The JAGGRAB protocol is used to 'grab' cache files from the file server and download them.
It is a text-based protocol, similar to HTTP/0.9, and the client will fall back to HTTP if JAGGRAB is unavailable. This generally happens in unsigned mode and helps users who are behind firewalls.
A request is simply the text JAGGRAB, a space, the path to the file and a newline character. Therefore, it is very similar to a HTTP/0.9 GET request.
In (perhaps all) new engine clients, the client prefixes the JAGGRAB request line with a single byte (value 17).
The response is simply the raw file data. Once the response is sent, the connection is closed.
There are a number of files which map to files in the cache.