Plug, Friend of Web Developers @shanelogsdon @slogsdon 

What is Plug? • Specification for composable modules • Connection adapters • github.com/elixir-lang/plug | hexdocs.pm/plug 

Function Plug (Plug.Conn.t, Plug.opts) :: Plug.Conn.t plug :my_function_plug plug :my_function_plug, opt_a: true 

Function Plug def json_header_plug(conn, _opts) do conn |> put_resp_content_type("application/json") end 

Module Plug init(Plug.opts) :: Plug.opts call(Plug.Conn.t, Plug.opts) :: Plug.Conn.t plug MyModulePlug plug MyModulePlug, opt_a: true 

Module Plug defmodule JSONHeaderPlug do def init(opts) do opts end def call(conn, _opts) do conn |> put_resp_content_type("application/json") end end 

Plug’s plugs • Plug.Parsers • Parses request bodies • Plug.Static • Serves static files • Plug.Logger • Logs requests via Logger • And more 

Plug’s other modules • Plug.Router • Simple HTTP router • Plug.Debugger • Displays formatted runtime errors • Plug.Builder • Conveniences for working with pipelines • And more 

Plug composition • Plug.Builder.plug/2 • Accumulates plugs + options to module attribute • Attribute values seen as pipeline • Plug.Builder.compile/3 • Expands pipeline into quoted terms 

Plug composition plug Plug.Logger plug Plug.Head 

Plug composition Module.register_attribute(:plugs, accumulate: true) # [] @plugs {Plug.Logger, [], true} # [{Plug.Logger, [], true} | @plugs] @plugs {Plug.Head, [], true} # [{Plug.Head, [], true} | @plugs] 

Plug composition case Plug.Logger.call(conn, Plug.Logger.init(opts)) do %Plug.Conn{} = c1 -> case Plug.Head.call(c, Plug.Head.init(opts)) do %Plug.Conn{} = c2 -> c2 _ -> :error end _ -> :error end 

Connection adapters • Plug.Conn.Adapter • Defines API for Plug to receive/send requests/responses via webservers • Adapters: • Cowboy (Plug.Adapters.Cowboy) • Conveniences can be added to adapters, e.g. Plug.Adapters.Cowboy.http/3 

Demo • $ mix new --sup our_app • Plug.Router (Plug.Builder) • Plug.Test 

Questions?