akkoma/lib/pleroma/web/media_proxy/controller.ex

defmodule Pleroma.Web.MediaProxy.MediaProxyController do
  use Pleroma.Web, :controller
  require Logger

  @httpoison Application.get_env(:pleroma, :httpoison)

  @max_body_length 25 * 1_048_576

  @cache_control %{
    default: "public, max-age=1209600",
    error: "public, must-revalidate, max-age=160"
  }

  def remote(conn, %{"sig" => sig, "url" => url}) do
    config = Application.get_env(:pleroma, :media_proxy, [])

    with true <- Keyword.get(config, :enabled, false),
         {:ok, url} <- Pleroma.Web.MediaProxy.decode_url(sig, url),
         {:ok, content_type, body} <- proxy_request(url) do
      conn
      |> put_resp_content_type(content_type)
      |> set_cache_header(:default)
      |> send_resp(200, body)
    else
      false ->
        send_error(conn, 404)

      {:error, :invalid_signature} ->
        send_error(conn, 403)

      {:error, {:http, _, url}} ->
        redirect_or_error(conn, url, Keyword.get(config, :redirect_on_failure, true))
    end
  end

  defp proxy_request(link) do
    headers = [
      {"user-agent",
       "Pleroma/MediaProxy; #{Pleroma.Web.base_url()} <#{
         Application.get_env(:pleroma, :instance)[:email]
       }>"}
    ]

    options =
      @httpoison.process_request_options([:insecure, {:follow_redirect, true}]) ++
        [{:pool, :default}]

    with {:ok, 200, headers, client} <- :hackney.request(:get, link, headers, "", options),
         headers = Enum.into(headers, Map.new()),
         {:ok, body} <- proxy_request_body(client),
         content_type <- proxy_request_content_type(headers, body) do
      {:ok, content_type, body}
    else
      {:ok, status, _, _} ->
        Logger.warn("MediaProxy: request failed, status #{status}, link: #{link}")
        {:error, {:http, :bad_status, link}}

      {:error, error} ->
        Logger.warn("MediaProxy: request failed, error #{inspect(error)}, link: #{link}")
        {:error, {:http, error, link}}
    end
  end

  defp set_cache_header(conn, key) do
    Plug.Conn.put_resp_header(conn, "cache-control", @cache_control[key])
  end

  defp redirect_or_error(conn, url, true), do: redirect(conn, external: url)
  defp redirect_or_error(conn, url, _), do: send_error(conn, 502, "Media proxy error: " <> url)

  defp send_error(conn, code, body \\ "") do
    conn
    |> set_cache_header(:error)
    |> send_resp(code, body)
  end

  defp proxy_request_body(client), do: proxy_request_body(client, <<>>)

  defp proxy_request_body(client, body) when byte_size(body) < @max_body_length do
    case :hackney.stream_body(client) do
      {:ok, data} -> proxy_request_body(client, <<body::binary, data::binary>>)
      :done -> {:ok, body}
      {:error, reason} -> {:error, reason}
    end
  end

  defp proxy_request_body(client, _) do
    :hackney.close(client)
    {:error, :body_too_large}
  end

  # TODO: the body is passed here as well because some hosts do not provide a content-type.
  # At some point we may want to use magic numbers to discover the content-type and reply a proper one.
  defp proxy_request_content_type(headers, _body) do
    headers["Content-Type"] || headers["content-type"] || "image/jpeg"
  end
end