go get github.com/ouqiang/goproxy

package main
import (
    "net/http"
    "time"
    "github.com/ouqiang/goproxy"
)
func main() {
    proxy := goproxy.New()
    server := &http.Server{
        Addr:         ":8080",
        Handler:      proxy,
        ReadTimeout:  1 * time.Minute,
        WriteTimeout: 1 * time.Minute,
    }
    err := server.ListenAndServe()
    if err != nil {
        panic(err)
    }
}

curl -x localhost:8080 https://www.baidu.com

package main
import (
    "crypto/tls"
    "net/http"
    "sync"
    "time"
    "github.com/ouqiang/goproxy"
)
// 实现证书缓存接口
type Cache struct {
    m sync.Map
}
func (c *Cache) Set(host string, cert *tls.Certificate) {
    c.m.Store(host, cert)
}
func (c *Cache) Get(host string) *tls.Certificate {
    v, ok := c.m.Load(host)
    if !ok {
        return nil
    }
    return v.(*tls.Certificate)
}
func main() {
    proxy := goproxy.New(goproxy.WithDecryptHTTPS(&Cache{}))
    server := &http.Server{
        Addr:         ":8080",
        Handler:      proxy,
        ReadTimeout:  1 * time.Minute,
        WriteTimeout: 1 * time.Minute,
    }
    err := server.ListenAndServe()
    if err != nil {
        panic(err)
    }
}

type Delegate interface {
    // Connect 收到客户端连接
    Connect(ctx *Context, rw http.ResponseWriter)
    // Auth 代理身份认证
    Auth(ctx *Context, rw http.ResponseWriter)
    // BeforeRequest HTTP请求前 设置X-Forwarded-For, 修改Header、Body
    BeforeRequest(ctx *Context)
    // BeforeResponse 响应发送到客户端前, 修改Header、Body、Status Code
    BeforeResponse(ctx *Context, resp *http.Response, err error)
    // ParentProxy 上级代理
    ParentProxy(*http.Request) (*url.URL, error)
    // Finish 本次请求结束
    Finish(ctx *Context)
    // 记录错误信息
    ErrorLog(err error)
}

type EventHandler struct{}
func (e *EventHandler) Connect(ctx *goproxy.Context, rw http.ResponseWriter) {
    // 保存的数据可以在后面的回调方法中获取
    ctx.Data["req_id"] = "uuid"
    // 禁止访问某个域名
    if strings.Contains(ctx.Req.URL.Host, "example.com") {
        rw.WriteHeader(http.StatusForbidden)
        ctx.Abort()
        return
    }
}
func (e *EventHandler) Auth(ctx *goproxy.Context, rw http.ResponseWriter)  {
    // 身份验证
}
func (e *EventHandler) BeforeRequest(ctx *goproxy.Context) {
    // 修改header
    ctx.Req.Header.Add("X-Request-Id", ctx.Data["req_id"].(string))
    // 设置X-Forwarded-For
    if clientIP, _, err := net.SplitHostPort(ctx.Req.RemoteAddr); err == nil {
        if prior, ok := ctx.Req.Header["X-Forwarded-For"]; ok {
            clientIP = strings.Join(prior, ", ") + ", " + clientIP
        }
        ctx.Req.Header.Set("X-Forwarded-For", clientIP)
    }
    // 读取Body
    body, err := ioutil.ReadAll(ctx.Req.Body)
    if err != nil {
        // 错误处理
        return
    }
    // Request.Body只能读取一次, 读取后必须再放回去
    // Response.Body同理
    ctx.Req.Body = ioutil.NopCloser(bytes.NewReader(body))
}
func (e *EventHandler) BeforeResponse(ctx *goproxy.Context, resp *http.Response, err error) {
    if err != nil {
        return
    }
    // 修改response
}
// 设置上级代理
func (e *EventHandler) ParentProxy(req *http.Request) (*url.URL, error) {
    return url.Parse("http://localhost:1087")
}
func (e *EventHandler) Finish(ctx *goproxy.Context) {
    fmt.Printf("请求结束 URL:%s\n", ctx.Req.URL)
}
// 记录错误日志
func (e *EventHandler) ErrorLog(err error) {
    log.Println(err)
}
func main() {
    proxy := goproxy.New(goproxy.WithDelegate(&EventHandler{}))
    server := &http.Server{
        Addr:         ":8080",
        Handler:      proxy,
        ReadTimeout:  1 * time.Minute,
        WriteTimeout: 1 * time.Minute,
    }
    err := server.ListenAndServe()
    if err != nil {
        panic(err)
    }
}