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250 lines
7.1 KiB
Go
250 lines
7.1 KiB
Go
package chunkedreader
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import (
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"context"
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"errors"
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"io"
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"sync"
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"github.com/rclone/rclone/fs"
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"github.com/rclone/rclone/fs/hash"
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)
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// io related errors returned by ChunkedReader
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var (
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ErrorFileClosed = errors.New("file already closed")
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ErrorInvalidSeek = errors.New("invalid seek position")
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)
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// ChunkedReader is a reader for a Object with the possibility
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// of reading the source in chunks of given size
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//
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// A initialChunkSize of <= 0 will disable chunked reading.
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type ChunkedReader struct {
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ctx context.Context
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mu sync.Mutex // protects following fields
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o fs.Object // source to read from
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rc io.ReadCloser // reader for the current open chunk
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offset int64 // offset the next Read will start. -1 forces a reopen of o
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chunkOffset int64 // beginning of the current or next chunk
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chunkSize int64 // length of the current or next chunk. -1 will open o from chunkOffset to the end
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initialChunkSize int64 // default chunkSize after the chunk specified by RangeSeek is complete
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maxChunkSize int64 // consecutive read chunks will double in size until reached. -1 means no limit
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customChunkSize bool // is the current chunkSize set by RangeSeek?
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closed bool // has Close been called?
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}
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// New returns a ChunkedReader for the Object.
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//
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// A initialChunkSize of <= 0 will disable chunked reading.
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// If maxChunkSize is greater than initialChunkSize, the chunk size will be
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// doubled after each chunk read with a maximun of maxChunkSize.
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// A Seek or RangeSeek will reset the chunk size to it's initial value
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func New(ctx context.Context, o fs.Object, initialChunkSize int64, maxChunkSize int64) *ChunkedReader {
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if initialChunkSize <= 0 {
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initialChunkSize = -1
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}
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if maxChunkSize != -1 && maxChunkSize < initialChunkSize {
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maxChunkSize = initialChunkSize
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}
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return &ChunkedReader{
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ctx: ctx,
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o: o,
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offset: -1,
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chunkSize: initialChunkSize,
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initialChunkSize: initialChunkSize,
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maxChunkSize: maxChunkSize,
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}
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}
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// Read from the file - for details see io.Reader
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func (cr *ChunkedReader) Read(p []byte) (n int, err error) {
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cr.mu.Lock()
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defer cr.mu.Unlock()
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if cr.closed {
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return 0, ErrorFileClosed
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}
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for reqSize := int64(len(p)); reqSize > 0; reqSize = int64(len(p)) {
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// the current chunk boundary. valid only when chunkSize > 0
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chunkEnd := cr.chunkOffset + cr.chunkSize
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fs.Debugf(cr.o, "ChunkedReader.Read at %d length %d chunkOffset %d chunkSize %d", cr.offset, reqSize, cr.chunkOffset, cr.chunkSize)
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switch {
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case cr.chunkSize > 0 && cr.offset == chunkEnd: // last chunk read completely
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cr.chunkOffset = cr.offset
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if cr.customChunkSize { // last chunkSize was set by RangeSeek
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cr.customChunkSize = false
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cr.chunkSize = cr.initialChunkSize
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} else {
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cr.chunkSize *= 2
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if cr.chunkSize > cr.maxChunkSize && cr.maxChunkSize != -1 {
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cr.chunkSize = cr.maxChunkSize
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}
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}
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// recalculate the chunk boundary. valid only when chunkSize > 0
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chunkEnd = cr.chunkOffset + cr.chunkSize
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fallthrough
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case cr.offset == -1: // first Read or Read after RangeSeek
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err = cr.openRange()
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if err != nil {
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return
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}
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}
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var buf []byte
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chunkRest := chunkEnd - cr.offset
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// limit read to chunk boundaries if chunkSize > 0
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if reqSize > chunkRest && cr.chunkSize > 0 {
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buf, p = p[0:chunkRest], p[chunkRest:]
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} else {
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buf, p = p, nil
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}
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var rn int
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rn, err = io.ReadFull(cr.rc, buf)
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n += rn
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cr.offset += int64(rn)
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if err != nil {
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if err == io.ErrUnexpectedEOF {
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err = io.EOF
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}
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return
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}
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}
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return n, nil
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}
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// Close the file - for details see io.Closer
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//
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// All methods on ChunkedReader will return ErrorFileClosed afterwards
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func (cr *ChunkedReader) Close() error {
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cr.mu.Lock()
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defer cr.mu.Unlock()
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if cr.closed {
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return ErrorFileClosed
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}
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cr.closed = true
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return cr.resetReader(nil, 0)
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}
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// Seek the file - for details see io.Seeker
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func (cr *ChunkedReader) Seek(offset int64, whence int) (int64, error) {
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return cr.RangeSeek(context.TODO(), offset, whence, -1)
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}
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// RangeSeek the file - for details see RangeSeeker
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//
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// The specified length will only apply to the next chunk opened.
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// RangeSeek will not reopen the source until Read is called.
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func (cr *ChunkedReader) RangeSeek(ctx context.Context, offset int64, whence int, length int64) (int64, error) {
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cr.mu.Lock()
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defer cr.mu.Unlock()
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fs.Debugf(cr.o, "ChunkedReader.RangeSeek from %d to %d length %d", cr.offset, offset, length)
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if cr.closed {
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return 0, ErrorFileClosed
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}
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size := cr.o.Size()
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switch whence {
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case io.SeekStart:
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cr.offset = 0
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case io.SeekEnd:
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cr.offset = size
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}
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// set the new chunk start
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cr.chunkOffset = cr.offset + offset
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// force reopen on next Read
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cr.offset = -1
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if length > 0 {
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cr.customChunkSize = true
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cr.chunkSize = length
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} else {
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cr.chunkSize = cr.initialChunkSize
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}
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if cr.chunkOffset < 0 || cr.chunkOffset >= size {
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cr.chunkOffset = 0
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return 0, ErrorInvalidSeek
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}
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return cr.chunkOffset, nil
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}
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// Open forces the connection to be opened
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func (cr *ChunkedReader) Open() (*ChunkedReader, error) {
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cr.mu.Lock()
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defer cr.mu.Unlock()
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if cr.rc != nil && cr.offset != -1 {
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return cr, nil
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}
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return cr, cr.openRange()
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}
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// openRange will open the source Object with the current chunk range
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//
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// If the current open reader implements RangeSeeker, it is tried first.
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// When RangeSeek fails, o.Open with a RangeOption is used.
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//
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// A length <= 0 will request till the end of the file
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func (cr *ChunkedReader) openRange() error {
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offset, length := cr.chunkOffset, cr.chunkSize
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fs.Debugf(cr.o, "ChunkedReader.openRange at %d length %d", offset, length)
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if cr.closed {
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return ErrorFileClosed
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}
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if rs, ok := cr.rc.(fs.RangeSeeker); ok {
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n, err := rs.RangeSeek(cr.ctx, offset, io.SeekStart, length)
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if err == nil && n == offset {
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cr.offset = offset
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return nil
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}
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if err != nil {
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fs.Debugf(cr.o, "ChunkedReader.openRange seek failed (%s). Trying Open", err)
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} else {
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fs.Debugf(cr.o, "ChunkedReader.openRange seeked to wrong offset. Wanted %d, got %d. Trying Open", offset, n)
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}
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}
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var rc io.ReadCloser
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var err error
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if length <= 0 {
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if offset == 0 {
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rc, err = cr.o.Open(cr.ctx, &fs.HashesOption{Hashes: hash.Set(hash.None)})
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} else {
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rc, err = cr.o.Open(cr.ctx, &fs.HashesOption{Hashes: hash.Set(hash.None)}, &fs.RangeOption{Start: offset, End: -1})
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}
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} else {
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rc, err = cr.o.Open(cr.ctx, &fs.HashesOption{Hashes: hash.Set(hash.None)}, &fs.RangeOption{Start: offset, End: offset + length - 1})
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}
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if err != nil {
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return err
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}
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return cr.resetReader(rc, offset)
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}
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// resetReader switches the current reader to the given reader.
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// The old reader will be Close'd before setting the new reader.
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func (cr *ChunkedReader) resetReader(rc io.ReadCloser, offset int64) error {
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if cr.rc != nil {
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if err := cr.rc.Close(); err != nil {
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return err
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}
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}
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cr.rc = rc
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cr.offset = offset
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return nil
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}
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var (
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_ io.ReadCloser = (*ChunkedReader)(nil)
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_ io.Seeker = (*ChunkedReader)(nil)
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_ fs.RangeSeeker = (*ChunkedReader)(nil)
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)
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