lmendelowski

lmendelowski

Ash Framework: A brief detour into LiveView process shenanigans (page 236)

Hello!
I’m neither an Elixir nor Phoenix or Ash expert, but I believe I found misinformation in the A brief detour into LiveView process shenanigans section in the book. The paragraph describes the authentication process for the LiveView process with Ash.Authentication as follows:

The page liveviews, such as TunezWeb.Artists.ShowLive, get the current user via an on_mount callback set up in your app’s router with ash_authentication_live_session. This callback will read the authentication token stored in the session, load the correct user record, and store it in socket.assigns.

I believe this information is not correct. According to ash_authentication_live_session docs:

Generate a live session wherein all subject assigns are copied from the conn into the socket.

Basically, this function copies all assigns from the conn object. The process of getting user_id from the session and loading it into conn.current_user happens in TunezWeb.Router via plug :load_from_session for the browser pipeline. This function comes from AshAuthentication.Plug.Helpers and is described in the documentation as:

Attempt to retrieve all actors from the connections’ session.

A wrapper around AshAuthentication.Plug.Helpers.retrieve_from_session/2 with the otp_app as extracted from the endpoint.

And if we look at mentioned AshAuthentication.Plug.Helpers.retrieve_from_session/2 function:

Attempt to retrieve all users from the connections’ session.

Iterates through all configured authentication resources for otp_app and retrieves any users stored in the session, loads them and stores them in the assigns under their subject name (with the prefix current_).

If there is no user present for a resource then the assign is set to nil.

PS. Thank you for the book. It’s an excellent resource on Ash Framework!

Most Liked

jamesharton

jamesharton

Hi :waving_hand:

As both a technical reviewer for the book and the author of Ash Authentication this section didn’t jump out at me as wrong - mainly, I suspect, because the memory of all the hoops LiveView forces us to jump through have been suppressed as a self-protection measure.

That said, let’s look at the code:

    # From lib/ash_authentication_phoenix/live_session.ex
    otp_app
    |> AshAuthentication.authenticated_resources()
    |> Stream.map(&{to_string(Info.authentication_subject_name!(&1)), &1})
    |> Enum.reduce(acc, fn {subject_name, resource}, session ->
      case Map.fetch(
             conn.assigns,
             String.to_existing_atom("current_#{subject_name}")
           ) do
        {:ok, user} when is_struct(user, resource) ->
          session
          |> Map.put(subject_name, AshAuthentication.user_to_subject(user))
          |> Map.put("tenant", Ash.PlugHelpers.get_tenant(conn))
          |> Map.put("context", Ash.PlugHelpers.get_context(conn))

        _ ->
          session
          |> Map.put("tenant", Ash.PlugHelpers.get_tenant(conn))
          |> Map.put("context", Ash.PlugHelpers.get_context(conn))
      end
    end)

So you’re right that if there is a current_X assign in the conn then it should be copied into the live session. It also copies what we call the subject (eg user?id=1234) into the session along with the tenant and any extra context.

I think where the confusion comes from is when working with nested live views the session is passed in, but not any of the assigns. This required us to add AshAuthentication.Phoenix.assign_new_resources/2 which can have the side-effect of loading the assigned users from the database if require_token_presence_for_authentication? is set to true.

I guess my answer is “:person_shrugging: you’re both right”

Where Next?

Popular Pragmatic Bookshelf topics Top

iPaul
page 37 ANTLRInputStream input = new ANTLRInputStream(is); as of ANTLR 4 .8 should be: CharStream stream = CharStreams.fromStream(i...
New
brianokken
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
leonW
I ran this command after installing the sample application: $ cards add do something --owner Brian And got a file not found error: Fil...
New
curtosis
Running mix deps.get in the sensor_hub directory fails with the following error: ** (Mix) No SSH public keys found in ~/.ssh. An ssh aut...
New
hgkjshegfskef
The test is as follows: Scenario: Intersecting a scaled sphere with a ray Given r ← ray(point(0, 0, -5), vector(0, 0, 1)) And s ← sphere...
New
Charles
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
creminology
Skimming ahead, much of the following is explained in Chapter 3, but new readers (like me!) will hit a roadblock in Chapter 2 with their ...
New
s2k
Hi all, currently I wonder how the Tailwind colours work (or don’t work). For example, in app/views/layouts/application.html.erb I have...
New
rainforest
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels. Before ...
New
dachristenson
I just bought this book to learn about Android development, and I’m already running into a major issue in Ch. 1, p. 20: “Update activity...
New

Other popular topics Top

PragmaticBookshelf
Machine learning can be intimidating, with its reliance on math and algorithms that most programmers don't encounter in their regular wor...
New
dasdom
No chair. I have a standing desk. This post was split into a dedicated thread from our thread about chairs :slight_smile:
New
AstonJ
poll poll Be sure to check out @Dusty’s article posted here: An Introduction to Alternative Keyboard Layouts It’s one of the best write-...
New
AstonJ
This looks like a stunning keycap set :orange_heart: A LEGENDARY KEYBOARD LIVES ON When you bought an Apple Macintosh computer in the e...
New
Exadra37
I am asking for any distro that only has the bare-bones to be able to get a shell in the server and then just install the packages as we ...
New
PragmaticBookshelf
Build highly interactive applications without ever leaving Elixir, the way the experts do. Let LiveView take care of performance, scalabi...
New
PragmaticBookshelf
Use WebRTC to build web applications that stream media and data in real time directly from one user to another, all in the browser. ...
New
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New
sir.laksmana_wenk
I’m able to do the “artistic” part of game-development; character designing/modeling, music, environment modeling, etc. However, I don’t...
New
PragmaticBookshelf
Use advanced functional programming principles, practical Domain-Driven Design techniques, and production-ready Elixir code to build scal...
New

Latest in Ash Framework

Sub Categories: