Index: add functions to handle the data structure

Index is not just the index file

index.go

@@ -66,6 +66,39 @@ func newIndexFromC(ptr *C.git_index) *Index {
 	return idx
 }
 
+// NewIndex allocates a new index. It won't be associated with any
+// file on the filesystem or repository
+func NewIndex() (*Index, error) {
+	var ptr *C.git_index
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	if err := C.git_index_new(&ptr); err < 0 {
+		return nil, MakeGitError(err)
+	}
+
+	return &Index{ptr: ptr}, nil
+}
+
+// Add adds or replaces the given entry to the index, making a copy of
+// the data
+func (v *Index) Add(entry *IndexEntry) error {
+	var centry C.git_index_entry
+
+	populateCIndexEntry(entry, &centry)
+	defer freeCIndexEntry(&centry)
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	if err := C.git_index_add(v.ptr, &centry); err < 0 {
+		return MakeGitError(err)
+	}
+
+	return nil
+}
+
 func (v *Index) AddByPath(path string) error {
 	cstr := C.CString(path)
 	defer C.free(unsafe.Pointer(cstr))

index_test.go

@@ -41,6 +41,36 @@ func TestIndexWriteTreeTo(t *testing.T) {
 	}
 }
 
+func TestIndexAddAndWriteTreeTo(t *testing.T) {
+	repo := createTestRepo(t)
+	defer os.RemoveAll(repo.Workdir())
+
+	odb, err := repo.Odb()
+	checkFatal(t, err)
+
+	blobID, err := odb.Write([]byte("foo\n"), ObjectBlob)
+	checkFatal(t, err)
+
+	idx, err := NewIndex()
+	checkFatal(t, err)
+
+	entry := IndexEntry {
+		Path: "README",
+		Id: blobID,
+		Mode: FilemodeBlob,
+	}
+
+	err = idx.Add(&entry)
+	checkFatal(t, err)
+
+	treeId, err := idx.WriteTreeTo(repo)
+	checkFatal(t, err)
+
+	if treeId.String() != "b7119b11e8ef7a1a5a34d3ac87f5b075228ac81e" {
+		t.Fatalf("%v", treeId.String())
+	}
+}
+
 func checkFatal(t *testing.T, err error) {
 	if err == nil {
 		return