Set $GOPATH to proper value.
Run server:
$ make server
Run client:
$ make client
Check app logs from the client:
# cat /var/log/app.log
...
2017/07/27 17:29:17 Listening on [::]:46199
2017/07/27 17:29:17 Listening on [::]:40323
2017/07/27 17:29:17 listen tcp :0: socket: too many open files
Up ulimit:
ulimit -n 256
Try to run app again:
# app
...
2017/07/27 17:31:20 Listening on [::]:39817
2017/07/27 17:31:20 Listening on [::]:37351
2017/07/27 17:31:20 Finished OK