KV

Mix.install(
  [
    # {:livebook_cluster, "0.1.1", git: "git@git.sr.ht:~minasmazar/livebook_cluster"},
    {:livebook_cluster, "0.1.1", path: Path.expand("~/workspace/livebook_cluster")},
    {:kino, "~> 0.14.1"},
    {:plug, "~> 1.16"},
    {:floki, "~> 0.36.2"},
    {:jason, "~> 1.4"}
  ],
  config: [
    livebook_cluster: [slug: "kv"]
  ]
)

Key/Value Store

defmodule KV do
  use GenServer

  def start_link(state \\ %{}) do
    GenServer.start_link(__MODULE__, state, name: __MODULE__)
  end

  def init(state) do
    LivebookCluster.subscribe()
    {:ok, state}
  end

  def get(key) do
    GenServer.call(__MODULE__, {:get, key})
  end

  def set(key, value) do
    GenServer.call(__MODULE__, {:set, key, value})
  end

  def get_or_set(key, callback) when is_function(callback) do
    get(key) || set(key, callback.())
  end

  def flush do
    GenServer.cast(__MODULE__, :flush)
  end

  def inspect do
    GenServer.call(__MODULE__, :inspect)
  end

  def handle_cast(:flush, _store), do: {:noreply, %{}}
  def handle_call(:inspect, _, store), do: {:reply, store, store}

  def handle_call({:get, key}, _, store) do
    with value <- Map.get(store, key) do
      {:reply, value, store}
    end
  end

  def handle_call({:set, key, value}, _, store) do
    with store <- Map.put(store, key, value) do
      {:reply, value, store}
    end
  end

  def handle_info({:set, key, value}, store) do
    with store <- Map.put(store, key, value) do
      {:noreply, store}
    end
  end
end

KV.start_link()

Inspect store

# KV.flush()
KV.inspect()

HTTP Server

defmodule ApiRouter do
  use Plug.Router

  plug :match
  plug :dispatch

  get "/:key" do
    value = KV.get(key)
    if value do
      send_resp(conn, 200, value)
    else
      send_resp(conn, 404, "not found")
    end
  end

  get "/:key/:value" do
    result = KV.set(key, value)
    send_resp(conn, 200, inspect result)
  end

  match _ do
    send_resp(conn, 404, "oops, not found")
  end
end

Kino.Proxy.listen(ApiRouter)

Deploy the preview, than open the link http://localhost/proxy/apps/kv/key/ to get the key and http://localhost/proxy/apps/kv/key/value to set the value! (or http://localhost:4002/sessions/ecj6um2cz6tyion4hyf42m5dfa7boh6kiwrgewv2nglc4qmm/key and http://localhost:4002/sessions/ecj6um2cz6tyion4hyf42m5dfa7boh6kiwrgewv2nglc4qmm/key/value for a development session).

N.B. the 4002 is the port I run Livebook on my devbox.

Credits

• https://news.livebook.dev/livebook-0.13-expose-an-http-api-from-your-notebook-2wE6GY