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package main

import (
	"io"
	"net"
	"net/http"
	"net/url"
	"strings"
)

type WebSocketProxy struct {
	Director func(*http.Request)
}

func (p *WebSocketProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	hj, ok := w.(http.Hijacker)
	if !ok {
		http.Error(w, "Not a hijacker", http.StatusInternalServerError)
		return
	}

	conn, _, err := hj.Hijack()
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	defer conn.Close()

	p.Director(r)

	_, port, err := net.SplitHostPort(r.URL.Host)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	if port == "" {
		r.URL.Host += ":http"
	}

	d, err := net.Dial("tcp", r.URL.Host)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	defer d.Close()

	err = r.Write(d)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	errc := make(chan error, 2)
	cp := func(dst io.Writer, src io.Reader) {
		_, err := io.Copy(dst, src)
		errc <- err
	}
	go cp(d, conn)
	go cp(conn, d)
	<-errc
}

func NewWebSocketProxy(target *url.URL) *WebSocketProxy {
	director := func(req *http.Request) {
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
	}
	return &WebSocketProxy{Director: director}
}

func isWebsocket(req *http.Request) bool {
	conn := req.Header.Get("Connection")
	if strings.ToLower(conn) == "upgrade" {
		upgrade := req.Header.Get("Upgrade")
		return strings.ToLower(upgrade) == "websocket"
	}
	return false
}