# How to use Rails ActionCable from an external client application Photo by [Umberto](https://unsplash.com/@umby?utm_source=medium&utm_medium=referral) on [Unsplash](https://unsplash.com?utm_source=medium&utm_medium=referral) > WebSockets is a beautiful way to allow the client-server communication using a persistent bidirectional channel without the client having to poll the server. In this article **I’d like to explain how to get started with websocket in Ruby on Rails from a generic application**. I wont’ dive into what is a Websocket or how to create a Rails project. I’ll just leave some links at the end of this article. ## First of all, WebSocket in Rails are called `ActionCable`. ### The problem Tutorials from the [official documentation](https://guides.rubyonrails.org/action_cable_overview.html#parent-channel-setup) or others like [this one](https://dev.to/nkemjiks/simple-chatroom-with-rails-6-and-actioncable-3bc3) explain how to configure the server part and show the code to subscribe and communicate from a Javascript frontend using the `rails/actioncable` node module. But **what if you have an API-only Rails project or you have a frontend other than JS**, like an Android or an iOS app? This is why I wrote this article. ### Get started! Let’s suppose we’ve a _Rails_ project and you run the command below ```sh rails generate channel Chat ``` it will generate a file called `_channel.rb` where we can handle the client subscriptions or/and we can write custom methods that will be called by the clients… To keep the things simple we’ll implement the `subscribed` method and we write from scratch a custom dummy method (`my_method`) that receive a `data` parameter. We’ll see later what `data` is. Let’s replace `` with `ChatChannel` for this example. Here’s how file looks like. ```ruby class ChatChannel < ApplicationCable::Channel def subscribed logger.info "subscribed" stream_from "chat_channel" end def my_method(data) puts data end end ``` > Our goal is reach the `subscribed` and the `my_method` methods from an external client other than JS or out of our Rails project. _Let’s start!!!_ ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1637873018968/FXJfTkWB_.jpeg) Photo by [Braden Collum](https://unsplash.com/@bradencollum?utm_source=medium&utm_medium=referral) on [Unsplash](https://unsplash.com?utm_source=medium&utm_medium=referral) _First question_: how to create a WebSocket client? Or can we use a “Postman” like client already available? There are many ways and libraries to establish a WebSocket connection for many platforms, but to get started I suggest this ready to use WebSocket clients * [http://www.websocket.org/echo.html](http://www.websocket.org/echo.html) * [this Chrome plugin](https://chrome.google.com/webstore/detail/websocket-test-client/fgponpodhbmadfljofbimhhlengambbn) _Second question_: which URL should I call? In my project routes I can’t see anything related to `ActionCable` * Firstly we have to change the protocol from `http/https` to `ws`. * Let’s suppose that our Rails project runs on `localhost`, port 3000. * By default without specifying anything else, Rails expose the WebSocket service on `/cable` path Putting these things together **the URL is `ws://localhost:3000/cable`** _Third question_: how we communicate? **Basically with JSON** **messages as specified by WebSocket protocol**. Like the `rails/actioncable` JS module, libraries provides an “SDK way” to manage these messages, but in our simple web clients we have a “Message field” to write the command in, nothing more. I strived to find what to format the request and at the time I write I guess there is a lot more to find out. To guide me to the right direction i found these two articles ([1](https://medium.com/@emikaijuin/connecting-to-action-cable-without-rails-d39a8aaa52d5), [2](https://thoughtbot.com/blog/talking-to-actioncable-without-rails)).The *2* also explain how to authenticate the user. To see the things working for a “step 0” in a simple way I’ll ignore this step. From the *1* I tried to copy/paste the string in the `sendTXT` method in the web client Message field as is (even with begin/end double quotes and all escape characters: `“{\\”command\\”:\\”subscribe\\”,\\”identifier\\”:\\”{\\\\\\”channel\\\\\\”:\\\\\\”ArduinoChannel\\\\\\”}\\”}”` ) but it didn’t work (I changed the name to my channel name first). I tried to remove the begin/end quotes and I thought that a problem was that the escape characters were too many. Hence I tried to serialize a dictionary representing the JSON above with the help of the Rails console . I finally obtained this JSON: ```json {"command": "subscribe","identifier": "{\"channel\": \"ChatChannel\"}"} ``` **It works!!!!** The web console answerd me “welcome”! Just take a look at the Rails log to be sure that the `subscribed` method had been called and printed “subscribed”. Yes!!! All right, then: How to call `my_method` method now? _Here’s the best part_: **we can pass as many parameters we want** and we can call any methods with a very similar JSON ```json {"command": "message","identifier": "{\"channel\": \"ChatChannel\"}", "data":"{\"action\": \"my_method\", \"code\":\"a\"}"} ``` The differences: * the command type has changed from “subscribe” to “message” * identifier **must** remain the same as the subscription * we added the `data` key with a JSON string (with all the escape characters) Let’s send this message from the console and have a look at the Rails log. We’ll see these lines * `ChatChannel#my_method({“code”=>”a”}).` It recognized the `action` keyword and interpreted the JSON as an hash parameter. If we print the `data` parameter we obtain indeed `{“action”=>”my\_method”, “code”=>”a”}` ### Our goal has reached!!! Great! Just a little last thing: in a normal Rails (http) controller method you can write this code: ```ruby ActionCable.server.broadcast("chat_channel","An update has arrived...") ``` You’re dispatching via WebSocket on the `chat_channel` the “An update has arrived…” string: this will be printed even on your web console. **Doesn’t it look like a notification** ### Further references To learn about WebSocket or creating a Rails project * [What is WebSocket?](https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API) * [Create a Rails app with Docker](https://docs.docker.com/compose/rails/) * [Rails official guide to create a new project](https://guides.rubyonrails.org/getting_started.html) *Thanks for reading…*