Problem with gRPC in snap

I create snap daemon from golang grpc server that work if i start it not in snap. But when i build snap, i get this error on client:
2017/06/28 14:58:28 transport: http2Client.notifyError got notified that the client transport was broken EOF.
2017/06/28 14:58:28 could not greet: rpc error: code = Internal desc = transport is closing
exit status 1

How can I expose tcp port, mb something need to write in snapcraft.yaml?