forked from TrueCloudLab/frostfs-node
cf73feb3f8
In this commit we implement algorithm for CRDT trees from https://martin.klepmann.com/papers/move-op.pdf Each tree is identified by the ID of a container it belongs to and the tree name itself. Essentially, it is a sequence of operations which should be applied in chronological order to get a usual tree representation. There are 2 backends for now: bbolt database and in-memory. In-memory backend is here for debugging and will eventually act as a memory-cache for the on-disk database. Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>
235 lines
4.9 KiB
Go
235 lines
4.9 KiB
Go
package pilorama
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// nodeInfo couples parent and metadata.
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type nodeInfo struct {
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Parent Node
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Meta Meta
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Timestamp Timestamp
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}
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// state represents state being replicated.
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type state struct {
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operations []LogMove
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tree
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}
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// newState constructs new empty tree.
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func newState() *state {
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return &state{
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tree: *newTree(),
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}
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}
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// undo un-does op and changes s in-place.
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func (s *state) undo(op *LogMove) {
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children := s.tree.childMap[op.Parent]
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for i := range children {
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if children[i] == op.Child {
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if len(children) > 1 {
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s.tree.childMap[op.Parent] = append(children[:i], children[i+1:]...)
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} else {
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delete(s.tree.childMap, op.Parent)
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}
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break
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}
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}
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if op.HasOld {
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s.tree.infoMap[op.Child] = op.Old
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oldChildren := s.tree.childMap[op.Old.Parent]
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for i := range oldChildren {
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if oldChildren[i] == op.Child {
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return
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}
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}
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s.tree.childMap[op.Old.Parent] = append(oldChildren, op.Child)
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} else {
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delete(s.tree.infoMap, op.Child)
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}
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}
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// Apply puts op in log at a proper position, re-applies all subsequent operations
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// from log and changes s in-place.
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func (s *state) Apply(op *Move) error {
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var index int
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for index = len(s.operations); index > 0; index-- {
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if s.operations[index-1].Time <= op.Time {
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break
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}
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}
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if index == len(s.operations) {
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s.operations = append(s.operations, s.do(op))
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return nil
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}
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s.operations = append(s.operations[:index+1], s.operations[index:]...)
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for i := len(s.operations) - 1; i > index; i-- {
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s.undo(&s.operations[i])
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}
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s.operations[index] = s.do(op)
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for i := index + 1; i < len(s.operations); i++ {
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s.operations[i] = s.do(&s.operations[i].Move)
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}
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return nil
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}
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// do performs a single move operation on a tree.
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func (s *state) do(op *Move) LogMove {
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lm := LogMove{
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Move: Move{
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Parent: op.Parent,
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Meta: op.Meta,
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Child: op.Child,
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},
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}
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_, parentInTree := s.tree.infoMap[op.Parent]
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shouldPut := !s.tree.isAncestor(op.Child, op.Parent) &&
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!(op.Parent != 0 && op.Parent != TrashID && !parentInTree)
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shouldRemove := op.Parent == TrashID
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p, ok := s.tree.infoMap[op.Child]
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if ok {
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lm.HasOld = true
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lm.Old = p
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}
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if !shouldPut {
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return lm
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}
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if shouldRemove {
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if ok {
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s.removeChild(op.Child, p.Parent)
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}
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delete(s.tree.infoMap, op.Child)
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return lm
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}
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if !ok {
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p.Timestamp = op.Time
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} else {
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s.removeChild(op.Child, p.Parent)
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}
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p.Meta = op.Meta
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p.Parent = op.Parent
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s.tree.infoMap[op.Child] = p
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s.tree.childMap[op.Parent] = append(s.tree.childMap[op.Parent], op.Child)
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return lm
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}
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func (s *state) removeChild(child, parent Node) {
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oldChildren := s.tree.childMap[parent]
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for i := range oldChildren {
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if oldChildren[i] == child {
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s.tree.childMap[parent] = append(oldChildren[:i], oldChildren[i+1:]...)
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break
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}
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}
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}
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func (s *state) timestamp() Timestamp {
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if len(s.operations) == 0 {
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return 0
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}
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return s.operations[len(s.operations)-1].Time + 1
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}
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func (s *state) findSpareID() Node {
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id := uint64(1)
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for _, ok := s.infoMap[id]; ok; _, ok = s.infoMap[id] {
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id++
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}
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return id
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}
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// tree is a mapping from the child nodes to their parent and metadata.
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type tree struct {
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infoMap map[Node]nodeInfo
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childMap map[Node][]Node
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}
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func newTree() *tree {
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return &tree{
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childMap: make(map[Node][]Node),
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infoMap: make(map[Node]nodeInfo),
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}
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}
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// isAncestor returns true if parent is an ancestor of a child.
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// For convenience, also return true if parent == child.
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func (t tree) isAncestor(parent, child Node) bool {
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for c := child; c != parent; {
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p, ok := t.infoMap[c]
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if !ok {
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return false
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}
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c = p.Parent
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}
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return true
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}
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// getPathPrefix descends by path constructed from values of attr until
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// there is no node corresponding to a path element. Returns the amount of nodes
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// processed and ID of the last node.
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func (t tree) getPathPrefix(attr string, path []string) (int, Node) {
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var curNode Node
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loop:
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for i := range path {
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children := t.childMap[curNode]
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for j := range children {
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f := t.infoMap[children[j]].Meta.GetAttr(attr)
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if string(f) == path[i] {
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curNode = children[j]
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continue loop
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}
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}
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return i, curNode
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}
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return len(path), curNode
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}
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// get returns list of nodes which have the specified path from root
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// descending by values of attr from meta.
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func (t tree) get(attr string, path []string, latest bool) []Node {
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if len(path) == 0 {
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return nil
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}
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i, curNode := t.getPathPrefix(attr, path[:len(path)-1])
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if i < len(path)-1 {
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return nil
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}
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var nodes []Node
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var lastTs Timestamp
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children := t.childMap[curNode]
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for i := range children {
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info := t.infoMap[children[i]]
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fileName := string(info.Meta.GetAttr(attr))
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if fileName == path[len(path)-1] {
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if latest {
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if info.Timestamp >= lastTs {
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nodes = append(nodes[:0], children[i])
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}
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} else {
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nodes = append(nodes, children[i])
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}
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}
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}
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return nodes
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}
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// getMeta returns meta information of node n.
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func (t tree) getMeta(n Node) Meta {
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return t.infoMap[n].Meta
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}
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