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

jon
Some minor things in the paper edition that says “3 2020” on the title page verso, not mentioned in the book’s errata online: p. 186 But...
New
iPaul
page 37 ANTLRInputStream input = new ANTLRInputStream(is); as of ANTLR 4 .8 should be: CharStream stream = CharStreams.fromStream(i...
New
simonpeter
When I try the command to create a pair of migration files I get an error. user=> (create-migration "guestbook") Execution error (Ill...
New
edruder
I thought that there might be interest in using the book with Rails 6.1 and Ruby 2.7.2. I’ll note what I needed to do differently here. ...
New
raul
Page 28: It implements io.ReaderAt on the store type. Sorry if it’s a dumb question but was the io.ReaderAt supposed to be io.ReadAt? ...
New
patoncrispy
I’m new to Rust and am using this book to learn more as well as to feed my interest in game dev. I’ve just finished the flappy dragon exa...
New
AndyDavis3416
@noelrappin Running the webpack dev server, I receive the following warning: ERROR in tsconfig.json TS18003: No inputs were found in c...
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
dtonhofer
@parrt In the context of Chapter 4.3, the grammar Java.g4, meant to parse Java 6 compilation units, no longer passes ANTLR (currently 4....
New
ggerico
I got this error when executing the plot files on macOS Ventura 13.0.1 with Python 3.10.8 and matplotlib 3.6.1: programming_ML/code/03_...
New

Other popular topics Top

New
PragmaticBookshelf
Machine learning can be intimidating, with its reliance on math and algorithms that most programmers don't encounter in their regular wor...
New
brentjanderson
Bought the Moonlander mechanical keyboard. Cherry Brown MX switches. Arms and wrists have been hurting enough that it’s time I did someth...
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
AstonJ
Do the test and post your score :nerd_face: :keyboard: If possible, please add info such as the keyboard you’re using, the layout (Qw...
New
AstonJ
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
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
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
NewsBot
Node.js v22.14.0 has been released. Link: Release 2025-02-11, Version 22.14.0 'Jod' (LTS), @aduh95 · nodejs/node · GitHub
New

Latest in Ash Framework

Sub Categories: