fs: add ChunkedReader

This commit is contained in:
Fabian Möller 2018-01-21 18:33:58 +01:00 committed by Nick Craig-Wood
parent a647c54888
commit 451cd6d971

View file

@ -0,0 +1,174 @@
package chunkedreader
import (
"io"
"sync"
"github.com/ncw/rclone/fs"
)
// 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 {
mu sync.Mutex
o fs.Object
rc io.ReadCloser
offset int64
chunkOffset int64
chunkSize int64
initialChunkSize int64
chunkGrowth bool
doSeek bool
}
// New returns a ChunkedReader for the Object.
//
// A initialChunkSize of 0 will disable chunked reading.
// If chunkGrowth is true, the chunk size will be doubled after each chunk read.
// A Seek or RangeSeek will reset the chunk size to it's initial value
func New(o fs.Object, initialChunkSize int64, chunkGrowth bool) *ChunkedReader {
if initialChunkSize < 0 {
initialChunkSize = 0
}
return &ChunkedReader{
o: o,
offset: -1,
chunkSize: initialChunkSize,
initialChunkSize: initialChunkSize,
chunkGrowth: chunkGrowth,
}
}
// 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()
for reqSize := int64(len(p)); reqSize > 0; reqSize = int64(len(p)) {
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)
if atChunkEnd := cr.offset == chunkEnd; cr.offset == -1 || atChunkEnd {
if atChunkEnd && cr.chunkSize > 0 {
if cr.doSeek {
cr.doSeek = false
cr.chunkSize = cr.initialChunkSize
} else if cr.chunkGrowth {
cr.chunkSize *= 2
}
cr.chunkOffset = cr.offset
}
err = cr.openRange()
if err != nil {
return
}
}
var buf []byte
chunkRest := chunkEnd - cr.offset
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 {
return
}
}
return n, nil
}
// Close the file - for details see io.Closer
func (cr *ChunkedReader) Close() error {
cr.mu.Lock()
defer cr.mu.Unlock()
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(offset, whence, -1)
}
// RangeSeek the file - for details see RangeSeeker
func (cr *ChunkedReader) RangeSeek(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", cr.offset, offset)
size := cr.o.Size()
switch whence {
case 0:
cr.offset = 0
case 2:
cr.offset = size
}
cr.chunkOffset = cr.offset + offset
cr.offset = -1
cr.doSeek = true
if length > 0 {
cr.chunkSize = length
} else {
cr.chunkSize = cr.initialChunkSize
}
return cr.offset, nil
}
// Open forces the connection to be opened
func (cr *ChunkedReader) Open() (*ChunkedReader, error) {
cr.mu.Lock()
defer cr.mu.Unlock()
return cr, cr.openRange()
}
// openRange will open the source Object with the given range
// 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)
var rc io.ReadCloser
var err error
if length <= 0 {
if offset == 0 {
rc, err = cr.o.Open()
} else {
rc, err = cr.o.Open(&fs.RangeOption{Start: offset, End: -1})
}
} else {
rc, err = cr.o.Open(&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)
)