edge/pkg/bundle/zim/content_entry.go

package zim

import (
	"bytes"
	"encoding/binary"
	"io"
	"log"

	"github.com/pkg/errors"
)

type zimCompression uint8

const (
	zimCompressionNoneZeno      zimCompression = 0
	zimCompressionNone          zimCompression = 1
	zimCompressionNoneZLib      zimCompression = 2
	zimCompressionNoneBZip2     zimCompression = 3
	zimCompressionNoneXZ        zimCompression = 4
	zimCompressionNoneZStandard zimCompression = 5
)

type ContentEntry struct {
	*BaseEntry
	mimeType     string
	clusterIndex uint32
	blobIndex    uint32
}

func (e *ContentEntry) Reader() (io.Reader, error) {
	data := make([]byte, 8)

	startClusterPtrOffset := e.reader.clusterPtrPos + (uint64(e.clusterIndex) * 8)
	if err := e.reader.readRange(int64(startClusterPtrOffset), data); err != nil {
		return nil, errors.WithStack(err)
	}

	startClusterOffset, err := readUint64(data, binary.LittleEndian)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	endClusterPtrOffset := e.reader.clusterPtrPos + (uint64(e.clusterIndex+1) * 8)
	if err := e.reader.readRange(int64(endClusterPtrOffset), data); err != nil {
		return nil, errors.WithStack(err)
	}

	endClusterOffset, err := readUint64(data, binary.LittleEndian)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	data = make([]byte, 1)
	if err := e.reader.readRange(int64(startClusterPtrOffset), data); err != nil {
		return nil, errors.WithStack(err)
	}

	clusterHeader := uint8(data[0])

	compression := (clusterHeader << 4) >> 4
	extended := (clusterHeader<<3)>>7 == 1

	log.Printf("%08b %v %04b %d %d %d", clusterHeader, extended, compression, compression, startClusterOffset, endClusterOffset)

	switch compression {
	case uint8(zimCompressionNoneZeno):
		fallthrough
	case uint8(zimCompressionNone):

	case uint8(zimCompressionNoneXZ):

	case uint8(zimCompressionNoneZStandard):

	case uint8(zimCompressionNoneZLib):
		fallthrough
	case uint8(zimCompressionNoneBZip2):
		fallthrough
	default:
		// return nil, errors.Wrapf(ErrCompressionAlgorithmNotSupported, "unexpected compression algorithm '%d'", compression)

	}

	var internal []byte
	buff := bytes.NewBuffer(internal)

	// blob starts at offset, blob ends at offset
	// var bs, be uint32

	// // LZMA: 4, Zstandard: 5
	// if compression == 4 || compression == 5 {
	// 	var blob []byte
	// 	var ok bool
	// 	var dec io.ReadCloser
	// 	if blob, ok = blobLookup(); !ok {
	// 		b, err := a.z.bytesRangeAt(start+1, end+1)
	// 		if err != nil {
	// 			return nil, err
	// 		}
	// 		bbuf := bytes.NewBuffer(b)
	// 		switch compression {
	// 		case 5:
	// 			dec, err = NewZstdReader(bbuf)

	// 		case 4:
	// 			dec, err = NewXZReader(bbuf)
	// 		}
	// 		if err != nil {
	// 			return nil, err
	// 		}
	// 		defer dec.Close()
	// 		// the decoded chunk are around 1MB
	// 		b, err = ioutil.ReadAll(dec)
	// 		if err != nil {
	// 			return nil, err
	// 		}
	// 		blob = make([]byte, len(b))
	// 		copy(blob, b)
	// 		// TODO: 2 requests for the same blob could occure at the same time
	// 		bcache.Add(a.cluster, blob)
	// 	} else {
	// 		bi, ok := bcache.Get(a.cluster)
	// 		if !ok {
	// 			return nil, errors.New("not in cache anymore")
	// 		}
	// 		blob = bi.([]byte)
	// 	}

	// 	bs, err = readInt32(blob[a.blob*4:a.blob*4+4], nil)
	// 	if err != nil {
	// 		return nil, err
	// 	}
	// 	be, err = readInt32(blob[a.blob*4+4:a.blob*4+4+4], nil)
	// 	if err != nil {
	// 		return nil, err
	// 	}

	// 	// avoid retaining all the chunk
	// 	c := make([]byte, be-bs)
	// 	copy(c, blob[bs:be])
	// 	return c, nil

	// } else if compression == 0 || compression == 1 {
	// 	// uncompresssed
	// 	startPos := start + 1
	// 	blobOffset := uint64(a.blob * 4)

	// 	bs, err := readInt32(a.z.bytesRangeAt(startPos+blobOffset, startPos+blobOffset+4))
	// 	if err != nil {
	// 		return nil, err
	// 	}

	// 	be, err := readInt32(a.z.bytesRangeAt(startPos+blobOffset+4, startPos+blobOffset+4+4))
	// 	if err != nil {
	// 		return nil, err
	// 	}

	// 	return a.z.bytesRangeAt(startPos+uint64(bs), startPos+uint64(be))
	// }

	return buff, nil
}

func (e *ContentEntry) Redirect() (*ContentEntry, error) {
	return e, nil
}

func (r *Reader) parseContentEntry(offset int64, base *BaseEntry) (*ContentEntry, error) {
	entry := &ContentEntry{
		BaseEntry: base,
	}

	data := make([]byte, 2)
	if err := r.readRange(offset, data); err != nil {
		return nil, errors.WithStack(err)
	}

	mimeTypeIndex, err := readUint16(data, binary.LittleEndian)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	if mimeTypeIndex >= uint16(len(r.mimeTypes)) {
		return nil, errors.Errorf("mime type index '%d' greater than mime types length '%d'", mimeTypeIndex, len(r.mimeTypes))
	}

	entry.mimeType = r.mimeTypes[mimeTypeIndex]

	data = make([]byte, 1)
	if err := r.readRange(offset+3, data); err != nil {
		return nil, errors.WithStack(err)
	}

	entry.namespace = Namespace(data[0])

	data = make([]byte, 4)
	if err := r.readRange(offset+8, data); err != nil {
		return nil, errors.WithStack(err)
	}

	clusterIndex, err := readUint32(data, binary.LittleEndian)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	entry.clusterIndex = clusterIndex

	if err := r.readRange(offset+12, data); err != nil {
		return nil, errors.WithStack(err)
	}

	blobIndex, err := readUint32(data, binary.LittleEndian)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	entry.blobIndex = blobIndex

	url, read, err := r.readStringAt(offset + 16)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	entry.url = url

	title, _, err := r.readStringAt(offset + 16 + read)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	entry.title = title

	return entry, nil
}