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|
package storage
import (
"bufio"
"bytes"
"context"
"fmt"
"io"
"io/ioutil"
storagedriver "github.com/docker/distribution/registry/storage/driver"
)
// TODO(stevvooe): Set an optimal buffer size here. We'll have to
// understand the latency characteristics of the underlying network to
// set this correctly, so we may want to leave it to the driver. For
// out of process drivers, we'll have to optimize this buffer size for
// local communication.
const fileReaderBufferSize = 4 << 20
// remoteFileReader provides a read seeker interface to files stored in
// storagedriver. Used to implement part of layer interface and will be used
// to implement read side of LayerUpload.
type fileReader struct {
driver storagedriver.StorageDriver
ctx context.Context
// identifying fields
path string
size int64 // size is the total size, must be set.
// mutable fields
rc io.ReadCloser // remote read closer
brd *bufio.Reader // internal buffered io
offset int64 // offset is the current read offset
err error // terminal error, if set, reader is closed
}
// newFileReader initializes a file reader for the remote file. The reader
// takes on the size and path that must be determined externally with a stat
// call. The reader operates optimistically, assuming that the file is already
// there.
func newFileReader(ctx context.Context, driver storagedriver.StorageDriver, path string, size int64) (*fileReader, error) {
return &fileReader{
ctx: ctx,
driver: driver,
path: path,
size: size,
}, nil
}
func (fr *fileReader) Read(p []byte) (n int, err error) {
if fr.err != nil {
return 0, fr.err
}
rd, err := fr.reader()
if err != nil {
return 0, err
}
n, err = rd.Read(p)
fr.offset += int64(n)
// Simulate io.EOR error if we reach filesize.
if err == nil && fr.offset >= fr.size {
err = io.EOF
}
return n, err
}
func (fr *fileReader) Seek(offset int64, whence int) (int64, error) {
if fr.err != nil {
return 0, fr.err
}
var err error
newOffset := fr.offset
switch whence {
case io.SeekCurrent:
newOffset += offset
case io.SeekEnd:
newOffset = fr.size + offset
case io.SeekStart:
newOffset = offset
}
if newOffset < 0 {
err = fmt.Errorf("cannot seek to negative position")
} else {
if fr.offset != newOffset {
fr.reset()
}
// No problems, set the offset.
fr.offset = newOffset
}
return fr.offset, err
}
func (fr *fileReader) Close() error {
return fr.closeWithErr(fmt.Errorf("fileReader: closed"))
}
// reader prepares the current reader at the lrs offset, ensuring its buffered
// and ready to go.
func (fr *fileReader) reader() (io.Reader, error) {
if fr.err != nil {
return nil, fr.err
}
if fr.rc != nil {
return fr.brd, nil
}
// If we don't have a reader, open one up.
rc, err := fr.driver.Reader(fr.ctx, fr.path, fr.offset)
if err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
// NOTE(stevvooe): If the path is not found, we simply return a
// reader that returns io.EOF. However, we do not set fr.rc,
// allowing future attempts at getting a reader to possibly
// succeed if the file turns up later.
return ioutil.NopCloser(bytes.NewReader([]byte{})), nil
default:
return nil, err
}
}
fr.rc = rc
if fr.brd == nil {
fr.brd = bufio.NewReaderSize(fr.rc, fileReaderBufferSize)
} else {
fr.brd.Reset(fr.rc)
}
return fr.brd, nil
}
// resetReader resets the reader, forcing the read method to open up a new
// connection and rebuild the buffered reader. This should be called when the
// offset and the reader will become out of sync, such as during a seek
// operation.
func (fr *fileReader) reset() {
if fr.err != nil {
return
}
if fr.rc != nil {
fr.rc.Close()
fr.rc = nil
}
}
func (fr *fileReader) closeWithErr(err error) error {
if fr.err != nil {
return fr.err
}
fr.err = err
// close and release reader chain
if fr.rc != nil {
fr.rc.Close()
}
fr.rc = nil
fr.brd = nil
return fr.err
}
|
