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

HarryDeveloper
Hi @venkats, It has been mentioned in the description of ‘Supervisory Job’ title that 2 things as mentioned below result in the same eff...
New
gilesdotcodes
In case this helps anyone, I’ve had issues setting up the rails source code. Here were the solutions: In Gemfile, change gem 'rails' t...
New
nicoatridge
Hi, I have just acquired Michael Fazio’s “Kotlin and Android Development” to learn about game programming for Android. I have a game in p...
New
jskubick
I found an issue in Chapter 7 regarding android:backgroundTint vs app:backgroundTint. How to replicate: load chapter-7 from zipfile i...
New
hazardco
On page 78 the following code appears: <%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
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
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
kolossal
Hi, I need some help, I’m new to rust and was learning through your book. but I got stuck at the last stage of distribution. Whenever I t...
New
mcpierce
@mfazio23 I’ve applied the changes from Chapter 5 of the book and everything builds correctly and runs. But, when I try to start a game,...
New
roadbike
From page 13: On Python 3.7, you can install the libraries with pip by running these commands inside a Python venv using Visual Studio ...
New

Other popular topics Top

siddhant3030
I’m thinking of buying a monitor that I can rotate to use as a vertical monitor? Also, I want to know if someone is using it for program...
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
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
foxtrottwist
A few weeks ago I started using Warp a terminal written in rust. Though in it’s current state of development there are a few caveats (tab...
New
AstonJ
If you want a quick and easy way to block any website on your Mac using Little Snitch simply… File > New Rule: And select Deny, O...
New
PragmaticBookshelf
Author Spotlight: VM Brasseur @vmbrasseur We have a treat for you today! We turn the spotlight onto Open Source as we sit down with V...
New
PragmaticBookshelf
Programming Ruby is the most complete book on Ruby, covering both the language itself and the standard library as well as commonly used t...
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
Get the comprehensive, insider information you need for Rails 8 with the new edition of this award-winning classic. Sam Ruby @rubys ...
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: