Requesting clarification on behavior with multiple IDnsRequestBlockingHandler

[ruifung]

As I am maintaining my own DNS App for LANCache support, I have often wondered how does T-DNS handle multiple Blocking/Authoritative DNS applications that will handle the same request.

Is there some kind of ordering if the requests are handled by multiple applications? Because from what I can find so far, this seems to be somewhat undefined?

Mostly because I implemented the LANCache logic using the Blocking handler.

Thanks

[ShreyasZare]

Thanks for asking. Currently the order is undefined as you guessed it. If one app returns no response then the other app gets to process the same request.

For your use-case, I would recommend that you use the IDnsAuthoritativeRequestHandler interface instead of IDnsRequestBlockingHandler since the later is intended to be used only for apps that block domain names.

[ruifung]

The IDnsAuthoritativeRequestHandler's behavior with multiple authoritative handlers seems undefined too?
How does it work with say, the Advanced Forwarding app?

[ShreyasZare]

Yes, its order is undefined too but, usually the app is supposed to respond only when it has some config for that domain in the request. With the Advanced Forwarding app configured with wildcard may cause it to answer all requests if its ordered before your app.

This will require some sort of ordering that can be configurable. Will plan some option to do that soon.

[ShreyasZare]

Technitium DNS Server v13.5 is now available that adds a new interface IDnsApplicationPreference which can be implemented to explicitly specify a preference value for the app. You can check how this has been implemented in this app.

The DNS server will sort the installed apps using the preference value so as to have a user-defined order in which requests to apps are processes.