unbound: Feature Request UCI Support for specifying the "interface:" option

Maintainer: @EricLuehrsen
Environment: OpenWrt 22.03.2 r19803-9a599fee93 / LuCI openwrt-22.03 branch git-22.288.45147-96ec0cd

Description:

Hello, I am looking to add a feature request to the unbound UCI option to allow forward the "interface:" option through the UCI.

I know there is currently a an iface_lan option in UCI that supports specifying a physical interface to unbound and that gets mapped into the UB_LIST_NEW_LAN variable.
The iface_lan option copies the ip subnet of the physical interface and stores it into the UB_LIST_NEW_LAN variable.

So for example if there was a bridge interface of "br-lan" with ip network address of 192.168.1.1/24

10: br-lan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
    link/ether c0:56:27:68:17:47 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.1/24 brd 192.168.1.255 scope global br-lan
       valid_lft forever preferred_lft forever
    inet6 fe80::c256:27ff:fe68:1747/64 scope link 
       valid_lft forever preferred_lft forever

It gets mapped into the UB_LIST_NEW_LAN variable with the value of "192.168.1.1/24"

The $UB_LIST_NEW_LAN variable then gets transformed into an unbound "access-control:" option which is based on the IP netblock here in unbound.sh.

That ultimately results in the following option being written to the generated unbound.conf in the example above.

access-control: 192.168.1.1/24 allow

The feature I am looking for is to support forwarding the physical interface directly as the interface: option to unbound.
i.e

interface: br-lan

This would allow interface-* based tag and view options to be used within the unbound_srv.conf file, as unbound requires that there is previous "interface:" option in order to use the tag and view options
Here is the documentation for the interface-view option.

It would be useful if it was possible in the UCI file to be able to specify the "interface: similar to the following

list interface "br-lan"
list interface "wan"
list interface "lo"

Additional Information

The unbound "interface-auto:" cannot be used for the "interface-*: options as that option causes the use of the "interface:" option to be ignored per this issue in the unbound github: https://github.com/NLnetLabs/unbound/issues/433#issuecomment-783962175

Workaround

There is an simple workaround involved by just adding the interface: option directly to the unbound_srv.conf file and disabling the interface_auto in UCI by setting it to 0

Side Note

The motivation for this feature request is me looking to use the interface-view option to perform interface base filtering using unbound on an interface such as "br-lan" instead of IP netblock based filtering on ranges such as "192.168.1.0/24"

I currently have to add a configuration like the following to the unbound_srv.conf to fit my use case

interface: br-lan
interface: open-lan
interface: lo
# Allow listening on localhost
do-not-query-localhost: no

interface-view: br-lan adblock-view

Start with net/unbound/files/unbound.uci and net/unbound/files/unbound.sh, especially the existing iface_lan, interface_auto, and generated configuration handling referenced in the issue. Trace how UCI options become unbound.conf directives; done means listed interfaces produce interface: entries while preserving the existing interface_auto behavior and enabling interface-view use.