Drab Manually publish to socket

[JanStevens]

Is it possible to have a separate gen server that then triggers an update for all connected clients using drab?

I have a GenServer that polls for data / transforms and then stores the results, what I want is to show a live feed of the resulting data whenever it changes in all the connected browsers.

What I had now is a recursive loop with a sleep in the drab method, ex:

  defp table_loop(socket) do
    :timer.sleep(2000)
    data =    ExpensiveData.get_current
    socket |> update!(:html, set: "<p>data<p>", on: ".table")
    table_loop(socket)
  end

It works but I wonder if there is a better way to do it. I would rather setup a GenEvent and let the GenServer send a notification that the data has changed so I can display it. This means I don't have to continually poll for updates like I do now in the above function.

Regards

[grych]

This is a known problem. I have it in my TODO list, but I still couldn't find a way how to resolve this.

The issue is that you need a Drab Server, which launches when the socket is created - on the client connect. After disconnect, the Drab Server and the socket is gone. What we need, is a kind of permanent socket and Drab, which we could use for a background broadcasting.

I've faced the similar issue while creating the presence demo. When user disconnects, there is no socket anymore, so I can't just broadcast a message to the others. I made an ugly hack there: got a random, connected socket and use it to broadcast.

I will keep this issue opened until I find the way to solve it correctly.

[grych]

This issue is solved with 0.5.0 (coming soon). Now, with broadcasting functions, you don't have to use the socket, but the subject, which doesn't have to be related to the socket.

[grych]

Fixed in v0.5.0

[JanStevens]

Hello,

Thanks looks awesome, just a question, I don't see in the guide / API any reference to the subject. So I'm not really sure how I should use it with poke and peek

[grych]

True, documentation is crappy in this topic. I am going to update it soon. Thanks for pointing it!

In general, there are subject creating functions: same_topic, same_controller and same_path. Use it instead of socket in broadcasting functions, example:

broadcast_js same_controller(MyApp.MyController), "console.log('bcast')"

it corresponds to controllers with

broadcasting :same_controller

[JanStevens]

And I can use this in a pure GenServer how? I should use Drab.Core.same_controller or should I use Drab.Commander first before it would work (even when its not really a commander).

[grych]

You need to have browsers connected with Drab first, so you need commander(s). Drab broadcast works with browsers connected with Drab only. Then you can broadcast from any part of code

[johannesE]

I am trying to do what you are saying and following the documentation but getting the following error:

You can see, that it's using the same path /items, meaning the browser is connected, but I'm probably missing something obvious.

[grych]

Unfortunatelly, I can't reproduce it. Can you please mention the phoenix and elixir version?

[grych]

@johannesE, could you please try to get https://github.com/grych/drab-example and run:

Drab.Core.broadcast_js Drab.Core.same_path("/"), "alert('a')"

on that?
So we would know if there is an issue with the environment or in the setup.

[johannesE]

When I run the example, I get [error] The client's requested channel transport version "2.0.0" does not match server's version requirements of "~> 1.0" every few seconds.
I use elixir 1.5.1 and used phx 1.3.0 in my app.

[grych]

What is the client (browser) version?

…

On 19 Aug 2017, at 14:13, Johannes ***@***.***> wrote: When I run the example, I get [error] The client's requested channel transport version "2.0.0" does not match server's version requirements of "~> 1.0" every few seconds. I use elixir 1.5.1 and used phx 1.3.0 in my app. — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#20 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAGK3srJmsfMy3R8rAD98FTxe7d5bA2dks5sZtFngaJpZM4N5aDz>.

-- Grych

[johannesE]

Ah, but the broadcast is working in the example app.

The browser is chromium Version 60.0.3112.78 (Developer Build) Built on Ubuntu , running on Ubuntu 17.04 (64-bit)

[johannesE]

[johannesE]

FYI: I did not set up If you want to use Drab.Query (jQuery based module) in my project. Everything except the broadcast is working though.

[grych]

1. About the broadcasting - if it works the example, it looks like it must be some misconfig. Is your code available somewhere?

2. About the protocol version error: are you using Phoenix 1.3.0 or some RC? I can see your error were changed in this commit. Please upgrade to official 1.3.0

EDIT: drab-example uses Phoenix 1.2, so forget about point 2. I will need to reproduce the issue somehow.

BTW Query is not required. Actually, drab-example does not use it.

[johannesE]

My code is here: https://github.com/octotreat/todomvc. I was trying to build something like this: http://todomvc.com/.
Mix.lock is showing that I'm using "phoenix": {:hex, :phoenix, "1.3.0",

The transport version error only happened in the example application. In there I was using phoenix 1.2.4, like you. The only difference is the elixir version (1.5.1 instead of 1.4), so I'm guessing that is the problem there. It will probably go away once you upgrade the example app to phoenix 1.3.0. So I think we should not focus on that one now.

[grych]

Thx! I managed to reproduce this issue with fresh Phoenix 1.3 installation. Interesting that it does not appear when running 1.3 over application built in 1.2.

[johannesE]

Cool. :-)
It cannot appear then because the installation of phoenix on your machine only changes the mix phx.new generator. Afterwards it's using the phoenix version specified in mix.lock, not the global installation.

[grych]

Actually the issue is because in P13 the endpoint is MyAppWeb.Endpoint, and pubsub is moved to MyApp.Endpoint. Drab is a hack over Phoenix, so it is looking for a pubsub module in the wrong place.

[grych]

@johannesE, could you please check with the fresh drab from master. It should be fixed.

[johannesE]

Yes, fixed :) Thank you!