How can I debug Rserve or see the structure of the evaluated data?
There is a special debug version of Rserve which displays a lot of information when run, among others all packets sent and results on the R side. By default it is compiled along with the regular version and can be found in the $RHOME/library/Rserve directory as Rserve.dbg. One way to run it is to use Rserve(TRUE) in R to start it.