main.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"net/http/httptest"
	"net/http/httputil"
	"net/url"
	"os/exec"
	"strings"
)

func awsS3(endpoint string) {
	log.Println(endpoint)
	out, err := exec.Command("aws", "--endpoint-url", endpoint, "s3", "ls", "s3://test").Output()
	if err != nil {
		log.Fatal(err)
	}
	log.Println(string(out))
}

func singleJoiningSlash(a, b string) string {
	aslash := strings.HasSuffix(a, "/")
	bslash := strings.HasPrefix(b, "/")
	switch {
	case aslash && bslash:
		return a + b[1:]
	case !aslash && !bslash:
		return a + "/" + b
	}
	return a + b
}

func NewDefaultReverseProxy(target *url.URL) *httputil.ReverseProxy {
	targetQuery := target.RawQuery
	director := func(req *http.Request) {
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
		if targetQuery == "" || req.URL.RawQuery == "" {
			req.URL.RawQuery = targetQuery + req.URL.RawQuery
		} else {
			req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
		}
		if _, ok := req.Header["User-Agent"]; !ok {
			// explicitly disable User-Agent so it's not set to default value
			req.Header.Set("User-Agent", "")
		}
		log.Printf("proxy request %+v", req.URL)
	}
	return &httputil.ReverseProxy{Director: director}
}

func main() {
	backendURL := "http://127.0.0.1:9000"
	rpURL, err := url.Parse(backendURL)
	if err != nil {
		fmt.Println("parse error", backendURL)
	}

	frontendProxy := httptest.NewServer(NewDefaultReverseProxy(rpURL))
	defer frontendProxy.Close()

	awsS3(frontendProxy.URL)

}