Old Engine/JAGGRAB Protocol
From RuneWiki
JAGGRAB runs on port 43595.
Basics
This protocol is essentially HTTP/0.9, see: https://www.w3.org/Protocols/HTTP/AsImplemented.html
The main difference is the client closes the connection, not the server. If you close the connection from the server the client will trigger an exception.
JAGGRAB was used as a fallback when a resource over HTTP was not available (due to a connection timeout or 404). It downloads the necessary BZip2 archives to bootstrap the client. They are stored in main_file_cache.idx0.
The remaining model, animation, midi, and map data is loaded on demand in a separate protocol.