Bug #3

Before transmitting a file, the server checks if:

1. The client has provided an Accept-Encoding header indicating support for the gzip algorithm.
2. There exists a .gz version of the file the server is about to serve. If both of these conditions are true, the compressed version of the resource is served instead.

Essentially, the same needs to be done for Brotli, which is more efficient and supported by most mainstream browsers. Adding support for this causes no trouble for older clients, so effectively there are no downsides, but the code will need to be refactored a bit because the existing code to perform the above two checks was designed only with gzip in mind.