func generateMaskingKey() (maskingKey []byte, err error) {
	maskingKey = make([]byte, 4)
	if _, err = io.ReadFull(rand.Reader, maskingKey); err != nil {
		return
	}
	return
}
generateMaskingKey generates a masking key for a frame.
package websocket
import (
	"bufio"
	"bytes"
	"crypto/rand"
	"crypto/sha1"
	"encoding/base64"
	"encoding/binary"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"strings"
)
const (
	websocketGUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
	closeStatusNormal            = 1000
	closeStatusGoingAway         = 1001
	closeStatusProtocolError     = 1002
	closeStatusUnsupportedData   = 1003
	closeStatusFrameTooLarge     = 1004
	closeStatusNoStatusRcvd      = 1005
	closeStatusAbnormalClosure   = 1006
	closeStatusBadMessageData    = 1007
	closeStatusPolicyViolation   = 1008
	closeStatusTooBigData        = 1009
	closeStatusExtensionMismatch = 1010
	maxControlFramePayloadLength = 125
)
var (
	ErrBadMaskingKey         = &ProtocolError{"bad masking key"}
	ErrBadPongMessage        = &ProtocolError{"bad pong message"}
	ErrBadClosingStatus      = &ProtocolError{"bad closing status"}
	ErrUnsupportedExtensions = &ProtocolError{"unsupported extensions"}
	ErrNotImplemented        = &ProtocolError{"not implemented"}
	handshakeHeader = map[string]bool{
		"Host":                   true,
		"Upgrade":                true,
		"Connection":             true,
		"Sec-Websocket-Key":      true,
		"Sec-Websocket-Origin":   true,
		"Sec-Websocket-Version":  true,
		"Sec-Websocket-Protocol": true,
		"Sec-Websocket-Accept":   true,
	}
)
type hybiFrameHeader struct {
	Fin        bool
	Rsv        [3]bool
	OpCode     byte
	Length     int64
	MaskingKey []byte
	data *bytes.Buffer
}
type hybiFrameReader struct {
	reader io.Reader
	header hybiFrameHeader
	pos    int64
	length int
}
func (frame *hybiFrameReader) Read(msg []byte) (n int, err error) {
	n, err = frame.reader.Read(msg)
	if err != nil {
		return 0, err
	}
	if frame.header.MaskingKey != nil {
		for i := 0; i < n; i++ {
			msg[i] = msg[i] ^ frame.header.MaskingKey[frame.pos%4]
			frame.pos++
		}
	}
	return n, err
}
func (frame *hybiFrameReader) PayloadType() byte { return frame.header.OpCode }
func (frame *hybiFrameReader) HeaderReader() io.Reader {
	if frame.header.data == nil {
		return nil
	}
	if frame.header.data.Len() == 0 {
		return nil
	}
	return frame.header.data
}
func (frame *hybiFrameReader) TrailerReader() io.Reader { return nil }
func (frame *hybiFrameReader) Len() (n int) { return frame.length }
type hybiFrameReaderFactory struct {
	*bufio.Reader
}
func (buf hybiFrameReaderFactory) NewFrameReader() (frame frameReader, err error) {
	hybiFrame := new(hybiFrameReader)
	frame = hybiFrame
	var header []byte
	var b byte
	b, err = buf.ReadByte()
	if err != nil {
		return
	}
	header = append(header, b)
	hybiFrame.header.Fin = ((header[0] >> 7) & 1) != 0
	for i := 0; i < 3; i++ {
		j := uint(6 - i)
		hybiFrame.header.Rsv[i] = ((header[0] >> j) & 1) != 0
	}
	hybiFrame.header.OpCode = header[0] & 0x0f
	b, err = buf.ReadByte()
	if err != nil {
		return
	}
	header = append(header, b)
	mask := (b & 0x80) != 0
	b &= 0x7f
	lengthFields := 0
	switch {
	case b <= 125:  
		hybiFrame.header.Length = int64(b)
	case b == 126:  
		lengthFields = 2
	case b == 127:  
		lengthFields = 8
	}
	for i := 0; i < lengthFields; i++ {
		b, err = buf.ReadByte()
		if err != nil {
			return
		}
		if lengthFields == 8 && i == 0 {  
			b &= 0x7f
		}
		header = append(header, b)
		hybiFrame.header.Length = hybiFrame.header.Length*256 + int64(b)
	}
	if mask {
		for i := 0; i < 4; i++ {
			b, err = buf.ReadByte()
			if err != nil {
				return
			}
			header = append(header, b)
			hybiFrame.header.MaskingKey = append(hybiFrame.header.MaskingKey, b)
		}
	}
	hybiFrame.reader = io.LimitReader(buf.Reader, hybiFrame.header.Length)
	hybiFrame.header.data = bytes.NewBuffer(header)
	hybiFrame.length = len(header) + int(hybiFrame.header.Length)
	return
}
type hybiFrameWriter struct {
	writer *bufio.Writer
	header *hybiFrameHeader
}
func (frame *hybiFrameWriter) Write(msg []byte) (n int, err error) {
	var header []byte
	var b byte
	if frame.header.Fin {
		b |= 0x80
	}
	for i := 0; i < 3; i++ {
		if frame.header.Rsv[i] {
			j := uint(6 - i)
			b |= 1 << j
		}
	}
	b |= frame.header.OpCode
	header = append(header, b)
	if frame.header.MaskingKey != nil {
		b = 0x80
	} else {
		b = 0
	}
	lengthFields := 0
	length := len(msg)
	switch {
	case length <= 125:
		b |= byte(length)
	case length < 65536:
		b |= 126
		lengthFields = 2
	default:
		b |= 127
		lengthFields = 8
	}
	header = append(header, b)
	for i := 0; i < lengthFields; i++ {
		j := uint((lengthFields - i - 1) * 8)
		b = byte((length >> j) & 0xff)
		header = append(header, b)
	}
	if frame.header.MaskingKey != nil {
		if len(frame.header.MaskingKey) != 4 {
			return 0, ErrBadMaskingKey
		}
		header = append(header, frame.header.MaskingKey...)
		frame.writer.Write(header)
		data := make([]byte, length)
		for i := range data {
			data[i] = msg[i] ^ frame.header.MaskingKey[i%4]
		}
		frame.writer.Write(data)
		err = frame.writer.Flush()
		return length, err
	}
	frame.writer.Write(header)
	frame.writer.Write(msg)
	err = frame.writer.Flush()
	return length, err
}
func (frame *hybiFrameWriter) Close() error { return nil }
type hybiFrameWriterFactory struct {
	*bufio.Writer
	needMaskingKey bool
}
func (buf hybiFrameWriterFactory) NewFrameWriter(payloadType byte) (frame frameWriter, err error) {
	frameHeader := &hybiFrameHeader{Fin: true, OpCode: payloadType}
	if buf.needMaskingKey {
		frameHeader.MaskingKey, err = generateMaskingKey()
		if err != nil {
			return nil, err
		}
	}
	return &hybiFrameWriter{writer: buf.Writer, header: frameHeader}, nil
}
type hybiFrameHandler struct {
	conn        *Conn
	payloadType byte
}
func (handler *hybiFrameHandler) HandleFrame(frame frameReader) (frameReader, error) {
	if handler.conn.IsServerConn() {
		if frame.(*hybiFrameReader).header.MaskingKey == nil {
			handler.WriteClose(closeStatusProtocolError)
			return nil, io.EOF
		}
	} else {
		if frame.(*hybiFrameReader).header.MaskingKey != nil {
			handler.WriteClose(closeStatusProtocolError)
			return nil, io.EOF
		}
	}
	if header := frame.HeaderReader(); header != nil {
		io.Copy(ioutil.Discard, header)
	}
	switch frame.PayloadType() {
	case ContinuationFrame:
		frame.(*hybiFrameReader).header.OpCode = handler.payloadType
	case TextFrame, BinaryFrame:
		handler.payloadType = frame.PayloadType()
	case CloseFrame:
		return nil, io.EOF
	case PingFrame, PongFrame:
		b := make([]byte, maxControlFramePayloadLength)
		n, err := io.ReadFull(frame, b)
		if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
			return nil, err
		}
		io.Copy(ioutil.Discard, frame)
		if frame.PayloadType() == PingFrame {
			if _, err := handler.WritePong(b[:n]); err != nil {
				return nil, err
			}
		}
		return nil, nil
	}
	return frame, nil
}
func (handler *hybiFrameHandler) WriteClose(status int) (err error) {
	handler.conn.wio.Lock()
	defer handler.conn.wio.Unlock()
	w, err := handler.conn.frameWriterFactory.NewFrameWriter(CloseFrame)
	if err != nil {
		return err
	}
	msg := make([]byte, 2)
	binary.BigEndian.PutUint16(msg, uint16(status))
	_, err = w.Write(msg)
	w.Close()
	return err
}
func (handler *hybiFrameHandler) WritePong(msg []byte) (n int, err error) {
	handler.conn.wio.Lock()
	defer handler.conn.wio.Unlock()
	w, err := handler.conn.frameWriterFactory.NewFrameWriter(PongFrame)
	if err != nil {
		return 0, err
	}
	n, err = w.Write(msg)
	w.Close()
	return n, err
}
func newHybiConn(config *Config, buf *bufio.ReadWriter, rwc io.ReadWriteCloser, request *http.Request) *Conn {
	if buf == nil {
		br := bufio.NewReader(rwc)
		bw := bufio.NewWriter(rwc)
		buf = bufio.NewReadWriter(br, bw)
	}
	ws := &Conn{config: config, request: request, buf: buf, rwc: rwc,
		frameReaderFactory: hybiFrameReaderFactory{buf.Reader},
		frameWriterFactory: hybiFrameWriterFactory{
			buf.Writer, request == nil},
		PayloadType:        TextFrame,
		defaultCloseStatus: closeStatusNormal}
	ws.frameHandler = &hybiFrameHandler{conn: ws}
	return ws
}