$ brew install protobuf

$ go get -u google.golang.org/grpc

$ go get -u github.com/golang/protobuf/protoc-gen-go

$ protoc -I helloworld/ helloworld/helloworld.proto --go_out=plugins=grpc:helloworld

$ protoc -I proto/book/ proto/book/book.proto --go_out=plugins=grpc:proto/book

$ go run greeter_server/main.go

$ go run greeter_client/main.go

$ go run server/book/main.go

$ go run client/book/main.go