Move storage package under registry package

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/storage/filereader.go

@@ -0,0 +1,201 @@
+package storage
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"time"
+
+	"github.com/docker/distribution/storagedriver"
+)
+
+// 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 layer size, must be set.
+	modtime time.Time
+
+	// 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
+}
+
+// Close the layer. Should be called when the resource is no longer needed.
+func (fr *fileReader) Close() error {
+	if fr.err != nil {
+		return fr.err
+	}
+
+	fr.err = ErrLayerClosed
+
+	// close and release reader chain
+	if fr.rc != nil {
+		fr.rc.Close()
+	}
+
+	fr.rc = nil
+	fr.brd = nil
+
+	return fr.err
+}
+
+// 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
+	}
+}