pre-Go1.12 websocket hijack+proxy

ws.go

	httpsServer := &http.Server{
		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			hj, isHJ := w.(http.Hijacker)
			if r.Header.Get("Upgrade") == "websocket" && isHJ {
				c, br, err := hj.Hijack()
				if err != nil {
					log.Printf("websocket websocket hijack: %v", err)
					http.Error(w, err.Error(), 500)
					return
				}
				defer c.Close()

				var be net.Conn
				if len(hostPorts) == 0 {
					backendHostPort := base.Host
					if !strings.Contains(backendHostPort, ":") {
						backendHostPort = net.JoinHostPort(backendHostPort, "443")
					}
					be, err = tls.DialWithDialer(dialer, "tcp", backendHostPort, tlsConfig)
				} else {
					for _, hostPort := range hostPorts {
						be, err = tls.DialWithDialer(dialer, "tcp", hostPort, tlsConfig)
						if err == nil {
							break
						}
					}
				}
				if err != nil {
					log.Printf("websocket Dial: %v", err)
					http.Error(w, err.Error(), 500)
					return
				}
				defer be.Close()
				if err := r.Write(be); err != nil {
					log.Printf("websocket backend write request: %v", err)
					http.Error(w, err.Error(), 500)
					return
				}
				errc := make(chan error, 1)
				go func() {
					n, err := io.Copy(be, br) // backend <- buffered reader
					if err != nil {
						err = fmt.Errorf("websocket: to copy backend from buffered reader: %v, %v", n, err)
					}
					errc <- err
				}()
				go func() {
					n, err := io.Copy(c, be) // raw conn <- backend
					if err != nil {
						err = fmt.Errorf("websocket: to raw conn from backend: %v, %v", n, err)
					}
					errc <- err
				}()
				if err := <-errc; err != nil {
					log.Print(err)
				}
				return
			}
			rp.ServeHTTP(w, r)
		}),
		TLSConfig: &tls.Config{
			NextProtos:     []string{"h2", "http/1.1"},
			GetCertificate: autoCertMan.GetCertificate,
		},
	}