ChatGdg - GDG Izmir 2017

A real-time chat application using websockets written in Elixir Phoenix Web Framework

To start finished version of the sample application written in this tutorial:

Install dependencies with mix deps.get
Create and migrate your database with mix ecto.create && mix ecto.migrate
Install Node.js dependencies with cd assets && npm install
Start Phoenix endpoint with mix phx.server

Now you can visit localhost:4000 from your browser.

Installing Requirements and Setting Up Development Environment

Follow the instructions.

Erlang 18 or later

When we install Elixir using instructions from the Elixir Installation Page, we will usually get Erlang too. If Erlang was not installed along with Elixir, please see the Erlang Instructions section of the Elixir Installation Page for instructions.

Elixir 1.4 or later

Mac OS X Macports Run: sudo port install elixir

Homebrew Update your homebrew to latest: brew update Run: brew install elixir

Phoenix

mix archive.install https://github.com/phoenixframework/archives/raw/master/phx_new.ez

node.js (>= 5.0.0)

Install from the link.

PostgreSQL

Install from the link.

inotify-tools (for linux users)

For Ubuntu 14.04/16.04

sudo apt-get install inotify-tool

For other distros download from here

Links taken from installation docs

Creating skeleton of a phoenix application with mix

mix phx.new chat_gdg

Press y and enter to fetch and install dependencies

Then the output should be:

* creating chat_gdg/assets/css/app.css
* creating chat_gdg/assets/css/phoenix.css
* creating chat_gdg/assets/js/app.js
* creating chat_gdg/assets/js/socket.js
* creating chat_gdg/assets/package.json
* creating chat_gdg/assets/static/robots.txt
* creating chat_gdg/assets/static/images/phoenix.png
* creating chat_gdg/assets/static/favicon.ico

Fetch and install dependencies? [Yn] Y
* running mix deps.get
* running mix deps.compile
* running cd assets && npm install && node node_modules/brunch/bin/brunch build

We are all set! Go into your application by running:

    $ cd chat_gdg

Then configure your database in config/dev.exs and run:

    $ mix ecto.create

Start your Phoenix app with:

    $ mix phx.server

You can also run your app inside IEx (Interactive Elixir) as:

    $ iex -S mix phx.server

Setting Configuration File

Open the chat_gdg/config/dev.exs file with a text editor and set the database credentials. Example:

# Configure your database
config :chat_gdg, ChatGdg.Repo,
  adapter: Ecto.Adapters.Postgres,
  username: "postgres",
  password: "postgres",
  database: "chat_gdg_dev",
  hostname: "localhost",
  pool_size: 10

Make sure database application is up and run these commands to fire up:

cd chat_gdg
mix ecto create
mix phx.server

Take a look at the application structure.

A simple hello world application is ready.

Now you can visit localhost:4000 from your browser.

Editing homepage

Take a look at the router.ex

In lib/chat_gdg_web/router.ex

  scope "/", ChatGdgWeb do
    pipe_through :browser # Use the default browser stack

    get "/", PageController, :index
  end

get "/", PageController, :index this line directs the Page Controller Now check the Page Controller

defmodule ChatGdgWeb.PageController do
  use ChatGdgWeb, :controller

  def index(conn, _params) do
    render conn, "index.html"
  end
end

In the Page Controller the index function renders the index.html template.

Let's edit the lib/chat_gdg_web/templates/page/index.html.eex as:

<div class="row">
  <div class="col-md-12 alert alert-info">
    Hello, <span id="User"><%= @conn.params["user"] %></span>!
  </div>
  <div class="col-md-8">
    <h2>Messages:</h2>
    <ul id="MessageList" class="list-unstyled" style="height: 400px; border: 1px solid black; overflow-y: auto; padding: 10px;" ></ul>
    <input type="text" id="NewMessage" class="form-control">
  </div>
  <div  class="col-md-4">
    <h2>Who’s Online</h2>
    <ul id="UserList" class="list-unstyled">
      <li>Loading online users...</li>
    </ul>
  </div>
</div>

Again visit localhost:4000 from your browser.

And http://0.0.0.0:4000/?user=joearms

In the index.html.eex Hello, <span id="User"><%= @conn.params["user"] %></span>! line the @conn.params["user"] shows us the user from the connection's query parameters.

Using Presence Module and Activating Channels

Presence Doc

Channels Doc

Generating Presence Module

We will use the Presence module to track users status (is online & online since)

Provides Presence tracking to processes and channels.

This behaviour provides presence features such as fetching presences for a given topic, as well as handling diffs of join and leave events as they occur in real-time. Using this module defines a supervisor and allows the calling module to implement the Phoenix.Tracker behaviour which starts a tracker process to handle presence information.

To create our presence with this command:

mix phx.gen.presence

output

* creating lib/chat_gdg_web/channels/presence.ex

Add your new module to your supervision tree,
in lib/chat_gdg/application.ex:

    children = [
      ...
      supervisor(ChatGdgWeb.Presence, []),
    ]

You're all set! See the Phoenix.Presence docs for more details:
http://hexdocs.pm/phoenix/Phoenix.Presence.html

Activating Channels

Let's activate the channel to use websockets:

Uncomment the this line in the lib/chat_gdg_web/channels/user_socket.ex

channel "room:*", ChatGdgWeb.RoomChannel

and edit the connect function:

def connect(%{"user" => user}, socket) do
    {:ok, assign(socket, :user, user)}
end

Then create a module to handle room channel: Create a file named room_channel.ex under lib/chat_gdg_web/channels

defmodule ChatGdg.RoomChannel do
    use ChatGdg.Web, :channel
    alias ChatGdg.Presence

    def join("room:lobby", _, socket) do
      send self(), :after_join
      {:ok, socket}
    end

    def handle_info(:after_join, socket) do
      Presence.track(socket, socket.assigns.user, %{
        online_at: :os.system_time(:milli_seconds)
      })
      push socket, "presence_state", Presence.list(socket)
      {:noreply, socket}
    end

    def connect(%{"user" => user}, socket) do
      {:ok, assign(socket, :user, user)}
    end

end

Modify the app.js file under the assets/js/ such as:

import "phoenix_html"
import {Socket, Presence} from "phoenix"

// get the user element from index.html
let user = document.getElementById("User").innerText

// generate a socket connection with the user parameter
let socket = new Socket("/socket", {params: {user: user}})
socket.connect()

// create an empty js object to handle presences
let presences = {}

let formatTimestamp = (timestamp) => {
  let date = new Date(timestamp)
  return date.toLocaleTimeString()
}
let listBy = (user, {metas: metas}) => {
  return {
    user: user,
    onlineAt: formatTimestamp(metas[0].online_at)
  }
}

// get the UserList element from index.html
let userList = document.getElementById("UserList")
let render = (presences) => {
  userList.innerHTML = Presence.list(presences, listBy)
    .map(presence => `
      <li>
        <b>${presence.user}</b>
        <br><small>online since ${presence.onlineAt}</small>
      </li>
    `)
    .join("")
}

// handle with the single channel
// create a connection between client and room:lobby channel and set the presences settings
let room = socket.channel("room:lobby", {})
room.on("presence_state", state => {
  presences = Presence.syncState(presences, state)
  render(presences)
})

room.on("presence_diff", diff => {
  presences = Presence.syncDiff(presences, diff)
  render(presences)
})

// join the room
room.join()

// get the NewMessage element from index.html
let messageInput = document.getElementById("NewMessage")
messageInput.addEventListener("keypress", (e) => {
  if (e.keyCode == 13 && messageInput.value != "") {
    room.push("message:new", messageInput.value)
    messageInput.value = ""
  }
})

let messageList = document.getElementById("MessageList")
let renderMessage = (message) => {
  let messageElement = document.createElement("li")
  messageElement.innerHTML = `
    <b>${message.user}</b>
    <i>${formatTimestamp(message.timestamp)}</i>
    <p>${message.body}</p>
  `
  messageList.appendChild(messageElement)
  messageList.scrollTop = messageList.scrollHeight;
}

room.on("message:new", message => renderMessage(message))

Creating the Database Schema (not Model!)

mix phx.gen.schema User users email:unique encrypt_pass:string

output:

* creating lib/chat_gdg/user.ex
* creating priv/repo/migrations/20171201161350_create_users.exs

Remember to update your repository by running migrations:

    $ mix ecto.migrate

take a look at model file and migration file:

cat priv/repo/migrations/20171201161350_create_users.exs

defmodule ChatGdg.Repo.Migrations.CreateUsers do
  use Ecto.Migration

  def change do
    create table(:users) do
      add :email, :string
      add :encrypt_pass, :string

      timestamps()
    end

    create unique_index(:users, [:email])
  end
end

cat lib/chat_gdg/user.ex

defmodule ChatGdg.User do
  use Ecto.Schema
  import Ecto.Changeset
  alias ChatGdg.User


  schema "users" do
    field :email, :string
    field :encrypt_pass, :string

    timestamps()
  end

  @doc false
  def changeset(%User{} = user, attrs) do
    user
    |> cast(attrs, [:email, :encrypt_pass])
    |> validate_required([:email, :encrypt_pass])
    |> unique_constraint(:email)
  end
end

Add a field line for real(!) password but not store with the functionality of virtual parameter

  schema "users" do
    field :email, :string
    field :encrypt_pass, :string
    field :password, :string, virtual: true

    timestamps()
  end

and edit the changeset function as below

  def changeset(%User{} = user, attrs) do
    user
    |> cast(attrs, [:email, :password])
    |> validate_required([:email, :password])
    |> unique_constraint(:email)
  end

Take a look at usage of virtual field in Ecto schema

Then apply the migration with the mix command

mix ecto.migrate

output:

Compiling 1 file (.ex)
Generated chat_gdg app
[info] == Running ChatGdg.Repo.Migrations.CreateUsers.change/0 forward
[info] create table users
[info] create index users_email_index
[info] == Migrated in 0.0s

Insert a sample data from iex shell

iex -S mix phx.server
Erlang/OTP 19 [erts-8.3] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

[info] Running ChatGdgWeb.Endpoint with Cowboy using http://0.0.0.0:4000
Interactive Elixir (1.4.0) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> 19:46:54 - info: compiled 6 files into 2 files, copied 3 in 914 ms
alias ChatGdg.Repo
ChatGdg.Repo
iex(2)> alias ChatGdg.User
ChatGdg.User
iex(3)> Repo.all(User)
[debug] QUERY OK source="users" db=1.7ms queue=0.1ms
SELECT u0."id", u0."email", u0."encrypt_pass", u0."inserted_at", u0."updated_at" FROM "users" AS u0 []
[]
iex(4)> Repo.insert(%User{email: "joearms@erlang.com", encrypt_pass: "password"})
[debug] QUERY OK db=7.8ms
INSERT INTO "users" ("email","encrypt_pass","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id" ["joearms@erlang.com", "password", {{2017, 12, 1}, {16, 49, 29, 841382}}, {{2017, 12, 1}, {16, 49, 29, 843639}}]
{:ok,
 %ChatGdg.User{__meta__: #Ecto.Schema.Metadata<:loaded, "users">,
  email: "joearms@erlang.com", encrypt_pass: "password", id: 1,
  inserted_at: ~N[2017-12-01 16:49:29.841382], password: nil,
  updated_at: ~N[2017-12-01 16:49:29.843639]}}

Generating UserController and UserView

Usage of Resources

To handle CRUD operations add UserController the router.ex with resources macro.

  scope "/", ChatGdgWeb do
    pipe_through :browser # Use the default browser stack
    resources "/users", UserController
    get "/", PageController, :index
  end

then check our new routes with the command:

mix phx.routes
Compiling 1 file (.ex)
user_path  GET     /users           ChatGdgWeb.UserController :index
user_path  GET     /users/:id/edit  ChatGdgWeb.UserController :edit
user_path  GET     /users/new       ChatGdgWeb.UserController :new
user_path  GET     /users/:id       ChatGdgWeb.UserController :show
user_path  POST    /users           ChatGdgWeb.UserController :create
user_path  PATCH   /users/:id       ChatGdgWeb.UserController :update
           PUT     /users/:id       ChatGdgWeb.UserController :update
user_path  DELETE  /users/:id       ChatGdgWeb.UserController :delete
page_path  GET     /                ChatGdgWeb.PageController :index

Controller

Create the skeleton of user_controller.ex at lib/chat_gdg_web/controllers/

defmodule ChatGdgWeb.UserController do
    use ChatGdgWeb, :controller

    alias ChatGdg.User
    alias ChatGdg.Repo

    def index(conn, _params) do
        users = Repo.all(User)
        render(conn, "index.html", users: users)
    end

    def show(conn, %{"id" => id}) do
        user = Repo.get!(User, id)
        render(conn, "show.html", user: user)
    end
end

View

And create the user_view.ex at lib/chat_gdg_web/views/

defmodule ChatGdgWeb.UserView do
    use ChatGdgWeb, :view
end

And finally create the index.html.eex at lib/chat_gdg_web/templates/user/

<h2>List of users</h2>

<table class="table">
  <thead>
    <tr>
      <th>Email</th>

      <th></th>
    </tr>
  </thead>
  <tbody>
<%= for user <- @users do %>
    <tr>
      <td><%= user.email %></td>
      <td class="text-right">
        <%= link "Profile", to: user_path(@conn, :show, user), class: "btn btn-default btn-xs" %>
        <%= link "Edit", to: user_path(@conn, :edit, user), class: "btn btn-default btn-xs" %>
        <%= link "Delete User", to: user_path(@conn, :delete, user), method: :delete, data: [confirm: "Are you sure?"], class: "btn btn-danger btn-xs" %>

      </td>
    </tr>

<% end %>
  </tbody>
</table>


<%= link "New user", to: user_path(@conn, :new) %>

Now visit localhost:4000/users from your browser and try the Profile button!

If you try to click Edit or Delete User buttons you will get error because we did not define new-create, edit-update and delete functions!

CRUD Operations

Create a User

To create a user we need to add new and create functions in the our controller. Add these functions to user_controller.ex

    def new(conn, _params) do
        changeset = User.changeset(%User{})
        render(conn, "new.html", changeset: changeset)
    end

    def create(conn, %{"user" => user_params}) do
        changeset = User.reg_changeset(%User{}, user_params)
        case Repo.insert(changeset) do
        {:ok, _user} ->
            conn
            |> put_flash(:info, "User created successfully.")
            |> redirect(to: user_path(conn, :index))
        {:error, changeset} ->
            render(conn, "new.html", changeset: changeset)
        end
    end

Then create a new.html.eex and form.html.eex template. form.html.eex will be inherited and handle in create and edit operations.

new.html.eex

<h2>Create a new User</h2>

<%= render "form.html", changeset: @changeset,
                        action: user_path(@conn, :create) %>

<%= link "Back", to: user_path(@conn, :index) %>

form.html.eex

<%= form_for @changeset, @action, fn f -> %>
  <%= if @changeset.action do %>
    <div class="alert alert-danger">
      <p>Oops, something went wrong! Please check the errors below.</p>
    </div>
  <% end %>

  <div class="form-group">
    <%= label f, :email, class: "control-label" %>
    <%= email_input f, :email, class: "form-control" %>
    <%= error_tag f, :email %>
  </div>

  <div class="form-group">
    <%= label f, :password, class: "control-label" %>
    <%= password_input f, :password, class: "form-control" %>
    <%= error_tag f, :password %>
  </div>

  <div class="form-group">
    <%= submit "Submit", class: "btn btn-primary" %>
  </div>
<% end %>

Now try to create a user:

http://0.0.0.0:4000/users/new

Update and Delete

To handle update and delete operations -as usual we did- now we will implement the edit, update and delete function to the user_controller.ex

    def edit(conn, %{"id" => id}) do
        user = Repo.get!(User, id)
        changeset = User.changeset(user)
        render(conn, "edit.html", user: user, changeset: changeset)
    end

    def update(conn, %{"id" => id, "user" => user_params}) do
        user = Repo.get!(User, id)
        changeset = User.changeset(user, user_params)

        case Repo.update(changeset) do
          {:ok, user} ->
            conn
            |> put_flash(:info, "User updated successfully.")
            |> redirect(to: user_path(conn, :show, user))
          {:error, changeset} ->
            render(conn, "edit.html", user: user, changeset: changeset)
        end
    end

    def delete(conn, %{"id" => id}) do
        user = Repo.get!(User, id)
        Repo.delete!(user)

        conn
        |> put_flash(:danger, "User deleted successfully.")
        |> redirect(to: user_path(conn, :index))
    end

And create and edit.html.eex template for editing user page.

edit.html.eex

<h2>Edit user</h2>

<%= render "form.html", changeset: @changeset,
                        action: user_path(@conn, :update, @user) %>

<%= link "Back", to: user_path(@conn, :index) %>

Now we able to use create, read, update and delete functions/operations.

Hash the Password

Do not store passwords in plain text. Are you asking why? Then check this out.

We need some functions, then we will search for a Elixir hashing library. Let's search a package from hex.pm

Search for 'hash' then inspect the results.

Let's use comeonin.

Copy the {:comeonin, "~> 3.0"} dependency and paste it to mix.exs. Your mix.exs file should be like this:

defp deps do
    [
      {:phoenix, "~> 1.3.0"},
      {:phoenix_pubsub, "~> 1.0"},
      {:phoenix_ecto, "~> 3.2"},
      {:postgrex, ">= 0.0.0"},
      {:phoenix_html, "~> 2.10"},
      {:phoenix_live_reload, "~> 1.0", only: :dev},
      {:gettext, "~> 0.11"},
      {:cowboy, "~> 1.0"},
      {:comeonin, "~> 3.0"}
    ]
  end

Then, get the dependencies and compile:

mix deps.get

Output:

Resolving Hex dependencies...
Dependency resolution completed:
  comeonin 3.2.0
  connection 1.0.4
  cowboy 1.1.2
  cowlib 1.0.2
  db_connection 1.1.2
  decimal 1.4.1
  ecto 2.2.6
  file_system 0.2.2
  gettext 0.13.1
  mime 1.1.0
  phoenix 1.3.0
  phoenix_ecto 3.3.0
  phoenix_html 2.10.5
  phoenix_live_reload 1.1.3
  phoenix_pubsub 1.0.2
  plug 1.4.3
  poison 3.1.0
  poolboy 1.5.1
  postgrex 0.13.3
  ranch 1.3.2
* Getting comeonin (Hex package)
  Checking package (https://repo.hex.pm/tarballs/comeonin-4.0.3.tar)
  Fetched package

mix deps.compile

Output:

===> Compiling ranch
===> Compiling poolboy
==> comeonin
Compiling 2 files (.ex)
Generated comeonin app
===> Compiling cowlib
===> Compiling cowboy

Now we can use the comeonin library in our application.

Let's and add two function which handles hashing password to the user.ex

  def reg_changeset(%User{} = user, attrs \\ %{}) do
    user
    |> changeset(attrs)
    |> cast(attrs, [:password], [])
    |> validate_required(:password, min: 5)
    |> hash_pw()
  end

  defp hash_pw(changeset) do
    case changeset do
      %Ecto.Changeset{valid?: true, changes: %{password: p}} ->
        put_change(changeset, :encrypt_pass, Comeonin.Pbkdf2.hashpwsalt(p))

      _ ->
        changeset
    end
  end

Then edit create and update in the user_controller.ex to use our new reg_changeset function.

    def create(conn, %{"user" => user_params}) do
        changeset = User.reg_changeset(%User{}, user_params)
        case Repo.insert(changeset) do
        {:ok, _user} ->
            conn
            |> put_flash(:info, "User created successfully.")
            |> redirect(to: user_path(conn, :index))
        {:error, changeset} ->
            render(conn, "new.html", changeset: changeset)
        end
    end

    def update(conn, %{"id" => id, "user" => user_params}) do
        user = Repo.get!(User, id)
        changeset = User.reg_changeset(user, user_params)

        case Repo.update(changeset) do
          {:ok, user} ->
            conn
            |> put_flash(:info, "User updated successfully.")
            |> redirect(to: user_path(conn, :show, user))
          {:error, changeset} ->
            render(conn, "edit.html", user: user, changeset: changeset)
        end
    end

User Authentication

Using Guardian as an Authenticator

We will use Guardian library to handle authentication in our application.

*Guardian is a token based authentication library for use with Elixir applications.

Guardian remains a functional system. It integrates with Plug, but can be used outside of it. If you're implementing a TCP/UDP protocol directly, or want to utilize your authentication via channels in Phoenix, Guardian is your friend.*

Let's add the dependency to mix.exs

  defp deps do
    [
      {:phoenix, "~> 1.3.0"},
      {:phoenix_pubsub, "~> 1.0"},
      {:phoenix_ecto, "~> 3.2"},
      {:postgrex, ">= 0.0.0"},
      {:phoenix_html, "~> 2.10"},
      {:phoenix_live_reload, "~> 1.0", only: :dev},
      {:gettext, "~> 0.11"},
      {:cowboy, "~> 1.0"},
      {:comeonin, "~> 3.0"},
      {:guardian, "~> 0.14"}
    ]
  end

mix deps.get

Output:

Resolving Hex dependencies...
Dependency resolution completed:
  base64url 0.0.1
  comeonin 3.2.0
  connection 1.0.4
  cowboy 1.1.2
  cowlib 1.0.2
  db_connection 1.1.2
  decimal 1.4.1
  ecto 2.2.6
  elixir_make 0.4.0
  file_system 0.2.2
  gettext 0.13.1
  guardian 0.14.5
  jose 1.8.4
  mime 1.1.0
  phoenix 1.3.0
  phoenix_ecto 3.3.0
  phoenix_html 2.10.5
  phoenix_live_reload 1.1.3
  phoenix_pubsub 1.0.2
  plug 1.4.3
  poison 3.1.0
  poolboy 1.5.1
  postgrex 0.13.3
  ranch 1.3.2
  uuid 1.1.8
* Getting guardian (Hex package)
  Checking package (https://repo.hex.pm/tarballs/guardian-0.14.5.tar)
  Using locally cached package
* Getting jose (Hex package)
  Checking package (https://repo.hex.pm/tarballs/jose-1.8.4.tar)
  Using locally cached package
* Getting uuid (Hex package)
  Checking package (https://repo.hex.pm/tarballs/uuid-1.1.8.tar)
  Using locally cached package
* Getting base64url (Hex package)
  Checking package (https://repo.hex.pm/tarballs/base64url-0.0.1.tar)
  Using locally cached package

mix deps.compile

===> Compiling base64url
==> jose
Compiling 89 files (.erl)
Compiling 8 files (.ex)
Generated jose app
===> Compiling ranch
==> poolboy (compile)
==> comeonin
make: Nothing to be done for `all'.
===> Compiling cowlib
===> Compiling cowboy
==> uuid
Compiling 1 file (.ex)
Generated uuid app
==> guardian
Compiling 21 files (.ex)
Generated guardian app

Then add the configuration parameters block to config/config.exs

config :guardian, Guardian,
  allowed_algos: ["HS512"], # optional
  verify_module: Guardian.JWT, # optional
  issuer: "ChatGdg",
  ttl: {30, :days},
  allowed_drift: 2000,
  verify_issuer: true, # optional
  secret_key: "dY3otygFOMcX1zXEwQ11JFIQdZp0Z+C0xEF1lx5gOpef/mYrsWu28dW++FBvm7qi",
  serializer: ChatGdg.GuardianSerializer

You can generate a secret key with the command:

mix phx.gen.secret

Ouput:

dY3otygFOMcX1zXEwQ11JFIQdZp0Z+C0xEF1lx5gOpef/mYrsWu28dW++FBvm7qi

Put it to secret_key parameter.

Now create a Guardian controller. Put it to chat_gdg/controller/guardian_serializer.ex

defmodule ChatGdg.GuardianSerializer do
  @behaviour Guardian.Serializer

  alias ChatGdg.Repo
  alias ChatGdg.User

  def for_token(user = %User{}), do: { :ok, "User:#{user.id}" }
  def for_token(_), do: { :error, "Unknown resource type" }

  def from_token("User:" <> id), do: { :ok, Repo.get(User, id) }
  def from_token(_), do: { :error, "Unknown resource type" }
end

Editing Router

Now here is the Plug rocks!

Modify the router.ex to handle authentication with Guardian and sessions, then our router.ex should be like that:

defmodule ChatGdgWeb.Router do
  use ChatGdgWeb, :router

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers
    plug Guardian.Plug.VerifySession
    plug Guardian.Plug.LoadResource
  end

  # define a new pipeline (browser authentication)
  pipeline :browser_auth do
    plug Guardian.Plug.VerifySession
    plug Guardian.Plug.EnsureAuthenticated, handler: ChatGdgWeb.Token
    plug Guardian.Plug.LoadResource
  end

  pipeline :api do
    plug :accepts, ["json"]
  end

  scope "/", ChatGdgWeb do
    pipe_through :browser

    # unauthorized users can only trig the new and create functions
    resources "/users", UserController, [:new, :create]

    # let's generate create and delete operations for sessions
    resources "/sessions", SessionController, only: [:create, :delete]

    # now we redirect the root path to SessionController to check users session
    get "/", SessionController, :new
  end

  # define a new pipeline which uses both :browser and :browser_auth for authenticated users
  scope "/", ChatGdgWeb do
    pipe_through [:browser, :browser_auth]

    # authenticated users can only trig the show, onde
    resources "/users", UserController, only: [:show, :index, :update]

    # in here we direct the authenticated users to chat screen with Page Controller
    get "/chat", PageController, :index
  end

  # Other scopes may use custom stacks.
  # scope "/api", ChatGdgWeb do
  #   pipe_through :api
  # end
end

Tokens

Let's create token handler token.ex:

defmodule ChatGdg.Token do
    use ChatGdgWeb, :controller

    def unauthenticated(conn, _params) do
        conn
        |> put_flash(:error, "You must be signed in!")
        |> redirect(to: session_path(conn, :new))
    end

    def unauthorized(conn, _params) do
        conn
        |> put_flash(:error, "You must be signed in!")
        |> redirect(to: session_path(conn, :new))
    end
end

Sessions

And add Session View and Session Controller

Let's define a simple view, session_view.ex:

defmodule ChatGdgWeb.SessionView do
    use ChatGdgWeb, :view
end

And our session controller, session_controller.ex:

defmodule ChatGdgWeb.SessionController do
    use ChatGdgWeb, :controller
    import ChatGdgWeb.Auth
    alias ChatGdg.Repo

    def new(conn, _params) do
        render(conn, "new.html")
    end

    def create(conn, %{"session" => %{"email" => user, "password" => password}}) do
      case login_with(conn, user, password, repo: Repo) do
        {:ok, conn} ->
          logged_user = Guardian.Plug.current_resource(conn)
          conn
          |> put_flash(:info, "logged in!")
          |> redirect(to: page_path(conn, :index))
        {:error, _reason, conn} ->
          conn
          |> put_flash(:error, "Wrong username/password")
          |> render("new.html")
      end
    end

    def delete(conn, _) do
        conn
        |> Guardian.Plug.sign_out
        |> redirect(to: "/")
    end

end

Final step for handling sessions is creating the template.

chat_gdg_web/templates/sessions/new.html.eex:

<h1>Sign In</h1>

<%= form_for @conn, session_path(@conn, :create), [as: :session], fn f -> %>
<div class="form-group">
  <%= label f, :email, class: "control-label" %>
    <%= email_input f, :email, class: "form-control" %>
    <%= error_tag f, :email %>
</div>

<div class="form-group">
    <%= label f, :password, class: "control-label" %>
    <%= password_input f, :password, class: "form-control" %>
    <%= error_tag f, :password %>
</div>

  <div class="form-group">
    <%= submit "Submit", class: "btn btn-primary" %>
  </div>

<% end %>

User Restrictions

To prevent the edit and delete operations without access we will implement user acces in the user_controller.ex

Edit the edit, update and delete functions as below:

    def edit(conn, %{"id" => id}) do
        user = Repo.get!(User, id)
        cond do
        user == Guardian.Plug.current_resource(conn) ->
            changeset = User.changeset(user)
            render(conn, "edit.html", user: user, changeset: changeset)
        :error ->
            conn
            |> put_flash(:error, "No access")
            |> redirect(to: user_path(conn, :index))
        end
    end

    def update(conn, %{"id" => id, "user" => user_params}) do
        user = Repo.get!(User, id)
        changeset = User.reg_changeset(user, user_params)
        cond do
        user == Guardian.Plug.current_resource(conn) ->
            case Repo.update(changeset) do
            {:ok, user} ->
                conn
                |> put_flash(:info, "User updated successfully.")
                |> redirect(to: user_path(conn, :show, user))
            {:error, changeset} ->
                render(conn, "edit.html", user: user, changeset: changeset)
        end
            :error ->
            conn
            |> put_flash(:error, "No access")
            |> redirect(to: user_path(conn, :index))
        end
    end

    def delete(conn, %{"id" => id}) do
        user = Repo.get!(User, id)
        cond do
        user == Guardian.Plug.current_resource(conn) ->
            Repo.delete!(user)
            conn
            |> Guardian.Plug.sign_out
            |> put_flash(:danger, "User deleted successfully.")
            |> redirect(to: session_path(conn, :new))
        :error ->
            conn
            |> put_flash(:error, "No access")
            |> redirect(to: user_path(conn, :index))
        end
    end

Changing Layout

Now let's modify the page layout according to user authentication.

Generate a Helper Function

Create a Helper View under the views:

defmodule ChatGdgWeb.ViewHelper do
    def current_user(conn), do: Guardian.Plug.current_resource(conn)
    def logged_in?(conn), do: Guardian.Plug.authenticated?(conn)
  end

Allow access to Helper View, add the line import ChatGdgWeb.ViewHelper to lib/chat_gdg_web.ex file:

def view do
    quote do
      use Phoenix.View, root: "lib/chat_gdg_web/templates",
                        namespace: ChatGdgWeb

      # Import convenience functions from controllers
      import Phoenix.Controller, only: [get_flash: 2, view_module: 1]

      # Use all HTML functionality (forms, tags, etc)
      use Phoenix.HTML

      import ChatGdgWeb.Router.Helpers
      import ChatGdgWeb.ErrorHelpers
      import ChatGdgWeb.Gettext
      import ChatGdgWeb.ViewHelper
    end
  end

And create a file named logged.html.eex under lib/chat_gdg_web/templates/layout:

<%= if logged_in?(@conn) do %>
  <%= link "Sign Out", to: session_path(@conn, :delete, :access),
    method: :delete, class: "btn btn-danger" %>
  <%= link "#{current_user(@conn).email}", to: user_path(@conn, :show, current_user(@conn)) %>

  <% else %>
  <%= link "Create an Account!", to: user_path(@conn, :new),
    class: "btn btn-info" %>
  <%= link "Sign in", to: session_path(@conn, :new),
      class: "btn btn-primary" %>
<% end %>

And to render it, modify the app.html.eex template add it inside the header tag:

<header class="header">
  <nav role="navigation">
    <ul class="nav nav-pills pull-right">
      <li><%= render "logged.html", conn: @conn %></li>
    </ul>
  </nav>
  <span class="logo"></span>
</header>

Show Username in the Chat Page

To show username (email in our design), use an embedded elixir function in the templates/page/index.html.eex file:

Change these lines:

<div class="col-md-12 alert alert-info">
  Hello, <span id="User"><%= @conn.params["user"] %></span>!
</div>

with these:

<div class="col-md-12 alert alert-info">
  Hello, <span id="User"><%= "#{current_user(@conn).email}" %></span>!
</div>

Entering Chat Room

Now add these lines to the user index template:

templates/user/index.html.eex

<%= link "New user", to: user_path(@conn, :new), class: "btn btn-info" %>

<%= if logged_in?(@conn) do %>
  <%= link "Chat", to: page_path(@conn, :index), class: "btn btn-success" %><br><br>
  <% else %>
<% end %>

Additional Resource

Phoenix Docs
Phoenix Book
Elixir Docs
Elixir School
Elixir Forum
Getting Started with Elixir
Getting Started with Erlang
Learn You Some Erlang
Hex.pm
How Discord Scaled Elixir to 5,000,000 Concurrent Users

Files

README.md

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README.md

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ChatGdg - GDG Izmir 2017

Table of Contents

Installing Requirements and Setting Up Development Environment

Erlang 18 or later

Elixir 1.4 or later

Phoenix

node.js (>= 5.0.0)

PostgreSQL

inotify-tools (for linux users)

Creating skeleton of a phoenix application with mix

Setting Configuration File

Editing homepage

Using Presence Module and Activating Channels

Generating Presence Module

Activating Channels

Creating the Database Schema (not Model!)

Insert a sample data from iex shell

Generating UserController and UserView

Usage of Resources

Controller

View

CRUD Operations

Create a User

Update and Delete

Hash the Password

User Authentication

Using Guardian as an Authenticator

Editing Router

Tokens

Sessions

User Restrictions

Changing Layout

Generate a Helper Function

Show Username in the Chat Page

Entering Chat Room

Additional Resource