commands/smudge: treat empty pointers as empty files

Closes git-lfs/git-lfs#1922.

commands/command_smudge.go

@@ -23,7 +23,8 @@ var (
 //
 // If the encoded LFS pointer is not parse-able as a pointer, the contents of
 // that file will instead be spooled to a temporary location on disk and then
-// copied out back to Git.
+// copied out back to Git. If the pointer file is empty, an empty file will be
+// written with no error.
 //
 // If the smudged object did not "pass" the include and exclude filterset, it
 // will not be downloaded, and the object will remain a pointer on disk, as if
@@ -35,13 +36,17 @@ var (
 func smudge(to io.Writer, from io.Reader, filename string, skip bool, filter *filepathfilter.Filter) error {
 	ptr, pbuf, perr := lfs.DecodeFrom(from)
 	if perr != nil {
-		if _, err := tools.Spool(to, pbuf); err != nil {
+		n, err := tools.Spool(to, pbuf)
+		if err != nil {
 			return errors.Wrap(err, perr.Error())
 		}
 
-		return errors.NewNotAPointerError(errors.Errorf(
-			"Unable to parse pointer at: %q", filename,
-		))
+		if n != 0 {
+			return errors.NewNotAPointerError(errors.Errorf(
+				"Unable to parse pointer at: %q", filename,
+			))
+		}
+		return nil
 	}
 
 	lfs.LinkOrCopyFromReference(ptr.Oid, ptr.Size)

test/test-malformed-pointers.sh

@@ -53,3 +53,35 @@ begin_test "malformed pointers"
   popd >/dev/null
 )
 end_test
+
+begin_test "empty pointers"
+(
+  set -e
+
+  reponame="empty-pointers"
+  setup_remote_repo "$reponame"
+  clone_repo "$reponame" "$reponame"
+
+  git lfs track "*.dat"
+  git add .gitattributes
+  git commit -m "initial commit"
+
+  touch empty.dat
+
+  git \
+    -c "filter.lfs.process=" \
+    -c "filter.lfs.clean=cat" \
+    -c "filter.lfs.required=false" \
+    add empty.dat
+  git commit -m "add empty pointer"
+
+  git push origin master
+
+  pushd .. >/dev/null
+    clone_repo "$reponame" "$reponame-assert"
+
+    [ "0" -eq "$(grep -c "empty.dat" clone.log)" ]
+    [ "0" -eq "$(wc -c < empty.dat)" ]
+  popd >/dev/null
+)
+end_test