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

Mmm
Hi, build fails on: bracket-lib = “~0.8.1” when running on Mac Mini M1 Rust version 1.5.0: Compiling winit v0.22.2 error[E0308]: mi...
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
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
leba0495
Hello! Thanks for the great book. I was attempting the Trie (chap 17) exercises and for number 4 the solution provided for the autocorre...
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
brunogirin
When installing Cards as an editable package, I get the following error: ERROR: File “setup.py” not found. Directory cannot be installe...
New
dsmith42
Hey there, I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “>...
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
rainforest
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels. Before ...
New
a.zampa
@mfazio23 I’m following the indications of the book and arriver ad chapter 10, but the app cannot be compiled due to an error in the Bas...
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
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
DevotionGeo
I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run com...
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
AstonJ
Was just curious to see if any were around, found this one: I got 51/100: Not sure if it was meant to buy I am sure at times the b...
New
PragmaticBookshelf
Author Spotlight Mike Riley @mriley This month, we turn the spotlight on Mike Riley, author of Portable Python Projects. Mike’s book ...
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
DevotionGeo
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New
PragmaticBookshelf
Author Spotlight: Peter Ullrich @PJUllrich Data is at the core of every business, but it is useless if nobody can access and analyze ...
New
PragmaticBookshelf
Build modern server-driven web applications using htmx. Whatever programming language you use, you’ll write less (and cleaner) code. ...
New

Latest in Ash Framework

Sub Categories: