Allow downloading via companion (#5561)

* Allow downloading via companion

* post request where not proxied for the download companion which made
  it impossible to download with the companion enabled

* Re-apply Channel to Channels rename which was pulled in

* Update src/invidious/routes/companion.cr

* doc: better comments for each route

---------

Co-authored-by: Fijxu <fijxu@nadeko.net>
Co-authored-by: Émilien (perso) <4016501+unixfox@users.noreply.github.com>

src/invidious/routes/companion.cr

@@ -1,5 +1,5 @@
 module Invidious::Routes::Companion
-  # /companion
+  # GET /companion
   def self.get_companion(env)
     url = env.request.path
     if env.request.query
@@ -16,6 +16,24 @@ module Invidious::Routes::Companion
     end
   end
 
+  # POST /companion
+  def self.post_companion(env)
+    url = env.request.path
+    if env.request.query
+      url += "?#{env.request.query}"
+    end
+
+    begin
+      COMPANION_POOL.client do |wrapper|
+        wrapper.client.post(url, env.request.headers, env.request.body) do |resp|
+          return self.proxy_companion(env, resp)
+        end
+      end
+    rescue ex
+    end
+  end
+
+
   def self.options_companion(env)
     url = env.request.path
     if env.request.query

src/invidious/routing.cr

@@ -227,6 +227,7 @@ module Invidious::Routing
   def register_companion_routes
     if CONFIG.invidious_companion.present?
       get "/companion/*", Routes::Companion, :get_companion
+      post "/companion/*", Routes::Companion, :post_companion
       options "/companion/*", Routes::Companion, :options_companion
     end
   end