git.squeep.com Git - akkoma/blob - lib/pleroma/web/media_proxy/media_proxy.ex

   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
   3 # SPDX-License-Identifier: AGPL-3.0-only
   4
   5 defmodule Pleroma.Web.MediaProxy do
   6   @base64_opts [padding: false]
   7
   8   def url(nil), do: nil
   9
  10   def url(""), do: nil
  11
  12   def url("/" <> _ = url), do: url
  13
  14   def url(url) do
  15     config = Application.get_env(:pleroma, :media_proxy, [])
  16
  17     if !Keyword.get(config, :enabled, false) or String.starts_with?(url, Pleroma.Web.base_url()) do
  18       url
  19     else
  20       secret = Application.get_env(:pleroma, Pleroma.Web.Endpoint)[:secret_key_base]
  21
  22       # Must preserve `%2F` for compatibility with S3 (https://git.pleroma.social/pleroma/pleroma/issues/580)
  23       replacement = get_replacement(url, ":2F:")
  24
  25       # The URL is url-decoded and encoded again to ensure it is correctly encoded and not twice.
  26       base64 =
  27         url
  28         |> String.replace("%2F", replacement)
  29         |> URI.decode()
  30         |> URI.encode()
  31         |> String.replace(replacement, "%2F")
  32         |> Base.url_encode64(@base64_opts)
  33
  34       sig = :crypto.hmac(:sha, secret, base64)
  35       sig64 = sig |> Base.url_encode64(@base64_opts)
  36
  37       build_url(sig64, base64, filename(url))
  38     end
  39   end
  40
  41   def decode_url(sig, url) do
  42     secret = Application.get_env(:pleroma, Pleroma.Web.Endpoint)[:secret_key_base]
  43     sig = Base.url_decode64!(sig, @base64_opts)
  44     local_sig = :crypto.hmac(:sha, secret, url)
  45
  46     if local_sig == sig do
  47       {:ok, Base.url_decode64!(url, @base64_opts)}
  48     else
  49       {:error, :invalid_signature}
  50     end
  51   end
  52
  53   def filename(url_or_path) do
  54     if path = URI.parse(url_or_path).path, do: Path.basename(path)
  55   end
  56
  57   def build_url(sig_base64, url_base64, filename \\ nil) do
  58     [
  59       Pleroma.Config.get([:media_proxy, :base_url], Pleroma.Web.base_url()),
  60       "proxy",
  61       sig_base64,
  62       url_base64,
  63       filename
  64     ]
  65     |> Enum.filter(fn value -> value end)
  66     |> Path.join()
  67   end
  68
  69   defp get_replacement(url, replacement) do
  70     if String.contains?(url, replacement) do
  71       get_replacement(url, replacement <> replacement)
  72     else
  73       replacement
  74     end
  75   end
  76 end