grpc-proxy

proxy.go

package main

import (
	"context"
	"crypto/tls"
	"flag"
	"log"
	"net"

	"github.com/mwitkow/grpc-proxy/proxy"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
	"google.golang.org/grpc/metadata"
)

func main() {
	listen := flag.String("listen", ":8080", "proxy listen address")
	upstream := flag.String("upstream", "127.0.0.1:50051", "upstream gRPC target")
	flag.Parse()

	// Dial the upstream once and reuse the conn for all requests
	cc, err := grpc.NewClient(*upstream,
		grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{
			MinVersion:         tls.VersionTLS12,
			ClientSessionCache: tls.NewLRUClientSessionCache(1024),
		})),
	)
	if err != nil {
		log.Fatalf("dial upstream: %v", err)
	}

	director := func(ctx context.Context, fullMethodName string) (context.Context, grpc.ClientConnInterface, error) {
		inMD, _ := metadata.FromIncomingContext(ctx)
		outMD := inMD.Copy()

		// Overwrite the authorization header with a static token.
		outMD.Set("authorization", "Bearer TOKEN")

		ctx = metadata.NewOutgoingContext(ctx, outMD)

		return ctx, cc, nil
	}

	s := grpc.NewServer(
		grpc.UnknownServiceHandler(proxy.TransparentHandler(director)),
	)

	l, err := net.Listen("tcp", *listen)
	if err != nil {
		log.Fatalf("listen: %v", err)
	}
	log.Printf("proxy listening on %s -> %s", *listen, *upstream)
	if err := s.Serve(l); err != nil {
		log.Fatal(err)
	}
}