Method WriteControl

conn.go:413–472

WriteControl writes a control message with the given deadline. The allowed message types are CloseMessage, PingMessage and PongMessage.

(messageType int, data []byte, deadline time.Time)

// WriteControl writes a control message with the given deadline. The allowed
// message types are CloseMessage, PingMessage and PongMessage.
func (c *Conn) WriteControl(messageType int, data []byte, deadline time.Time) error {
	if !isControl(messageType) {
		return errBadWriteOpCode
	}
	if len(data) > maxControlFramePayloadSize {
		return errInvalidControlFrame
	}

	b0 := byte(messageType) | finalBit
	b1 := byte(len(data))
	if !c.isServer {
		b1 |= maskBit
	}

	buf := make([]byte, 0, maxFrameHeaderSize+maxControlFramePayloadSize)
	buf = append(buf, b0, b1)

	if c.isServer {
		buf = append(buf, data...)
	} else {
		key := newMaskKey()
		buf = append(buf, key[:]...)
		buf = append(buf, data...)
		maskBytes(key, 0, buf[6:])
	}

	d := 1000 * time.Hour
	if !deadline.IsZero() {
		d = deadline.Sub(time.Now())
		if d < 0 {
			return errWriteTimeout
		}
	}

	timer := time.NewTimer(d)
	select {
	case <-c.mu:
		timer.Stop()
	case <-timer.C:
		return errWriteTimeout
	}
	defer func() { c.mu <- struct{}{} }()

	c.writeErrMu.Lock()
	err := c.writeErr
	c.writeErrMu.Unlock()
	if err != nil {
		return err
	}

	c.conn.SetWriteDeadline(deadline)
	_, err = c.conn.Write(buf)
	if err != nil {
		return c.writeFatal(err)
	}
	if messageType == CloseMessage {
		c.writeFatal(ErrCloseSent)
	}