Elixir Plug for PDF generation with WKHTMLTOPDF

pdf_plug.ex

defmodule Sample.PdfPlug do
  import Plug.Conn
  import Plug.Upload

  @wkhtmltopdf_path System.find_executable("wkhtmltopdf")

  def init(opts) do
    opts
  end

  def call(conn, opts) do
    case Regex.match?(~r/.*(pdf)$/, conn.request_path) do
      true -> generate_pdf(conn, opts)
      false ->
        conn
    end
  end

  defp generate_pdf(conn, opts) do
    url = "#{conn.scheme}://#{conn.host}:#{conn.port}#{conn.request_path}"
    {:ok, file} = random_file("test")
    conn = fetch_cookies(conn)
    args = ["-q"] ++ join_cookies(conn.req_cookies) ++ join_options(opts) ++ [String.replace(url, ".pdf", ""), file]
    System.cmd(@wkhtmltopdf_path, args)
    conn
      |> send_file(200, file)
      |> halt
  end

  defp join_cookies(cookies) when cookies == %{}, do: []
  defp join_cookies(cookies) do
    cookies
      |> Enum.map(fn{k,v} -> ["--cookie", "#{k}", "#{URI.encode(v)}"] end)
      |> List.flatten
  end

  defp join_options(options) do
    options
      |> Enum.map(fn{k,v} -> ["--#{k}", "#{v}"] end)
      |> List.flatten
  end
end

sample_router.ex

pipeline :browser do
  plug :accepts, ["html"]
  plug :fetch_session
  plug :fetch_flash
  plug :protect_from_forgery
  plug :put_secure_browser_headers
  plug Sample.PdfPlug, orientation: 'landscape'
end

# Explicitly include the .pdf endpoint ex. report.pdf in paths