Broadcast to socket without channel

It may be easier to find an answer if you share what effect you are trying to achieve.

Are you trying to send a message to exactly one of the user’s connections? i.e. they have multiple browsers / mobile app connections and you want to send a message to a specific one, but not all the others? Or something else?

Let’s say each client connects to server using a token, token is self contained according to Phoenix.Token

1. Assign a user connected to socket

def connect(%{"token" => token}, socket) do
  {:ok, data} = Phoenix.Token.verify(secret, user_salt, token, max_age: 86400)
  {:ok, assign(socket, :user, %{id: token})}
end

2. Generate a socket id via

def id(socket), do: "socket.users:#{socket.assigns[:user].id}"

Then somewhere in code send to socket.users:[user_id] some data. Let’s say I opened mobile app and web page with user_id equals to 1 then when I call something like Endpoint.broadcast_to_socket("socket:users:[user_id]")

Sorry, but I do not quite understand what the question is

What you described is how it works: given the id/1 function, you can use that in Endpoint.broadcast, e.g.:

MyApp.Endpoint.broadcast("users_socket:" <> user_id, "mymessage", %{})

And then all the connections with user_id would receive that message.

Are you sure that I am able to do this without connection to any channel?

Here are the docs for Phoenix.Socket.id/1. It has that exact example there Give it a try!

Yeah. I did
If I send hardcoded disconnect as per example it drops connection
But if it looks like

TheAPp.Web.Endpoint.broadcast("socket.users:1", "Hello", %{})

nothing happens
Still the question is that possible to send some piece of data to the client without channels using a socket id
P.S. Without channel means no channel modules at all and no joining

Looking into it more, you do apparently need to connect to a channel. sorry for the noise.

However, you can easily create a users: channel that does not require any special auth:

  def join(<<"user:", id :: binary>>, payload, socket) do
    if socket.assigns.user.id == id do
      send(self(), :after_join)
      {:ok, socket}
    else
      {:error, %{reason: "unauthorized"}}
    end
  end

.. or similar.

and then you can broadcast to the channel. Is there a specific reason you are avoiding connecting to the channel?

That’s the point that it hasn’t an extra “connection” when it is already opened socket there for any data.

Channels do not create an extra network connection. They are multiplexed over the socket. On the server-side channels are quite cheap. So I wouldn’t worry about that.

MyApp.Endpoint.broadcast("users_socket:" <> user_id, "mymessage", %{})

I think it would only work for "disconnect". I remember struggling with it here How to put something in a socket's assigns from another process - #7 by idi527