Basic protoc plugin example

buf.gen.yaml

version: v1
plugins:
  - plugin: test
    path: ["go", "run", "protoc-gen-test.go"]
    out: gen

Makefile

default:
	buf generate buf.build/bufbuild/eliza

protoc-gen-test.go

package main

import (
	"google.golang.org/protobuf/encoding/protojson"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/pluginpb"
	"io"
	"os"
)

func main() {
	// A plugin is just a program that reads a CodeGeneratorRequest
	// from stdin, so let's read from stdin, and parse the request:
	stdin, _ := io.ReadAll(os.Stdin)
	req := &pluginpb.CodeGeneratorRequest{}
	_ = proto.Unmarshal(stdin, req)
	// Note that pluginpb is just a precompiled version of the plugin
	// contract definition google/protobuf/compiler/plugin.proto
	// that's provided for convenience.

	// A plugin writes a CodeGeneratorResponse to stdout. Let's do
	// that here. We're going to generate a file req.json, where we
	// simply dump the request, but in human-readable JSON format.
	res := &pluginpb.CodeGeneratorResponse{}
	res.File = append(res.File, &pluginpb.CodeGeneratorResponse_File{
		Name:    proto.String("req.json"),
		Content: proto.String(protojson.Format(req)),
	})
	stdout, _ := proto.Marshal(res)
	_, _ = os.Stdout.Write(stdout)
}