Refactor layerReader into fileReader

This change separates out the remote file reader functionality from layer
reprsentation data. More importantly, issues with seeking have been fixed and
thoroughly tested.

storage/layerreader.go

@@ -1,10 +1,6 @@
 package storage
 
 import (
-	"bufio"
-	"fmt"
-	"io"
-	"os"
 	"time"
 
 	"github.com/docker/docker-registry/digest"
@@ -13,22 +9,11 @@ import (
 // layerReadSeeker implements Layer and provides facilities for reading and
 // seeking.
 type layerReader struct {
-	layerStore *layerStore
-	rc         io.ReadCloser
-	brd        *bufio.Reader
+	fileReader
 
 	name      string // repo name of this layer
 	digest    digest.Digest
-	path      string
 	createdAt time.Time
-
-	// offset is the current read offset
-	offset int64
-
-	// size is the total layer size, if available.
-	size int64
-
-	closedErr error // terminal error, if set, reader is closed
 }
 
 var _ Layer = &layerReader{}
@@ -44,131 +29,3 @@ func (lrs *layerReader) Digest() digest.Digest {
 func (lrs *layerReader) CreatedAt() time.Time {
 	return lrs.createdAt
 }
-
-func (lrs *layerReader) Read(p []byte) (n int, err error) {
-	if err := lrs.closed(); err != nil {
-		return 0, err
-	}
-
-	rd, err := lrs.reader()
-	if err != nil {
-		return 0, err
-	}
-
-	n, err = rd.Read(p)
-	lrs.offset += int64(n)
-
-	// Simulate io.EOR error if we reach filesize.
-	if err == nil && lrs.offset >= lrs.size {
-		err = io.EOF
-	}
-
-	// TODO(stevvooe): More error checking is required here. If the reader
-	// times out for some reason, we should reset the reader so we re-open the
-	// connection.
-
-	return n, err
-}
-
-func (lrs *layerReader) Seek(offset int64, whence int) (int64, error) {
-	if err := lrs.closed(); err != nil {
-		return 0, err
-	}
-
-	var err error
-	newOffset := lrs.offset
-
-	switch whence {
-	case os.SEEK_CUR:
-		newOffset += int64(whence)
-	case os.SEEK_END:
-		newOffset = lrs.size + int64(whence)
-	case os.SEEK_SET:
-		newOffset = int64(whence)
-	}
-
-	if newOffset < 0 {
-		err = fmt.Errorf("cannot seek to negative position")
-	} else if newOffset >= lrs.size {
-		err = fmt.Errorf("cannot seek passed end of layer")
-	} else {
-		if lrs.offset != newOffset {
-			lrs.resetReader()
-		}
-
-		// No problems, set the offset.
-		lrs.offset = newOffset
-	}
-
-	return lrs.offset, err
-}
-
-// Close the layer. Should be called when the resource is no longer needed.
-func (lrs *layerReader) Close() error {
-	if lrs.closedErr != nil {
-		return lrs.closedErr
-	}
-	// TODO(sday): Must export this error.
-	lrs.closedErr = fmt.Errorf("layer closed")
-
-	// close and release reader chain
-	if lrs.rc != nil {
-		lrs.rc.Close()
-		lrs.rc = nil
-	}
-	lrs.brd = nil
-
-	return lrs.closedErr
-}
-
-// reader prepares the current reader at the lrs offset, ensuring its buffered
-// and ready to go.
-func (lrs *layerReader) reader() (io.Reader, error) {
-	if err := lrs.closed(); err != nil {
-		return nil, err
-	}
-
-	if lrs.rc != nil {
-		return lrs.brd, nil
-	}
-
-	// If we don't have a reader, open one up.
-	rc, err := lrs.layerStore.driver.ReadStream(lrs.path, uint64(lrs.offset))
-
-	if err != nil {
-		return nil, err
-	}
-
-	lrs.rc = rc
-
-	if lrs.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.
-		lrs.brd = bufio.NewReader(lrs.rc)
-	} else {
-		lrs.brd.Reset(lrs.rc)
-	}
-
-	return lrs.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 (lrs *layerReader) resetReader() {
-	if err := lrs.closed(); err != nil {
-		return
-	}
-	if lrs.rc != nil {
-		lrs.rc.Close()
-		lrs.rc = nil
-	}
-}
-
-func (lrs *layerReader) closed() error {
-	return lrs.closedErr
-}