A simple http proxy in Go

proxy.go

package main

import (
	"fmt"
	"io"
	"net/http"
	"time"
)

var client = http.Client{Timeout: 5 * time.Second}

func proxy(scheme, host string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		fmt.Printf("proxy: %v://%v%v\n", scheme, host, r.URL.Path)
		r2 := r.Clone(r.Context())
		r2.URL.Scheme = scheme
		r2.URL.Host = host
		r2.RequestURI = ""

		resp, err := client.Do(r2)
		if err != nil {
			fmt.Printf("bad gateway: %v\n", err)
			w.WriteHeader(http.StatusBadGateway)
			_, _ = fmt.Fprintf(w, `bad gateway: %v`, err)
			return
		}

		header := w.Header()
		for k, vs := range resp.Header {
			for _, v := range vs {
				header.Add(k, v)
			}
		}
		w.WriteHeader(resp.StatusCode)
		if _, err = io.Copy(w, resp.Body); err != nil {
			fmt.Printf("gateway error: %v\n", err)
		}
	}
}

func main() {
	h := http.NewServeMux()
	h.Handle("/", proxy("http", "localhost:8081"))
	h.Handle("/api/", proxy("http", "localhost:8080"))
	h.Handle("/doc/", proxy("http", "localhost:8080"))
	s := http.Server{
		Addr:    ":8000",
		Handler: h,
	}
	fmt.Printf("proxy is listening on :8000\n")
	err := s.ListenAndServe()
	fmt.Printf("%v\n", err)
}