The protocol of the Farm Spy Daemon

The farm spy daemon creates a TCP/IP socket and puts itself in a listening state. On the other side, remote spy processes connect themselves to the same socket and starts the communication.

Since the farm spy daemon and the remote spy processes can run on different platforms, the eventual byte swapping is done at the farm spy daemon level. In this way, the remote spy processes can ignore this problem and work with their internal rapresentation.

A data retreival cycle is made of:

1. A request from a remote spy process: (3 unsigned ints)

   Offset	Name	Meaning
   0	magic	Must be FARMSPYD_MAGIC_NUMBER (defined in farmprog_defs.h)
   4	last_event_nr	The last event number received (0 to get the first)
   8	max_events	Maximum number of events in the packet

2. The response from the farm spy daemon: (header + data)
   • header: (3 unsigned ints)

     Offset	Name	Meaning
     0	magic	Must be FARMSPYD_MAGIC_NUMBER (defined in farmprog_defs.h)
     4	event_nr	The event number of the current data (ignore if size==0)
     8	size	The size of the data (0 if no data available)

   • data as present in the circular buffer (size bytes)