4 files changed, 55 insertions, 10 deletions
diff --git a/storage/filesystem/internal/dotgit/dotgit.go b/storage/filesystem/internal/dotgit/dotgit.go
index f9763d1..1281b7e 100644
--- a/storage/filesystem/internal/dotgit/dotgit.go
+++ b/storage/filesystem/internal/dotgit/dotgit.go
@@ -18,6 +18,7 @@ const (
 	suffix         = ".git"
 	packedRefsPath = "packed-refs"
 	configPath     = "config"
+	indexPath      = "index"
 	shallowPath    = "shallow"
 
 	objectsPath = "objects"
@@ -72,6 +73,16 @@ func (d *DotGit) Config() (billy.File, error) {
 	return d.fs.Open(configPath)
 }
 
+// IndexWriter returns a file pointer for write to the index file
+func (d *DotGit) IndexWriter() (billy.File, error) {
+	return d.fs.Create(indexPath)
+}
+
+// Index returns a file pointer for read to the index file
+func (d *DotGit) Index() (billy.File, error) {
+	return d.fs.Open(indexPath)
+}
+
 // ShallowWriter returns a file pointer for write to the shallow file
 func (d *DotGit) ShallowWriter() (billy.File, error) {
 	return d.fs.Create(shallowPath)
diff --git a/storage/filesystem/internal/dotgit/dotgit_test.go b/storage/filesystem/internal/dotgit/dotgit_test.go
index 48f02f0..bff90af 100644
--- a/storage/filesystem/internal/dotgit/dotgit_test.go
+++ b/storage/filesystem/internal/dotgit/dotgit_test.go
@@ -154,6 +154,38 @@ func (s *SuiteDotGit) TestConfigWriteAndConfig(c *C) {
 	c.Assert(string(cnt), Equals, "foo")
 }
 
+func (s *SuiteDotGit) TestIndex(c *C) {
+	fs := fixtures.Basic().ByTag(".git").One().DotGit()
+	dir := New(fs)
+
+	idx, err := dir.Index()
+	c.Assert(err, IsNil)
+	c.Assert(idx, NotNil)
+}
+
+func (s *SuiteDotGit) TestIndexWriteAndIndex(c *C) {
+	tmp, err := ioutil.TempDir("", "dot-git")
+	c.Assert(err, IsNil)
+	defer os.RemoveAll(tmp)
+
+	fs := osfs.New(tmp)
+	dir := New(fs)
+
+	f, err := dir.IndexWriter()
+	c.Assert(err, IsNil)
+
+	_, err = f.Write([]byte("foo"))
+	c.Assert(err, IsNil)
+
+	f, err = dir.Index()
+	c.Assert(err, IsNil)
+
+	cnt, err := ioutil.ReadAll(f)
+	c.Assert(err, IsNil)
+
+	c.Assert(string(cnt), Equals, "foo")
+}
+
 func (s *SuiteDotGit) TestShallow(c *C) {
 	fs := fixtures.Basic().ByTag(".git").One().DotGit()
 	dir := New(fs)
diff --git a/storage/filesystem/object.go b/storage/filesystem/object.go
index 1001032..b82ca30 100644
--- a/storage/filesystem/object.go
+++ b/storage/filesystem/object.go
@@ -17,13 +17,13 @@ import (
 
 type ObjectStorage struct {
 	dir   *dotgit.DotGit
-	index map[plumbing.Hash]index
+	index map[plumbing.Hash]idx
 }
 
 func newObjectStorage(dir *dotgit.DotGit) (ObjectStorage, error) {
 	s := ObjectStorage{
 		dir:   dir,
-		index: make(map[plumbing.Hash]index, 0),
+		index: make(map[plumbing.Hash]idx, 0),
 	}
 
 	return s, s.loadIdxFiles()
@@ -45,13 +45,13 @@ func (s *ObjectStorage) loadIdxFiles() error {
 }
 
 func (s *ObjectStorage) loadIdxFile(h plumbing.Hash) error {
-	idx, err := s.dir.ObjectPackIdx(h)
+	idxfile, err := s.dir.ObjectPackIdx(h)
 	if err != nil {
 		return err
 	}
 
-	s.index[h] = make(index)
-	return s.index[h].Decode(idx)
+	s.index[h] = make(idx)
+	return s.index[h].Decode(idxfile)
 }
 
 func (s *ObjectStorage) NewEncodedObject() plumbing.EncodedObject {
@@ -64,9 +64,9 @@ func (s *ObjectStorage) PackfileWriter() (io.WriteCloser, error) {
 		return nil, err
 	}
 
-	w.Notify = func(h plumbing.Hash, idx idxfile.Idxfile) {
-		s.index[h] = make(index)
-		for _, e := range idx.Entries {
+	w.Notify = func(h plumbing.Hash, idxfile idxfile.Idxfile) {
+		s.index[h] = make(idx)
+		for _, e := range idxfile.Entries {
 			s.index[h][e.Hash] = int64(e.Offset)
 		}
 	}
@@ -244,9 +244,9 @@ func (s *ObjectStorage) buildPackfileIters(
 	return iters, nil
 }
 
-type index map[plumbing.Hash]int64
+type idx map[plumbing.Hash]int64
 
-func (i index) Decode(r io.Reader) error {
+func (i idx) Decode(r io.Reader) error {
 	idx := &idxfile.Idxfile{}
 
 	d := idxfile.NewDecoder(r)
diff --git a/storage/filesystem/storage.go b/storage/filesystem/storage.go
index a60d0f4..56f84b8 100644
--- a/storage/filesystem/storage.go
+++ b/storage/filesystem/storage.go
@@ -13,6 +13,7 @@ import (
 type Storage struct {
 	ObjectStorage
 	ReferenceStorage
+	IndexStorage
 	ShallowStorage
 	ConfigStorage
 }
@@ -28,6 +29,7 @@ func NewStorage(fs billy.Filesystem) (*Storage, error) {
 	return &Storage{
 		ObjectStorage:    o,
 		ReferenceStorage: ReferenceStorage{dir: dir},
+		IndexStorage:     IndexStorage{dir: dir},
 		ShallowStorage:   ShallowStorage{dir: dir},
 		ConfigStorage:    ConfigStorage{dir: dir},
 	}, nil