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diff --git a/lib/pleroma/web/media_proxy.ex b/lib/pleroma/web/media_proxy.ex
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+++ b/lib/pleroma/web/media_proxy.ex
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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.MediaProxy do
+  alias Pleroma.Config
+  alias Pleroma.Helpers.UriHelper
+  alias Pleroma.Upload
+  alias Pleroma.Web
+  alias Pleroma.Web.MediaProxy.Invalidation
+
+  @base64_opts [padding: false]
+  @cache_table :banned_urls_cache
+
+  def cache_table, do: @cache_table
+
+  @spec in_banned_urls(String.t()) :: boolean()
+  def in_banned_urls(url), do: elem(Cachex.exists?(@cache_table, url(url)), 1)
+
+  def remove_from_banned_urls(urls) when is_list(urls) do
+    Cachex.execute!(@cache_table, fn cache ->
+      Enum.each(Invalidation.prepare_urls(urls), &Cachex.del(cache, &1))
+    end)
+  end
+
+  def remove_from_banned_urls(url) when is_binary(url) do
+    Cachex.del(@cache_table, url(url))
+  end
+
+  def put_in_banned_urls(urls) when is_list(urls) do
+    Cachex.execute!(@cache_table, fn cache ->
+      Enum.each(Invalidation.prepare_urls(urls), &Cachex.put(cache, &1, true))
+    end)
+  end
+
+  def put_in_banned_urls(url) when is_binary(url) do
+    Cachex.put(@cache_table, url(url), true)
+  end
+
+  def url(url) when is_nil(url) or url == "", do: nil
+  def url("/" <> _ = url), do: url
+
+  def url(url) do
+    if enabled?() and url_proxiable?(url) do
+      encode_url(url)
+    else
+      url
+    end
+  end
+
+  @spec url_proxiable?(String.t()) :: boolean()
+  def url_proxiable?(url) do
+    not local?(url) and not whitelisted?(url)
+  end
+
+  def preview_url(url, preview_params \\ []) do
+    if preview_enabled?() do
+      encode_preview_url(url, preview_params)
+    else
+      url(url)
+    end
+  end
+
+  def enabled?, do: Config.get([:media_proxy, :enabled], false)
+
+  # Note: media proxy must be enabled for media preview proxy in order to load all
+  #   non-local non-whitelisted URLs through it and be sure that body size constraint is preserved.
+  def preview_enabled?, do: enabled?() and !!Config.get([:media_preview_proxy, :enabled])
+
+  def local?(url), do: String.starts_with?(url, Pleroma.Web.base_url())
+
+  def whitelisted?(url) do
+    %{host: domain} = URI.parse(url)
+
+    mediaproxy_whitelist_domains =
+      [:media_proxy, :whitelist]
+      |> Config.get()
+      |> Enum.map(&maybe_get_domain_from_url/1)
+
+    whitelist_domains =
+      if base_url = Config.get([Upload, :base_url]) do
+        %{host: base_domain} = URI.parse(base_url)
+        [base_domain | mediaproxy_whitelist_domains]
+      else
+        mediaproxy_whitelist_domains
+      end
+
+    domain in whitelist_domains
+  end
+
+  defp maybe_get_domain_from_url("http" <> _ = url) do
+    URI.parse(url).host
+  end
+
+  defp maybe_get_domain_from_url(domain), do: domain
+
+  defp base64_sig64(url) do
+    base64 = Base.url_encode64(url, @base64_opts)
+
+    sig64 =
+      base64
+      |> signed_url()
+      |> Base.url_encode64(@base64_opts)
+
+    {base64, sig64}
+  end
+
+  def encode_url(url) do
+    {base64, sig64} = base64_sig64(url)
+
+    build_url(sig64, base64, filename(url))
+  end
+
+  def encode_preview_url(url, preview_params \\ []) do
+    {base64, sig64} = base64_sig64(url)
+
+    build_preview_url(sig64, base64, filename(url), preview_params)
+  end
+
+  def decode_url(sig, url) do
+    with {:ok, sig} <- Base.url_decode64(sig, @base64_opts),
+         signature when signature == sig <- signed_url(url) do
+      {:ok, Base.url_decode64!(url, @base64_opts)}
+    else
+      _ -> {:error, :invalid_signature}
+    end
+  end
+
+  defp signed_url(url) do
+    :crypto.hmac(:sha, Config.get([Web.Endpoint, :secret_key_base]), url)
+  end
+
+  def filename(url_or_path) do
+    if path = URI.parse(url_or_path).path, do: Path.basename(path)
+  end
+
+  def base_url do
+    Config.get([:media_proxy, :base_url], Web.base_url())
+  end
+
+  defp proxy_url(path, sig_base64, url_base64, filename) do
+    [
+      base_url(),
+      path,
+      sig_base64,
+      url_base64,
+      filename
+    ]
+    |> Enum.filter(& &1)
+    |> Path.join()
+  end
+
+  def build_url(sig_base64, url_base64, filename \\ nil) do
+    proxy_url("proxy", sig_base64, url_base64, filename)
+  end
+
+  def build_preview_url(sig_base64, url_base64, filename \\ nil, preview_params \\ []) do
+    uri = proxy_url("proxy/preview", sig_base64, url_base64, filename)
+
+    UriHelper.modify_uri_params(uri, preview_params)
+  end
+
+  def verify_request_path_and_url(
+        %Plug.Conn{params: %{"filename" => _}, request_path: request_path},
+        url
+      ) do
+    verify_request_path_and_url(request_path, url)
+  end
+
+  def verify_request_path_and_url(request_path, url) when is_binary(request_path) do
+    filename = filename(url)
+
+    if filename && not basename_matches?(request_path, filename) do
+      {:wrong_filename, filename}
+    else
+      :ok
+    end
+  end
+
+  def verify_request_path_and_url(_, _), do: :ok
+
+  defp basename_matches?(path, filename) do
+    basename = Path.basename(path)
+    basename == filename or URI.decode(basename) == filename or URI.encode(basename) == filename
+  end
+end