Function Plugs and Module Plugs

A Plug manipulates data in conn structs. It’s a Module that has a ‘Conn’ Struct. It takes and returns that conn struct between modules.

It allows state management when combined with Agents and Genservers (like Live View). The state is held by the struct and then is passed between Modules. The ability to pass data turns Plugs into Elixir webservers

It has two types:

• Module Plug
• Function Plug

These are functions that get a Plug.Conn struct and give a Plug.Conn struct.

Module Plugs

These need to be initialized.

This is a large function, as a Module, that needs to be initialized with additional data such as state (i.e. initial state). This makes it more complicated than a function plug

Setting

defmodule App.Modulename do
  import Plug.Conn

  def init(options) do
    options
  end

  def call(conn, _options) do 
  end

end

Calling

alias ModulePlugName
plug ModulePlugName, [option: "Blah"] when action is [:index]

Controller 

alias Appname.Plugname

plug

function_name.(1,2,3,4)

Function Plugs

These add a conn to a Module function. It is a simple function that receives a conn struct, manipulates it, and outputs the modified conn struct

How to Create Function Plugs

1. Create new Module “test” with import Plug.conn
2. Write the function def function_plug(conn, _options) that uses assign()
3. In the controller, use that Function Plug Module by importing it
4. Call function plug :blah
5. Render it in the view with <%= @conn.assigns[:blah] %>

Function Plugs take 2 items:

• conn
• options

If data is available in conn then use function plugs.

Calling

defmodule App.TotalController do
  import App.ModuleName
  plug :get_total
  ..
end 

Setting non_piped and piped Function Plugs

defmodule App.ModuleName do
  import Plug.Conn

  def non_pipe(conn, options) do 
    assign(conn, :non_pipe, 123)
  end

  def piped(conn, _options) do
    conn
    |> put_resp_content_type("text/plain") 
    |> send_resp(200, "From a Piped Function Plug that outputted this data inside this conn struct")
  end

end 

Calling in Elixir

plug :non_piped

Calling in Phoenix View

<%= @conn.assigns[:non_piped] %>
<%= @non_piped %>

Assigns

assign(key: "#{data.attrib}")