gRPC v2 Reverse Proxy

main.go

// author: Gary A. Stafford
// site: https://programmaticponderings.com
// license: MIT License
// purpose: gRPC Gateway / Reverse Proxy
// reference: https://github.com/grpc-ecosystem/grpc-gateway

package main

import (
	"context"
	"flag"
	lrf "github.com/banzaicloud/logrus-runtime-formatter"
	pb "github.com/garystafford/protobuf/greeting/v3"
	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
	"github.com/sirupsen/logrus"
	"google.golang.org/grpc"
	"google.golang.org/grpc/metadata"
	"net/http"
	"os"
)

var (
	logLevel    = getEnv("LOG_LEVEL", "info")
	port        = getEnv("PORT", ":50051")
	URLServiceA = getEnv("SERVICE_A_URL", "service-a:50051")
	log         = logrus.New()
)

func injectHeadersIntoMetadata(ctx context.Context, req *http.Request) metadata.MD {
	//https://aspenmesh.io/2018/04/tracing-grpc-with-istio/
	otHeaders := []string{
		"x-request-id",
		"x-b3-traceid",
		"x-b3-spanid",
		"x-b3-parentspanid",
		"x-b3-sampled",
		"x-b3-flags",
		"x-ot-span-context"}

	var pairs []string

	for _, h := range otHeaders {
		if v := req.Header.Get(h); len(v) > 0 {
			pairs = append(pairs, h, v)
		}
	}
	return metadata.Pairs(pairs...)
}

type annotator func(context.Context, *http.Request) metadata.MD

func chainGrpcAnnotators(annotators ...annotator) annotator {
	return func(c context.Context, r *http.Request) metadata.MD {
		var mds []metadata.MD
		for _, a := range annotators {
			mds = append(mds, a(c, r))
		}
		return metadata.Join(mds...)
	}
}

func run() error {
	ctx := context.Background()
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	annotators := []annotator{injectHeadersIntoMetadata}

	mux := runtime.NewServeMux(
		runtime.WithMetadata(chainGrpcAnnotators(annotators...)),
	)

	opts := []grpc.DialOption{grpc.WithInsecure()}
	err := pb.RegisterGreetingServiceHandlerFromEndpoint(ctx, mux, URLServiceA, opts)
	if err != nil {
		return err
	}

	return http.ListenAndServe(port, mux)
}

func getEnv(key, fallback string) string {
	if value, ok := os.LookupEnv(key); ok {
		return value
	}
	return fallback
}

func init() {
	childFormatter := logrus.JSONFormatter{}
	runtimeFormatter := &lrf.Formatter{ChildFormatter: &childFormatter}
	runtimeFormatter.Line = true
	log.Formatter = runtimeFormatter
	log.Out = os.Stdout
	level, err := logrus.ParseLevel(logLevel)
	if err != nil {
		log.Error(err)
	}
	log.Level = level
}

func main() {
	flag.Parse()

	if err := run(); err != nil {
		log.Fatal(err)
	}
}