Compiling with protoc

Learn to generate Go code with protoc.

Compiling with protoc

A .proto file is turned into code by the protoc compiler and two Go plugins: protoc-gen-go generates messages and protoc-gen-go-grpc generates service interfaces.

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

protoc --go_out=. --go_opt=paths=source_relative \
  --go-grpc_out=. --go-grpc_opt=paths=source_relative \
  selam.proto

Output: selam.pb.go and selam_grpc.pb.go.

Don't edit generated code

Generated .pb.go files aren't edited by hand; changes go into the .proto and the code is regenerated. To avoid remembering the command, a directive is added to a source file and go generate ./... is run:

//go:generate protoc --go_out=. --go-grpc_out=. selam.proto

Tools such as Buf also simplify compiling and compatibility checks.

Exercise Generated interface

Write a simplified version of the server interface generated by protoc-gen-go-grpc: type SelamlayiciServer interface { Selam(ad string) (string, error) }. Write type sunucu struct{} that satisfies it and check it at compile time with var _ SelamlayiciServer = sunucu{}; then print sunucu{}.Selam("Go").

Show example solution

package main

import "fmt"

type SelamlayiciServer interface {
    Selam(ad string) (string, error)
}

type sunucu struct{}

func (sunucu) Selam(ad string) (string, error) { return "Merhaba " + ad, nil }

var _ SelamlayiciServer = sunucu{}

func main() {
    fmt.Println(sunucu{}.Selam("Go"))
}

Test yourself

Which plugin generates the service interfaces (Server/Client)?
- protoc-gen-go-grpc
- protoc-gen-go
- go vet
- gofmt
Show answer

protoc-gen-go-grpc — protoc-gen-go generates only message types; client and server code come from protoc-gen-go-grpc.

Message output

protoc ____=. --go-grpc_out=. selam.proto

Show answer

protoc --go_out=. --go-grpc_out=. selam.proto

Tool and output

protoc

.proto compiler
protoc-gen-go

selam.pb.go
protoc-gen-go-grpc

selam_grpc.pb.go
go generate

Runs the directives

Next lesson: gRPC server

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