support source:markdown in RSS feed

lib/pleroma/web/feed/feed_view.ex

@@ -112,4 +112,30 @@ defmodule Pleroma.Web.Feed.FeedView do
     |> html_escape()
     |> safe_to_string()
   end
+
+  # Encoding newlines, e.g., per XML spec
+  def rss_escape(nil), do: ""
+  def rss_escape(data) when is_binary(data) do
+    data
+    |> rss_escape_string()
+    |> to_string()
+  end
+
+  defp rss_escape_string(""), do: ""
+  defp rss_escape_string(<<"&"::utf8, rest::binary>>), do: rss_escape_entity(rest)
+  defp rss_escape_string(<<"<"::utf8, rest::binary>>), do: ["&lt;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<">"::utf8, rest::binary>>), do: ["&gt;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<"\""::utf8, rest::binary>>), do: ["&quot;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<"'"::utf8, rest::binary>>), do: ["&apos;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<"\t"::utf8, rest::binary>>), do: ["&#9;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<"\n"::utf8, rest::binary>>), do: ["&#10;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<"\r\n"::utf8, rest::binary>>), do: ["&#10;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<"\r"::utf8, rest::binary>>), do: ["&#13;" | rss_escape_string(rest)]
+  defp rss_escape_string(<<c::utf8, rest::binary>>), do: [c | rss_escape_string(rest)]
+  defp rss_escape_entity(<<"amp;"::utf8, rest::binary>>), do: ["&amp;" | rss_escape_string(rest)]
+  defp rss_escape_entity(<<"lt;"::utf8, rest::binary>>), do: ["&lt;" | rss_escape_string(rest)]
+  defp rss_escape_entity(<<"gt;"::utf8, rest::binary>>), do: ["&gt;" | rss_escape_string(rest)]
+  defp rss_escape_entity(<<"quot;"::utf8, rest::binary>>), do: ["&quot;" | rss_escape_string(rest)]
+  defp rss_escape_entity(<<"apos;"::utf8, rest::binary>>), do: ["&apos;" | rss_escape_string(rest)]
+  defp rss_escape_entity(rest), do: ["&amp;" | rss_escape_string(rest)]
 end

lib/pleroma/web/templates/feed/feed/_activity.rss.eex

@@ -14,6 +14,10 @@
     <description><%= escape(@data["summary"]) %></description>
   <% end %>
 
+  <%= if get_in(@data, ["source", "mediaType"]) == "text/markdown" do %>
+    <source:markdown><%= rss_escape(get_in(@data, ["source", "content"])) %></source:markdown>
+  <% end %>
+
   <%= if @activity.local do %>
     <link><%= @data["id"] %></link>
   <% else %>