package rootfs import ( "path/filepath" "sort" "strings" ) // tree is a way to store directory paths for whiteouts. // It is semi-optimized for reads and non-optimized for writes; // See Merge() and HasPrefix for trade-offs. type tree struct { name string children []*tree end bool } // newTree creates a new tree from a given path. func newTree(paths ...string) *tree { t := &tree{name: ".", children: []*tree{}} for _, path := range paths { t.Add(path) } return t } // Add adds a sequence to a tree func (t *tree) Add(path string) { t.add(strings.Split(filepath.Clean(path), "/")) } // HasPrefix returns if tree contains a prefix matching a given sequence. // Search algorithm is naive: it does linear search when going through the // nodes instead of binary-search. Since we expect number of children to be // really small (usually 1 or 2), it does not really matter. If you find a // real-world container with 30+ whiteout paths on a single path, please ping // the author/maintainer of this code. func (t *tree) HasPrefix(path string) bool { return t.hasprefix(strings.Split(filepath.Clean(path), "/")) } // Merge merges adds t2 to t. It is not optimized for speed, since it's walking // full branch for every other branch. func (t *tree) Merge(t2 *tree) { t.merge(t2, []string{}) } // String stringifies a tree func (t *tree) String() string { if len(t.children) == 0 { return "" } res := &stringer{[]string{}} res.stringify(t, []string{}) sort.Strings(res.res) return strings.Join(res.res, ":") } func (t *tree) add(nodes []string) { if len(nodes) == 0 { t.end = true return } for i := range t.children { if t.children[i].name == nodes[0] { t.children[i].add(nodes[1:]) return } } newNode := &tree{name: nodes[0]} t.children = append(t.children, newNode) newNode.add(nodes[1:]) } func (t *tree) hasprefix(nodes []string) bool { if len(nodes) == 0 { return t.end } if t.end { return true } for i := range t.children { if t.children[i].name == nodes[0] { return t.children[i].hasprefix(nodes[1:]) } } return false } type stringer struct { res []string } func (s *stringer) stringify(t *tree, acc []string) { if t.name == "" { return } acc = append(acc, t.name) if t.end { s.res = append(s.res, strings.Join(acc, "/")) } for _, child := range t.children { s.stringify(child, acc) } } func (t *tree) merge(t2 *tree, acc []string) { if t2.end { t.add(append(acc[1:], t2.name)) } acc = append(acc, t2.name) for _, child := range t2.children { t.merge(child, acc) } }