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