Proxy Server / Golang (2)

Go言語のProxyServerによるBodyデータの変更は下記でも試しましたが、それからかなり時が経っていることから最近の環境で新たに試してみました。（今回はHeaderの追加もしています）

Proxy Server / Golang

package main

import(
        "io"
        "log"
        "net/url"
        "net/http"
        "net/http/httputil"
        "fmt"
        "strings"
)
func main() {
        remote, err := url.Parse("http://decode.red")
        if err != nil {
                panic(err)
        }

        handler := func(p *httputil.ReverseProxy) func(http.ResponseWriter, *http.Request) {

                return func(w http.ResponseWriter, r *http.Request) {

                        log.Println(r.URL)
                        r.Host = remote.Host
                        
                        b, e := httputil.DumpRequest(r, false) // true : body dump
                        if e != nil {
                            fmt.Println(e)
                        } else {
                            fmt.Println(string(b))
                        }
                        w.Header().Set("X-Test-Header", "Header Value")
                        mod := func(res *http.Response) error {

                                dump, err := httputil.DumpResponse(res, true)
                                if err != nil {
                                        log.Fatal(err)
                                }
                                fmt.Printf("%s", string(dump))
                                
                                b, err := io.ReadAll(res.Body)
                                if err != nil {
                                        log.Fatal(err)
                                }
                                s := string(b)
                                s = strings.Replace(s, "</body>", "<center>END!<center></body>", 1)
                                io.WriteString(w, s)

                                return nil
                        }
                        p.ModifyResponse = mod
                        p.ServeHTTP(w, r)
                }
        }
        proxy := httputil.NewSingleHostReverseProxy(remote)

        http.HandleFunc("/", handler(proxy))
        err = http.ListenAndServe(":8081", nil)
        if err != nil {
                panic(err)
        }
}

package main

import(

"io"

"log"

"net/url"

"net/http"

"net/http/httputil"

"fmt"

"strings"

)

func main() {

remote, err := url.Parse("http://decode.red")

if err != nil {

panic(err)

}

handler := func(p *httputil.ReverseProxy) func(http.ResponseWriter, *http.Request) {

return func(w http.ResponseWriter, r *http.Request) {

log.Println(r.URL)

r.Host = remote.Host

b, e := httputil.DumpRequest(r, false) // true : body dump

if e != nil {

fmt.Println(e)

} else {

fmt.Println(string(b))

}

w.Header().Set("X-Test-Header", "Header Value")

mod := func(res *http.Response) error {

dump, err := httputil.DumpResponse(res, true)

if err != nil {

log.Fatal(err)

}

fmt.Printf("%s", string(dump))

b, err := io.ReadAll(res.Body)

if err != nil {

log.Fatal(err)

}

s := string(b)

s = strings.Replace(s, "</body>", "<center>END!<center></body>", 1)

io.WriteString(w, s)

return nil

}

p.ModifyResponse = mod

p.ServeHTTP(w, r)

}

proxy := httputil.NewSingleHostReverseProxy(remote)

http.HandleFunc("/", handler(proxy))

err = http.ListenAndServe(":8081", nil)

if err != nil {

panic(err)

}

サーバ起動

go run main.go

実行結果

$ curl -D - localhost:8081
HTTP/1.1 200 OK
X-Test-Header: Header Value
Date: Sun, 10 Sep 2023 07:56:22 GMT
Content-Length: 1565
Content-Type: text/html; charset=utf-8

<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8" />
<title>IT教育サポート/ DECODE Education</title>
</head>
<body style="font-family:sans-serif; font-size:12px">
<center>
...(中略)...
<div  style="font-family:san-serif; font-size:14px; font-weight:bold; color:gray; text-align:right">
&copy; 2014-2023 DECODE Education
</dir>
<br>
<center>END!<center></body>
</html>

$ curl -D - localhost:8081

HTTP/1.1 200 OK

X-Test-Header: Header Value

Date: Sun, 10 Sep 2023 07:56:22 GMT

Content-Length: 1565

Content-Type: text/html; charset=utf-8

<!DOCTYPE html>

<head>

<title>IT教育サポート/ DECODE Education</title>

</head>

...(中略)...

</dir>

<br>

</html>

ここでBodyの文字列置換部分(io.ReadAll から io.WriteString まで)をコメントアウトしてもう一度実行します。

$ curl -D - localhost:8081
HTTP/1.1 200 OK
Accept-Ranges: bytes
Content-Length: 1545
Content-Type: text/html
Date: Sun, 10 Sep 2023 08:12:00 GMT
Etag: "609-60121eec99200"
Last-Modified: Sun, 23 Jul 2023 06:51:52 GMT
Server: nginx
X-Test-Header: Header Value

<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8" />
<title>IT教育サポート/ DECODE Education</title>
</head>
<body style="font-family:sans-serif; font-size:12px">
<center>
...(中略)...
<div  style="font-family:san-serif; font-size:18px; font-weight:bold; color:gray; text-align:right">
</div>
<div  style="font-family:san-serif; font-size:14px; font-weight:bold; color:gray; text-align:right">
&copy; 2014-2023 DECODE Education
</dir>
<br>
</body>
</html>

$ curl -D - localhost:8081

HTTP/1.1 200 OK

Accept-Ranges: bytes

Content-Length: 1545

Content-Type: text/html

Date: Sun, 10 Sep 2023 08:12:00 GMT

Etag: "609-60121eec99200"

Last-Modified: Sun, 23 Jul 2023 06:51:52 GMT

Server: nginx

X-Test-Header: Header Value

<!DOCTYPE html>

<head>

<title>IT教育サポート/ DECODE Education</title>

</head>

...(中略)...

</div>

</dir>

<br>

</body>

</html>

headerの部分がかわりました。ハンドラーの中なのでそのやり方に沿ってやる必要がありそうです。
（最初はまったのでメモ）

参考）
https://gist.github.com/JalfResi/6287706
https://qiita.com/convto/items/64e8f090198a4cf7a4fc
https://qiita.com/hayabusa_3288/items/9fd2da8bc3bd6310d576
https://www.zono.dev/post/2021-01-03-http-dumpresponse-dumprequest-golang/
https://zenn.dev/hsaki/books/golang-httpserver-internal/viewer/httphandler#http.response%E5%9E%8B