---
type: concept
tags: [parking, architecture, devices, setup]
sources: [parking-system-architecture]
updated: 2026-06-15
---

# Device Discovery

An optional driver capability: **find devices on the LAN** so the admin doesn't have to type
connection details by hand during [[first-run-setup]]. Modeled generically so any driver can
opt in.

> Implementation-derived (from `@parking/devices` + setup API/UI), not the source doc.

## The capability

A driver may implement `DiscoverableDriver` — `discover() => DiscoveredDevice[]`. Each found
device carries an `id`, a `label`, a `config` blob to **auto-fill** the setup form, and `info`
(firmware, MAC, …). The [[device-registry]]'s `isDiscoverable()` guard lets the system treat it
as optional; the setup catalog returns a `discoverable` list of driver ids.

> **No current driver implements discovery.** The [[dingtian-relay]] board uses a fixed IP
> (entered/known at setup). The capability remains for future UDP-discoverable devices (cameras
> via ONVIF, etc.). The worked example below is the (removed) UHPPOTE driver — kept because the
> **broadcast gotchas are transferable** to any UDP discovery we add later.

## UHPPOTE discovery (historical example)

The [[uhppote-controller]] supported discovery natively: a **UDP broadcast** (`get-devices` on
port `60000`) that **every controller on the LAN answers** with its serial, IP, netmask, gateway,
MAC, firmware version, and date. The `uhppoted` lib exposed this as `getDevices(ctx)`; the
(now-removed) `uhppote` driver mapped each result into a `DiscoveredDevice` (serial → id, IP →
host). **Was verified on real hardware** (serial 225088491).

### Broadcast gotchas (learned the hard way — see [[wsl-dev-networking]])

These cost real debugging time; the (removed) `uhppote` driver handled all three, and any future
UDP-discovery driver will need to as well:

1. **Broadcast to the *subnet-directed* address, not the global `255.255.255.255`.** The
   `uhppoted` lib only calls `setBroadcast(true)` when the target matches a **local interface's
   subnet broadcast** (e.g. `10.0.10.255`). For the global address it skips it, so the `send`
   fails with **`EACCES`**. The driver computes the subnet broadcast from `os.networkInterfaces()`.
2. **A host with multiple interfaces must broadcast on *all* subnets.** With several NICs (LAN,
   VPN/Tailscale, docker bridges) the controller is on only one. Picking the first interface
   misses it; the driver broadcasts on every subnet and dedupes by serial.
3. **For *unicast* ops (status / open), the lib's `Config` broadcast must match the target's
   subnet** — it governs reply routing, so a mismatched broadcast makes `getStatus` time out even
   though `openDoor` "succeeds". The driver sets the broadcast per the target host's subnet. (This
   was the health-check "offline/timeout" bug: a 5 s timeout dropped to 24 ms once fixed.)

Also: concurrent `uhppoted` calls collide on the `:60001` reply-listener port (EACCES / dropped
replies), so the driver **serializes** all controller I/O. Override the broadcast with
`UHPPOTE_BROADCAST` for unusual setups.

## Flow

1. The setup catalog flags `uhppote` as discoverable.
2. Admin clicks **Scan** → `GET /api/setup/discover/:driverId` (admin-only).
3. The server runs `discover()` and **health-checks each found device** so the admin sees
   reachability before assigning.
4. Selecting a result **auto-fills serial + host**; the admin then assigns + binds it.

## Deployment notes

- Discovery is an **L2 broadcast**: the host and controller must share a layer-2 segment. Works
  on the isolated device VLAN ([[network-isolation]]). A routed/NAT'd network (e.g. WSL2 NAT mode
  — see [[wsl-dev-networking]]) blocks it entirely.
- Discovery shares the same unauthenticated UDP exposure as everything else UHPPOTE — another
  reason the controllers live on an isolated VLAN ([[uhppote-udp-protocol]]).
- Cameras (Hikvision/Dahua via ONVIF/WS-Discovery) could implement the same interface later.