object: get object size without reading whole object

Signed-off-by: Jeremy Stribling <strib@alum.mit.edu>

3 files changed, 28 insertions, 0 deletions

diff --git a/plumbing/format/packfile/packfile.go b/plumbing/format/packfile/packfile.go
index 852a834..dbd5d4b 100644
--- a/plumbing/format/packfile/packfile.go
+++ b/plumbing/format/packfile/packfile.go
@@ -90,6 +90,22 @@ func (p *Packfile) GetByOffset(o int64) (plumbing.EncodedObject, error) {
 	return p.nextObject()
 }
 
+func (p *Packfile) GetSizeByOffset(o int64) (size int64, err error) {
+	if _, err := p.s.SeekFromStart(o); err != nil {
+		if err == io.EOF || isInvalid(err) {
+			return 0, plumbing.ErrObjectNotFound
+		}
+
+		return 0, err
+	}
+
+	h, err := p.nextObjectHeader()
+	if err != nil {
+		return 0, err
+	}
+	return h.Length, nil
+}
+
 func (p *Packfile) nextObjectHeader() (*ObjectHeader, error) {
 	h, err := p.s.NextObjectHeader()
 	p.s.pendingObject = nil
diff --git a/plumbing/storer/object.go b/plumbing/storer/object.go
index 92aa629..2ac9b09 100644
--- a/plumbing/storer/object.go
+++ b/plumbing/storer/object.go
@@ -40,6 +40,8 @@ type EncodedObjectStorer interface {
 	// HasEncodedObject returns ErrObjNotFound if the object doesn't
 	// exist.  If the object does exist, it returns nil.
 	HasEncodedObject(plumbing.Hash) error
+	// EncodedObjectSize returns the plaintext size of the encoded object.
+	EncodedObjectSize(plumbing.Hash) (int64, error)
 }
 
 // DeltaObjectStorer is an EncodedObjectStorer that can return delta
diff --git a/plumbing/storer/object_test.go b/plumbing/storer/object_test.go
index 6b4fe0f..bc22f7b 100644
--- a/plumbing/storer/object_test.go
+++ b/plumbing/storer/object_test.go
@@ -141,6 +141,16 @@ func (o *MockObjectStorage) HasEncodedObject(h plumbing.Hash) error {
 	return plumbing.ErrObjectNotFound
 }
 
+func (o *MockObjectStorage) EncodedObjectSize(h plumbing.Hash) (
+	size int64, err error) {
+	for _, o := range o.db {
+		if o.Hash() == h {
+			return o.Size(), nil
+		}
+	}
+	return 0, plumbing.ErrObjectNotFound
+}
+
 func (o *MockObjectStorage) EncodedObject(t plumbing.ObjectType, h plumbing.Hash) (plumbing.EncodedObject, error) {
 	for _, o := range o.db {
 		if o.Hash() == h {