如何使用proxy.modifyresponse?

我已经实现了最基本的反向代理来拉一个页面,然后在正文中添加一些内容。不幸的是,我添加到html的尝试没有生效。下面的代码只显示了原始页面,但没有我在响应之前准备的“猴子”。你还需要打什么电话才能让它工作?我最终想用这个来代替自定义css的css。

package main

import (
    "log"
    "net/http"
    "net/http/httputil"
    "net/url"
    "fmt"
    "github.com/PuerkitoBio/goquery"
    "bytes"
)

type Director func(*http.Request)

func (f Director) Then(g Director) Director {
    return func(req *http.Request) {
        f(req)
        g(req)
    }
}

func hostDirector(host string) Director {
    return func(req *http.Request) {
        req.Host = host
    }
}

func UpdateResponse(r *http.Response) error {
    doc, err := goquery.NewDocumentFromReader(r.Body)
    if err != nil{
        //log.New("Research")
        log.Fatal("Bad doc %v", err)
        return err
    }
    html, err := goquery.OuterHtml(doc.First())
    if err != nil{
        log.Fatal("Bad html %v", err)
        return err
    }
    fmt.Printf("Body %v", html)
    r.Write(bytes.NewBufferString("monkeys"+html))

    return nil
}

func main() {
    url, _ := url.Parse("http://cnn.com/")
    proxy := httputil.NewSingleHostReverseProxy(url)

    d := proxy.Director
    // sequence the default director with our host director
    proxy.Director = Director(d).Then(hostDirector(url.Hostname()))
    proxy.ModifyResponse = UpdateResponse
    http.Handle("/", proxy)
    log.Fatal(http.ListenAndServe(":9090", nil))
}