git/odb/pack: introduce *Object to encapsulate typed data

git/odb/pack/object.go

@@ -0,0 +1,27 @@
+package pack
+
+// Object is an encapsulation of an object found in a packfile, or a packed
+// object.
+type Object struct {
+	// data is the front-most element of the delta-base chain, and when
+	// resolved, yields the uncompressed data of this object.
+	data Chain
+	// typ is the underlying object's type. It is not the type of the
+	// front-most chain element, rather, the type of the actual object.
+	typ PackedObjectType
+}
+
+// Unpack resolves the delta-base chain and returns an uncompressed, unpacked,
+// and full representation of the data encoded by this object.
+//
+// If there was any error in unpacking this object, it is returned immediately,
+// and the object's data can be assumed to be corrupt.
+func (o *Object) Unpack() ([]byte, error) {
+	return o.data.Unpack()
+}
+
+// Type returns the underlying object's type. Rather than the type of the
+// front-most delta-base component, it is the type of the object itself.
+func (o *Object) Type() PackedObjectType {
+	return o.typ
+}

git/odb/pack/object_test.go

@@ -0,0 +1,47 @@
+package pack
+
+import (
+	"testing"
+
+	"github.com/git-lfs/git-lfs/errors"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestObjectTypeReturnsObjectType(t *testing.T) {
+	o := &Object{
+		typ: TypeCommit,
+	}
+
+	assert.Equal(t, TypeCommit, o.Type())
+}
+
+func TestObjectUnpackUnpacksData(t *testing.T) {
+	expected := []byte{0x1, 0x2, 0x3, 0x4}
+
+	o := &Object{
+		data: &ChainSimple{
+			X: expected,
+		},
+	}
+
+	data, err := o.Unpack()
+
+	assert.Equal(t, expected, data)
+	assert.NoError(t, err)
+}
+
+func TestObjectUnpackPropogatesErrors(t *testing.T) {
+	expected := errors.New("git/odb/pack: testing")
+
+	o := &Object{
+		data: &ChainSimple{
+			Err: expected,
+		},
+	}
+
+	data, err := o.Unpack()
+
+	assert.Nil(t, data)
+	assert.Equal(t, expected, err)
+}