dotgit: synced write packfile and index generation

11 files changed, 314 insertions, 101 deletions

diff --git a/common_test.go b/common_test.go
index d35abd3..d95ccf5 100644
--- a/common_test.go
+++ b/common_test.go
@@ -55,8 +55,9 @@ func (s *BaseSuite) buildRepositories(c *C) {
 		defer f.Close()
 
 		n := packfile.NewScanner(f)
-		d := packfile.NewDecoder(n, r.s.ObjectStorage())
-		_, err := d.Decode()
+		d, err := packfile.NewDecoder(n, r.s.ObjectStorage())
+		c.Assert(err, IsNil)
+		_, err = d.Decode()
 		c.Assert(err, IsNil)
 
 		s.Repositories[fixture.URL] = r
@@ -151,7 +152,8 @@ func unpackFixtures(c *C, fixtures ...[]packedFixture) map[string]*Repository {
 			c.Assert(err, IsNil, comment)
 
 			r := packfile.NewScanner(f)
-			d := packfile.NewDecoder(r, repos[fixture.url].s.ObjectStorage())
+			d, err := packfile.NewDecoder(r, repos[fixture.url].s.ObjectStorage())
+			c.Assert(err, IsNil, comment)
 			_, err = d.Decode()
 			c.Assert(err, IsNil, comment)
 			c.Assert(f.Close(), IsNil, comment)
diff --git a/examples/clone/main.go b/examples/clone/main.go
index f95dc8f..0fa5fe6 100644
--- a/examples/clone/main.go
+++ b/examples/clone/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"io"
 	"os"
 	"path/filepath"
@@ -15,15 +16,15 @@ func main() {
 	url := os.Args[1]
 	directory := os.Args[2]
 
-	r := git.NewMemoryRepository()
+	r, err := git.NewFilesystemRepository(directory)
+	checkIfError(err)
 
 	// Clone the given repository, using depth we create a shallow clone :
 	// > git clone <url> --depth 1
 	color.Blue("git clone %s --depth 1 %s", url, directory)
 
-	err := r.Clone(&git.CloneOptions{
-		URL:   url,
-		Depth: 1,
+	err = r.Clone(&git.CloneOptions{
+		URL: url,
 	})
 	checkIfError(err)
 
@@ -34,6 +35,9 @@ func main() {
 	commit, err := r.Commit(ref.Hash())
 	checkIfError(err)
 
+	fmt.Println(commit)
+	os.Exit(0)
+
 	// ... we get all the files from the commit
 	files, err := commit.Files()
 	checkIfError(err)
diff --git a/formats/idxfile/decoder_test.go b/formats/idxfile/decoder_test.go
index 8ce2bc7..02167a7 100644
--- a/formats/idxfile/decoder_test.go
+++ b/formats/idxfile/decoder_test.go
@@ -42,8 +42,9 @@ func (s *IdxfileSuite) TestDecodeCRCs(c *C) {
 	scanner := packfile.NewScanner(f.Packfile())
 	storage := memory.NewStorage()
 
-	pd := packfile.NewDecoder(scanner, storage.ObjectStorage())
-	_, err := pd.Decode()
+	pd, err := packfile.NewDecoder(scanner, storage.ObjectStorage())
+	c.Assert(err, IsNil)
+	_, err = pd.Decode()
 	c.Assert(err, IsNil)
 
 	i := &Idxfile{Version: VersionSupported}
diff --git a/formats/packfile/decoder.go b/formats/packfile/decoder.go
index c4b9182..4606a3f 100644
--- a/formats/packfile/decoder.go
+++ b/formats/packfile/decoder.go
@@ -30,11 +30,13 @@ var (
 	// ErrZLib is returned by Decode when there was an error unzipping
 	// the packfile contents.
 	ErrZLib = NewError("zlib reading error")
-	// ErrNotSeeker not seeker supported
-	ErrNotSeeker = NewError("no seeker capable decode")
 	// ErrCannotRecall is returned by RecallByOffset or RecallByHash if the object
 	// to recall cannot be returned.
 	ErrCannotRecall = NewError("cannot recall object")
+	// ErrNonSeekable is returned if a NewDecoder is used with a non-seekable
+	// reader and without a core.ObjectStorage or ReadObjectAt method is called
+	// without a seekable scanner
+	ErrNonSeekable = NewError("non-seekable scanner")
 )
 
 // Decoder reads and decodes packfiles from an input stream.
@@ -49,16 +51,25 @@ type Decoder struct {
 }
 
 // NewDecoder returns a new Decoder that reads from r.
-func NewDecoder(s *Scanner, o core.ObjectStorage) *Decoder {
+func NewDecoder(s *Scanner, o core.ObjectStorage) (*Decoder, error) {
+	if !s.IsSeekable && o == nil {
+		return nil, ErrNonSeekable
+	}
+
+	var tx core.TxObjectStorage
+	if o != nil {
+		tx = o.Begin()
+	}
+
 	return &Decoder{
 		s:  s,
 		o:  o,
-		tx: o.Begin(),
+		tx: tx,
 
 		offsetToHash: make(map[int64]core.Hash, 0),
 		hashToOffset: make(map[core.Hash]int64, 0),
 		crcs:         make(map[core.Hash]uint32, 0),
-	}
+	}, nil
 }
 
 // Decode reads a packfile and stores it in the value pointed to by s.
@@ -76,6 +87,10 @@ func (d *Decoder) doDecode() error {
 		return err
 	}
 
+	if d.o == nil {
+		return d.readObjects(count)
+	}
+
 	if err := d.readObjects(count); err != nil {
 		if err := d.tx.Rollback(); err != nil {
 			return nil
@@ -89,10 +104,19 @@ func (d *Decoder) doDecode() error {
 
 func (d *Decoder) readObjects(count uint32) error {
 	for i := 0; i < int(count); i++ {
-		_, err := d.ReadObject()
+		obj, err := d.ReadObject()
 		if err != nil {
 			return err
 		}
+
+		if d.o == nil {
+			continue
+		}
+
+		if _, err := d.tx.Set(obj); err != nil {
+			return err
+		}
+
 	}
 
 	return nil
@@ -105,7 +129,7 @@ func (d *Decoder) ReadObject() (core.Object, error) {
 		return nil, err
 	}
 
-	obj := d.o.NewObject()
+	obj := d.newObject()
 	obj.SetSize(h.Length)
 	obj.SetType(h.Type)
 	var crc uint32
@@ -128,15 +152,23 @@ func (d *Decoder) ReadObject() (core.Object, error) {
 	d.setOffset(hash, h.Offset)
 	d.setCRC(hash, crc)
 
-	if _, err := d.tx.Set(obj); err != nil {
-		return nil, err
+	return obj, nil
+}
+
+func (d *Decoder) newObject() core.Object {
+	if d.o == nil {
+		return &core.MemoryObject{}
 	}
 
-	return obj, nil
+	return d.o.NewObject()
 }
 
 // ReadObjectAt reads an object at the given location
 func (d *Decoder) ReadObjectAt(offset int64) (core.Object, error) {
+	if !d.s.IsSeekable {
+		return nil, ErrNonSeekable
+	}
+
 	beforeJump, err := d.s.Seek(offset)
 	if err != nil {
 		return nil, err
@@ -204,23 +236,29 @@ func (d *Decoder) setCRC(h core.Hash, crc uint32) {
 }
 
 func (d *Decoder) recallByOffset(o int64) (core.Object, error) {
+	if d.s.IsSeekable {
+		return d.ReadObjectAt(o)
+	}
+
 	if h, ok := d.offsetToHash[o]; ok {
 		return d.tx.Get(core.AnyObject, h)
 	}
 
-	return d.ReadObjectAt(o)
+	return nil, core.ErrObjectNotFound
 }
 
 func (d *Decoder) recallByHash(h core.Hash) (core.Object, error) {
+	if d.s.IsSeekable {
+		if o, ok := d.hashToOffset[h]; ok {
+			return d.ReadObjectAt(o)
+		}
+	}
+
 	obj, err := d.tx.Get(core.AnyObject, h)
 	if err != core.ErrObjectNotFound {
 		return obj, err
 	}
 
-	if o, ok := d.hashToOffset[h]; ok {
-		return d.ReadObjectAt(o)
-	}
-
 	return nil, core.ErrObjectNotFound
 }
 
diff --git a/formats/packfile/decoder_test.go b/formats/packfile/decoder_test.go
index 9fe6142..cbf727e 100644
--- a/formats/packfile/decoder_test.go
+++ b/formats/packfile/decoder_test.go
@@ -25,56 +25,72 @@ func (s *ReaderSuite) TestDecode(c *C) {
 		scanner := NewScanner(f.Packfile())
 		storage := memory.NewStorage()
 
-		d := NewDecoder(scanner, storage.ObjectStorage())
+		d, err := NewDecoder(scanner, storage.ObjectStorage())
+		c.Assert(err, IsNil)
 
 		ch, err := d.Decode()
 		c.Assert(err, IsNil)
 		c.Assert(ch, Equals, f.PackfileHash)
 
-		AssertObjects(c, storage, []string{
-			"918c48b83bd081e863dbe1b80f8998f058cd8294",
-			"af2d6a6954d532f8ffb47615169c8fdf9d383a1a",
-			"1669dce138d9b841a518c64b10914d88f5e488ea",
-			"a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
-			"b8e471f58bcbca63b07bda20e428190409c2db47",
-			"35e85108805c84807bc66a02d91535e1e24b38b9",
-			"b029517f6300c2da0f4b651b8642506cd6aaf45d",
-			"32858aad3c383ed1ff0a0f9bdf231d54a00c9e88",
-			"d3ff53e0564a9f87d8e84b6e28e5060e517008aa",
-			"c192bd6a24ea1ab01d78686e417c8bdc7c3d197f",
-			"d5c0f4ab811897cadf03aec358ae60d21f91c50d",
-			"49c6bb89b17060d7b4deacb7b338fcc6ea2352a9",
-			"cf4aa3b38974fb7d81f367c0830f7d78d65ab86b",
-			"9dea2395f5403188298c1dabe8bdafe562c491e3",
-			"586af567d0bb5e771e49bdd9434f5e0fb76d25fa",
-			"9a48f23120e880dfbe41f7c9b7b708e9ee62a492",
-			"5a877e6a906a2743ad6e45d99c1793642aaf8eda",
-			"c8f1d8c61f9da76f4cb49fd86322b6e685dba956",
-			"a8d315b2b1c615d43042c3a62402b8a54288cf5c",
-			"a39771a7651f97faf5c72e08224d857fc35133db",
-			"880cd14280f4b9b6ed3986d6671f907d7cc2a198",
-			"fb72698cab7617ac416264415f13224dfd7a165e",
-			"4d081c50e250fa32ea8b1313cf8bb7c2ad7627fd",
-			"eba74343e2f15d62adedfd8c883ee0262b5c8021",
-			"c2d30fa8ef288618f65f6eed6e168e0d514886f4",
-			"8dcef98b1d52143e1e2dbc458ffe38f925786bf2",
-			"aa9b383c260e1d05fbbf6b30a02914555e20c725",
-			"6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
-			"dbd3641b371024f44d0e469a9c8f5457b0660de1",
-			"e8d3ffab552895c19b9fcf7aa264d277cde33881",
-			"7e59600739c96546163833214c36459e324bad0a",
-		})
+		AssertObjects(c, storage, expectedHashes)
+	})
+}
 
+func (s *ReaderSuite) TestDecodeInMemory(c *C) {
+	fixtures.Basic().Test(c, func(f *fixtures.Fixture) {
+		scanner := NewScanner(f.Packfile())
+		d, err := NewDecoder(scanner, nil)
+		c.Assert(err, IsNil)
+
+		ch, err := d.Decode()
+		c.Assert(err, IsNil)
+		c.Assert(ch, Equals, f.PackfileHash)
 	})
 }
+
+var expectedHashes = []string{
+	"918c48b83bd081e863dbe1b80f8998f058cd8294",
+	"af2d6a6954d532f8ffb47615169c8fdf9d383a1a",
+	"1669dce138d9b841a518c64b10914d88f5e488ea",
+	"a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
+	"b8e471f58bcbca63b07bda20e428190409c2db47",
+	"35e85108805c84807bc66a02d91535e1e24b38b9",
+	"b029517f6300c2da0f4b651b8642506cd6aaf45d",
+	"32858aad3c383ed1ff0a0f9bdf231d54a00c9e88",
+	"d3ff53e0564a9f87d8e84b6e28e5060e517008aa",
+	"c192bd6a24ea1ab01d78686e417c8bdc7c3d197f",
+	"d5c0f4ab811897cadf03aec358ae60d21f91c50d",
+	"49c6bb89b17060d7b4deacb7b338fcc6ea2352a9",
+	"cf4aa3b38974fb7d81f367c0830f7d78d65ab86b",
+	"9dea2395f5403188298c1dabe8bdafe562c491e3",
+	"586af567d0bb5e771e49bdd9434f5e0fb76d25fa",
+	"9a48f23120e880dfbe41f7c9b7b708e9ee62a492",
+	"5a877e6a906a2743ad6e45d99c1793642aaf8eda",
+	"c8f1d8c61f9da76f4cb49fd86322b6e685dba956",
+	"a8d315b2b1c615d43042c3a62402b8a54288cf5c",
+	"a39771a7651f97faf5c72e08224d857fc35133db",
+	"880cd14280f4b9b6ed3986d6671f907d7cc2a198",
+	"fb72698cab7617ac416264415f13224dfd7a165e",
+	"4d081c50e250fa32ea8b1313cf8bb7c2ad7627fd",
+	"eba74343e2f15d62adedfd8c883ee0262b5c8021",
+	"c2d30fa8ef288618f65f6eed6e168e0d514886f4",
+	"8dcef98b1d52143e1e2dbc458ffe38f925786bf2",
+	"aa9b383c260e1d05fbbf6b30a02914555e20c725",
+	"6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+	"dbd3641b371024f44d0e469a9c8f5457b0660de1",
+	"e8d3ffab552895c19b9fcf7aa264d277cde33881",
+	"7e59600739c96546163833214c36459e324bad0a",
+}
+
 func (s *ReaderSuite) TestDecodeCRCs(c *C) {
 	f := fixtures.Basic().ByTag("ofs-delta").One()
 
 	scanner := NewScanner(f.Packfile())
 	storage := memory.NewStorage()
 
-	d := NewDecoder(scanner, storage.ObjectStorage())
-	_, err := d.Decode()
+	d, err := NewDecoder(scanner, storage.ObjectStorage())
+	c.Assert(err, IsNil)
+	_, err = d.Decode()
 	c.Assert(err, IsNil)
 
 	var sum uint64
@@ -88,9 +104,8 @@ func (s *ReaderSuite) TestDecodeCRCs(c *C) {
 func (s *ReaderSuite) TestReadObjectAt(c *C) {
 	f := fixtures.Basic().One()
 	scanner := NewScanner(f.Packfile())
-	storage := memory.NewStorage()
-
-	d := NewDecoder(scanner, storage.ObjectStorage())
+	d, err := NewDecoder(scanner, nil)
+	c.Assert(err, IsNil)
 
 	// when the packfile is ref-delta based, the offsets are required
 	if f.Is("ref-delta") {
diff --git a/formats/packfile/scanner.go b/formats/packfile/scanner.go
index 86092a1..a5e4215 100644
--- a/formats/packfile/scanner.go
+++ b/formats/packfile/scanner.go
@@ -49,6 +49,10 @@ type Scanner struct {
 	// is waiting to be read
 	pendingObject    *ObjectHeader
 	version, objects uint32
+
+	// lsSeekable says if this scanner can do Seek or not, to have a Scanner
+	// seekable a r implementing io.Seeker is required
+	IsSeekable bool
 }
 
 // NewScanner returns a new Scanner based on a reader, if the given reader
@@ -65,7 +69,8 @@ func NewScanner(r io.Reader) *Scanner {
 			newByteReadSeeker(seeker),
 			crc,
 		},
-		crc: crc,
+		crc:        crc,
+		IsSeekable: ok,
 	}
 }
 
diff --git a/remote.go b/remote.go
index 8e2d8a8..3e341fa 100644
--- a/remote.go
+++ b/remote.go
@@ -174,8 +174,12 @@ func (r *Remote) updateObjectStorage(reader io.Reader) error {
 	}
 
 	stream := packfile.NewScanner(reader)
-	d := packfile.NewDecoder(stream, s)
-	_, err := d.Decode()
+	d, err := packfile.NewDecoder(stream, s)
+	if err != nil {
+		return err
+	}
+
+	_, err = d.Decode()
 	return err
 }
 
diff --git a/storage/filesystem/internal/dotgit/dotgit.go b/storage/filesystem/internal/dotgit/dotgit.go
index cacda68..54113d5 100644
--- a/storage/filesystem/internal/dotgit/dotgit.go
+++ b/storage/filesystem/internal/dotgit/dotgit.go
@@ -8,12 +8,12 @@ import (
 	"io"
 	"os"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"gopkg.in/src-d/go-git.v4/core"
 	"gopkg.in/src-d/go-git.v4/formats/idxfile"
 	"gopkg.in/src-d/go-git.v4/formats/packfile"
-	"gopkg.in/src-d/go-git.v4/storage/memory"
 	"gopkg.in/src-d/go-git.v4/utils/fs"
 )
 
@@ -227,35 +227,35 @@ func isHexAlpha(b byte) bool {
 }
 
 type PackWriter struct {
-	fs fs.Filesystem
-	sr io.ReadCloser
-	sw io.WriteCloser
-	fw fs.File
-	mw io.Writer
+	Notify func(h core.Hash, i idxfile.Idxfile)
 
+	fs       fs.Filesystem
+	fr, fw   fs.File
+	synced   *syncedReader
 	checksum core.Hash
 	index    idxfile.Idxfile
 	result   chan error
-	Notify   func(h core.Hash, i idxfile.Idxfile)
 }
 
 func newPackWrite(fs fs.Filesystem) (*PackWriter, error) {
-	temp := sha1.Sum([]byte(time.Now().String()))
-	filename := fmt.Sprintf(".%x", temp)
+	seed := sha1.Sum([]byte(time.Now().String()))
+	tmp := fs.Join(objectsPath, packPath, fmt.Sprintf("tmp_pack_%x", seed))
 
-	fw, err := fs.Create(fs.Join(objectsPath, packPath, filename))
+	fw, err := fs.Create(tmp)
 	if err != nil {
 		return nil, err
 	}
 
-	sr, sw := io.Pipe()
+	fr, err := fs.Open(tmp)
+	if err != nil {
+		return nil, err
+	}
 
 	writer := &PackWriter{
 		fs:     fs,
 		fw:     fw,
-		sr:     sr,
-		sw:     sw,
-		mw:     io.MultiWriter(sw, fw),
+		fr:     fr,
+		synced: newSyncedReader(fw, fr),
 		result: make(chan error),
 	}
 
@@ -264,10 +264,12 @@ func newPackWrite(fs fs.Filesystem) (*PackWriter, error) {
 }
 
 func (w *PackWriter) buildIndex() {
-	defer w.sr.Close()
-	o := memory.NewStorage().ObjectStorage()
-	s := packfile.NewScanner(w.sr)
-	d := packfile.NewDecoder(s, o)
+	s := packfile.NewScanner(w.synced)
+	d, err := packfile.NewDecoder(s, nil)
+	if err != nil {
+		w.result <- err
+		return
+	}
 
 	checksum, err := d.Decode()
 	if err != nil {
@@ -287,8 +289,8 @@ func (w *PackWriter) buildIndex() {
 	w.result <- err
 }
 
-func (w *PackWriter) Write(p []byte) (int, error) {
-	return w.mw.Write(p)
+func (w *PackWriter) Write(p []byte) (n int, err error) {
+	return w.synced.Write(p)
 }
 
 func (w *PackWriter) Close() error {
@@ -296,20 +298,18 @@ func (w *PackWriter) Close() error {
 		close(w.result)
 	}()
 
-	if err := w.fw.Close(); err != nil {
-		return err
-	}
-
-	if err := w.sw.Close(); err != nil {
-		return err
-	}
-
-	if err := <-w.result; err != nil {
-		return err
+	pipe := []func() error{
+		func() error { return <-w.result },
+		w.fr.Close,
+		w.fw.Close,
+		w.synced.Close,
+		w.save,
 	}
 
-	if err := w.save(); err != nil {
-		return err
+	for i, f := range pipe {
+		if err := f(); err != nil {
+			return err
+		}
 	}
 
 	if w.Notify != nil {
@@ -342,3 +342,93 @@ func (w *PackWriter) encodeIdx(writer io.Writer) error {
 	_, err := e.Encode(&w.index)
 	return err
 }
+
+type syncedReader struct {
+	w io.Writer
+	r io.ReadSeeker
+
+	blocked, done uint32
+	written, read uint64
+	news          chan bool
+}
+
+func newSyncedReader(w io.Writer, r io.ReadSeeker) *syncedReader {
+	return &syncedReader{
+		w:    w,
+		r:    r,
+		news: make(chan bool),
+	}
+}
+
+func (s *syncedReader) Write(p []byte) (n int, err error) {
+	defer func() {
+		written := atomic.AddUint64(&s.written, uint64(n))
+		read := atomic.LoadUint64(&s.read)
+		if written > read {
+			s.wake()
+		}
+	}()
+
+	n, err = s.w.Write(p)
+	return
+}
+
+func (s *syncedReader) Read(p []byte) (n int, err error) {
+	defer func() { atomic.AddUint64(&s.read, uint64(n)) }()
+
+	s.sleep()
+	n, err = s.r.Read(p)
+	if err == io.EOF && !s.isDone() {
+		if n == 0 {
+			return s.Read(p)
+		}
+
+		return n, nil
+	}
+
+	return
+}
+
+func (s *syncedReader) isDone() bool {
+	return atomic.LoadUint32(&s.done) == 1
+}
+
+func (s *syncedReader) isBlocked() bool {
+	return atomic.LoadUint32(&s.blocked) == 1
+}
+
+func (s *syncedReader) wake() {
+	if s.isBlocked() {
+		//	fmt.Println("wake")
+		atomic.StoreUint32(&s.blocked, 0)
+		s.news <- true
+	}
+}
+
+func (s *syncedReader) sleep() {
+	read := atomic.LoadUint64(&s.read)
+	written := atomic.LoadUint64(&s.written)
+	if read >= written {
+		atomic.StoreUint32(&s.blocked, 1)
+		//	fmt.Println("sleep", read, written)
+		<-s.news
+	}
+
+}
+
+func (s *syncedReader) Seek(offset int64, whence int) (int64, error) {
+	if whence == io.SeekCurrent {
+		return s.r.Seek(offset, whence)
+	}
+
+	p, err := s.r.Seek(offset, whence)
+	s.read = uint64(p)
+
+	return p, err
+}
+
+func (s *syncedReader) Close() error {
+	atomic.StoreUint32(&s.done, 1)
+	close(s.news)
+	return nil
+}
diff --git a/storage/filesystem/internal/dotgit/dotgit_test.go b/storage/filesystem/internal/dotgit/dotgit_test.go
index ca2b5b4..f105c58 100644
--- a/storage/filesystem/internal/dotgit/dotgit_test.go
+++ b/storage/filesystem/internal/dotgit/dotgit_test.go
@@ -7,6 +7,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -191,3 +192,47 @@ func (s *SuiteDotGit) TestNewObjectPack(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(stat.Size(), Equals, int64(1940))
 }
+
+func (s *SuiteDotGit) TestSyncedReader(c *C) {
+	tmpw, err := ioutil.TempFile("", "example")
+	c.Assert(err, IsNil)
+
+	tmpr, err := os.Open(tmpw.Name())
+	c.Assert(err, IsNil)
+
+	defer func() {
+		tmpw.Close()
+		tmpr.Close()
+		os.Remove(tmpw.Name())
+	}()
+
+	synced := newSyncedReader(tmpw, tmpr)
+
+	go func() {
+		for i := 0; i < 281; i++ {
+			_, err := synced.Write([]byte(strconv.Itoa(i) + "\n"))
+			c.Assert(err, IsNil)
+		}
+
+		synced.Close()
+	}()
+
+	o, err := synced.Seek(1002, io.SeekStart)
+	c.Assert(err, IsNil)
+	c.Assert(o, Equals, int64(1002))
+
+	head := make([]byte, 3)
+	n, err := io.ReadFull(synced, head)
+	c.Assert(err, IsNil)
+	c.Assert(n, Equals, 3)
+	c.Assert(string(head), Equals, "278")
+
+	o, err = synced.Seek(1010, io.SeekStart)
+	c.Assert(err, IsNil)
+	c.Assert(o, Equals, int64(1010))
+
+	n, err = io.ReadFull(synced, head)
+	c.Assert(err, IsNil)
+	c.Assert(n, Equals, 3)
+	c.Assert(string(head), Equals, "280")
+}
diff --git a/storage/filesystem/object.go b/storage/filesystem/object.go
index dc21d0b..03939ce 100644
--- a/storage/filesystem/object.go
+++ b/storage/filesystem/object.go
@@ -161,7 +161,11 @@ func (s *ObjectStorage) getFromPackfile(h core.Hash) (core.Object, error) {
 	defer f.Close()
 
 	p := packfile.NewScanner(f)
-	d := packfile.NewDecoder(p, memory.NewStorage().ObjectStorage())
+	d, err := packfile.NewDecoder(p, memory.NewStorage().ObjectStorage())
+	if err != nil {
+		return nil, err
+	}
+
 	d.SetOffsets(s.index[pack])
 	return d.ReadObjectAt(offset)
 }
@@ -285,7 +289,11 @@ func newPackfileIter(
 		return nil, err
 	}
 
-	d := packfile.NewDecoder(s, memory.NewStorage().ObjectStorage())
+	d, err := packfile.NewDecoder(s, memory.NewStorage().ObjectStorage())
+	if err != nil {
+		return nil, err
+	}
+
 	return &packfileIter{f: f, d: d, t: t, total: total, seen: seen}, nil
 }
 
diff --git a/tree_diff_test.go b/tree_diff_test.go
index 9a0b04c..44f6910 100644
--- a/tree_diff_test.go
+++ b/tree_diff_test.go
@@ -49,7 +49,8 @@ func (s *DiffTreeSuite) SetUpSuite(c *C) {
 		c.Assert(err, IsNil)
 
 		r := packfile.NewScanner(f)
-		d := packfile.NewDecoder(r, s.repos[fixRepo.url].s.ObjectStorage())
+		d, err := packfile.NewDecoder(r, s.repos[fixRepo.url].s.ObjectStorage())
+		c.Assert(err, IsNil)
 		_, err = d.Decode()
 		c.Assert(err, IsNil)