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filereader.go
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filereader.go
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package storage
import (
"bufio"
"bytes"
"fmt"
"io"
"io/ioutil"
"os"
"time"
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
// identifying fields
path string
size int64 // size is the total size, must be set.
modtime time.Time // TODO(stevvooe): This is not needed anymore.
// 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 read takes
// on the offset and size at the time the reader is created. If the underlying
// file changes, one must create a new fileReader.
func newFileReader(driver storagedriver.StorageDriver, path string) (*fileReader, error) {
rd := &fileReader{
driver: driver,
path: path,
}
// Grab the size of the layer file, ensuring existence.
if fi, err := driver.Stat(path); err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
// NOTE(stevvooe): We really don't care if the file is not
// actually present for the reader. If the caller needs to know
// whether or not the file exists, they should issue a stat call
// on the path. There is still no guarantee, since the file may be
// gone by the time the reader is created. The only correct
// behavior is to return a reader that immediately returns EOF.
default:
// Any other error we want propagated up the stack.
return nil, err
}
} else {
if fi.IsDir() {
return nil, fmt.Errorf("cannot read a directory")
}
// Fill in file information
rd.size = fi.Size()
rd.modtime = fi.ModTime()
}
return rd, 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 os.SEEK_CUR:
newOffset += int64(offset)
case os.SEEK_END:
newOffset = fr.size + int64(offset)
case os.SEEK_SET:
newOffset = int64(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.ReadStream(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 {
// 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.
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
}