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

Without reading the entire object into memory.

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

Author: strib

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 {