I'm building a HomeKit app that discovers Thread devices and visualizes the mesh topology. I can detect device roles (Router vs End Device via characteristic 0x0703) and identify Border Routers (via _meshcop._udp), but I cannot determine which Router is the parent of a given End Device. Any Thread device can act as a Router (a Nanoleaf bulb, an Eve plug, not just HomePods), and End Devices attach to these Routers as children. That parent-child relationship is what I'm trying to map, but there's no RLOC16, neighbor table, or parent identifier exposed through any available API.
I've tested every path I can find. Here's what I've tried on a network with 44 Thread devices and 6 Border Routers:
What works (partially)
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HAP Thread Management Service (0x0701) gives me the device role from characteristic 0x0703, the OpenThread version from 0x0706, and node capabilities from 0x0702. That's the complete set of characteristics on that service. None of them contain RLOC16, parent Router, or neighbor data. This service also only exists on HAP-native Thread devices. My 20 Matter-over-Thread devices (Aqara, Eve Door, SmartWings, Onvis S4) don't have it at all.
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MeshCoP Bonjour (_meshcop._udp) identifies Border Routers and the network name/Extended PAN ID. No topology data about other mesh nodes.
What doesn't work
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ThreadNetwork framework (THClient) - retrieveAllCredentials() returns error Code 3 because the app can't access credentials stored by Apple Home. Even if it worked, THCredentials only contains network config (name, PAN ID, channel), not topology.
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Direct CoAP queries - Border Routers don't route traffic from WiFi to Thread management ports. Mesh-local addresses aren't reachable. No Thread NWInterface in Network.framework.
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Network.framework - No visibility into the Thread mesh from the WiFi side.
The only remaining path I can see (but it's not practical)
- Matter cluster 0x0035 (Thread Network Diagnostics) appears to have exactly what I need: RLOC16, NeighborTable with isChild boolean, RouteTable. I haven't implemented this because it requires commissioning each device individually onto my app's own Matter fabric via Multi-Admin. That's 21 separate user-initiated pairing actions on my network. I can't ask end users to do that.
The core issue
Every Thread Router (whether it's a HomePod acting as a Border Router or a Nanoleaf bulb acting as a mesh Router) knows its own children and neighbors. The Border Routers also maintain route tables covering the mesh backbone. This data exists on the user's own devices but none of it is exposed to third-party apps.
Even something minimal would help. HMAccessory already exposes matterNodeID as a cross-protocol identifier. Exposing RLOC16 the same way would be enough, since parent-child relationships are encoded in the address itself (ParentRLOC = ChildRLOC & 0xFC00).
Has anyone found another approach I'm missing?
Thanks in advance for any pointers.