Plug Examples

Plug Examples

Basic Plug Example

defmodule MyApp.HelloWorld do
  @behaviour Plug
  
  def init(options), do: options
  
  def call(conn, _opts) do
    conn
    |> put_resp_content_type("text/plain")
    |> send_resp(200, "Hello, world!")
  end
end

Redirecting Plug Example

defmodule MyApp.Redirect do
  @behaviour Plug
  
  def init(options), do: options
  
  def call(conn, _opts) do
    conn
    |> put_resp_content_type("text/html")
    |> put_resp_header("location", "https://elixir-lang.org")
    |> send_resp(301, "")
  end
end

Logging Plug Example

defmodule MyApp.Logger do
  @behaviour Plug
  
  def init(options), do: options
  
  def call(conn, _opts) do
    conn
    |> IO.inspect(label: "Request")
    |> Plug.Conn.forward(conn)
    |> IO.inspect(label: "Response")
  end
end

Authentication Plug Example

defmodule MyApp.Authenticate do
  @behaviour Plug

  def init(options), do: options

  def call(conn, _opts) do
    case Plug.Conn.get_req_header(conn, "authorization") do
      nil -> send_unauthorized(conn)
      "Bearer " <> token ->
        case authenticate(token) do
          {:ok, _user} -> Plug.Conn.forward(conn)
          {:error, _reason} -> send_unauthorized(conn)
        end
      _ -> send_unauthorized(conn)
    end
  end

  defp send_unauthorized(conn) do
    conn
    |> put_resp_content_type("text/plain")
    |> send_resp(401, "Unauthorized")
  end

  defp authenticate(token) do
    # Your authentication logic here
  end
end

Routing Plug Example

defmodule MyApp.Router do
  @behaviour Plug.Router
  
  use Plug.Builder

  plug :match
  plug :dispatch

  get "/" do
    send_resp(conn, 200, "Hello, Elixir!")
  end

  match _ do
    send_resp(conn, 404, "Route not found")
  end
end

Database Query Plug Example

defmodule MyApp.DatabaseQuery do
  @behaviour Plug

  def init(options), do: options

  def call(conn, _opts) do
    query = Plug.Conn.get_query_params(conn)
    result = MyApp.Database.query(query)
    conn
    |> put_resp_content_type("text/plain")
    |> send_resp(200, "#{inspect(result)}")
  end
end

Auth middleware composition

defmodule MyApp.AuthPipeline do
  use Plug.Builder

  plug MyApp.Authenticate
  plug MyApp.Logger
  plug MyApp.Router
end