path normalization fixed for relative paths

btrfs/src/path.rs

@@ -38,12 +38,24 @@ pub trait Path: AsRef<[u8]> {
                 Segment::NoOp | Segment::CurrentDir => {}
                 Segment::Root | Segment::File(_) => segments.push_back(segment),
                 Segment::ParentDir => {
-                    if segments.back() != Some(&Segment::Root) {
+                    match segments.back() {
+                        // parent of root is still root, so do nothing
+                        Some(&Segment::Root) => {}
+                        // relative path has to contain parentdir going up past
+                        // the current dir if segments already contain a
+                        // parentdir we know we must be in a relative path above
+                        // the current dir
+                        None | Some(&Segment::ParentDir) => {
+                            segments.push_back(segment);
+                        }
+                        // some path exists, pop up to parent
+                        _ => {
                             segments.pop_back();
                         }
                     }
                 }
             }
+        }
 
         NormalizedPath { segments }
     }
@@ -168,6 +180,31 @@ mod tests {
         assert_eq!(iter.next(), Some(&b"some.file"[..]));
         assert_eq!(iter.next(), None);
     }
+
+    #[test]
+    fn test_normalizing() {
+        // normalizes to "/path"
+        let path = b"///../../some/../path".normalize();
+        let mut iter = path.into_iter();
+        assert_eq!(iter.next(), Some(Segment::Root));
+        assert_eq!(iter.next(), Some(Segment::File(&b"path"[..])));
+        assert_eq!(iter.next(), None);
+
+        // normalizes to "../../path"
+        let path = b"../../some/../path".normalize();
+        let mut iter = path.into_iter();
+        assert_eq!(iter.next(), Some(Segment::ParentDir));
+        assert_eq!(iter.next(), Some(Segment::ParentDir));
+        assert_eq!(iter.next(), Some(Segment::File(&b"path"[..])));
+        assert_eq!(iter.next(), None);
+
+        // normalizes to "../.."
+        let path = b".././../some/../path/..".normalize();
+        let mut iter = path.into_iter();
+        assert_eq!(iter.next(), Some(Segment::ParentDir));
+        assert_eq!(iter.next(), Some(Segment::ParentDir));
+        assert_eq!(iter.next(), None);
+    }
 }
 
 #[cfg(test)]