Refactor FilteredCompressHandler to inherit from stdlib

This changes its behavior to align with the stdlib variant in that
compression is now delayed till the moment that the server begins to
send a response.

This allows the handler to avoid compressing empty responses,and
safeguards against any double compression of content that may occur
if another handler decides to compressi ts response.

This does however come at the drawback(?) of it now removing
`content-length` headers on requests if it exists; since compression
makes the value inaccurate anyway.

See: crystal-lang/crystal#9625

Author: syeopite

src/invidious/helpers/handlers.cr

@@ -61,28 +61,13 @@ class Kemal::ExceptionHandler
   end
 end
 
-class FilteredCompressHandler < Kemal::Handler
+class FilteredCompressHandler < HTTP::CompressHandler
   exclude ["/videoplayback", "/videoplayback/*", "/vi/*", "/sb/*", "/ggpht/*", "/api/v1/auth/notifications"]
   exclude ["/api/v1/auth/notifications", "/data_control"], "POST"
 
-  def call(env)
-    return call_next env if exclude_match? env
-
-    {% if flag?(:without_zlib) %}
-      call_next env
-    {% else %}
-      request_headers = env.request.headers
-
-      if request_headers.includes_word?("Accept-Encoding", "gzip")
-        env.response.headers["Content-Encoding"] = "gzip"
-        env.response.output = Compress::Gzip::Writer.new(env.response.output, sync_close: true)
-      elsif request_headers.includes_word?("Accept-Encoding", "deflate")
-        env.response.headers["Content-Encoding"] = "deflate"
-        env.response.output = Compress::Deflate::Writer.new(env.response.output, sync_close: true)
-      end
-
-      call_next env
-    {% end %}
+  def call(context)
+    return call_next context if exclude_match? context
+    super
   end
 end