The client is making a range request 0-1023 to the http server. It prefers gzip compression with
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
in the request.
The actual content length depends on the transfer encoding and data: If you use identity, no compression is applied and the content length is 1024; if you use gzip, the actual content length depends on the data that is to be compressed.