edge/pkg/bundle/zim/uncompressed_blob_reader.go

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2023-10-11 11:18:32 +02:00
package zim
import (
"io"
"sync"
"github.com/pkg/errors"
)
type UncompressedBlobReader struct {
reader *Reader
blobStartOffset uint64
blobEndOffset uint64
blobSize int
readOffset int
blobData []byte
loadBlobOnce sync.Once
loadBlobErr error
}
// Size implements BlobReader.
func (r *UncompressedBlobReader) Size() (int64, error) {
return int64(r.blobEndOffset - r.blobStartOffset), nil
}
// Close implements io.ReadCloser.
func (r *UncompressedBlobReader) Close() error {
clear(r.blobData)
return nil
}
// Read implements io.ReadCloser.
func (r *UncompressedBlobReader) Read(p []byte) (n int, err error) {
blobData, err := r.loadBlob()
if err != nil {
return 0, errors.WithStack(err)
}
chunkLength := len(p)
remaining := int(len(blobData) - r.readOffset)
if chunkLength > remaining {
chunkLength = remaining
}
chunk := blobData[r.readOffset : r.readOffset+chunkLength]
r.readOffset += chunkLength
copy(p, chunk)
if chunkLength == remaining {
return chunkLength, io.EOF
}
return chunkLength, nil
}
func (r *UncompressedBlobReader) loadBlob() ([]byte, error) {
r.loadBlobOnce.Do(func() {
data := make([]byte, r.blobEndOffset-r.blobStartOffset)
err := r.reader.readRange(int64(r.blobStartOffset), data)
if err != nil {
r.loadBlobErr = errors.WithStack(err)
return
}
r.blobData = data
})
if r.loadBlobErr != nil {
return nil, errors.WithStack(r.loadBlobErr)
}
return r.blobData, nil
}
func NewUncompressedBlobReader(reader *Reader, blobStartOffset, blobEndOffset uint64, blobSize int) *UncompressedBlobReader {
return &UncompressedBlobReader{
reader: reader,
blobStartOffset: blobStartOffset,
blobEndOffset: blobEndOffset,
blobSize: blobSize,
readOffset: 0,
}
}
var _ BlobReader = &UncompressedBlobReader{}