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206 lines
6.4 KiB
206 lines
6.4 KiB
package merkle
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import (
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"bytes"
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"errors"
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"fmt"
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"github.com/tendermint/tendermint/crypto/tmhash"
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)
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const (
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// MaxAunts is the maximum number of aunts that can be included in a SimpleProof.
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// This corresponds to a tree of size 2^100, which should be sufficient for all conceivable purposes.
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// This maximum helps prevent Denial-of-Service attacks by limitting the size of the proofs.
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MaxAunts = 100
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)
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// SimpleProof represents a simple Merkle proof.
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// NOTE: The convention for proofs is to include leaf hashes but to
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// exclude the root hash.
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// This convention is implemented across IAVL range proofs as well.
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// Keep this consistent unless there's a very good reason to change
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// everything. This also affects the generalized proof system as
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// well.
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type SimpleProof struct {
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Total int `json:"total"` // Total number of items.
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Index int `json:"index"` // Index of item to prove.
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LeafHash []byte `json:"leaf_hash"` // Hash of item value.
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Aunts [][]byte `json:"aunts"` // Hashes from leaf's sibling to a root's child.
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}
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// SimpleProofsFromByteSlices computes inclusion proof for given items.
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// proofs[0] is the proof for items[0].
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func SimpleProofsFromByteSlices(items [][]byte) (rootHash []byte, proofs []*SimpleProof) {
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trails, rootSPN := trailsFromByteSlices(items)
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rootHash = rootSPN.Hash
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proofs = make([]*SimpleProof, len(items))
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for i, trail := range trails {
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proofs[i] = &SimpleProof{
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Total: len(items),
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Index: i,
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LeafHash: trail.Hash,
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Aunts: trail.FlattenAunts(),
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}
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}
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return
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}
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// Verify that the SimpleProof proves the root hash.
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// Check sp.Index/sp.Total manually if needed
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func (sp *SimpleProof) Verify(rootHash []byte, leaf []byte) error {
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leafHash := leafHash(leaf)
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if sp.Total < 0 {
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return errors.New("proof total must be positive")
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}
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if sp.Index < 0 {
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return errors.New("proof index cannot be negative")
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}
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if !bytes.Equal(sp.LeafHash, leafHash) {
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return fmt.Errorf("invalid leaf hash: wanted %X got %X", leafHash, sp.LeafHash)
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}
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computedHash := sp.ComputeRootHash()
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if !bytes.Equal(computedHash, rootHash) {
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return fmt.Errorf("invalid root hash: wanted %X got %X", rootHash, computedHash)
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}
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return nil
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}
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// Compute the root hash given a leaf hash. Does not verify the result.
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func (sp *SimpleProof) ComputeRootHash() []byte {
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return computeHashFromAunts(
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sp.Index,
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sp.Total,
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sp.LeafHash,
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sp.Aunts,
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)
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}
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// String implements the stringer interface for SimpleProof.
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// It is a wrapper around StringIndented.
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func (sp *SimpleProof) String() string {
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return sp.StringIndented("")
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}
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// StringIndented generates a canonical string representation of a SimpleProof.
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func (sp *SimpleProof) StringIndented(indent string) string {
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return fmt.Sprintf(`SimpleProof{
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%s Aunts: %X
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%s}`,
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indent, sp.Aunts,
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indent)
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}
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// ValidateBasic performs basic validation.
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// NOTE: it expects the LeafHash and the elements of Aunts to be of size tmhash.Size,
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// and it expects at most MaxAunts elements in Aunts.
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func (sp *SimpleProof) ValidateBasic() error {
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if sp.Total < 0 {
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return errors.New("negative Total")
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}
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if sp.Index < 0 {
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return errors.New("negative Index")
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}
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if len(sp.LeafHash) != tmhash.Size {
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return fmt.Errorf("expected LeafHash size to be %d, got %d", tmhash.Size, len(sp.LeafHash))
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}
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if len(sp.Aunts) > MaxAunts {
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return fmt.Errorf("expected no more than %d aunts, got %d", MaxAunts, len(sp.Aunts))
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}
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for i, auntHash := range sp.Aunts {
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if len(auntHash) != tmhash.Size {
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return fmt.Errorf("expected Aunts#%d size to be %d, got %d", i, tmhash.Size, len(auntHash))
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}
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}
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return nil
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}
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// Use the leafHash and innerHashes to get the root merkle hash.
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// If the length of the innerHashes slice isn't exactly correct, the result is nil.
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// Recursive impl.
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func computeHashFromAunts(index int, total int, leafHash []byte, innerHashes [][]byte) []byte {
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if index >= total || index < 0 || total <= 0 {
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return nil
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}
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switch total {
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case 0:
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panic("Cannot call computeHashFromAunts() with 0 total")
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case 1:
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if len(innerHashes) != 0 {
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return nil
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}
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return leafHash
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default:
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if len(innerHashes) == 0 {
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return nil
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}
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numLeft := getSplitPoint(total)
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if index < numLeft {
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leftHash := computeHashFromAunts(index, numLeft, leafHash, innerHashes[:len(innerHashes)-1])
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if leftHash == nil {
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return nil
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}
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return innerHash(leftHash, innerHashes[len(innerHashes)-1])
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}
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rightHash := computeHashFromAunts(index-numLeft, total-numLeft, leafHash, innerHashes[:len(innerHashes)-1])
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if rightHash == nil {
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return nil
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}
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return innerHash(innerHashes[len(innerHashes)-1], rightHash)
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}
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}
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// SimpleProofNode is a helper structure to construct merkle proof.
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// The node and the tree is thrown away afterwards.
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// Exactly one of node.Left and node.Right is nil, unless node is the root, in which case both are nil.
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// node.Parent.Hash = hash(node.Hash, node.Right.Hash) or
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// hash(node.Left.Hash, node.Hash), depending on whether node is a left/right child.
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type SimpleProofNode struct {
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Hash []byte
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Parent *SimpleProofNode
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Left *SimpleProofNode // Left sibling (only one of Left,Right is set)
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Right *SimpleProofNode // Right sibling (only one of Left,Right is set)
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}
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// FlattenAunts will return the inner hashes for the item corresponding to the leaf,
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// starting from a leaf SimpleProofNode.
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func (spn *SimpleProofNode) FlattenAunts() [][]byte {
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// Nonrecursive impl.
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innerHashes := [][]byte{}
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for spn != nil {
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switch {
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case spn.Left != nil:
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innerHashes = append(innerHashes, spn.Left.Hash)
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case spn.Right != nil:
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innerHashes = append(innerHashes, spn.Right.Hash)
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default:
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break
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}
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spn = spn.Parent
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}
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return innerHashes
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}
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// trails[0].Hash is the leaf hash for items[0].
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// trails[i].Parent.Parent....Parent == root for all i.
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func trailsFromByteSlices(items [][]byte) (trails []*SimpleProofNode, root *SimpleProofNode) {
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// Recursive impl.
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switch len(items) {
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case 0:
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return nil, nil
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case 1:
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trail := &SimpleProofNode{leafHash(items[0]), nil, nil, nil}
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return []*SimpleProofNode{trail}, trail
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default:
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k := getSplitPoint(len(items))
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lefts, leftRoot := trailsFromByteSlices(items[:k])
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rights, rightRoot := trailsFromByteSlices(items[k:])
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rootHash := innerHash(leftRoot.Hash, rightRoot.Hash)
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root := &SimpleProofNode{rootHash, nil, nil, nil}
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leftRoot.Parent = root
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leftRoot.Right = rightRoot
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rightRoot.Parent = root
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rightRoot.Left = leftRoot
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return append(lefts, rights...), root
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}
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}
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