Phoenix Channel sending messages from a client outside the project

Question

I wanted to send a message to my user channel of my Phoenix Application. I have joined a user_token with the channel as users:user_token in the user_channel.ex . I was successful doing it from another controller called the toy_controller by calling a broadcast method. The broadcast method is in the user channel. And I have written a jQuery file to handle the events. I was looking for something which can send messages to the same channel from outside of the project, because I wanted to do some IoT stuff. I have tried a python module called occamy.socket and the JS client of Phoenix that it uses internally. Then, I found a disconnection always. I can't figure out the exact address of the websocket connection from Phoenix. If I am trying it with that Phoenix npm library in that project folder itself, it says ReferenceError: window is not defined always. And, I think it is because of the initialization part of the socket in the web/static/js/socket.js file where it's written as

let socket = new Socket("/socket", {params: {token: window.userToken}})                              

, but I am not sure. The thing that I have tried is below

var Socket = require("phoenix-socket").Socket;
var socket = new Socket("ws://localhost:4000/socket");

In the python client, I was also trying to connect to this address and got a disconnection error. I want to do it for IoT purposes, where I want to monitor sensor data of a user. Each user will be having their own sensors to be monitored. So, I have configured the channel topic:subtopic channel as users:user_token . I need to send messages from my raspberry pi to this channel using those unique tokens of the users. My user_channel, user.js, app.js and socket.js are given below.

//web/static/js/socket.js
import {Socket} from "phoenix"

let socket = new Socket("/socket", {params: {token: window.userToken}})


socket.connect()


export default socket

//web/static/app.js


import "phoenix_html"
import user from "./user"

#web/channels/user_channel.ex
defmodule Tworit.UserChannel do
    use Tworit.Web, :channel

    def join("users:" <> user_token, payload, socket) do
        if authorized?(payload) do
          {:ok, "Joined To User:#{user_token}", socket}
      else
          {:error, %{reason: "unauthorized"}}
      end
    end


    def handle_in("ping", payload, socket) do
        {:reply, {:ok, payload}, socket}
    end


    def handle_in("shout", payload, socket) do
       broadcast socket, "shout", payload
       {:noreply, socket}
    end


    def handle_out(event, payload, socket) do
        push socket, event, payload
        {:noreply, socket}
    end


     defp authorized?(_payload) do
       true
     end

    def broadcast_change(toy, current_user) do
       payload = %{
        "name" => toy.name,
        "body" => toy.body
       }
      Tworit.Endpoint.broadcast("users:#{current_user.token}", "change", payload)
    end

end

//web/static/js/user.js
import socket from "./socket"

$(function() {
  let ul = $("ul#em")

  if (ul.length) {
    var token = ul.data("id")
    var topic = "users:" + token
		
    // Join the topic
    let channel = socket.channel(topic, {})
    channel.join()
      .receive("ok", data => {
        console.log("Joined topic", topic)
      })
      .receive("error", resp => {
        console.log("Unable to join topic", topic)
      })
    channel.on("change", toy => {
	    console.log("Change:", toy);
	    $("#message").append(toy["name"])
    })
  }
});

Answer 1

Finally, I am able to send and receive messages asynchronously from a python program. It uses websockets asyncio module from python. I figured out the various events required for phoenix channels like 'phx_join' for joining a topic and all. So, the following program worked.

import asyncio
import websockets
import json
import time
from random import randint
import serial

from pyfirmata import Arduino, util

board = Arduino('/dev/ttyACM1')

it = util.Iterator(board)
it.start()
board.analog[0].enable_reporting()
board.analog[1].enable_reporting()
board.analog[2].enable_reporting()
board.analog[3].enable_reporting()

import RPi.GPIO as gpio

gpio.setmode(gpio.BCM)
gpio.setup(14, gpio.OUT)


async def main():
    async with websockets.connect('ws://IP_addr:4000/socket/websocket') as websocket:
        data = dict(topic="users:user_token", event="phx_join", payload={}, ref=None)
        #this method joins the phoenix channel
        await websocket.send(json.dumps(data))

        print("Joined")

        while True:
            msg = await retrieve() # waits for data from arduino analog pins
            await websocket.send(json.dumps(msg)) # sends the sensor output to phoenix channel

            print("sent")
            call = await websocket.recv() # waits for anything from the phoenix server
            control = json.loads(call)

            # I have sent values from 2 buttons for swicthing a led with event 'control'

            if(control['event'] == "control"):
                event(control['payload']['val']) #swiches the led as per the input from event 'control'


            print("< {}".format(call))

def event(val):
    if(val == "on"):
        gpio.output(14, True)
    if(val == "off"):
        gpio.output(14, False)

async def retrieve():
    #analog read
    load = board.analog[0].read()
    pf = board.analog[1].read()
    reading = board.analog[2].read()
    thd = board.analog[3].read()
    output = {"load": load, "pf": pf, "reading": reading,"thd": thd}

    msg = dict(topic="users:user_token", event="sensor_output", payload=output, ref=None) # with 
    #event "sensor_outputs" 
    #the phoenix server displays the data on to a page.

    print(msg)
    return(msg)

asyncio.get_event_loop().run_until_complete(main())
asyncio.get_event_loop().run_forever()