Simplify pack.List

src/cmds/restic/cmd_dump.go

@@ -126,14 +126,18 @@ func printPacks(repo *repository.Repository, wr io.Writer) error {
 		name := job.Data.(string)
 
 		h := backend.Handle{Type: backend.Data, Name: name}
-		ldr := pack.BackendLoader{Backend: repo.Backend(), Handle: h}
 
-		unpacker, err := pack.NewUnpacker(repo.Key(), ldr)
+		blobInfo, err := repo.Backend().Stat(h)
 		if err != nil {
 			return nil, err
 		}
 
-		return unpacker.Entries, nil
+		blobs, err := pack.List(repo.Key(), backend.ReaderAt(repo.Backend(), h), blobInfo.Size)
+		if err != nil {
+			return nil, err
+		}
+
+		return blobs, nil
 	}
 
 	jobCh := make(chan worker.Job)

src/restic/checker/checker.go

@@ -1,6 +1,7 @@
 package checker
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"sync"
@@ -676,7 +677,7 @@ func checkPack(r *repository.Repository, id backend.ID) error {
 		return fmt.Errorf("Pack ID does not match, want %v, got %v", id.Str(), hash.Str())
 	}
 
-	blobs, err := pack.List(r.Key(), pack.BufferLoader(buf))
+	blobs, err := pack.List(r.Key(), bytes.NewReader(buf), int64(len(buf)))
 	if err != nil {
 		return err
 	}

src/restic/pack/pack.go

@@ -228,67 +228,73 @@ func (p *Packer) String() string {
 	return fmt.Sprintf("<Packer %d blobs, %d bytes>", len(p.blobs), p.bytes)
 }
 
-const (
-	preloadHeaderSize = 2048
-	maxHeaderSize     = 16 * 1024 * 1024
-)
-
-// List returns the list of entries found in a pack file.
-func List(k *crypto.Key, ldr Loader) (entries []Blob, err error) {
+// readHeaderLength returns the header length read from the end of the file
+// encoded in little endian.
+func readHeaderLength(rd io.ReaderAt, size int64) (uint32, error) {
+	off := size - int64(binary.Size(uint32(0)))
 
-	// read the last 2048 byte, this will mostly be enough for the header, so
-	// we do not need another round trip.
-	buf := make([]byte, preloadHeaderSize)
-	n, err := ldr.Load(buf, -int64(len(buf)))
+	buf := make([]byte, binary.Size(uint32(0)))
+	n, err := rd.ReadAt(buf, off)
+	if err != nil {
+		return 0, err
+	}
 
-	if err == io.ErrUnexpectedEOF {
-		err = nil
-		buf = buf[:n]
+	if n != len(buf) {
+		return 0, errors.New("not enough bytes read")
 	}
 
+	return binary.LittleEndian.Uint32(buf), nil
+}
+
+const maxHeaderSize = 16 * 1024 * 1024
+
+// readHeader reads the header at the end of rd. size is the length of the
+// whole data accessible in rd.
+func readHeader(rd io.ReaderAt, size int64) ([]byte, error) {
+	hl, err := readHeaderLength(rd, size)
 	if err != nil {
-		return nil, fmt.Errorf("Load at -%d failed: %v", len(buf), err)
+		return nil, err
 	}
-	buf = buf[:n]
-
-	bs := binary.Size(uint32(0))
-	p := len(buf) - bs
 
-	// read the length from the end of the buffer
-	length := int(binary.LittleEndian.Uint32(buf[p : p+bs]))
-	buf = buf[:p]
+	if int64(hl) > size-int64(binary.Size(hl)) {
+		return nil, errors.New("header is larger than file")
+	}
 
-	if length > maxHeaderSize {
-		return nil, fmt.Errorf("header too large (%d bytes)", length)
+	if int64(hl) > maxHeaderSize {
+		return nil, errors.New("header is larger than maxHeaderSize")
 	}
 
-	// if the header is longer than the preloaded buffer, call the loader again.
-	if length > len(buf) {
-		buf = make([]byte, length)
-		n, err := ldr.Load(buf, -int64(len(buf)+bs))
-		if err != nil {
-			return nil, fmt.Errorf("Load at -%d failed: %v", len(buf), err)
-		}
+	buf := make([]byte, int(hl))
+	n, err := rd.ReadAt(buf, size-int64(hl)-int64(binary.Size(hl)))
+	if err != nil {
+		return nil, err
+	}
 
-		if n != len(buf) {
-			return nil, fmt.Errorf("not enough header bytes read: wanted %v, got %v", len(buf), n)
-		}
+	if n != len(buf) {
+		return nil, errors.New("not enough bytes read")
 	}
 
-	buf = buf[len(buf)-length:]
+	return buf, nil
+}
+
+// List returns the list of entries found in a pack file.
+func List(k *crypto.Key, rd io.ReaderAt, size int64) (entries []Blob, err error) {
+	buf, err := readHeader(rd, size)
+	if err != nil {
+		return nil, err
+	}
 
-	// read header
 	hdr, err := crypto.Decrypt(k, buf, buf)
 	if err != nil {
 		return nil, err
 	}
 
-	rd := bytes.NewReader(hdr)
+	hdrRd := bytes.NewReader(hdr)
 
 	pos := uint(0)
 	for {
 		e := headerEntry{}
-		err = binary.Read(rd, binary.LittleEndian, &e)
+		err = binary.Read(hdrRd, binary.LittleEndian, &e)
 		if err == io.EOF {
 			break
 		}

src/restic/pack/pack_test.go

@@ -47,7 +47,7 @@ func newPack(t testing.TB, k *crypto.Key, lengths []int) ([]Buf, []byte, uint) {
 	return bufs, packData, p.Size()
 }
 
-func verifyBlobs(t testing.TB, bufs []Buf, k *crypto.Key, ldr pack.Loader, packSize uint) {
+func verifyBlobs(t testing.TB, bufs []Buf, k *crypto.Key, rd io.ReaderAt, packSize uint) {
 	written := 0
 	for _, buf := range bufs {
 		written += len(buf.data)
@@ -63,7 +63,7 @@ func verifyBlobs(t testing.TB, bufs []Buf, k *crypto.Key, ldr pack.Loader, packS
 	Equals(t, uint(written), packSize)
 
 	// read and parse it again
-	entries, err := pack.List(k, ldr)
+	entries, err := pack.List(k, rd, int64(packSize))
 	OK(t, err)
 	Equals(t, len(entries), len(bufs))
 
@@ -76,7 +76,7 @@ func verifyBlobs(t testing.TB, bufs []Buf, k *crypto.Key, ldr pack.Loader, packS
 			buf = make([]byte, int(e.Length))
 		}
 		buf = buf[:int(e.Length)]
-		n, err := ldr.Load(buf, int64(e.Offset))
+		n, err := rd.ReadAt(buf, int64(e.Offset))
 		OK(t, err)
 		buf = buf[:n]
 
@@ -91,7 +91,7 @@ func TestCreatePack(t *testing.T) {
 
 	bufs, packData, packSize := newPack(t, k, testLens)
 	Equals(t, uint(len(packData)), packSize)
-	verifyBlobs(t, bufs, k, pack.BufferLoader(packData), packSize)
+	verifyBlobs(t, bufs, k, bytes.NewReader(packData), packSize)
 }
 
 var blobTypeJSON = []struct {
@@ -128,8 +128,7 @@ func TestUnpackReadSeeker(t *testing.T) {
 
 	handle := backend.Handle{Type: backend.Data, Name: id.String()}
 	OK(t, b.Save(handle, packData))
-	ldr := pack.BackendLoader{Backend: b, Handle: handle}
-	verifyBlobs(t, bufs, k, ldr, packSize)
+	verifyBlobs(t, bufs, k, backend.ReaderAt(b, handle), packSize)
 }
 
 func TestShortPack(t *testing.T) {
@@ -142,6 +141,5 @@ func TestShortPack(t *testing.T) {
 
 	handle := backend.Handle{Type: backend.Data, Name: id.String()}
 	OK(t, b.Save(handle, packData))
-	ldr := pack.BackendLoader{Backend: b, Handle: handle}
-	verifyBlobs(t, bufs, k, ldr, packSize)
+	verifyBlobs(t, bufs, k, backend.ReaderAt(b, handle), packSize)
 }

src/restic/repository/repack.go

@@ -1,6 +1,7 @@
 package repository
 
 import (
+	"bytes"
 	"io"
 	"restic/backend"
 	"restic/crypto"
@@ -32,7 +33,7 @@ func Repack(repo *Repository, packs backend.IDSet, keepBlobs pack.BlobSet) (err
 
 		debug.Log("Repack", "pack %v loaded (%d bytes)", packID.Str(), len(buf))
 
-		blobs, err := pack.List(repo.Key(), pack.BufferLoader(buf))
+		blobs, err := pack.List(repo.Key(), bytes.NewReader(buf), int64(len(buf)))
 		if err != nil {
 			return err
 		}

src/restic/repository/repository.go

@@ -554,9 +554,7 @@ func (r *Repository) ListPack(id backend.ID) ([]pack.Blob, int64, error) {
 		return nil, 0, err
 	}
 
-	ldr := pack.BackendLoader{Backend: r.Backend(), Handle: h}
-
-	blobs, err := pack.List(r.Key(), ldr)
+	blobs, err := pack.List(r.Key(), backend.ReaderAt(r.Backend(), h), blobInfo.Size)
 	if err != nil {
 		return nil, 0, err
 	}