(A/I)XFR-in/out (with TSIG), NOTIFY-in/out + demo zone persistence.

[ximon18]

Based on the service-layering branch.

Manually tested as both primary and secondary with NSD and BIND.

Still lots to do:

• [ ] Design review (and revisit if feedback requires it). E.g. some of the streaming support might warrant being handled less as a hack/extension of the existing client code and perhaps instead as a separate new XFR client module? (Update: The XFR client module now exists, but review feedback suggests to exclude streaming support from ComposeRequest and create a new streaming capable trait like ComposeRequest to use with the existing clients)
• [x] Sync with latest changes on main.
• [x] Remove notions of primary and secondary, instead allow XFR-in/out and NOTIFY to be enabled/allow per direction per zone ala how NSD supports XFR and NOTIFY. (Update: Primary and secondary notions are still present but no longer mutually exclusive)
• [ ] More error handling & remove unwraps/panics.
• [ ] Code cleanup.
• [x] Add tests (e.g. Stelline tests based on existing Unbound and NSD tests).
• [ ] Extend Catalog to actually act like an RFC 9432 Catalog zone?
• [ ] Revisit the various related RFCs and implement/omit/defer missing logic.
  • [ ] Add IXFR diff purging.
  • [ ] Add IXFR diff condensation.
  • [ ] Add NOTIFY retry tracking.
• [x] Remove NOTIFY-set discovery? (Update: NOTIFY-set discovery is still present but disabled by default)
• [x] TSIG signing of both XFR-in and XFR-out.
• [ ] Improve w.r.t memory usage, minimizing copies, support for Cargo features such as no std, etc.
• [x] Add and use more traits to make smaller units reusable instead of making the new middleware components dependent on one catalog impl, and add more strategy traits for making certain logic replaceable? (Update: Some traits were added, to decouple catalog from XFR client and middleware for example)
• [ ] Documentation
• [ ] Improved examples?

Introduces the following new major components:

Component	Description
Catalog	- For primary zones: "on-zone-change" triggered sending of NOTIFY messages zones to "secondaries". - For "secondary" zones: NOTIFY-in and SOA timer based SOA query and (A/I)XFR-out.
XfrMiddlewareSvc	Handling of (A/I)XFR-in requests. Requires a Catalog.
NotifyMiddlewareSvc	Handling of NOTIFY-in requests. Requires a Catalog.
TsigMiddlewareSvc	Verify TSIG signed requests and sign responses.
net::client::auth::Connection	TSIG signing and validation client layer for signing request(-stream)s and validating response(-stream)s. Used by Catalog.

Zone persistence on change (either edit to a local primary zone or sync of a local secondary zone with changes obtained from a remote primary) is demonstrated in examples/serve-zone.rs via the ArchiveZone impl of the ZoneStore trait and by using the same Zone wrapping "hack" that Catalog uses to monitor zones for changes.

[ximon18]

Thx @tertsdiepraam !

The code is not finished functionally yet, thus certainly not in terms of docs, comments, examples etc either.

So I'd suggest to limit yourself to high level review at this point.

I'd be happy to walk you through it if you would appreciate that, either in person next week or online before then.

[tertsdiepraam]

Oh yeah don't mind me. I was just interested to look through it and figured I'd comment on some things while I was going through it. I'd love a walkthrough at some point though.