Quick ProtoBuf

Posted on September 2, 2022
Tags: codeetc

1 Install protobuf compiler

sudo dnf install protobuf-compiler

protoc by default only outputs cpp, java, js ,python ,c# ,php,ruby,objc.
Notice it DOES NOT output golang (we need to install a plugin)

2 setup for golang

go env GOPATH
#/home/rhel/go

The above command works if you have go installed but sometimes your terminal doesnt set $GOPATH

echo $GOPATH

if it doesnt exist then modify your .zshrc

the .zshrc file should look like below

{bash filename=.zshrc} export GOPATH=$(go env GOPATH) export GOBIN=$GOPATH/bin export PATH=$PATH:$GOPATH:$GOBIN

install protoc plugin for golang

go install google.golang.org/protobuf/cmd/protoc-gen-go@latest

3 Example MTA API

go mod init mydemo
  1. Download the gtfs-realtime.proto file
  2. Download
go get google.golang.org/protobuf
go mod download github.com/golang/protobuf

make a folder named out

protoc -I=./ --go_out=./ ./gtfs-realtime.proto
protoc -I=./ --go_out=./ ./nyct-subway.proto

In the gtfs-realtime.proto add the line
option go_package = "/bleh";

Then it will work and create a file gtfs-realtime.pb.go

**notice that we import pb "mydemo/bleh" because mydemo is our regular golang package name, and bleh is the folder holding our .pb.go file generated from option go_package = "/bleh";

package main

import(
	// pb "[root_golang_package_name]/[proto_file_option_go_name]"
	pb "mydemo/bleh"
	"fmt"
)
func main(){
	fmt.Println(pb.FeedHeader_FULL_DATASET)
}
curl -H 'x-api-key: XXXXXXXXXXXXXXXXXXXXXXXXXX' \
  -O \
  -L https://api-endpoint.mta.info/Dataservice/mtagtfsfeeds/nyct%2Fgtfs-bdfm

4 protoc compiler

syntax = "proto3";

option go_package = "google.golang.org/grpc/examples/helloworld/helloworld";
option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}
//in Go we embed the protobuf Server into our server struct
type server struct {
	pb.UnimplementedGreeterServer 
}

// SayHello implements helloworld.GreeterServer
func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
	log.Printf("Received: %v", in.GetName())
	return &pb.HelloReply{Message: "Hello " + in.GetName()}, nil
}

func main() {
	flag.Parse()
	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	s := grpc.NewServer()
	pb.RegisterGreeterServer(s, &server{}) //IMPORTANT &server{}
	log.Printf("server listening at %v", lis.Addr())
	if err := s.Serve(lis); err != nil {
		log.Fatalf("failed to serve: %v", err)
	}
}

Observe the similarity between Golang and C++ server grpc implementation.

class GreeterServiceImpl final : public Greeter::Service {
  Status SayHello(ServerContext* context, const HelloRequest* request, HelloReply* reply) override {
    std::string prefix("Hello ");
    reply->set_message(prefix + request->name());
    return Status::OK;
  }
};

void main(){
  GreeterServiceImpl service;
  ...
  builder.RegisterService(&service);
  // Finally assemble the server.
}