emit-fleet

emit-fleet — a hub and N devices over one socket

One project, three Fronds, two deployments. No broker, no infrastructure.

fronds/fleet/entities/   Recalibrate, Reading   ← the contract, declared ONCE
fronds/hub/handlers/     FleetHandler            ← announces down, listens up
fronds/node/handlers/    SensorHandler           ← listens down, announces up

pnpm install && pnpm -r build

# terminal 1
pnpm hub

# terminals 2, 3, 4
NODE_ID=sensor-1 pnpm node
NODE_ID=sensor-2 pnpm node
NODE_ID=sensor-3 pnpm node

fronds: ['fleet', 'hub'] and fronds: ['fleet', 'node'] are the whole deployment statement. Both halves sit on the same disk; each process loads its own subset, which is why nothing local can shortcut the tunnel.

The three things it shows

1. It reconnects. Start a device before the hub:

[sensor-9] link down — retrying in 500ms
[sensor-9] link down — retrying in 1000ms
[sensor-9] link down — retrying in 2000ms
[sensor-9] link down — retrying in 4000ms
[sensor-9] connected — listens to recalibrate     ← the hub appeared; nobody touched it

Backoff doubles and stops at 5 s. A device may be down for hours.

2. Readings come UP the same socket. A device behind a NAT cannot be called — it calls, and the connection is bidirectional:

[hub] sensor-1 → 25.8°C
[hub] sensor-2 → 23.7°C

The hub calls app.deliver(fact, payload) and not the emission value: resolving that would carry the reading straight back out through onEmit and echo it to the whole fleet. Receiving and announcing are two operations; only one of them leaves.

3. One device can be addressed — in the data.

→ sensor-2 only: offset -3
[hub] recalibrate → 3 device(s)
  [sensor-1] recalibration for sensor-2 — not mine
  [sensor-2] recalibrated, offset -3
  [sensor-3] recalibration for sensor-2 — not mine

remotes: names a kind of Frond, never an instance, so the device's name travels with the fact and each one decides for itself. It works, and the cost is on the screen: three devices woken for an order meant for one. At five hundred it is no longer a detail.

What it does not do

• Nothing is held. A device that was offline when an order went out never gets it. That is exactly what a queue adds, and the tunnel has none.
• The hub believes what a device says about itself. Identity arrives on the wire and nothing re-establishes it — see the repository's known issues.
• One socket per device, in one process. Fine for a hundred, a single point at scale.