在 Go 中编写一个简单的反向代理

转自：https://twin.sh/articles/43/writing-a-simple-reverse-proxy-in-go

由于 httputil 包的NewSingleHostReverseProxy功能，在 Go 中编写反向代理绝对是一种乐趣。

package main

import (
    "crypto/tls"
    "log"
    "net/http"
    "net/http/httputil"
    "net/url"
    "time"
)

var (
    targetUrl *url.URL
)

func main() {
    var err error
    targetUrl, err = url.Parse("https://url-to-direct/")
    if err != nil {
        panic(err)
    }

    handler := http.NewServeMux()
    handler.HandleFunc("/", proxyHandler)

    server := &http.Server{
        Addr:         ":8080",
        Handler:      handler,
        ReadTimeout:  15 * time.Second,
        WriteTimeout: 15 * time.Second,
        IdleTimeout:  15 * time.Second,
    }
    server.SetKeepAlivesEnabled(true)
    log.Printf("Listening on %s\n", server.Addr)
    log.Fatal(server.ListenAndServe())
}

func proxyHandler(writer http.ResponseWriter, request *http.Request) {
    http.DefaultTransport.(*http.Transport).TLSClientConfig = &tls.Config{InsecureSkipVerify: true}
    httputil.NewSingleHostReverseProxy(targetUrl).ServeHTTP(writer, request)
}

请注意，如果接收端有反向代理（即 Nginx、Traefik、Ambassador 等），您很可能还需要将请求主机覆盖到目标主机：

func proxyHandler(writer http.ResponseWriter, request *http.Request) {
    http.DefaultTransport.(*http.Transport).TLSClientConfig = &tls.Config{InsecureSkipVerify: true}
    request.Host = targetUrl.Host
    httputil.NewSingleHostReverseProxy(targetUrl).ServeHTTP(writer, request)
}

如果您想通过代理上的特定路径公开代理服务，而不是将其公开/，那么您可以执行以下操作：

handler.HandleFunc("/external-service/", externalServiceHandler)

// ...

func externalServiceHandler(writer http.ResponseWriter, request *http.Request) {
    http.DefaultTransport.(*http.Transport).TLSClientConfig = &tls.Config{InsecureSkipVerify: true}
    request.Host = targetUrl.Host
    request.URL.Path = strings.TrimPrefix(request.URL.Path, "/external-service")
    httputil.NewSingleHostReverseProxy(targetUrl).ServeHTTP(writer, request)
}

请记住，虽然如果您使用代理来访问 API，这不会导致任何问题，但如果您尝试代理到前端应用程序，则很可能会遇到奇怪的问题，因为绝对和相对路径。