Forward parameters given in &params= from Atom feeds

Any parameters given in &params=... are appended to /watch URLs.  This
allows e.g. passing &raw=1&listen=1 to a playlist of music and use an
rss reader like newsboat as a media player, like so:

    https://invidio.us/feed/playlist/XXX?params=%26raw%3D1%listen%3D1

All three feeds--channels, playlists, subscriptions--are supported.

src/invidious.cr

@@ -2630,6 +2630,8 @@ get "/feed/channel/:ucid" do |env|
 
   ucid = env.params.url["ucid"]
 
+  params = HTTP::Params.parse(env.params.query["params"]? || "")
+
   begin
     channel = get_about_info(ucid, locale)
   rescue ex
@@ -2690,7 +2692,7 @@ get "/feed/channel/:ucid" do |env|
       end
 
       videos.each do |video|
-        video.to_xml(host_url, channel.auto_generated, xml)
+        video.to_xml(host_url, channel.auto_generated, params, xml)
       end
     end
   end
@@ -2721,6 +2723,8 @@ get "/feed/private" do |env|
   page = env.params.query["page"]?.try &.to_i?
   page ||= 1
 
+  params = HTTP::Params.parse(env.params.query["params"]? || "")
+
   videos, notifications = get_subscription_feed(PG_DB, user, max_results, page)
   host_url = make_host_url(config, Kemal.config)
 
@@ -2734,7 +2738,7 @@ get "/feed/private" do |env|
       xml.element("title") { xml.text translate(locale, "Invidious Private Feed for `x`", user.email) }
 
       (notifications + videos).each do |video|
-        video.to_xml(locale, host_url, xml)
+        video.to_xml(locale, host_url, params, xml)
       end
     end
   end
@@ -2747,6 +2751,8 @@ get "/feed/playlist/:plid" do |env|
 
   plid = env.params.url["plid"]
 
+  params = HTTP::Params.parse(env.params.query["params"]? || "")
+
   host_url = make_host_url(config, Kemal.config)
   path = env.request.path
 
@@ -2757,10 +2763,10 @@ get "/feed/playlist/:plid" do |env|
   document.xpath_nodes(%q(//*[@href]|//*[@url])).each do |node|
     node.attributes.each do |attribute|
       case attribute.name
-      when "url"
-        node["url"] = "#{host_url}#{URI.parse(node["url"]).full_path}"
-      when "href"
-        node["href"] = "#{host_url}#{URI.parse(node["href"]).full_path}"
+      when "url", "href"
+        full_path = URI.parse(node[attribute.name]).full_path
+        query_string_opt = full_path.starts_with?("/watch?v=") ? "&#{params}" : ""
+        node[attribute.name] = "#{host_url}#{full_path}#{query_string_opt}"
       end
     end
   end

src/invidious/channels.cr

@@ -41,13 +41,15 @@ struct ChannelVideo
     end
   end
 
-  def to_xml(locale, host_url, xml : XML::Builder)
+  def to_xml(locale, host_url, query_params, xml : XML::Builder)
+    query_params["v"] = self.id
+
     xml.element("entry") do
       xml.element("id") { xml.text "yt:video:#{self.id}" }
       xml.element("yt:videoId") { xml.text self.id }
       xml.element("yt:channelId") { xml.text self.ucid }
       xml.element("title") { xml.text self.title }
-      xml.element("link", rel: "alternate", href: "#{host_url}/watch?v=#{self.id}")
+      xml.element("link", rel: "alternate", href: "#{host_url}/watch?#{query_params}")
 
       xml.element("author") do
         xml.element("name") { xml.text self.author }
@@ -56,7 +58,7 @@ struct ChannelVideo
 
       xml.element("content", type: "xhtml") do
         xml.element("div", xmlns: "http://www.w3.org/1999/xhtml") do
-          xml.element("a", href: "#{host_url}/watch?v=#{self.id}") do
+          xml.element("a", href: "#{host_url}/watch?#{query_params}") do
             xml.element("img", src: "#{host_url}/vi/#{self.id}/mqdefault.jpg")
           end
         end

src/invidious/search.cr

@@ -1,11 +1,13 @@
 struct SearchVideo
-  def to_xml(host_url, auto_generated, xml : XML::Builder)
+  def to_xml(host_url, auto_generated, query_params, xml : XML::Builder)
+    query_params["v"] = self.id
+
     xml.element("entry") do
       xml.element("id") { xml.text "yt:video:#{self.id}" }
       xml.element("yt:videoId") { xml.text self.id }
       xml.element("yt:channelId") { xml.text self.ucid }
       xml.element("title") { xml.text self.title }
-      xml.element("link", rel: "alternate", href: "#{host_url}/watch?v=#{self.id}")
+      xml.element("link", rel: "alternate", href: "#{host_url}/watch?#{query_params}")
 
       xml.element("author") do
         if auto_generated
@@ -19,7 +21,7 @@ struct SearchVideo
 
       xml.element("content", type: "xhtml") do
         xml.element("div", xmlns: "http://www.w3.org/1999/xhtml") do
-          xml.element("a", href: "#{host_url}/watch?v=#{self.id}") do
+          xml.element("a", href: "#{host_url}/watch?#{query_params}") do
             xml.element("img", src: "#{host_url}/vi/#{self.id}/mqdefault.jpg")
           end
         end
@@ -40,12 +42,12 @@ struct SearchVideo
     end
   end
 
-  def to_xml(host_url, auto_generated, xml : XML::Builder | Nil = nil)
+  def to_xml(host_url, auto_generated, query_params, xml : XML::Builder | Nil = nil)
     if xml
-      to_xml(host_url, auto_generated, xml)
+      to_xml(host_url, auto_generated, query_params, xml)
     else
       XML.build do |json|
-        to_xml(host_url, auto_generated, xml)
+        to_xml(host_url, auto_generated, query_params, xml)
       end
     end
   end