`LiveView` Chat Tutorial

Why? 🤷

We really wanted a Free & Open Source real-world example with full code, tests and auth.
We wrote this so we could point people in our team/community learning Phoenix LiveView to it.
This LiveView example/tutorial takes you from zero to fully functioning app in 20 minutes.

What? 💬

Here is the table of contents of what you can expect to cover in this example/tutorial:

LiveView Chat Tutorial
Why? 🤷
What? 💬
Who? 👤
How? 💻
What's Next?

Who? 👤

Anyone learning Phoenix LiveView wanting a self-contained tutorial including: Setup, Testing, Authentication, Presence,

How? 💻

0. Prerequisites

It's recommended, though not required, that you follow the LiveView Counter Tutorial as this one is more advanced. At least, checkout the list of prerequisites so you know what you need to have installed on your computer before you start this adventure!

Provided you have Elixir, Phoenix and Postgres installed, you're good to go!

1. Create `Phoenix` App

Start by creating the new liveview_chat Phoenix application:

mix phx.new liveview_chat --no-mailer --no-dashboard

We don't need email or dashboard features so we're excluding them from our app. You can learn more about creating new Phoenix apps by running: mix help phx.new

Run mix deps.get to retrieve the dependencies. then create the liveview_chat_dev Postgres database by running the command:

mix ecto.setup

You should see output similar to the following:

The database for LiveviewChat.Repo has been created

14:20:19.71 [info]  Migrations already up

Once that command succeeds You should now be able to start the application by running the command:

mix phx.server

You will see terminal output similar to the following:

[info] Running LiveviewChatWeb.Endpoint with cowboy 2.9.0 at 127.0.0.1:4000 (http)
[debug] Downloading esbuild from https://registry.npmjs.org/esbuild-darwin-64/-/esbuild-darwin-64-0.14.29.tgz
[info] Access LiveviewChatWeb.Endpoint at http://localhost:4000
[watch] build finished, watching for changes...

When you open the URL: http://localhost:4000 in your web browser you should see something similar to:

2. Create `live` Directory, `LiveView` Controller and Template

Create the lib/liveview_chat_web/live folder and the controller at lib/liveview_chat_web/live/message_live.ex:

defmodule LiveviewChatWeb.MessageLive do
  use LiveviewChatWeb, :live_view

  def mount(_params, _session, socket) do
    {:ok, socket}
  end

  def render(assigns) do
    LiveviewChatWeb.MessageView.render("messages.html", assigns)
  end
end

Note: neither the file name nor the code has the word "controller" anywhere. Hopefully it's not confusing. It's a "controller" in the sense that it controls what happens in the app.

A LiveView controller requires the functions mount/3 and render/1 to be defined.
To keep the controller simple the mount/3 is just returning the {:ok, socket} tuple without any changes. The render/1 invokes LiveviewChatWeb.MessageView.render/2 (included with Phoenix) which renders the messages.html.heex template which we will define below.

Create the lib/liveview_chat_web/views/message_view.ex file:

defmodule LiveviewChatWeb.MessageView do
  use LiveviewChatWeb, :view
end

This is similar to regular Phoenix view; nothing special/interesting here.

Next, create the lib/liveview_chat_web/templates/message directory, then create
lib/liveview_chat_web/templates/message/messages.html.heex file and add the following line of HTML:

<h1>LiveView Message Page</h1>

Finally, to make the root layout simpler, open the lib/liveview_chat_web/templates/layout/root.html.heex file and update the contents of the <body> to:

<body>
  <header>
    <section class="container">
      <h1>LiveView Chat Example</h1>
    </section>
  </header>
  <%= @inner_content %>
</body>

3. Update `router.ex`

Now that you've created the necessary files, open the router lib/liveview_chat_web/router.ex replace the default route PageController controller:

get "/", PageController, :index

with MessageLive controller:

scope "/", LiveviewChatWeb do
  pipe_through :browser

  live "/", MessageLive
end

Now if you refresh the page you should see the following:

4. Update Tests

At this point we have made a few changes that mean our automated test suite will no longer pass ... Run the tests in your command line with the following command:

mix test

You will see output similar to the following:

Generated liveview_chat app
..

  1) test GET / (LiveviewChatWeb.PageControllerTest)
     test/liveview_chat_web/controllers/page_controller_test.exs:4
     Assertion with =~ failed
     code:  assert html_response(conn, 200) =~ "Welcome to Phoenix!"
     left:  "<!DOCTYPE html><html lang=\"en\"> <head> <meta charset=\"utf-8\"> <meta http-equiv=\"X-UA-Compatible\" content=\"IE=edge\">
     <title data-suffix=\" · Phoenix Framework\">LiveviewChat · Phoenix Framework</title> <link phx-track-static rel=\"stylesheet\" href=\"/assets/app.css\">    <script defer phx-track-static type=\"text/javascript\" src=\"/assets/app.js\"></script>  </head>  
     <body> <header> <section class=\"container\"> 
     <h1>LiveView Chat Example</h1></section> </header>
     <h1>LiveView Message Page</h1></main></div>  </body></html>"
     right: "Welcome to Phoenix!"
     stacktrace:
       test/liveview_chat_web/controllers/page_controller_test.exs:6: (test)

Finished in 0.03 seconds (0.02s async, 0.01s sync)
3 tests, 1 failure

This is because the page_controller_test.exs is still expecting the homepage to contain the "Welcome to Phoenix!" text.

Let's update the tests! Create the test/liveview_chat_web/live folder and the message_live_test.exs file within it: test/liveview_chat_web/live/message_live_test.exs

Add the following test code to it:

defmodule LiveviewChatWeb.MessageLiveTest do
  use LiveviewChatWeb.ConnCase
  import Phoenix.LiveViewTest

  test "disconnected and connected mount", %{conn: conn} do
    conn = get(conn, "/")
    assert html_response(conn, 200) =~ "LiveView Message Page"

    {:ok, _view, _html} = live(conn)
  end
end

We are testing that the / endpoint is accessible and has the text "LiveView Message Page" on the page.

See also the LiveViewTest module for more information about testing and liveView.

Finally you can delete all the default generated code linked to the PageController:

rm test/liveview_chat_web/controllers/page_controller_test.exs
rm lib/liveview_chat_web/controllers/page_controller.ex
rm test/liveview_chat_web/views/page_view_test.exs
rm lib/liveview_chat_web/views/page_view.ex
rm -r lib/liveview_chat_web/templates/page

You can now run the test again with mix test command. You should see the following (tests passing):

Generated liveview_chat app
...

Finished in 0.1 seconds (0.06s async, 0.1s sync)
3 tests, 0 failures

Randomized with seed 841084

5. Migration and Schema

With the LiveView structure defined, we can focus on creating messages. The database will save the message and the name of the sender. Let's create a new schema and migration:

mix phx.gen.schema Message messages name:string message:string

Note: don't forget to run mix ecto.migrate to create the new messages table in the database.

We can now update the Message schema to add functions for creating new messages and listing the existing messages. We'll also update the changeset to add requirements and validations on the message text. Open the lib/liveview_chat/message.ex file and update the code with the following:

defmodule LiveviewChat.Message do
  use Ecto.Schema
  import Ecto.Changeset
  import Ecto.Query
  alias LiveviewChat.Repo
  alias __MODULE__

  schema "messages" do
    field :message, :string
    field :name, :string

    timestamps()
  end

  @doc false
  def changeset(message, attrs) do
    message
    |> cast(attrs, [:name, :message])
    |> validate_required([:name, :message])
    |> validate_length(:message, min: 2)
  end

  def create_message(attrs) do
    %Message{}
    |> changeset(attrs)
    |> Repo.insert()
  end

  def list_messages do
    Message
    |> limit(20)
    |> order_by(desc: :inserted_at)
    |> Repo.all()
  end
end

We have added the validate_length function on the message input to ensure that messages have at least 2 characters. This is just an example to show how the changeset validation works with the form on the LiveView page.

We then created the create_message/1 and list_messages/0 functions. Similar to phoenix-chat-example we limit the number of messages returned to the latest 20.

6 Update `mount/3` function

Open the lib/liveview_chat_web/live/message_live.ex file and add the following line at line 3:

alias LiveviewChat.Message

Next update the mount/3 function in the lib/liveview_chat_web/live/message_live.ex file to use the list_messages function:

def mount(_params, _session, socket) do
  messages = Message.list_messages() |> Enum.reverse()
  changeset = Message.changeset(%Message{}, %{})
  {:ok, assign(socket, changeset: changeset, messages: messages)}
end

mount/3 will now get the list of messages and create a changeset that will be used for the message form. We then assign the changeset and the messages to the socket which will display them on the liveView page.

7. Update Template

Update the messages.html.heex template to the following code:

<ul id='msg-list' phx-update="append">
  <%= for message <- @messages do %>
    <li id={"msg-#{message.id}"}>
      <b><%= message.name %>:</b>
      <%= message.message %>
    </li>
  <% end %>
</ul>

<.form let={f} for={@changeset} id="form" phx-submit="new_message" phx-hook="Form">
  <%= text_input f, :name, id: "name", placeholder: "Your name", autofocus: "true"  %>
  <%= error_tag f, :name %>

  <%= text_input f, :message, id: "msg", placeholder: "Your message"  %>
  <%= error_tag f, :message %>

  <%= submit "Send"%>
</.form>

It first displays the new messages and then provides a form for people to create a new message.

If you refresh the page, you should see the following:

The <.form></.form> syntax is how to use the form function component.

A function component is any function that receives an assigns map as argument and returns a rendered struct built with the ~H sigil.

7.1 Update the Test Assertion

Finally let's make sure the test are still passing by updating the assert in the test/liveview_chat_web/live/message_live_test.exs file to:

assert html_response(conn, 200) =~ "LiveView Chat"

As we have deleted the LiveView Message Page h1 title, we can instead test for the title in the root layout and make sure the page is still displayed correctly.

8. Handle Message Creation Events

At the moment if we run the Phoenix app mix phx.server and submit the form in the browser nothing will happen. If we look at the server log, we see the following:

** (UndefinedFunctionError) function LiveviewChatWeb.MessageLive.handle_event/3
  is undefined or private
  (liveview_chat 0.1.0) LiveviewChatWeb.MessageLive.handle_event("new_message",
  %{"_csrf_token" => "fyVPIls_XRBuGwlkMhxsFAciRRkpAVUOLW5k4UoR7JF1uZ5z2Dundigv",
  "message" => %{"message" => "", "name" => ""}}, #Phoenix.LiveView.Socket

On submit the form is creating a new event defined with phx-submit:

<.form let={f} for={@changeset} id="form" phx-submit="new_message">

However this event is not managed on the server yet, we can fix this by adding the handle_event/3 function in lib/liveview_chat_web/live/message_live.ex:

def handle_event("new_message", %{"message" => params}, socket) do
  case Message.create_message(params) do
    {:error, changeset} ->
      {:noreply, assign(socket, changeset: changeset)}

    {:ok, _message} ->
      changeset = Message.changeset(%Message{}, %{"name" => params["name"]})
      {:noreply, assign(socket, changeset: changeset)}
    end
end

The create_message function is called with the values from the form. If an error occurs while trying to save the information in the database, for example the changeset can return an error if the name or the message is empty or if the message is too short, the changeset is assigned again to the socket. This will allow the form to display the error information:

If the message is saved without any errors, we are creating a new changeset which contains the name from the form to avoid people having to enter their name again in the form, and we assign the new changeset to the socket.

8.1 Test Message Creation Validation

Now the form is displayed we can add the following tests to test/liveview_chat_web/live/message_live_test.exs:

  import Plug.HTML, only: [html_escape: 1]

  test "name can't be blank", %{conn: conn} do
    {:ok, view, _html} = live(conn, "/")

    assert view
           |> form("#form", message: %{name: "", message: "hello"})
           |> render_submit() =~ html_escape("can't be blank")
  end

  test "message", %{conn: conn} do
    {:ok, view, _html} = live(conn, "/")

    assert view
           |> form("#form", message: %{name: "Simon", message: ""})
           |> render_submit() =~ html_escape("can't be blank")
  end

  test "minimum message length", %{conn: conn} do
    {:ok, view, _html} = live(conn, "/")

    assert view
           |> form("#form", message: %{name: "Simon", message: "h"})
           |> render_submit() =~ "should be at least 2 character(s)"
  end

We are using the form/3 function to select the form and trigger the submit event with different values for the name and the message. We are testing that errors are properly displayed.

9. PubSub

Instead of having to reload the page to see the newly created messages, we can use PubSub (Publish Subscribe) to inform all connected clients that a new message has been created and to update the UI to display the new message.

Open the lib/liveview_chat/message.ex file and add the following line near the top:

alias Phoenix.PubSub

Next add the following 3 functions:

  def subscribe() do
    PubSub.subscribe(LiveviewChat.PubSub, "liveview_chat")
  end

  def notify({:ok, message}, event) do
    PubSub.broadcast(LiveviewChat.PubSub, "liveview_chat", {event, message})
  end

  def notify({:error, reason}, _event), do: {:error, reason}

subscribe/0 will be called when a client has properly displayed the liveView page and listen for new messages. It is just a wrapper function for Phoenix.PubSub.subscribe.

notify/2 is invoked each time a new message is created to broadcast the message to the connected clients. Repo.insert can either returns {:ok, message} or {:error, reason}, so we need to define notify/2 handle both cases.

9.1 Notify Connected Clients of New Messages

Update the create_message/1 function in message.ex to invoke our newly created notify/2 function:

  def create_message(attrs) do
    %Message{}
    |> changeset(attrs)
    |> Repo.insert()
    |> notify(:message_created)
  end

9.2 Update `mount/3`

We can now connect the client when the LiveView page is rendered. At the top of the lib/liveview_chat_web/live/message_live.ex file, add the following line:

alias LiveviewChat.PubSub

Then update the mount/3 function with:

def mount(_params, _session, socket) do
  if connected?(socket), do: Message.subscribe()

  messages = Message.list_messages() |> Enum.reverse()
  changeset = Message.changeset(%Message{}, %{})
  {:ok, assign(socket, messages: messages, changeset: changeset)}
end

mount/3 now checks the socket is connected then calls the new Message.subscribe/0 function.

9.3 Update `handle_event/3`

Since the return value of create_message/1 has changed, we need to update handle_event/3 to the following:

def handle_event("new_message", %{"message" => params}, socket) do
  case Message.create_message(params) do
    {:error, changeset} ->
      {:noreply, assign(socket, changeset: changeset)}

    :ok -> # broadcast returns :ok (just the atom!) if there are no errors
      changeset = Message.changeset(%Message{}, %{"name" => params["name"]})
      {:noreply, assign(socket, changeset: changeset)}
  end
end

9.4 Create `handle_info/2`

The last step is to handle the :message_created event by defining the handle_info/2 function in lib/liveview_chat_web/live/message_live.ex:

def handle_info({:message_created, message}, socket) do
  messages = socket.assigns.messages ++ [message]
  {:noreply, assign(socket, messages: messages)}
end

When the event is received, the new message is added to the list of existing messages. The new list is then assigned to the socket which will update the UI to display the new message.

9.5 Test Messages are Displaying

Add the following tests to test/liveview_chat_web/live/message_live_test.exs to ensure that messages are correctly displayed on the page:

test "message form submitted correctly", %{conn: conn} do
  {:ok, view, _html} = live(conn, "/")

  assert view
         |> form("#form", message: %{name: "Simon", message: "hi"})
         |> render_submit()

  assert render(view) =~ "<b>Simon:</b>"
  assert render(view) =~ "hi"
end

test "handle_info/2", %{conn: conn} do
  {:ok, view, _html} = live(conn, "/")
  assert render(view)
  # send :created_message event when the message is created
  Message.create_message(%{"name" => "Simon", "message" => "hello"})
  # test that the name and the message is displayed
  assert render(view) =~ "<b>Simon:</b>"
  assert render(view) =~ "hello"
end

You should now have a functional chat application using liveView! Run the Phoenix App with:

mix phx.server

Visit the App localhost:4000 in 2 or more browsers, and send yourself some messages!

10. Hooks

One issue we can notice is that the message input doesn't always reset to an empty value after sending a message using the Enter key on the input field. This forces us to remove the previous message manually before writing and sending a new one.

The reason is:

The JavaScript client is always the source of truth for current input values. For any given input with focus, LiveView will never overwrite the input's current value, even if it deviates from the server's rendered updates. see: https://hexdocs.pm/phoenix_live_view/form-bindings.html#javascript-client-specifics

Our solution is to use phx-hook to run some javascript on the client after one of the LiveView life-cycle callbacks (mounted, beforeUpdated, updated, destroyed, disconnected, reconnected).

Let's add a hook to monitor when the message form is updated. In the message.html.heex file add the phx-hook attribute to the <.form> element:

<.form let={f} for={@changeset} id="form" phx-submit="new_message" phx-hook="Form">

Then in the assets/js/app.js file, add the following JavaScript logic:

// get message input element
let msg = document.getElementById('msg');                                           

// define "Form" hook, the name must match the one
// defined with phx-hoo="Form"
let Hooks = {}
Hooks.Form = {
  // Each time the form is updated run the code in the callback
  updated() {
    // If no error displayed reset the message value
    if(document.getElementsByClassName('invalid-feedback').length == 0) {
      msg.value = '';
    }
  }
}

let csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content")
let liveSocket = new LiveSocket("/live", Socket, {params: {_csrf_token: csrfToken}, hooks: Hooks}) // Add hooks: Hooks

The main logic to reset the message value is contained inside the updated() callback function:

if(document.getElementsByClassName('invalid-feedback').length == 0) {
  msg.value = '';
}

Before setting the value to an empty string, we check first that no errors are displayed on the form by checking for the invalid-feedback CSS class. (read more about feedback: https://hexdocs.pm/phoenix_live_view/form-bindings.html#phx-feedback-for )

The final step is to set the hooks on the liveSocket with hooks: Hooks. The message input should now be reset when a new message is added!

11. Optional: Temporary assigns

At the moment the mount/3 function first initializes the list of messages by loading the latest 20 messages from the database:

def mount(_params, _session, socket) do
  if connected?(socket), do: Message.subscribe()

  messages = Message.list_messages() |> Enum.reverse() # get the list of messages
  changeset = Message.changeset(%Message{}, %{})

  {:ok, assign(socket, messages: messages, changeset: changeset)} ## assigns messages to socket
end

Then each time a new message is created the handle_info function append the message to the list of messages:

def handle_info({:message_created, message}, socket) do
  messages = socket.assigns.messages ++ [message] # append new message to the existing list
  {:noreply, assign(socket, messages: messages)}
end

This can cause issues if the list of messages becomes too long as all the messages are kept in memory on the server.

To minimize the use of the memory, we can define messages as a temporary assign:

def mount(_params, _session, socket) do
  if connected?(socket), do: Message.subscribe()

  messages = Message.list_messages() |> Enum.reverse()
  changeset = Message.changeset(%Message{}, %{})

  {:ok, assign(socket, messages: messages, changeset: changeset),
  temporary_assigns: [messages: []]}
end

The list of messages is retrieved once, then it is reset to an empty list.

Now the handle_info/2 only needs to assign the new message to the socket:

def handle_info({:message_created, message}, socket) do
  {:noreply, assign(socket, messages: [message])}
end

Finally the heex messages template listens for any changes in the list of messages with phx-update and appends the new message to the existing displayed list.

<ul id='msg-list' phx-update="append">
   <%= for message <- @messages do %>
     <li id={message.id}>
       <b><%= message.name %>:</b>
       <%= message.message %>
     </li>
   <% end %>
</ul>

See also the Phoenix temporary-assigns documentation page: https://hexdocs.pm/phoenix_live_view/dom-patching.html#temporary-assigns

12. Authentication

Currently the name field is left to the person to define manually before they send a message. This is fine in a basic demo app, but we know we can do better. In this section we'll add authentication using auth_plug. That will allow people using the App to authenticate with their GitHub or Google account and then pre-fill the name in the message form.

12.1 Create `AUTH_API_KEY`

As per the instructions first create a new API Key at https://authdemo.fly.dev/ e.g:

Then create an .env file and add your new created api key:

export AUTH_API_KEY=88SwQGzaZoJYXs6ihvwMy2dRVtm6KVeg4tSCjRKtwDvMUYUbi/88SwQDatWtSTMd2rKPnaZsAWFNpbf4vv2ZK7JW2nwuSypMeg/authdemo.fly.dev

Note: for security reasons, this is not a valid API key. Please create your own, it's free and takes less than a minute.

12.2 Install `auth_plug` ⬇️

Add the auth_plug package to your dependencies. In mix.exs file update your deps function and add:

{:auth_plug, "~> 1.4.10"}

This dependency will create new sessions for you and communicate with the dwyl auth application.

Don't forget to:

load your key: source .env
get the dependencies: mix deps.get

Make sure the AUTH_API_KEY is accessible before the new dependency is compiled.
You can recompile the dependencies with mix deps.compile --force.

Now we can start adding the authentication feature.

12.3 Create the Optional Auth Pipeline in `router.ex`

To allow [unauthenticated] "guest" users access to the chat we use the AuthPlugOptional plug. Read more at optional auth.

In the router.ex file, we create a new Plug pipeline:

# define the new pipeline using auth_plug
pipeline :authOptional, do: plug(AuthPlugOptional)

Next update the scope "/", LiveviewChatWeb do block to the following:

scope "/", LiveviewChatWeb do
  pipe_through [:browser, :authOptional]

  live "/", MessageLive
  get "/login", AuthController, :login
  get "/logout", AuthController, :logout
end

We are now allowing authentication to be optional for all the routes in the router. Easy, hey? 😉

12.4 Create `AuthController`

Create the AuthController with both login/2 and logout/2 functions.

Create a new file: lib/liveview_chat_web/controllers/auth_controller.ex and add the following code:

defmodule LiveviewChatWeb.AuthController do
  use LiveviewChatWeb, :controller

  def login(conn, _params) do
    redirect(conn, external: AuthPlug.get_auth_url(conn, "/"))
  end

  def logout(conn, _params) do
    conn
    |> AuthPlug.logout()
    |> put_status(302)
    |> redirect(to: "/")
  end
end

The login/2 function redirects to the dwyl auth app. Read more about how to use the AuthPlug.get_auth_url/2 function. Once authenticated the user will be redirected to the / endpoint and a jwt session is created on the client.

The logout/2 function invokes AuthPlug.logout/1 which removes the (JWT) session and redirects back to the homepage.

12.5 Create `on_mount/4` functions

LiveView provides the on_mount callback that lets us run code before the mount. We'll use this callback to verify the jwt session and assign the person (Map) and loggedin (boolean) values to the socket.

In the lib/liveview_chat_web/controllers/auth_controller.ex file add the following code to define two versions of mount/4:

# import the assign_new function from LiveView
import Phoenix.LiveView, only: [assign_new: 3]

# pattern match on :default auth and check session has jwt
def on_mount(:default, _params, %{"jwt" => jwt} = _session, socket) do
  # verify and retrieve jwt stored data
  claims = AuthPlug.Token.verify_jwt!(jwt)

  # assigns the person and the loggedin values
  socket =
    socket
    |> assign_new(:person, fn ->
      AuthPlug.Helpers.strip_struct_metadata(claims)
    end)
    |> assign_new(:loggedin, fn -> true end)

  {:cont, socket}
end

# when jwt is not defined just returns the current socket
def on_mount(:default, _params, _session, socket) do
  socket = assign_new(socket, :loggedin, fn -> false end)
  {:cont, socket}
end

assign_new/3 assigns a value to the socket if it doesn't exists.

Once the on_mount/2 callback is defined, we can call it in our lib/liveview_chat_web/live/message_live.ex file:

defmodule LiveviewChatWeb.MessageLive do
  use LiveviewChatWeb, :live_view
  alias LiveviewChat.Message
  # run authentication on mount
  on_mount LiveviewChatWeb.AuthController

We now have all the logic to let people authenticate, we just need to update our root layout file lib/liveview_chat_web/templates/layout/root.html.heex to display a login (or logout) link:

<body>
  <header>
    <section class="container">
      <nav>
        <ul>
          <%= if @loggedin do %>
            <li>
              <img width="40px" src={@person.picture}/>
            </li>
            <li><%= link "logout", to: "/logout" %></li>
          <% else %>
            <li><%= link "Login", to: "/login" %></li>
          <% end %>
        </ul>
      </nav>
      <h1>LiveView Chat Example</h1>
    </section>
  </header>
  <%= @inner_content %>
</body>

If the person is not yet loggedin we display a login link otherwise the logout link is displayed.

The last step is to display the name of the logged-in person in the name field of the message form. For that we can update the form changeset in the mount function to set the name parameters:

def mount(_params, _session, socket) do
  if connected?(socket), do: Message.subscribe()

  # add name parameter if loggedin
  changeset =
    if socket.assigns.loggedin do
      Message.changeset(%Message{}, %{"name" => socket.assigns.person["givenName"]})
    else
      Message.changeset(%Message{}, %{})
    end

  messages = Message.list_messages() |> Enum.reverse()

  {:ok, assign(socket, messages: messages, changeset: changeset),
   temporary_assigns: [messages: []]}
end

You can now run the application and be able to login/logout!

14. Presence

In this section we will use Phoenix Presence to display a list of people who are currently using the application.

The first step is to create the lib/liveview_chat/presence.ex file:

defmodule LiveviewChat.Presence do
  use Phoenix.Presence,
    otp_app: :liveview_chat,
    pubsub_server: LiveviewChat.PubSub
end

Then in lib/liveview_chat/application.ex we add the newly created Presence module to the list of applications for the supervisor to start:

  def start(_type, _args) do
    children = [
      # Start the Ecto repository
      LiveviewChat.Repo,
      # Start the Telemetry supervisor
      LiveviewChatWeb.Telemetry,
      # Start the PubSub system
      {Phoenix.PubSub, name: LiveviewChat.PubSub},
      # Presence
      LiveviewChat.Presence,
      # Start the Endpoint (http/https)
      LiveviewChatWeb.Endpoint
      # Start a worker by calling: LiveviewChat.Worker.start_link(arg)
      # {LiveviewChat.Worker, arg}
    ]
...

We are now ready to use the Presence features in our liveview endpoint.
In the lib/liveview_chat_web/live/message_live.ex file, update the mount function with the following:

  @presence_topic "liveview_chat_presence"

  def mount(_params, _session, socket) do
    if connected?(socket) do
      Message.subscribe()

      {id, name} =
        if socket.assigns.loggedin do
          {socket.assigns.person["id"], socket.assigns.person["givenName"]}
        else
          {socket.id, "guest"}
        end

      {:ok, _} = Presence.track(self(), @presence_topic, id, %{name: name})
      Phoenix.PubSub.subscribe(PubSub, @presence_topic)
    end

    changeset =
      if socket.assigns.loggedin do
        Message.changeset(%Message{}, %{"name" => socket.assigns.person["givenName"]})
      else
        Message.changeset(%Message{}, %{})
      end

    messages = Message.list_messages() |> Enum.reverse()

    {:ok,
     assign(socket,
       messages: messages,
       changeset: changeset,
       presence: get_presence_names()
     ), temporary_assigns: [messages: []]}
  end

Let's recap the main changes to the mount/3 function:

First we create the module attribute @presence_topic to define the topic we'll use with the Presence functions.

The following part of the code defines a tuple containing an id of the person and their name. The name will default to "guest" if the person is not loggedin.

{id, name} =
    if socket.assigns.loggedin do
        {socket.assigns.person["id"], socket.assigns.person["givenName"]}
     else
        {socket.id, "guest"}
    end

Secondly we use the track/4 function to let Presence knows that a new client is looking at the application:

{:ok, _} = Presence.track(self(), @presence_topic, id, %{name: name})

Third we use PubSub to listen to Presence changes (person joining or leaving the application):

Phoenix.PubSub.subscribe(PubSub, @presence_topic)

Finally we create a new presence assign in the socket:

presence: get_presence_names()

get_presence_names function will return a list of loggedin users and if any the number of "guest" users.

Add the following code at the end of the MessageLive module:

  defp get_presence_names() do
    Presence.list(@presence_topic)
    |> Enum.map(fn {_k, v} -> List.first(v.metas).name end)
    |> group_names()
  end

  # return list of names and number of guests
  defp group_names(names) do
    loggedin_names = Enum.filter(names, fn name -> name != "guest" end)

    guest_names =
      Enum.count(names, fn name -> name == "guest" end)
      |> guest_names()

    if guest_names do
      [guest_names | loggedin_names]
    else
      loggedin_names
    end
  end

  defp guest_names(0), do: nil
  defp guest_names(1), do: "1 guest"
  defp guest_names(n), do: "#{n} guests"

The important function call in the code above is Presence.list(@presence_topic). The list/1 function returns the list of users using the application. The function group_names and guest_names are just here to manipulate the Presence data returned by list, see https://hexdocs.pm/phoenix/Phoenix.Presence.html#c:list/1-presence-data-structure

So far we've tracked new people using the chat page in the mount function and we've been using PubSub to listen to presence changes. The final step is to handle these changes by adding a handle_info function:

def handle_info(%{event: "presence_diff", payload: _diff}, socket) do
  { :noreply, assign(socket, presence: get_presence_names())}
end

Finally, a diff of presence join and leave events will be sent to the clients as they happen in real-time with the "presence_diff" event.

The handle_info function catches the presence_diff event and reassigns to the socket the presence value with the result of the get_presence_names function call.

To display the names we add the following in the lib/liveview_chat_web/templates/message/messages.html.heex template file:

<b>People currently using the app:</b>
<ul>
   <%= for name <- @presence do %>
     <li>
       <%= name %>
     </li>
   <% end %>
</ul>

You should now be able to run the application and see the loggedin users and the number of guest users.

We can test that the template has been properly updated by adding these two tests in test/liveview_chat_web/live/message_live_test.exs :

  test "1 guest online", %{conn: conn} do
    {:ok, view, _html} = live(conn, "/")

    assert render(view) =~ "1 guest"
  end

  test "2 guests online", %{conn: conn} do
    {:ok, _view, _html} = live(conn, "/")
    {:ok, view2, _html} = live(conn, "/")

    assert render(view2) =~ "2 guests"
  end

15. Tailwind CSS Stylin'

If you're new to Tailwind, please see: https://github.com/dwyl/learn-tailwind

Replace the contents of lib/liveview_chat_web/templates/layout/root.html.heex with:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8"/>
    <meta http-equiv="X-UA-Compatible" content="IE=edge"/>
    <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
    <meta name="csrf-token" content={csrf_token_value()}>
    <%= live_title_tag assigns[:page_title] || "LiveviewChat", suffix: " · Phoenix Framework" %>
    <script defer phx-track-static type="text/javascript" src={Routes.static_path(@conn, "/assets/app.js")}></script>
    <script src="https://cdn.tailwindcss.com"></script>
  </head>
  <body>
    <header class="bg-slate-800 w-full min-h-[15%] pt-5 pb-1 mb-2">
      <section>
        <nav>
          <div class="text-white width-[10%] float-left ml-3 -mt-5 align-middle">
          <b>People in Chat:</b>
          <ul>
            <%= for name <- @presence do %>
              <li>
                <%= name %>
              </li>
            <% end %>
          </ul>
          </div>

          <ul class="float-right mr-3">
            <%= if @loggedin do %>
              <li>
                <img width="42px" src={@person.picture} class="-mt-3"/>
              </li>
              <li class="text-white">
                <%= link "logout", to: "/logout" %>
              </li>
            <% else %>
              <li class="bg-green-600 text-white rounded-xl px-4 py-2 w-full mb-2 font-bold">
                <%= link "Login", to: "/login" %>
              </li>
            <% end %>
          </ul>
        </nav>
        <h1 class="text-3xl mb-4 text-center font-mono text-white">LiveView Chat Example</h1>
      </section>
    </header>
    <%= @inner_content %>
  </body>
</html>

And then replace the contents of lib/liveview_chat_web/templates/message/messages.html.heex with:

<ul id='msg-list' phx-update="append">
   <%= for message <- @messages do %>
     <li id={"msg-#{message.id}"} class="px-5">
       <small class="float-right text-xs align-middle ">
         <%= message.inserted_at %>
       </small>
       <b><%= message.name %>:</b>
       <%= message.message %>
     </li>
   <% end %>
</ul>

<footer class="fixed bottom-0 w-full bg-slate-300 pb-2 px-5 pt-2">
<.form let={f} for={@changeset} id="form" phx-submit="new_message" phx-hook="Form">

  <%= if @loggedin do %>
    <%= text_input f, :name, id: "name", value: @person.givenName,
    class: "hidden" %>
  <% else %>
    <%= text_input f, :name, id: "name", placeholder: "Name", autofocus: "true",
     class: "border p-2 w-9/12 mb-2 mt-2 mr2" %>
     <span class="italic text-2xl ml-4">or</span>
     <span class="bg-green-600 text-white rounded-xl px-4 py-2 mb-2 mt-3 float-right">
       <%= link "Login", to: "/login" %>
     </span>
    <%= error_tag f, :name %>
  <% end %>

   <%= text_input f, :message, id: "msg", placeholder: "Message",
   class: "border p-2 w-10/12  mb-2 mt-2 float-left"  %>
   <p class=" text-amber-600">
    <%= error_tag f, :message %>
   </p>
   <%= submit "Send", class: "bg-sky-600 text-white rounded-xl px-4 py-2 mt-2 float-right" %>
 </.form>
</footer>

You should now have a UI/layout that looks like this:

If you have questions about any of the Tailwind classes used, please spend 2 mins Googling and then if you're still stuck, open an issue.

What's Next?

If you found this example useful, please ⭐️ the GitHub repository so we (and others) know you liked it!

Here are a few other repositories you might want to read:

github.com/dwyl/phoenix-chat-example A chat application using Phoenix Socket
github.com/dwyl/phoenix-liveview-counter-tutorial
github.com/dwyl/phoenix-liveview-todo-list-tutorial

Any questions or suggestions? Do not hesitate to open new issues!

Thank you!

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.formatter.exs		.formatter.exs
.gitignore		.gitignore
Dockerfile		Dockerfile
README.md		README.md
coveralls.json		coveralls.json
fly.toml		fly.toml
mix.exs		mix.exs
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LiveView Chat Tutorial

Why? 🤷

What? 💬

Who? 👤

How? 💻

0. Prerequisites

1. Create Phoenix App

2. Create live Directory, LiveView Controller and Template

3. Update router.ex

4. Update Tests

5. Migration and Schema

6 Update mount/3 function

7. Update Template

7.1 Update the Test Assertion

8. Handle Message Creation Events

8.1 Test Message Creation Validation

9. PubSub

9.1 Notify Connected Clients of New Messages

9.2 Update mount/3

9.3 Update handle_event/3

9.4 Create handle_info/2

9.5 Test Messages are Displaying

10. Hooks

11. Optional: Temporary assigns

12. Authentication

12.1 Create AUTH_API_KEY

12.2 Install auth_plug ⬇️

12.3 Create the Optional Auth Pipeline in router.ex

12.4 Create AuthController

12.5 Create on_mount/4 functions

14. Presence

15. Tailwind CSS Stylin'

What's Next?

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