ipld-eth-statedb/trie_by_cid/trie/iterator.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package trie

import (
	"bytes"
	"errors"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/trie"
)

// NodeIterator is a re-export of the go-ethereum interface
type NodeIterator = trie.NodeIterator

// Iterator is a key-value trie iterator that traverses a Trie.
type Iterator struct {
	nodeIt NodeIterator

	Key   []byte // Current data key on which the iterator is positioned on
	Value []byte // Current data value on which the iterator is positioned on
	Err   error
}

// NewIterator creates a new key-value iterator from a node iterator.
// Note that the value returned by the iterator is raw. If the content is encoded
// (e.g. storage value is RLP-encoded), it's caller's duty to decode it.
func NewIterator(it NodeIterator) *Iterator {
	return &Iterator{
		nodeIt: it,
	}
}

// Next moves the iterator forward one key-value entry.
func (it *Iterator) Next() bool {
	for it.nodeIt.Next(true) {
		if it.nodeIt.Leaf() {
			it.Key = it.nodeIt.LeafKey()
			it.Value = it.nodeIt.LeafBlob()
			return true
		}
	}
	it.Key = nil
	it.Value = nil
	it.Err = it.nodeIt.Error()
	return false
}

// Prove generates the Merkle proof for the leaf node the iterator is currently
// positioned on.
func (it *Iterator) Prove() [][]byte {
	return it.nodeIt.LeafProof()
}

// nodeIteratorState represents the iteration state at one particular node of the
// trie, which can be resumed at a later invocation.
type nodeIteratorState struct {
	hash    common.Hash // Hash of the node being iterated (nil if not standalone)
	node    node        // Trie node being iterated
	parent  common.Hash // Hash of the first full ancestor node (nil if current is the root)
	index   int         // Child to be processed next
	pathlen int         // Length of the path to this node
}

type nodeIterator struct {
	trie  *Trie                // Trie being iterated
	stack []*nodeIteratorState // Hierarchy of trie nodes persisting the iteration state
	path  []byte               // Path to the current node
	err   error                // Failure set in case of an internal error in the iterator

	resolver trie.NodeResolver // Optional intermediate resolver above the disk layer
}

// errIteratorEnd is stored in nodeIterator.err when iteration is done.
var errIteratorEnd = errors.New("end of iteration")

// seekError is stored in nodeIterator.err if the initial seek has failed.
type seekError struct {
	key []byte
	err error
}

func (e seekError) Error() string {
	return "seek error: " + e.err.Error()
}

func newNodeIterator(trie *Trie, start []byte) NodeIterator {
	if trie.Hash() == emptyRoot {
		return &nodeIterator{
			trie: trie,
			err:  errIteratorEnd,
		}
	}
	it := &nodeIterator{trie: trie}
	it.err = it.seek(start)
	return it
}

func (it *nodeIterator) AddResolver(resolver trie.NodeResolver) {
	it.resolver = resolver
}

func (it *nodeIterator) Hash() common.Hash {
	if len(it.stack) == 0 {
		return common.Hash{}
	}
	return it.stack[len(it.stack)-1].hash
}

func (it *nodeIterator) Parent() common.Hash {
	if len(it.stack) == 0 {
		return common.Hash{}
	}
	return it.stack[len(it.stack)-1].parent
}

func (it *nodeIterator) Leaf() bool {
	return hasTerm(it.path)
}

func (it *nodeIterator) LeafKey() []byte {
	if len(it.stack) > 0 {
		if _, ok := it.stack[len(it.stack)-1].node.(valueNode); ok {
			return hexToKeyBytes(it.path)
		}
	}
	panic("not at leaf")
}

func (it *nodeIterator) LeafBlob() []byte {
	if len(it.stack) > 0 {
		if node, ok := it.stack[len(it.stack)-1].node.(valueNode); ok {
			return node
		}
	}
	panic("not at leaf")
}

func (it *nodeIterator) LeafProof() [][]byte {
	if len(it.stack) > 0 {
		if _, ok := it.stack[len(it.stack)-1].node.(valueNode); ok {
			hasher := newHasher(false)
			defer returnHasherToPool(hasher)
			proofs := make([][]byte, 0, len(it.stack))

			for i, item := range it.stack[:len(it.stack)-1] {
				// Gather nodes that end up as hash nodes (or the root)
				node, hashed := hasher.proofHash(item.node)
				if _, ok := hashed.(hashNode); ok || i == 0 {
					proofs = append(proofs, nodeToBytes(node))
				}
			}
			return proofs
		}
	}
	panic("not at leaf")
}

func (it *nodeIterator) Path() []byte {
	return it.path
}

func (it *nodeIterator) NodeBlob() []byte {
	if it.Hash() == (common.Hash{}) {
		return nil // skip the non-standalone node
	}
	blob, err := it.resolveBlob(it.Hash().Bytes(), it.Path())
	if err != nil {
		it.err = err
		return nil
	}
	return blob
}

func (it *nodeIterator) Error() error {
	if it.err == errIteratorEnd {
		return nil
	}
	if seek, ok := it.err.(seekError); ok {
		return seek.err
	}
	return it.err
}

// Next moves the iterator to the next node, returning whether there are any
// further nodes. In case of an internal error this method returns false and
// sets the Error field to the encountered failure. If `descend` is false,
// skips iterating over any subnodes of the current node.
func (it *nodeIterator) Next(descend bool) bool {
	if it.err == errIteratorEnd {
		return false
	}
	if seek, ok := it.err.(seekError); ok {
		if it.err = it.seek(seek.key); it.err != nil {
			return false
		}
	}
	// Otherwise step forward with the iterator and report any errors.
	state, parentIndex, path, err := it.peek(descend)
	it.err = err
	if it.err != nil {
		return false
	}
	it.push(state, parentIndex, path)
	return true
}

func (it *nodeIterator) seek(prefix []byte) error {
	// The path we're looking for is the hex encoded key without terminator.
	key := keybytesToHex(prefix)
	key = key[:len(key)-1]
	// Move forward until we're just before the closest match to key.
	for {
		state, parentIndex, path, err := it.peekSeek(key)
		if err == errIteratorEnd {
			return errIteratorEnd
		} else if err != nil {
			return seekError{prefix, err}
		} else if bytes.Compare(path, key) >= 0 {
			return nil
		}
		it.push(state, parentIndex, path)
	}
}

// init initializes the iterator.
func (it *nodeIterator) init() (*nodeIteratorState, error) {
	root := it.trie.Hash()
	state := &nodeIteratorState{node: it.trie.root, index: -1}
	if root != emptyRoot {
		state.hash = root
	}
	return state, state.resolve(it, nil)
}

// peek creates the next state of the iterator.
func (it *nodeIterator) peek(descend bool) (*nodeIteratorState, *int, []byte, error) {
	// Initialize the iterator if we've just started.
	if len(it.stack) == 0 {
		state, err := it.init()
		return state, nil, nil, err
	}
	if !descend {
		// If we're skipping children, pop the current node first
		it.pop()
	}

	// Continue iteration to the next child
	for len(it.stack) > 0 {
		parent := it.stack[len(it.stack)-1]
		ancestor := parent.hash
		if (ancestor == common.Hash{}) {
			ancestor = parent.parent
		}
		state, path, ok := it.nextChild(parent, ancestor)
		if ok {
			if err := state.resolve(it, path); err != nil {
				return parent, &parent.index, path, err
			}
			return state, &parent.index, path, nil
		}
		// No more child nodes, move back up.
		it.pop()
	}
	return nil, nil, nil, errIteratorEnd
}

// peekSeek is like peek, but it also tries to skip resolving hashes by skipping
// over the siblings that do not lead towards the desired seek position.
func (it *nodeIterator) peekSeek(seekKey []byte) (*nodeIteratorState, *int, []byte, error) {
	// Initialize the iterator if we've just started.
	if len(it.stack) == 0 {
		state, err := it.init()
		return state, nil, nil, err
	}
	if !bytes.HasPrefix(seekKey, it.path) {
		// If we're skipping children, pop the current node first
		it.pop()
	}

	// Continue iteration to the next child
	for len(it.stack) > 0 {
		parent := it.stack[len(it.stack)-1]
		ancestor := parent.hash
		if (ancestor == common.Hash{}) {
			ancestor = parent.parent
		}
		state, path, ok := it.nextChildAt(parent, ancestor, seekKey)
		if ok {
			if err := state.resolve(it, path); err != nil {
				return parent, &parent.index, path, err
			}
			return state, &parent.index, path, nil
		}
		// No more child nodes, move back up.
		it.pop()
	}
	return nil, nil, nil, errIteratorEnd
}

func (it *nodeIterator) resolveHash(hash hashNode, path []byte) (node, error) {
	if it.resolver != nil {
		if blob := it.resolver(it.trie.owner, path, common.BytesToHash(hash)); len(blob) > 0 {
			if resolved, err := decodeNode(hash, blob); err == nil {
				return resolved, nil
			}
		}
	}
	return it.trie.resolveHash(hash, path)
}

func (it *nodeIterator) resolveBlob(hash hashNode, path []byte) ([]byte, error) {
	if it.resolver != nil {
		if blob := it.resolver(it.trie.owner, path, common.BytesToHash(hash)); len(blob) > 0 {
			return blob, nil
		}
	}
	return it.trie.resolveBlob(hash, path)
}

func (st *nodeIteratorState) resolve(it *nodeIterator, path []byte) error {
	if hash, ok := st.node.(hashNode); ok {
		resolved, err := it.resolveHash(hash, path)
		if err != nil {
			return err
		}
		st.node = resolved
		st.hash = common.BytesToHash(hash)
	}
	return nil
}

func findChild(n *fullNode, index int, path []byte, ancestor common.Hash) (node, *nodeIteratorState, []byte, int) {
	var (
		child     node
		state     *nodeIteratorState
		childPath []byte
	)
	for ; index < len(n.Children); index++ {
		if n.Children[index] != nil {
			child = n.Children[index]
			hash, _ := child.cache()
			state = &nodeIteratorState{
				hash:    common.BytesToHash(hash),
				node:    child,
				parent:  ancestor,
				index:   -1,
				pathlen: len(path),
			}
			childPath = append(childPath, path...)
			childPath = append(childPath, byte(index))
			return child, state, childPath, index
		}
	}
	return nil, nil, nil, 0
}

func (it *nodeIterator) nextChild(parent *nodeIteratorState, ancestor common.Hash) (*nodeIteratorState, []byte, bool) {
	switch node := parent.node.(type) {
	case *fullNode:
		// Full node, move to the first non-nil child.
		if child, state, path, index := findChild(node, parent.index+1, it.path, ancestor); child != nil {
			parent.index = index - 1
			return state, path, true
		}
	case *shortNode:
		// Short node, return the pointer singleton child
		if parent.index < 0 {
			hash, _ := node.Val.cache()
			state := &nodeIteratorState{
				hash:    common.BytesToHash(hash),
				node:    node.Val,
				parent:  ancestor,
				index:   -1,
				pathlen: len(it.path),
			}
			path := append(it.path, node.Key...)
			return state, path, true
		}
	}
	return parent, it.path, false
}

// nextChildAt is similar to nextChild, except that it targets a child as close to the
// target key as possible, thus skipping siblings.
func (it *nodeIterator) nextChildAt(parent *nodeIteratorState, ancestor common.Hash, key []byte) (*nodeIteratorState, []byte, bool) {
	switch n := parent.node.(type) {
	case *fullNode:
		// Full node, move to the first non-nil child before the desired key position
		child, state, path, index := findChild(n, parent.index+1, it.path, ancestor)
		if child == nil {
			// No more children in this fullnode
			return parent, it.path, false
		}
		// If the child we found is already past the seek position, just return it.
		if bytes.Compare(path, key) >= 0 {
			parent.index = index - 1
			return state, path, true
		}
		// The child is before the seek position. Try advancing
		for {
			nextChild, nextState, nextPath, nextIndex := findChild(n, index+1, it.path, ancestor)
			// If we run out of children, or skipped past the target, return the
			// previous one
			if nextChild == nil || bytes.Compare(nextPath, key) >= 0 {
				parent.index = index - 1
				return state, path, true
			}
			// We found a better child closer to the target
			state, path, index = nextState, nextPath, nextIndex
		}
	case *shortNode:
		// Short node, return the pointer singleton child
		if parent.index < 0 {
			hash, _ := n.Val.cache()
			state := &nodeIteratorState{
				hash:    common.BytesToHash(hash),
				node:    n.Val,
				parent:  ancestor,
				index:   -1,
				pathlen: len(it.path),
			}
			path := append(it.path, n.Key...)
			return state, path, true
		}
	}
	return parent, it.path, false
}

func (it *nodeIterator) push(state *nodeIteratorState, parentIndex *int, path []byte) {
	it.path = path
	it.stack = append(it.stack, state)
	if parentIndex != nil {
		*parentIndex++
	}
}

func (it *nodeIterator) pop() {
	last := it.stack[len(it.stack)-1]
	it.path = it.path[:last.pathlen]
	it.stack[len(it.stack)-1] = nil
	it.stack = it.stack[:len(it.stack)-1]
}