segment_header.go

package dvb

import "encoding/binary"

const (
	segmentHeaderSize = 6
)

// SegmentHeader represents common fields of each segment
type SegmentHeader struct {
	// This field shall contain the value '0000 1111' (0x0F)
	SyncByte uint8

	// This field shall contain the value 0x13, as listed in table 7 (0x13)
	SegmentType uint8

	// The page_id identifies the subtitle service of the data contained in this subtitling_segment. Segments with a
	// page_id value signalled in the subtitling descriptor as the composition page id, carry subtitling data specific for one
	// subtitle service. Accordingly, segments with the page_id signalled in the subtitling descriptor as the ancillary page id,
	// carry data that may be shared by multiple subtitle services.
	PageID uint16

	// This field shall indicate the number of bytes contained in the segment following the segment_length field
	SegmentLength uint16
}

func (h SegmentHeader) MarshalSize() int {
	return segmentHeaderSize
}

func (h SegmentHeader) Marshal() ([]byte, error) {
	if h.SyncByte != segmentSyncByte {
		return nil, ErrIncorrectSyncByte
	}
	buf := make([]byte, h.MarshalSize())
	copy(buf[0:], []uint8{h.SyncByte, h.SegmentType})
	copy(buf[2:], U16toU8LE(h.PageID))
	copy(buf[4:], U16toU8LE(h.SegmentLength))
	return buf, nil
}

// nolint makezero
func (h SegmentHeader) MarshalSlow() ([]byte, error) {
	if h.SyncByte != segmentSyncByte {
		return nil, ErrIncorrectSyncByte
	}
	buf := make([]byte, h.MarshalSize())
	buf = append(buf, []byte{h.SyncByte, h.SegmentType}...)
	buf = append(buf, U16toU8LE(h.PageID)...)
	buf = append(buf, U16toU8LE(h.SegmentLength)...)
	return buf, nil
}

func (h *SegmentHeader) Unmarshal(buf []byte) error {
	if buf == nil {
		return ErrNilBuffer
	}

	if len(buf) < segmentHeaderSize {
		return ErrShortBuffer
	}

	if buf[0] != segmentSyncByte {
		return ErrIncorrectSyncByte
	}
	h.SyncByte = buf[0]
	h.SegmentType = buf[1]
	h.PageID = binary.LittleEndian.Uint16(buf[2:4])

	// NOTE: have an exception for one type of segment
	h.SegmentLength = binary.BigEndian.Uint16(buf[4:6])

	return nil
}

func createSegmentHeader(segmentType uint8, pageID uint16, segmentLength uint16) SegmentHeader {
	return SegmentHeader{
		SyncByte:      segmentSyncByte,
		SegmentType:   segmentType,
		PageID:        pageID,
		SegmentLength: segmentLength,
	}
}