Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
249 lines (221 sloc) 6.91 KB
package chunkedreader
import (
"context"
"errors"
"io"
"sync"
"github.com/ncw/rclone/fs"
)
// io related errors returned by ChunkedReader
var (
ErrorFileClosed = errors.New("file already closed")
ErrorInvalidSeek = errors.New("invalid seek position")
)
// ChunkedReader is a reader for a Object with the possibility
// of reading the source in chunks of given size
//
// A initialChunkSize of <= 0 will disable chunked reading.
type ChunkedReader struct {
ctx context.Context
mu sync.Mutex // protects following fields
o fs.Object // source to read from
rc io.ReadCloser // reader for the current open chunk
offset int64 // offset the next Read will start. -1 forces a reopen of o
chunkOffset int64 // beginning of the current or next chunk
chunkSize int64 // length of the current or next chunk. -1 will open o from chunkOffset to the end
initialChunkSize int64 // default chunkSize after the chunk specified by RangeSeek is complete
maxChunkSize int64 // consecutive read chunks will double in size until reached. -1 means no limit
customChunkSize bool // is the current chunkSize set by RangeSeek?
closed bool // has Close been called?
}
// New returns a ChunkedReader for the Object.
//
// A initialChunkSize of <= 0 will disable chunked reading.
// If maxChunkSize is greater than initialChunkSize, the chunk size will be
// doubled after each chunk read with a maximun of maxChunkSize.
// A Seek or RangeSeek will reset the chunk size to it's initial value
func New(ctx context.Context, o fs.Object, initialChunkSize int64, maxChunkSize int64) *ChunkedReader {
if initialChunkSize <= 0 {
initialChunkSize = -1
}
if maxChunkSize != -1 && maxChunkSize < initialChunkSize {
maxChunkSize = initialChunkSize
}
return &ChunkedReader{
ctx: ctx,
o: o,
offset: -1,
chunkSize: initialChunkSize,
initialChunkSize: initialChunkSize,
maxChunkSize: maxChunkSize,
}
}
// Read from the file - for details see io.Reader
func (cr *ChunkedReader) Read(p []byte) (n int, err error) {
cr.mu.Lock()
defer cr.mu.Unlock()
if cr.closed {
return 0, ErrorFileClosed
}
for reqSize := int64(len(p)); reqSize > 0; reqSize = int64(len(p)) {
// the current chunk boundary. valid only when chunkSize > 0
chunkEnd := cr.chunkOffset + cr.chunkSize
fs.Debugf(cr.o, "ChunkedReader.Read at %d length %d chunkOffset %d chunkSize %d", cr.offset, reqSize, cr.chunkOffset, cr.chunkSize)
switch {
case cr.chunkSize > 0 && cr.offset == chunkEnd: // last chunk read completely
cr.chunkOffset = cr.offset
if cr.customChunkSize { // last chunkSize was set by RangeSeek
cr.customChunkSize = false
cr.chunkSize = cr.initialChunkSize
} else {
cr.chunkSize *= 2
if cr.chunkSize > cr.maxChunkSize && cr.maxChunkSize != -1 {
cr.chunkSize = cr.maxChunkSize
}
}
// recalculate the chunk boundary. valid only when chunkSize > 0
chunkEnd = cr.chunkOffset + cr.chunkSize
fallthrough
case cr.offset == -1: // first Read or Read after RangeSeek
err = cr.openRange()
if err != nil {
return
}
}
var buf []byte
chunkRest := chunkEnd - cr.offset
// limit read to chunk boundaries if chunkSize > 0
if reqSize > chunkRest && cr.chunkSize > 0 {
buf, p = p[0:chunkRest], p[chunkRest:]
} else {
buf, p = p, nil
}
var rn int
rn, err = io.ReadFull(cr.rc, buf)
n += rn
cr.offset += int64(rn)
if err != nil {
if err == io.ErrUnexpectedEOF {
err = io.EOF
}
return
}
}
return n, nil
}
// Close the file - for details see io.Closer
//
// All methods on ChunkedReader will return ErrorFileClosed afterwards
func (cr *ChunkedReader) Close() error {
cr.mu.Lock()
defer cr.mu.Unlock()
if cr.closed {
return ErrorFileClosed
}
cr.closed = true
return cr.resetReader(nil, 0)
}
// Seek the file - for details see io.Seeker
func (cr *ChunkedReader) Seek(offset int64, whence int) (int64, error) {
return cr.RangeSeek(context.TODO(), offset, whence, -1)
}
// RangeSeek the file - for details see RangeSeeker
//
// The specified length will only apply to the next chunk opened.
// RangeSeek will not reopen the source until Read is called.
func (cr *ChunkedReader) RangeSeek(ctx context.Context, offset int64, whence int, length int64) (int64, error) {
cr.mu.Lock()
defer cr.mu.Unlock()
fs.Debugf(cr.o, "ChunkedReader.RangeSeek from %d to %d length %d", cr.offset, offset, length)
if cr.closed {
return 0, ErrorFileClosed
}
size := cr.o.Size()
switch whence {
case io.SeekStart:
cr.offset = 0
case io.SeekEnd:
cr.offset = size
}
// set the new chunk start
cr.chunkOffset = cr.offset + offset
// force reopen on next Read
cr.offset = -1
if length > 0 {
cr.customChunkSize = true
cr.chunkSize = length
} else {
cr.chunkSize = cr.initialChunkSize
}
if cr.chunkOffset < 0 || cr.chunkOffset >= size {
cr.chunkOffset = 0
return 0, ErrorInvalidSeek
}
return cr.chunkOffset, nil
}
// Open forces the connection to be opened
func (cr *ChunkedReader) Open() (*ChunkedReader, error) {
cr.mu.Lock()
defer cr.mu.Unlock()
if cr.rc != nil && cr.offset != -1 {
return cr, nil
}
return cr, cr.openRange()
}
// openRange will open the source Object with the current chunk range
//
// If the current open reader implements RangeSeeker, it is tried first.
// When RangeSeek fails, o.Open with a RangeOption is used.
//
// A length <= 0 will request till the end of the file
func (cr *ChunkedReader) openRange() error {
offset, length := cr.chunkOffset, cr.chunkSize
fs.Debugf(cr.o, "ChunkedReader.openRange at %d length %d", offset, length)
if cr.closed {
return ErrorFileClosed
}
if rs, ok := cr.rc.(fs.RangeSeeker); ok {
n, err := rs.RangeSeek(cr.ctx, offset, io.SeekStart, length)
if err == nil && n == offset {
cr.offset = offset
return nil
}
if err != nil {
fs.Debugf(cr.o, "ChunkedReader.openRange seek failed (%s). Trying Open", err)
} else {
fs.Debugf(cr.o, "ChunkedReader.openRange seeked to wrong offset. Wanted %d, got %d. Trying Open", offset, n)
}
}
var rc io.ReadCloser
var err error
if length <= 0 {
if offset == 0 {
rc, err = cr.o.Open(cr.ctx)
} else {
rc, err = cr.o.Open(cr.ctx, &fs.RangeOption{Start: offset, End: -1})
}
} else {
rc, err = cr.o.Open(cr.ctx, &fs.RangeOption{Start: offset, End: offset + length - 1})
}
if err != nil {
return err
}
return cr.resetReader(rc, offset)
}
// resetReader switches the current reader to the given reader.
// The old reader will be Close'd before setting the new reader.
func (cr *ChunkedReader) resetReader(rc io.ReadCloser, offset int64) error {
if cr.rc != nil {
if err := cr.rc.Close(); err != nil {
return err
}
}
cr.rc = rc
cr.offset = offset
return nil
}
var (
_ io.ReadCloser = (*ChunkedReader)(nil)
_ io.Seeker = (*ChunkedReader)(nil)
_ fs.RangeSeeker = (*ChunkedReader)(nil)
)
You can’t perform that action at this time.