Elixir Plug TLDR

Serve files from priv/web folder and sub folders.

use Plug.Router

plug :match
plug :dispatch

match "/*glob" do
  case glob do
    [] ->
      path("index.html") # or whatever your index file is
      |> send_file(conn)
    _ ->
      path(Path.join(glob))
      |> send_file(conn)
  end
end

def path(parts) do
  if Mix.env != :dev do
    Path.join(:code.priv_dir(:my_application), "web") |> Path.join(parts)
  else
    # Assume current working directory is mix project folder
    Path.join("priv/web", parts)
  end
end

def send_file(path, conn) when (is_binary(path)) do
  case not File.dir?(path) and File.exists?(path) do
    true ->
      conn
      |> put_resp_header("content-type", MIME.from_path(path))
      |> send_file(200, path)
    false -> send_resp(conn, 404, "Not found")
  end
end

Parse all sorts of parameters. Need Poison library for parsing JSON. Check conn.params for parsed result, e.g. if the key is "filename" then conn.params["filename"].

plug Plug.Parsers, parsers: [:urlencoded, :multipart, :json],
                     pass: ["text/*"],
                     json_decoder: Poison

post "user/get/*user_id" do
  rs = with [user_id] <- conn.params["user_id"], # from url
       fields <- conn.params["fields"], # from json post body
       true <- not is_nil(user_id),
       rep <- (fn ->
          IO.puts "GET user #{user_id}"
          case get_user(user_id, fields) do
            {:ok, u} -> %{"result": u}
            {:error, reason} -> %{"error": reason}
          end
       end).(),
  do: {:ok, rep}
  case rs do
    {:ok, rep} ->
      send_resp(conn, 200, Poison.encode!(rep))
    _ ->
      send_resp(conn, 400, "Bad request")
  end
end