gRPC Revese Proxy

main.go

// https://github.com/golang/go/issues/29928#issuecomment-458743053
package main

import (
	"crypto/tls"
	"flag"
	"log"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"

	"golang.org/x/net/http2"
)

// argument parser
var (
	upstream    string
	httpsSocket string
	httpsCert   string
	httpsKey    string
)

func init() {
	flag.StringVar(&upstream, "upstream", "http://localhost:8080", "upstream (http://<ip>:<port>)")
	flag.StringVar(&httpsSocket, "socket", ":18080", "local socket")
	// openssl genrsa 2048 > server.key
	// openssl req -new -key server.key > server.csr
	// common name must be server host (ex: localhost)
	// openssl x509 -in server.csr -days 3650 -req -signkey server.key -sha256 > server.crt
	flag.StringVar(&httpsCert, "cert", "server.crt", "ssl cert")
	flag.StringVar(&httpsKey, "key", "server.key", "key")
	flag.Parse()
}

// main function
func main() {
	log.SetPrefix("[proxy] ")
	log.SetOutput(os.Stdout)
	if upstream == "" {
		log.Fatal("ERROR: missing argument upstream ")
	}
	url, _ := url.Parse(upstream)
	proxy := &Upstream{target: url, proxy: httputil.NewSingleHostReverseProxy(url)}

	mux := http.NewServeMux()
	mux.HandleFunc("/", proxy.handle)
	log.Fatal(http.ListenAndServeTLS(httpsSocket, httpsCert, httpsKey, mux))

}

// Upstream ...
type Upstream struct {
	target *url.URL
	proxy  *httputil.ReverseProxy
}

func (p *Upstream) handle(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("X-Forwarded-For", r.Host)
	p.proxy.Transport =
		&http2.Transport{
			AllowHTTP: true,
			DialTLS: func(network, addr string, cfg *tls.Config) (net.Conn, error) {
				ta, err := net.ResolveTCPAddr(network, addr)
				if err != nil {
					return nil, err
				}
				return net.DialTCP(network, nil, ta)
			},
		}
	p.proxy.ServeHTTP(w, r)
}