protoc-gen-gotemplate/slides

[fit] Protobuf & Code Generation

2016, by Manfred Touron (@moul)

---

overview

• go-kit is an amazing framework to develop strong micro services
• but it requires a lot of boilerplate code
• return on experience on go-kit boilerplate code generation

---

protobuf?

• limited to exchanges (methods and models)
• extendable with plugins
• contract-based
• universal

---

code generation?

• the good old ./generate.sh bash script
• go:generate
• make
• protobuf + protoc-gen-gotemplate

---

go-kit

• protobuf-first, rpc-first service framework in Golang
• abstract services, endpoints, transports
• requires a lot of boilerplate code in multiple packages

---

example: session.proto

syntax = "proto3";
package session;

service SessionService {
  rpc Login(LoginRequest) returns (LoginResponse) {}
}

message LoginRequest {
  string username = 1;
  string password = 2;
}

message LoginResponse {
  string token = 1;
  string err_msg = 2;
}

---

example: session.go

package sessionsvc

import (
	"fmt"
	"golang.org/x/net/context"
	pb "github.com/moul/protoc-gen-gotemplate/examples/go-kit/services/session/gen/pb"
)

type Service struct{}

func New() pb.SessionServiceServer {
	return &Service{}
}

func (svc *Service) Login(ctx context.Context, in *pb.LoginRequest) (*pb.LoginResponse, error) {
    // custon code here
	return nil, fmt.Errorf("not implemented")
}

---

example: {{.File.Package}}/gen/transports/http/http.go.tmpl

// source: templates/{{.File.Package}}/gen/transports/http/http.go.tmpl
package {{.File.Package}}_httptransport
import (
    gokit_endpoint "github.com/go-kit/kit/endpoint"
	httptransport "github.com/go-kit/kit/transport/http"
	endpoints "github.com/moul/protoc-gen-gotemplate/examples/go-kit/services/{{.File.Package}}/gen/endpoints"
	pb "github.com/moul/protoc-gen-gotemplate/examples/go-kit/services/{{.File.Package}}/gen/pb"
)

// result: services/user/gen/transports/http/http.go
package user_httptransport
import (
	gokit_endpoint "github.com/go-kit/kit/endpoint"
	httptransport "github.com/go-kit/kit/transport/http"
	endpoints "github.com/moul/protoc-gen-gotemplate/examples/go-kit/services/user/gen/endpoints"
	pb "github.com/moul/protoc-gen-gotemplate/examples/go-kit/services/user/gen/pb"
)

---

example: {{.File.Package}}/gen/transports/http/http.go.tmpl

// source: templates/{{.File.Package}}/gen/transports/http/http.go.tmpl
{{range .Service.Method}}
func Make{{.Name}}Handler(ctx context.Context, svc pb.{{$file.Package | title}}ServiceServer, endpoint gokit_endpoint.Endpoint) *httptransport.Server {
	return httptransport.NewServer(
		ctx,
		endpoint,
		decode{{.Name}}Request,
		encode{{.Name}}Response,
                []httptransport.ServerOption{}...,
	)
}
{{end}}

// result: services/user/gen/transports/http/http.go
func MakeGetUserHandler(ctx context.Context, svc pb.UserServiceServer, endpoint gokit_endpoint.Endpoint) *httptransport.Server {
	return httptransport.NewServer(
		ctx,
		endpoint,
		decodeGetUserRequest,
		encodeGetUserResponse,
		[]httptransport.ServerOption{}...,
	)
}

---

example: {{.File.Package}}/gen/transports/http/http.go.tmpl

// source: templates/{{.File.Package}}/gen/transports/http/http.go.tmpl
func RegisterHandlers(ctx context.Context, svc pb.{{$file.Package | title}}ServiceServer, mux *http.ServeMux, endpoints endpoints.Endpoints) error {
	{{range .Service.Method}}
        log.Println("new HTTP endpoint: \"/{{.Name}}\" (service={{$file.Package | title}})")
	mux.Handle("/{{.Name}}", Make{{.Name}}Handler(ctx, svc, endpoints.{{.Name}}Endpoint))
	{{end}}
	return nil
}

// result: services/user/gen/transports/http/http.go
func RegisterHandlers(ctx context.Context, svc pb.UserServiceServer, mux *http.ServeMux, endpoints endpoints.Endpoints) error {

	log.Println("new HTTP endpoint: \"/CreateUser\" (service=User)")
	mux.Handle("/CreateUser", MakeCreateUserHandler(ctx, svc, endpoints.CreateUserEndpoint))

	log.Println("new HTTP endpoint: \"/GetUser\" (service=User)")
	mux.Handle("/GetUser", MakeGetUserHandler(ctx, svc, endpoints.GetUserEndpoint))

	return nil
}

---

protoc --gogo_out=plugins=grpc:. ./services/*/*.proto

---

protoc --gotemplate_out=template_dir=./templates:services ./services/*/*.proto

---

---

3 services

6 methods

149 custom lines

1429 generated lines

business focus

---

generation usages

• go-kit boilerplate (see examples/go-kit)
• k8s configuration
• Dockerfile
• documentation
• unit-tests
• fun

---

pros

• small custom codebase
• templates shipped with code
• hardly typed, no reflects
• genericity
• contrat terms (protobuf) respected
• not limited to a language

---

cons

• the author needs to write its own templates
• sometimes difficult to generate valid code
• not enough helpers around the code generation yet

---

improvement ideas

• Support protobufs extensions (i.e, annotations.probo)
• Generate one file from multiple services
• Add more helpers around the code generation

---

conclusion

• Useful to keep everything standard
• The awesomeness of go-kit without the hassle of writing boilerplate code
• Always up-to-date with the contracts

---

questions?

github.com/moul/protoc-gen-gotemplate

@moul