Go 如何调试httputil.NewSingleHostReverseProxy

问题：

我正转向一个HTTPS地址

我想知道为什么要搬走

req.Host=req.URL.Host

导致它失败。而不是返回

{“code”：“OBRI.FR.Request.Invalid”，“Id”：“c37baec213dd1227”，“Message”：“解析请求参数时出错”，“Errors”：[{“ErrorCode”：“UK.OBIE.Header.Missing”，“Message”：“Missing Request Header'x-fapi-financial-Id'用于字符串类型的方法参数”，“Url”：”"https://docs.ob.forgerock.financial/errors#UK.OBIE.Header.Missing“}]}

它返回一个

404

我想跟踪代理返回的调用 当我取消注释行

req.Host=req.URL.Host

时，httputil.NewSingleHostReverseProxy正在生成

提出这样的请求：

$ curl http://localhost:8989/open-banking/v2.0/accounts

下面的代码（

main.go

）：

---

将proxy.Transport字段设置为在委托给默认传输之前转储请求的实现：

package main

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

type DebugTransport struct{}

func (DebugTransport) RoundTrip(r *http.Request) (*http.Response, error) {
        b, err := httputil.DumpRequestOut(r, false)
        if err != nil {
                return nil, err
        }
        fmt.Println(string(b))
        return http.DefaultTransport.RoundTrip(r)
}

func main() {
        target, _ := url.Parse("https://example.com:443")
        log.Printf("forwarding to -> %s\n", target)

        proxy := httputil.NewSingleHostReverseProxy(target)

        proxy.Transport = DebugTransport{}

        http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
                req.Host = req.URL.Host

                proxy.ServeHTTP(w, req)
        })

        log.Fatal(http.ListenAndServe(":8989", nil))
}

此程序的输出如下所示：

2018/10/26 13:06:35 forwarding to -> https://example.com:443
GET / HTTP/1.1
Host: example.com:443
User-Agent: HTTPie/0.9.4
Accept: */*
Accept-Encoding: gzip, deflate
X-Forwarded-For: 127.0.0.1

或者，在删除请求主机分配后：

2018/10/26 13:06:54 forwarding to -> https://example.com:443
GET / HTTP/1.1
Host: localhost:8989
User-Agent: HTTPie/0.9.4
Accept: */*
Accept-Encoding: gzip, deflate
X-Forwarded-For: 127.0.0.1

由于Web服务器经常使用主机头将请求路由到正确的虚拟主机或后端服务器，因此，意外的主机头（“上例中的localhost:8989”）会导致服务器以404响应是有道理的

使用httputil.ReverseProxy设置主机头通常通过

Director

功能完成：

    target, err := url.Parse("https://example.com:443")
    if err != nil {
            log.Fatal(err)
    }
    log.Printf("forwarding to -> %s\n", target)

    proxy := httputil.NewSingleHostReverseProxy(target)

    d := proxy.Director
    proxy.Director = func(r *http.Request) {
            d(r) // call default director

            r.Host = target.Host // set Host header as expected by target
    }

    log.Fatal(http.ListenAndServe(":8989", proxy))

    target, err := url.Parse("https://example.com:443")
    if err != nil {
            log.Fatal(err)
    }
    log.Printf("forwarding to -> %s\n", target)

    proxy := httputil.NewSingleHostReverseProxy(target)

    d := proxy.Director
    proxy.Director = func(r *http.Request) {
            d(r) // call default director

            r.Host = target.Host // set Host header as expected by target
    }

    log.Fatal(http.ListenAndServe(":8989", proxy))