2 files changed, 29 insertions, 4 deletions

diff --git a/plumbing/format/packfile/decoder.go b/plumbing/format/packfile/decoder.go
index 3d475b2..26a2a01 100644
--- a/plumbing/format/packfile/decoder.go
+++ b/plumbing/format/packfile/decoder.go
@@ -207,12 +207,16 @@ func (d *Decoder) decodeObjectsWithObjectStorerTx(count int) error {
 // constructor, if the object decoded is not equals to the specified one, nil will
 // be returned
 func (d *Decoder) DecodeObject() (plumbing.EncodedObject, error) {
+	return d.doDecodeObject(d.decoderType)
+}
+
+func (d *Decoder) doDecodeObject(t plumbing.ObjectType) (plumbing.EncodedObject, error) {
 	h, err := d.s.NextObjectHeader()
 	if err != nil {
 		return nil, err
 	}
 
-	if d.decoderType == plumbing.AnyObject {
+	if t == plumbing.AnyObject {
 		return d.decodeByHeader(h)
 	}
 
@@ -279,6 +283,7 @@ func (d *Decoder) decodeByHeader(h *ObjectHeader) (plumbing.EncodedObject, error
 	obj := d.newObject()
 	obj.SetSize(h.Length)
 	obj.SetType(h.Type)
+
 	var crc uint32
 	var err error
 	switch h.Type {
@@ -315,7 +320,8 @@ func (d *Decoder) newObject() plumbing.EncodedObject {
 // returned is added into a internal index. This is intended to be able to regenerate
 // objects from deltas (offset deltas or reference deltas) without an package index
 // (.idx file). If Decode wasn't called previously objects offset should provided
-// using the SetOffsets method.
+// using the SetOffsets method. It decodes the object regardless of the Decoder
+// type.
 func (d *Decoder) DecodeObjectAt(offset int64) (plumbing.EncodedObject, error) {
 	if !d.s.IsSeekable {
 		return nil, ErrNonSeekable
@@ -333,7 +339,7 @@ func (d *Decoder) DecodeObjectAt(offset int64) (plumbing.EncodedObject, error) {
 		}
 	}()
 
-	return d.DecodeObject()
+	return d.doDecodeObject(plumbing.AnyObject)
 }
 
 func (d *Decoder) fillRegularObjectContent(obj plumbing.EncodedObject) (uint32, error) {
diff --git a/plumbing/format/packfile/decoder_test.go b/plumbing/format/packfile/decoder_test.go
index ecf7c81..5d1530c 100644
--- a/plumbing/format/packfile/decoder_test.go
+++ b/plumbing/format/packfile/decoder_test.go
@@ -293,7 +293,7 @@ func (s *ReaderSuite) TestDecodeCRCs(c *C) {
 	c.Assert(int(sum), Equals, 78022211966)
 }
 
-func (s *ReaderSuite) TestReadObjectAt(c *C) {
+func (s *ReaderSuite) TestDecodeObjectAt(c *C) {
 	f := fixtures.Basic().One()
 	scanner := packfile.NewScanner(f.Packfile())
 	d, err := packfile.NewDecoder(scanner, nil)
@@ -311,6 +311,25 @@ func (s *ReaderSuite) TestReadObjectAt(c *C) {
 	c.Assert(obj.Hash().String(), Equals, "6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
 }
 
+func (s *ReaderSuite) TestDecodeObjectAtForType(c *C) {
+	f := fixtures.Basic().One()
+	scanner := packfile.NewScanner(f.Packfile())
+	d, err := packfile.NewDecoderForType(scanner, nil, plumbing.TreeObject)
+	c.Assert(err, IsNil)
+
+	// when the packfile is ref-delta based, the offsets are required
+	if f.Is("ref-delta") {
+		d.SetIndex(getIndexFromIdxFile(f.Idx()))
+	}
+
+	// the objects at reference 186, is a delta, so should be recall,
+	// without being read before.
+	obj, err := d.DecodeObjectAt(186)
+	c.Assert(err, IsNil)
+	c.Assert(obj.Type(), Equals, plumbing.CommitObject)
+	c.Assert(obj.Hash().String(), Equals, "6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
+}
+
 func (s *ReaderSuite) TestIndex(c *C) {
 	f := fixtures.Basic().One()
 	scanner := packfile.NewScanner(f.Packfile())