Use a dedicated endpoind for downloads

This allows us to not pass file name ("title") in the form
data and to enforce some sanity checks

src/invidious.cr

@@ -236,6 +236,7 @@ before_all do |env|
             "/api/manifest/",
             "/videoplayback",
             "/latest_version",
+            "/download",
           }.any? { |r| env.request.resource.starts_with? r }
 
   if env.request.cookies.has_key? "SID"
@@ -348,6 +349,8 @@ end
   Invidious::Routing.get "/e/:id", Invidious::Routes::Watch, :redirect
   Invidious::Routing.get "/redirect", Invidious::Routes::Misc, :cross_instance_redirect
 
+  Invidious::Routing.post "/download", Invidious::Routes::Watch, :download
+
   Invidious::Routing.get "/embed/", Invidious::Routes::Embed, :redirect
   Invidious::Routing.get "/embed/:id", Invidious::Routes::Embed, :show
 

src/invidious/frontend/watch_page.cr

@@ -26,12 +26,16 @@ module Invidious::Frontend::WatchPage
     return String.build(4000) do |str|
       str << "<form"
       str << " class=\"pure-form pure-form-stacked\""
-      str << " action='/latest_version'"
-      str << " method='get'"
+      str << " action='/download'"
+      str << " method='post'"
       str << " rel='noopener'"
       str << " target='_blank'>"
       str << '\n'
 
+      # Hidden inputs for video id and title
+      str << "<input type='hidden' name='id' value='" << video.id << "'/>\n"
+      str << "<input type='hidden' name='title' value='" << HTML.escape(video.title) << "'/>\n"
+
       str << "\t<div class=\"pure-control-group\">\n"
 
       str << "\t\t<label for='download_widget'>"
@@ -48,8 +52,7 @@ module Invidious::Frontend::WatchPage
 
         height = itag_to_metadata?(option["itag"]).try &.["height"]?
 
-        title = URI.encode_www_form("#{video.title}-#{video.id}.#{mimetype.split("/")[1]}")
-        value = {"id": video.id, "itag": option["itag"], "title": title}.to_json
+        value = {"itag": option["itag"], "ext": mimetype.split("/")[1]}.to_json
 
         str << "\t\t\t<option value='" << value << "'>"
         str << (height || "~240") << "p - " << mimetype
@@ -61,8 +64,7 @@ module Invidious::Frontend::WatchPage
       video_assets.video_streams.each do |option|
         mimetype = option["mimeType"].as_s.split(";")[0]
 
-        title = URI.encode_www_form("#{video.title}-#{video.id}.#{mimetype.split("/")[1]}")
-        value = {"id": video.id, "itag": option["itag"], "title": title}.to_json
+        value = {"itag": option["itag"], "ext": mimetype.split("/")[1]}.to_json
 
         str << "\t\t\t<option value='" << value << "'>"
         str << option["qualityLabel"] << " - " << mimetype << " @ " << option["fps"] << "fps - video only"
@@ -74,8 +76,7 @@ module Invidious::Frontend::WatchPage
       video_assets.audio_streams.each do |option|
         mimetype = option["mimeType"].as_s.split(";")[0]
 
-        title = URI.encode_www_form("#{video.title}-#{video.id}.#{mimetype.split("/")[1]}")
-        value = {"id": video.id, "itag": option["itag"], "title": title}.to_json
+        value = {"itag": option["itag"], "ext": mimetype.split("/")[1]}.to_json
 
         str << "\t\t\t<option value='" << value << "'>"
         str << mimetype << " @ " << (option["bitrate"]?.try &.as_i./ 1000) << "k - audio only"
@@ -85,8 +86,7 @@ module Invidious::Frontend::WatchPage
       # Subtitles (a.k.a "closed captions")
 
       video_assets.captions.each do |caption|
-        title = URI.encode_www_form("#{video.title}-#{video.id}.#{caption.language_code}.vtt")
-        value = {"id": video.id, "label": caption.name, "title": title}.to_json
+        value = {"label": caption.name, "ext": "#{caption.language_code}.vtt"}.to_json
 
         str << "\t\t\t<option value='" << value << "'>"
         str << translate(locale, "download_subtitles", translate(locale, caption.name))

src/invidious/routes/api/v1/videos.cr

@@ -23,7 +23,11 @@ module Invidious::Routes::API::V1::Videos
     env.response.content_type = "application/json"
 
     id = env.params.url["id"]
-    region = env.params.query["region"]?
+    region = env.params.query["region"]? || env.params.body["region"]?
+
+    if id.nil? || id.size != 11 || !id.matches?(/^[\w-]+$/)
+      return error_json(400, "Invalid video ID")
+    end
 
     # See https://github.com/ytdl-org/youtube-dl/blob/6ab30ff50bf6bd0585927cb73c7421bef184f87a/youtube_dl/extractor/youtube.py#L1354
     # It is possible to use `/api/timedtext?type=list&v=#{id}` and

src/invidious/routes/video_playback.cr

@@ -242,31 +242,25 @@ module Invidious::Routes::VideoPlayback
   # YouTube /videoplayback links expire after 6 hours,
   # so we have a mechanism here to redirect to the latest version
   def self.latest_version(env)
-    if env.params.query["download_widget"]?
-      download_widget = JSON.parse(env.params.query["download_widget"])
+    id = env.params.query["id"]?
+    itag = env.params.query["itag"]?.try &.to_i?
 
-      id = download_widget["id"].as_s
-      title = URI.decode_www_form(download_widget["title"].as_s)
-
-      if label = download_widget["label"]?
-        return env.redirect "/api/v1/captions/#{id}?label=#{label}&title=#{title}"
-      else
-        itag = download_widget["itag"].as_s.to_i
-        local = "true"
-      end
+    # Sanity checks
+    if id.nil? || id.size != 11 || !id.matches?(/^[\w-]+$/)
+      return error_template(400, "Invalid video ID")
     end
 
-    id ||= env.params.query["id"]?
-    itag ||= env.params.query["itag"]?.try &.to_i
+    if itag.nil? || itag <= 0 || itag >= 1000
+      return error_template(400, "Invalid itag")
+    end
 
     region = env.params.query["region"]?
+    local = (env.params.query["local"]? == "true")
 
-    local ||= env.params.query["local"]?
-    local ||= "false"
-    local = local == "true"
+    title = env.params.query["title"]?
 
-    if !id || !itag
-      haltf env, status_code: 400, response: "TESTING"
+    if title && CONFIG.disabled?("downloads")
+      return error_template(403, "Administrator has disabled this endpoint.")
     end
 
     video = get_video(id, region: region)
@@ -278,8 +272,10 @@ module Invidious::Routes::VideoPlayback
       haltf env, status_code: 404
     end
 
-    url = URI.parse(url).request_target.not_nil! if local
-    url = "#{url}&title=#{title}" if title
+    if local
+      url = URI.parse(url).request_target.not_nil!
+      url += "&title=#{URI.encode_www_form(title, space_to_plus: false)}" if title
+    end
 
     return env.redirect url
   end

src/invidious/routes/watch.cr

@@ -289,4 +289,52 @@ module Invidious::Routes::Watch
       return error_template(404, "The requested clip doesn't exist")
     end
   end
+
+  def self.download(env)
+    if CONFIG.disabled?("downloads")
+      return error_template(403, "Administrator has disabled this endpoint.")
+    end
+
+    title = env.params.body["title"]? || ""
+    video_id = env.params.body["id"]? || ""
+    selection = env.params.body["download_widget"]?
+
+    if title.empty? || video_id.empty? || selection.nil?
+      return error_template(400, "Missing form data")
+    end
+
+    download_widget = JSON.parse(selection)
+    extension = download_widget["ext"].as_s
+
+    filename = URI.encode_www_form(
+      "#{video_id}-#{title}.#{extension}",
+      space_to_plus: false
+    )
+
+    # Pass form parameters as URL parameters for the handlers of both
+    # /latest_version and /api/v1/captions. This avoids an un-necessary
+    # redirect and duplicated (and hazardous) sanity checks.
+    env.params.query["id"] = video_id
+    env.params.query["title"] = filename
+
+    # Delete the useless ones
+    env.params.body.delete("id")
+    env.params.body.delete("title")
+    env.params.body.delete("download_widget")
+
+    if label = download_widget["label"]?
+      # URL params specific to /api/v1/captions/:id
+      env.params.query["label"] = URI.encode_www_form(label.as_s, space_to_plus: false)
+
+      return Invidious::Routes::API::V1::Videos.captions(env)
+    elsif itag = download_widget["itag"]?.try &.as_i
+      # URL params specific to /latest_version
+      env.params.query["itag"] = itag.to_s
+      env.params.query["local"] = "true"
+
+      return Invidious::Routes::VideoPlayback.latest_version(env)
+    else
+      return error_template(400, "Invalid label or itag")
+    end
+  end
 end