/*
Copyright 2019 The Knative Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package websocket

import (
	"bufio"
	"fmt"
	"net"
	"net/http"
)

// HijackIfPossible calls Hijack() on the given http.ResponseWriter if it implements
// http.Hijacker interface, which is required for net/http/httputil/reverseproxy
// to handle connection upgrade/switching protocol.  Otherwise returns an error.
func HijackIfPossible(w http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
	hj, ok := w.(http.Hijacker)
	if !ok {
		return nil, nil, fmt.Errorf("wrapped writer of type %T can't be hijacked", w)
	}
	return hj.Hijack()
}