[Go] Working on a go example plus fixing go grpc code (#6448)

Implemented server.go and half implemented client.go

Finishes implementation for greeter go example

Update grpc code for monster.fbs

Adds a couple of cpp methods

Adhere to gofmt standards

Adds a readme for issues with grpc

grpc/examples/go/greeter/server/go.mod

@@ -0,0 +1,11 @@
+module github.com/google/flatbuffers/grpc/examples/go/greeter/server
+
+go 1.15
+
+replace github.com/google/flatbuffers/grpc/examples/go/greeter/models v0.0.0 => ../models
+
+require (
+	github.com/google/flatbuffers v1.12.0
+	github.com/google/flatbuffers/grpc/examples/go/greeter/models v0.0.0
+	google.golang.org/grpc v1.35.0
+)

grpc/examples/go/greeter/server/main.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+
+	flatbuffers "github.com/google/flatbuffers/go"
+	models "github.com/google/flatbuffers/grpc/examples/go/greeter/models"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/encoding"
+)
+
+var (
+	greetings = [...]string{"Hi", "Hallo", "Ciao"}
+)
+
+type greeterServer struct {
+	models.UnimplementedGreeterServer
+}
+
+func (s *greeterServer) SayHello(ctx context.Context, request *models.HelloRequest) (*flatbuffers.Builder, error) {
+	v := request.Name()
+	var m string
+	if v == nil {
+		m = "Unknown"
+	} else {
+		m = string(v)
+	}
+	b := flatbuffers.NewBuilder(0)
+	idx := b.CreateString("welcome " + m)
+	models.HelloReplyStart(b)
+	models.HelloReplyAddMessage(b, idx)
+	b.Finish(models.HelloReplyEnd(b))
+	return b, nil
+}
+
+func (s *greeterServer) SayManyHellos(request *models.HelloRequest, stream models.Greeter_SayManyHellosServer) error {
+	v := request.Name()
+	var m string
+	if v == nil {
+		m = "Unknown"
+	} else {
+		m = string(v)
+	}
+	b := flatbuffers.NewBuilder(0)
+
+	for _, greeting := range greetings {
+		idx := b.CreateString(greeting + " " + m)
+		models.HelloReplyStart(b)
+		models.HelloReplyAddMessage(b, idx)
+		b.Finish(models.HelloReplyEnd(b))
+		if err := stream.Send(b); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func newServer() *greeterServer {
+	s := &greeterServer{}
+	return s
+}
+
+func main() {
+	lis, err := net.Listen("tcp", fmt.Sprintf("localhost:%d", 3000))
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+	grpcServer := grpc.NewServer()
+	encoding.RegisterCodec(flatbuffers.FlatbuffersCodec{})
+	models.RegisterGreeterServer(grpcServer, newServer())
+	if err := grpcServer.Serve(lis); err != nil {
+		fmt.Print(err)
+		panic(err)
+	}
+}