Controlling Philips Hue

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Run in Livebook 
Mix.install([
  {:hue, "~> 0.2"},
  {:kino, "~> 0.19"}
])

What this notebook does

This is the hue library's worked example: it finds your bridge, pairs with it, controls lights by name, and watches state changes stream in live. Run it top to bottom against a real bridge on your network.

The first run pairs — you'll press the bridge's round link button once. The result is saved to your user config directory, so every later run reconnects without asking.

Saved credentials

An application key is a password. This cell keeps it out of the notebook file itself, in your platform's user config directory under hue_livebooks/hue.json — so every copy of these notebooks, cloned, badge-launched, or deployed as a Livebook app, shares one pairing:

  • Linux — ~/.config/hue_livebooks/hue.json
  • macOS — ~/Library/Application Support/hue_livebooks/hue.json
  • Windows — %APPDATA%\hue_livebooks\hue.json

Delete that file to start over from discovery.

creds_path =
  Path.join(to_string(:filename.basedir(:user_config, "hue_livebooks")), "hue.json")

saved =
  case File.read(creds_path) do
    {:ok, json} -> Jason.decode!(json)
    {:error, :enoent} -> nil
    {:error, reason} -> raise "could not read #{creds_path}: #{inspect(reason)}"
  end

if saved, do: :reconnecting, else: :first_run

Find the bridge

Hue.Discovery.discover/1 runs mDNS and Philips' cloud endpoint in parallel, then verifies each candidate with a real connection and pins the certificate it finds — the SSH host-key model, because a Hue bridge's certificate can't be verified any conventional way. The pin rides along in the returned Hue.Bridge.Info and every later connection checks against it.

If discovery finds nothing — mDNS is silent on routed networks, with no error to explain why — this cell crashes with a MatchError on the empty list. The escape hatch is Hue.Discovery.identify/2 with the bridge's IP: it captures the fingerprint on first contact the same way discover/1 does.

On a re-run this cell rebuilds that Info from the saved file instead.

bridge_info =
  if saved do
    %Hue.Bridge.Info{
      host: saved["host"],
      port: saved["port"],
      bridge_id: saved["bridge_id"],
      fingerprint: saved["fingerprint"]
    }
  else
    {:ok, [first | _]} = Hue.Discovery.discover()
    first
  end

Pair

Press the round link button on your bridge, then run this cell — the bridge only honours pairing requests for about thirty seconds after a press, and this cell polls for up to a minute, so either order works if you're quick.

On a re-run, the saved key is used and nothing is sent to the bridge.

application_key =
  if saved do
    saved["application_key"]
  else
    {:ok, %{application_key: key}} =
      Hue.Pairing.pair_when_pressed(bridge_info, app: "livebook")

    File.mkdir_p!(Path.dirname(creds_path))

    File.write!(
      creds_path,
      Jason.encode!(%{
        host: bridge_info.host,
        port: bridge_info.port,
        bridge_id: bridge_info.bridge_id,
        fingerprint: bridge_info.fingerprint,
        application_key: key
      })
    )

    File.chmod!(creds_path, 0o600)

    key
  end

:paired

Start the live bridge

Hue.Bridge never starts itself — it's a child_spec you place in your own supervision tree, the way Finch or Redix are. In an application that looks like:

children = [
  {Hue.Bridge, name: MyApp.Hue, client: client}
]

In Livebook, Kino.start_child/1 is that same placement. On start the bridge fetches everything once to seed its cache, then holds an eventstream open to keep it current; :live means both are done. Kino ties the child's lifetime to this cell rather than to the runtime, so re-running it tears down the old bridge and starts a fresh one — no error, no restart required, the Livebook analogue of a supervisor restarting a child.

{:ok, client} = Hue.from_bridge(bridge_info, application_key: application_key)
{:ok, _supervisor} = Kino.start_child({Hue.Bridge, name: LivebookHue, client: client})

Enum.reduce_while(1..50, nil, fn _, _ ->
  case Hue.Bridge.status(LivebookHue) do
    :live ->
      {:halt, :live}

    status ->
      Process.sleep(200)
      {:cont, status}
  end
end)
|> case do
  :live -> :live
  status -> raise "bridge did not reach :live within 10s, last status: #{inspect(status)}"
end

What's in the house

Reads are :ets.lookup calls in your own process — they never touch the bridge or even the bridge's process. A light's own metadata is deprecated in CLIP v2, so names are resolved through the owning device, which Hue.Bridge.name_of/3 does for you.

{:ok, lights} = Hue.Light.list(LivebookHue)

lights
|> Enum.map(fn light ->
  %{
    name: Hue.Bridge.name_of(LivebookHue, :light, light["id"]),
    on: get_in(light, ["on", "on"]),
    brightness: get_in(light, ["dimming", "brightness"])
  }
end)
|> Enum.sort_by(& &1.name)
|> Kino.DataTable.new(name: "Lights")

Rooms and scenes carry their own authoritative names:

{:ok, rooms} = Hue.Room.list(LivebookHue)
{:ok, scenes} = Hue.Scene.list(LivebookHue)

Kino.Layout.grid(
  [
    Kino.DataTable.new(
      Enum.map(rooms, &%{room: get_in(&1, ["metadata", "name"])}),
      name: "Rooms"
    ),
    Kino.DataTable.new(
      Enum.map(scenes, &%{scene: get_in(&1, ["metadata", "name"])}),
      name: "Scenes"
    )
  ],
  columns: 2
)

Control, by name

Pick one of your lights from the table above and use its name here. Writes accept :on, :brightness (percent), :color (hex, RGB tuple, or xy), :kelvin, and :transition (milliseconds). A capability the light doesn't have — colour on a white-only bulb — returns {:error, %Hue.Error{}}; a malformed value raises, because that's a bug in the code, not a fact about the bulb.

light = "Desk Lamp"

:ok = Hue.Light.set(LivebookHue, light, on: true, brightness: 40)

set returns when the write is accepted, not when the light has changed — writes are coalesced and paced so a burst never floods the bridge. When you need confirmation, await: true blocks until the confirming event comes back down the eventstream:

Hue.Light.set(LivebookHue, light, color: "#ff8800", transition: 400, await: true)

Rooms, zones, and scenes work the same way — Hue.Room.set/3, Hue.Zone.set/3, Hue.Scene.recall/3:

# :ok = Hue.Room.set(LivebookHue, "Living Room", on: false)
# :ok = Hue.Scene.recall(LivebookHue, "Relax")
:skipped

A control panel, elsewhere

Driving lights from forms is a different job from learning the API, so it has its own notebook: control_panel.livemd is a full interface to your bridge — rooms, lights, scenes, management — and it reuses the credentials this notebook just saved, so it connects without pairing again.

Watch it live

Subscribing delivers {:hue, %Hue.Event{}} to the calling process, and the subscription dies with that process — so the listener below is a supervised task that subscribes itself. Flip a light in the Hue app, or re-run the set calls above, and watch the deltas arrive. Notice a single change fans out: the bridge also recomputes group aggregates, so one light produces a grouped_light event too.

frame = Kino.Frame.new(placeholder: false)

{:ok, _listener} =
  Kino.start_child(
    {Task,
     fn ->
       :ok = Hue.Bridge.subscribe(LivebookHue)

       Stream.repeatedly(fn ->
         receive do
           {:hue, event} ->
             name = Hue.Bridge.name_of(LivebookHue, event.resource_type, event.rid)

             Kino.Frame.append(
               frame,
               Kino.Markdown.new(
                 "`#{event.resource_type}` **#{name || event.rid}** → `#{inspect(event.data)}`"
               )
             )
         end
       end)
       |> Stream.run()
     end}
  )

frame

Where to next

Everything this notebook did, your application does with the same calls: put {Hue.Bridge, name: MyApp.Hue, client: client} in your supervision tree, store the application key like the password it is, and read the moduledocs — Hue.Bridge for the live model and its failure semantics, Hue.Light for writes, Hue.Resource for the stateless layer-1 escape hatch this notebook never needed.