babeld ubus output contains duplicate keys (was: luci-app-babeld: Missing neighbour)

[marek22k]

Steps to reproduce:

1. go to: Status → Babeld tab
2. look at the status

Actual behavior:

One neighbor is displayed.

Expected behavior:

Two neighbors are displayed as with UBUS binding:

# ubus call babeld get_neighbours
{
	"IPv4": {
		
	},
	"IPv6": {
		"fe80::2923": {
			"dev": "crxnbandura2",
			"hello-reach": 65535,
			"uhello-reach": 0,
			"rxcost": 40,
			"txcost": 40,
			"rtt": "0.000",
			"channel": -2,
			"if_up": true
		},
		"fe80::2923": {
			"dev": "crxnbandura1",
			"hello-reach": 65535,
			"uhello-reach": 0,
			"rxcost": 40,
			"txcost": 40,
			"rtt": "0.000",
			"channel": -2,
			"if_up": true
		}
	}
}

Additional Information:

I have attached a picture.

OpenWrt version information from system /etc/openwrt_release

DISTRIB_ID='OpenWrt'
DISTRIB_RELEASE='22.03.3'
DISTRIB_REVISION='r20028-43d71ad93e'
DISTRIB_TARGET='ramips/mt76x8'
DISTRIB_ARCH='mipsel_24kc'
DISTRIB_DESCRIPTION='OpenWrt 22.03.3 r20028-43d71ad93e'
DISTRIB_TAINTS=''

Ping on maintainers: @jonnytischbein @PolynomialDivision @aparcar
(I am sorry if I am pinging you and you are not the maintainers, however there is nothing in the files about this and you are in the commit history).

[jow-]

It's a bug in the JSON output produced by https://github.com/openwrt/routing/blob/master/babeld/src/ubus.c - note the duplicate dictionary key fe80::2923 - we can't fix this on the LuCI side.

[jow-]

@PolynomialDivision

[PolynomialDivision]

It's a bug in the JSON output produced by https://github.com/openwrt/routing/blob/master/babeld/src/ubus.c - note the duplicate dictionary key fe80::2923 - we can't fix this on the LuCI side.

Yes. You are right. We could change it to [IP]%[DEV] to fix duplicate addressing? Or we sort it by the device first?

[jow-]

We could change it to [IP]%[DEV] to fix duplicate addressing

Sounds sensible to me! Just make sure to only do that for fe80... link local addresses, others are guaranteed to be unique on the local system.

[PolynomialDivision]

I think it is possible that this still brings some duplicate entries with it. Maybe @jech can say something to it, how we can do the sorting in the best manner? Or how we can arrange the json output so we don't have any duplicate keys.

[marek22k]

Actually, a link-local IP address must not occur twice on an interface. The DAD should exist for this purpose. Alternatively, the whole thing could perhaps be represented as an array?

[jech]

Right. Neighbours are indexed by (adress, interface). It is perfectly normal to see the same neighbour on two interfaces: if a router A has two radios tuned at the same frequency, or two Ethernet interfaces connected to a single switch, then it will see all neighbors twice, once over each interface. The protocol is designed to handle this case gracefully.

I see two solutions to your problem:

1. Use a string of the form address%interface as the key, as @PolynomialDivision suggested.
2. Use the address of the struct neighbor as the key. This is the approach used by Babeld's native dumping code:
   https://github.com/jech/babeld/blob/master/local.c#L163

[marek22k]

Personally, I think the former suggestion is nicer.