checking. So the synthetic rules should not only rewrite the NXDOMAIN answers, but also check and rewrite NSECs which is wrong on so many levels. Therefore the code really needs to be inserted before we start providing proofs and that again requires an API to change a query processing plan ⛵