Function readFrameHeader

frame.go:52–102

readFrameHeader reads a header from the reader. See https://tools.ietf.org/html/rfc6455#section-5.2.

(r *bufio.Reader, readBuf []byte)

// readFrameHeader reads a header from the reader.
// See https://tools.ietf.org/html/rfc6455#section-5.2.
func readFrameHeader(r *bufio.Reader, readBuf []byte) (h header, err error) {
	defer errd.Wrap(&err, "failed to read frame header")

	b, err := r.ReadByte()
	if err != nil {
		return header{}, err
	}

	h.fin = b&(1<<7) != 0
	h.rsv1 = b&(1<<6) != 0
	h.rsv2 = b&(1<<5) != 0
	h.rsv3 = b&(1<<4) != 0

	h.opcode = opcode(b & 0xf)

	b, err = r.ReadByte()
	if err != nil {
		return header{}, err
	}

	h.masked = b&(1<<7) != 0

	payloadLength := b &^ (1 << 7)
	switch {
	case payloadLength < 126:
		h.payloadLength = int64(payloadLength)
	case payloadLength == 126:
		_, err = io.ReadFull(r, readBuf[:2])
		h.payloadLength = int64(binary.BigEndian.Uint16(readBuf))
	case payloadLength == 127:
		_, err = io.ReadFull(r, readBuf)
		h.payloadLength = int64(binary.BigEndian.Uint64(readBuf))
	}
	if err != nil {
		return header{}, err
	}

	if h.payloadLength < 0 {
		return header{}, fmt.Errorf("received negative payload length: %v", h.payloadLength)
	}

	if h.masked {
		_, err = io.ReadFull(r, readBuf[:4])
		if err != nil {
			return header{}, err
		}
		h.maskKey = binary.LittleEndian.Uint32(readBuf)
	}

	return h, nil
}

// maxControlPayload is the maximum length of a control frame payload.
// See https://tools.ietf.org/html/rfc6455#section-5.5.