proxy grpc traffic with http

grpc_proxy.go

package main

import (
	"crypto/tls"
	"errors"
	"log"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"strings"

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

func main() {
	p, err := proxyForGRPC("https://localhost:8081", &tls.Config{InsecureSkipVerify: true})
	if err != nil {
		log.Fatal(err)
	}

	hf := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.ProtoMajor == 2 && strings.Contains(r.Header.Get("Content-Type"), "application/grpc") {
			p.ServeHTTP(w, r)
			return
		}
		w.Write([]byte("hey there"))
	})

	log.Fatal(http.ListenAndServeTLS(":8080", "cert.pem", "key.pem", hf))
}

func proxyForGRPC(backendURL string, conf *tls.Config) (*httputil.ReverseProxy, error) {
	u, err := url.Parse(backendURL)
	if err != nil {
		return nil, err
	}
	if u.Scheme != "https" {
		return nil, errors.New("can only proxy to a TLS backend")
	}
	dialTLS := func(network, addr string, cfg *tls.Config) (net.Conn, error) {
		return tls.Dial(network, addr, conf)
	}
	transport := &http2.Transport{DialTLS: dialTLS}
	p := httputil.NewSingleHostReverseProxy(u)
	p.Transport = transport
	return p, nil

}