tree: add a Size() method for getting plaintext size

plumbing/format/packfile/packfile.go

@@ -90,6 +90,24 @@ func (p *Packfile) GetByOffset(o int64) (plumbing.EncodedObject, error) {
 	return p.nextObject()
 }
 
+// GetSizeByOffset retrieves the size of the encoded object from the
+// packfile with the given offset.
+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

plumbing/object/tree.go

@@ -87,6 +87,17 @@ func (t *Tree) File(path string) (*File, error) {
 	return NewFile(path, e.Mode, blob), nil
 }
 
+// Size returns the plaintext size of an object, without reading it
+// into memory.
+func (t *Tree) Size(path string) (int64, error) {
+	e, err := t.FindEntry(path)
+	if err != nil {
+		return 0, ErrEntryNotFound
+	}
+
+	return t.s.EncodedObjectSize(e.Hash)
+}
+
 // Tree returns the tree identified by the `path` argument.
 // The path is interpreted as relative to the tree receiver.
 func (t *Tree) Tree(path string) (*Tree, error) {

plumbing/object/tree_test.go

@@ -98,6 +98,12 @@ func (s *TreeSuite) TestFileFailsWithExistingTrees(c *C) {
 	c.Assert(err, Equals, ErrFileNotFound)
 }
 
+func (s *TreeSuite) TestSize(c *C) {
+	size, err := s.Tree.Size("LICENSE")
+	c.Assert(err, IsNil)
+	c.Assert(size, Equals, int64(1072))
+}
+
 func (s *TreeSuite) TestFiles(c *C) {
 	var count int
 	err := s.Tree.Files().ForEach(func(f *File) error {

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

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 {

storage/filesystem/object.go

@@ -160,6 +160,79 @@ func (s *ObjectStorage) HasEncodedObject(h plumbing.Hash) (err error) {
 	return nil
 }
 
+func (s *ObjectStorage) encodedObjectSizeFromUnpacked(h plumbing.Hash) (
+	size int64, err error) {
+	f, err := s.dir.Object(h)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return 0, plumbing.ErrObjectNotFound
+		}
+
+		return 0, err
+	}
+
+	r, err := objfile.NewReader(f)
+	if err != nil {
+		return 0, err
+	}
+	defer ioutil.CheckClose(r, &err)
+
+	_, size, err = r.Header()
+	return size, err
+}
+
+func (s *ObjectStorage) encodedObjectSizeFromPackfile(h plumbing.Hash) (
+	size int64, err error) {
+	if err := s.requireIndex(); err != nil {
+		return 0, err
+	}
+
+	pack, _, offset := s.findObjectInPackfile(h)
+	if offset == -1 {
+		return 0, plumbing.ErrObjectNotFound
+	}
+
+	f, err := s.dir.ObjectPack(pack)
+	if err != nil {
+		return 0, err
+	}
+	defer ioutil.CheckClose(f, &err)
+
+	idx := s.index[pack]
+	hash, err := idx.FindHash(offset)
+	if err == nil {
+		obj, ok := s.deltaBaseCache.Get(hash)
+		if ok {
+			return obj.Size(), nil
+		}
+	} else if err != nil && err != plumbing.ErrObjectNotFound {
+		return 0, err
+	}
+
+	var p *packfile.Packfile
+	if s.deltaBaseCache != nil {
+		p = packfile.NewPackfileWithCache(idx, s.dir.Fs(), f, s.deltaBaseCache)
+	} else {
+		p = packfile.NewPackfile(idx, s.dir.Fs(), f)
+	}
+
+	return p.GetSizeByOffset(offset)
+}
+
+// EncodedObjectSize returns the plaintext size of the given object,
+// without actually reading the full object data from storage.
+func (s *ObjectStorage) EncodedObjectSize(h plumbing.Hash) (
+	size int64, err error) {
+	size, err = s.encodedObjectSizeFromUnpacked(h)
+	if err != nil && err != plumbing.ErrObjectNotFound {
+		return 0, err
+	} else if err == nil {
+		return size, nil
+	}
+
+	return s.encodedObjectSizeFromPackfile(h)
+}
+
 // EncodedObject returns the object with the given hash, by searching for it in
 // the packfile and the git object directories.
 func (s *ObjectStorage) EncodedObject(t plumbing.ObjectType, h plumbing.Hash) (plumbing.EncodedObject, error) {

storage/filesystem/object_test.go

@@ -83,6 +83,44 @@ func (s *FsSuite) TestGetFromPackfileKeepDescriptors(c *C) {
 	})
 }
 
+func (s *FsSuite) TestGetSizeOfObjectFile(c *C) {
+	fs := fixtures.ByTag(".git").ByTag("unpacked").One().DotGit()
+	o := NewObjectStorage(dotgit.New(fs), cache.NewObjectLRUDefault())
+
+	// Get the size of `tree_walker.go`.
+	expected := plumbing.NewHash("cbd81c47be12341eb1185b379d1c82675aeded6a")
+	size, err := o.EncodedObjectSize(expected)
+	c.Assert(err, IsNil)
+	c.Assert(size, Equals, int64(2412))
+}
+
+func (s *FsSuite) TestGetSizeFromPackfile(c *C) {
+	fixtures.Basic().ByTag(".git").Test(c, func(f *fixtures.Fixture) {
+		fs := f.DotGit()
+		o := NewObjectStorage(dotgit.New(fs), cache.NewObjectLRUDefault())
+
+		// Get the size of `binary.jpg`.
+		expected := plumbing.NewHash("d5c0f4ab811897cadf03aec358ae60d21f91c50d")
+		size, err := o.EncodedObjectSize(expected)
+		c.Assert(err, IsNil)
+		c.Assert(size, Equals, int64(76110))
+	})
+}
+
+func (s *FsSuite) TestGetSizeOfAllObjectFiles(c *C) {
+	fs := fixtures.ByTag(".git").One().DotGit()
+	o := NewObjectStorage(dotgit.New(fs), cache.NewObjectLRUDefault())
+
+	// Get the size of `tree_walker.go`.
+	err := o.ForEachObjectHash(func(h plumbing.Hash) error {
+		size, err := o.EncodedObjectSize(h)
+		c.Assert(err, IsNil)
+		c.Assert(size, Not(Equals), int64(0))
+		return nil
+	})
+	c.Assert(err, IsNil)
+}
+
 func (s *FsSuite) TestGetFromPackfileMultiplePackfiles(c *C) {
 	fs := fixtures.ByTag(".git").ByTag("multi-packfile").One().DotGit()
 	o := NewObjectStorage(dotgit.New(fs), cache.NewObjectLRUDefault())

storage/memory/storage.go

@@ -122,6 +122,16 @@ func (o *ObjectStorage) HasEncodedObject(h plumbing.Hash) (err error) {
 	return nil
 }
 
+func (o *ObjectStorage) EncodedObjectSize(h plumbing.Hash) (
+	size int64, err error) {
+	obj, ok := o.Objects[h]
+	if !ok {
+		return 0, plumbing.ErrObjectNotFound
+	}
+
+	return obj.Size(), nil
+}
+
 func (o *ObjectStorage) EncodedObject(t plumbing.ObjectType, h plumbing.Hash) (plumbing.EncodedObject, error) {
 	obj, ok := o.Objects[h]
 	if !ok || (plumbing.AnyObject != t && obj.Type() != t) {