How to pass plug loaded data to LiveView components

Question

Hi I'm using different domain names to load different data sets. I'm currently using a custom plug to load the correct domain id based on the hostname. E.g. got this in my endpoint.ex just before the router:

plug WebApp.DomainCheck
socket "/live", Phoenix.LiveView.Socket, websocket: [connect_info: [session: @session_options]]
...
plug WebApp.Router

And

defmodule WebApp.DomainCheck do
  import Plug.Conn
  @behaviour Plug

  def init([]), do: []

  def call(conn, _options \\ []) do
    domains = Model.load_allowed_domains()
    case Map.get(domains, conn.host) do
      nil ->
        conn
        |> resp(401, "Domain not allowed")
        |> halt()

      domain_id ->
        conn
        |> assign(:domain_id, domain_id)
    end
  end
end

Now this works for normal View as I have the domain_id assign in each of them. But how do I get the domain data injected into my LiveViews as well from a plug?

Currently I've code duplicated the same domain check into every LiveViews mount() page:

defmodule WebApp.WelcomeLive do
  use WebApp, :live_view

  @impl true
  def mount(_args, _session, socket) do
    domains = Model.load_allowed_domains()
    host = socket.host_uri.host
    case Map.get(domains, host) do
      nil -> {:error, "Domain not allowed"}
      domain_id -> {:ok, assign(socket, :domain_id, domain_id)}
    end
  end

Is there any way I can make a plug effective in pushing this data down to the live views without need to add code to each mount?

Answer 1

I had a similar use case in my app where my plug puts the a user struct on the assigns and I wanted to keep that data inside live view without reloading all stuff.

The only way I could achieve that was using the option session from the live route passing it a MFA.

In the router you will have something like

live "/page", WebApp.SomeLiveView, :show, session: {WebAppp.Helpers, :keep_domain_id, []}

and your WebApp.Helpers will have that function returning what you want to be passed to your live view as session.

defmodule WebApp.Helpers do
  def keep_domain_id(conn) do
    %{"domain_id" => conn.assigns.domain_id}
  end
end

Then in your mount on you will have "domain_id" key in your session

defmodule WebApp.WelcomeLive do
  use WebApp, :live_view

  @impl true
  def mount(_args, %{"domain_id" => domain} = _session, socket) do
    ...
  end
end