去 httputil.ReverseProxy 不覆盖主机头

Question

我基本上是在尝试编写一个反向代理服务器，以便当我 curl localhost:8080/get 时，它将请求代理到 https://nghttp2.org/httpbin/get。

注意：上面列出的https://nghttp2.org/httpbin/get 服务是http/2。但是这种行为也会发生在 http/1 上，例如 https://httpbin.org/get。

我为此使用httputil.ReverseProxy，并且我正在重写URL，同时自定义Host 标头以不将localhost:8080 泄漏到实际后端。

但是，无论我在标头上设置多少次，请求仍然会以Host: localhost:8080 到达后端。同样，我使用mitmproxy 窥探请求，看起来net/http.Client 将:authority 伪标头设置为localhost:8080

这是我的源代码：

package main

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

func main() {
    proxy := &httputil.ReverseProxy{
        Transport: roundTripper(rt),
        Director: func(req *http.Request) {
            req.URL.Scheme = "https"
            req.URL.Host = "nghttp2.org"
            req.URL.Path = "/httpbin" + req.URL.Path
            req.Header.Set("Host", "nghttp2.org") // <--- I set it here first
        },
    }
    log.Fatal(http.ListenAndServe(":8080", proxy))
}

func rt(req *http.Request) (*http.Response, error) {
    log.Printf("request received. url=%s", req.URL)
    req.Header.Set("Host", "nghttp2.org") // <--- I set it here as well
    defer log.Printf("request complete. url=%s", req.URL)

    return http.DefaultTransport.RoundTrip(req)
}


// roundTripper makes func signature a http.RoundTripper
type roundTripper func(*http.Request) (*http.Response, error)
func (f roundTripper) RoundTrip(req *http.Request) (*http.Response, error) { return f(req) }

当我查询curl localhost:8080/get 时，请求被代理到https://nghttp2.org/httpbin/get。回显的响应清楚地表明，我设置 Host 标头的指令没有做任何事情：

{
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip",
    "Host": "localhost:8080",
    "User-Agent": "curl/7.54.0"
  },
  "origin": "2601:602:9c02:16c2:fca3:aaab:3914:4a71",
  "url": "https://localhost:8080/httpbin/get"
}

mitmproxy snooping 还清楚地表明该请求是在 :authority 伪标头设置为 localhost:8080 的情况下发出的：

Answer 1

来自http.Requestdocs：

        // For server requests, Host specifies the host on which the URL
        // is sought. Per RFC 7230, section 5.4, this is either the value
        // of the "Host" header or the host name given in the URL itself.
        // It may be of the form "host:port". For international domain
        // names, Host may be in Punycode or Unicode form. Use
        // golang.org/x/net/idna to convert it to either format if
        // needed.
        // To prevent DNS rebinding attacks, server Handlers should
        // validate that the Host header has a value for which the
        // Handler considers itself authoritative. The included
        // ServeMux supports patterns registered to particular host
        // names and thus protects its registered Handlers.
        //
        // For client requests, Host optionally overrides the Host
        // header to send. If empty, the Request.Write method uses
        // the value of URL.Host. Host may contain an international
        // domain name.
        Host string

所以URL.Host 的值仅在request.Host 为空的情况下使用，情况并非如此。设置request.Host 应该可以解决问题：

req.Host = "nghttp2.org"

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