Go의 역방향 프록시에서 응답 본문에 어떻게 액세스할 수 있나요?

package main

import (
    "net/http"
    "net/http/httputil"
    "net/url"
)

func main() {
    target := &url.URL{Scheme: "http", Host: "www.google.com"}
    proxy := httputil.NewSingleHostReverseProxy(target)

    http.Handle("/google", proxy)
    http.ListenAndServe(":8099", nil)
}

func rewriteBody(resp *http.Response) (err error) {
    b, err := ioutil.ReadAll(resp.Body) // Read html
    if err != nil {
        return  err
    }
    err = resp.Body.Close()
    if err != nil {
        return err
    }
    b = bytes.Replace(b, []byte("server"), []byte("schmerver"), -1) // replace html
    body := ioutil.NopCloser(bytes.NewReader(b))
    resp.Body = body
    resp.ContentLength = int64(len(b))
    resp.Header.Set("Content-Length", strconv.Itoa(len(b)))
    return nil
}

target, _ := url.Parse("http://example.com")
proxy := httputil.NewSingleHostReverseProxy(target)
proxy.ModifyResponse = rewriteBody