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

jimmykiang
This test is broken right out of the box… — FAIL: TestAgent (7.82s) agent_test.go:77: Error Trace: agent_test.go:77 agent_test.go:...
New
New
yulkin
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
herminiotorres
Hi @Margaret , On page VII the book tells us the example and snippets will be all using Elixir version 1.11 But on page 3 almost the en...
New
AleksandrKudashkin
On the page xv there is an instruction to run bin/setup from the main folder. I downloaded the source code today (12/03/21) and can’t see...
New
fynn
This is as much a suggestion as a question, as a note for others. Locally the SGP30 wasn’t available, so I ordered a SGP40. On page 53, ...
New
akraut
The markup used to display the uploaded image results in a Phoenix.LiveView.HTMLTokenizer.ParseError error. lib/pento_web/live/product_l...
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
mert
AWDWR 7, page 152, page 153: Hello everyone, I’m a little bit lost on the hotwire part. I didn’t fully understand it. On page 152 @rub...
New
tkhobbes
After some hassle, I was able to finally run bin/setup, now I have started the rails server but I get this error message right when I vis...
New

Other popular topics Top

PragmaticBookshelf
Design and develop sophisticated 2D games that are as much fun to make as they are to play. From particle effects and pathfinding to soci...
New
AstonJ
Curious to know which languages and frameworks you’re all thinking about learning next :upside_down_face: Perhaps if there’s enough peop...
New
PragmaticBookshelf
From finance to artificial intelligence, genetic algorithms are a powerful tool with a wide array of applications. But you don't need an ...
New
New
AstonJ
Just done a fresh install of macOS Big Sur and on installing Erlang I am getting: asdf install erlang 23.1.2 Configure failed. checking ...
New
AstonJ
In case anyone else is wondering why Ruby 3 doesn’t show when you do asdf list-all ruby :man_facepalming: do this first: asdf plugin-upd...
New
PragmaticBookshelf
Leverage Elixir and the Nx ecosystem to build intelligent applications that solve real-world problems in computer vision, natural languag...
New
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New
PragmaticBookshelf
Escape callback hell and ship fast, clean code that reads as smoothly as it runs. Squash bugs and stamp out memory leaks with an intuitiv...
New
Fl4m3Ph03n1x
Background Lately I am in a quest to find a good quality TTS ai generation tool to run locally in order to create audio for some videos I...
New

Latest in Ash Framework

Sub Categories: