You could use one of those in combination with something to pack your data like json or msgpack:
I am implementing RPC implementation based on msgpack-nim
https://github.com/akiradeveloper/msgpack-rpc-nim
but it's still buggy if you use MultiFuture feature with connection pooling (odds are AsyncSocket seems to non-reusable)
You are able to see what's available with this module by seeing this
https://rawgit.com/akiradeveloper/msgpack-rpc-nim/master/msgpack_rpc.html