go-ethereum/trie/iterator.go

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// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
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//
// The go-ethereum library is free software: you can redistribute it and/or modify
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// 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,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// 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/>.
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package trie
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import "github.com/ethereum/go-ethereum/common"
// Iterator is a key-value trie iterator that traverses a Trie.
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type Iterator struct {
trie *Trie
nodeIt *NodeIterator
keyBuf []byte
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Key []byte // Current data key on which the iterator is positioned on
Value []byte // Current data value on which the iterator is positioned on
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}
// NewIterator creates a new key-value iterator.
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func NewIterator(trie *Trie) *Iterator {
return &Iterator{
trie: trie,
nodeIt: NewNodeIterator(trie),
keyBuf: make([]byte, 0, 64),
Key: nil,
}
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}
// Next moves the iterator forward one key-value entry.
func (it *Iterator) Next() bool {
for it.nodeIt.Next() {
if it.nodeIt.Leaf {
it.Key = it.makeKey()
it.Value = it.nodeIt.LeafBlob
return true
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}
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}
it.Key = nil
it.Value = nil
return false
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}
func (it *Iterator) makeKey() []byte {
key := it.keyBuf[:0]
for _, se := range it.nodeIt.stack {
switch node := se.node.(type) {
case *fullNode:
if se.child <= 16 {
key = append(key, byte(se.child))
}
case *shortNode:
if hasTerm(node.Key) {
key = append(key, node.Key[:len(node.Key)-1]...)
} else {
key = append(key, node.Key...)
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}
}
}
return decodeCompact(key)
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}
// 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)
child int // Child to be processed next
}
// NodeIterator is an iterator to traverse the trie post-order.
type NodeIterator struct {
trie *Trie // Trie being iterated
stack []*nodeIteratorState // Hierarchy of trie nodes persisting the iteration state
Hash common.Hash // Hash of the current node being iterated (nil if not standalone)
Node node // Current node being iterated (internal representation)
Parent common.Hash // Hash of the first full ancestor node (nil if current is the root)
Leaf bool // Flag whether the current node is a value (data) node
LeafBlob []byte // Data blob contained within a leaf (otherwise nil)
Error error // Failure set in case of an internal error in the iterator
}
// NewNodeIterator creates an post-order trie iterator.
func NewNodeIterator(trie *Trie) *NodeIterator {
if trie.Hash() == emptyState {
return new(NodeIterator)
}
return &NodeIterator{trie: trie}
}
// 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.
func (it *NodeIterator) Next() bool {
// If the iterator failed previously, don't do anything
if it.Error != nil {
return false
}
// Otherwise step forward with the iterator and report any errors
if err := it.step(); err != nil {
it.Error = err
return false
}
return it.retrieve()
}
// step moves the iterator to the next node of the trie.
func (it *NodeIterator) step() error {
if it.trie == nil {
// Abort if we reached the end of the iteration
return nil
}
if len(it.stack) == 0 {
// Initialize the iterator if we've just started.
root := it.trie.Hash()
state := &nodeIteratorState{node: it.trie.root, child: -1}
if root != emptyRoot {
state.hash = root
}
it.stack = append(it.stack, state)
} else {
// Continue iterating at the previous node otherwise.
it.stack = it.stack[:len(it.stack)-1]
if len(it.stack) == 0 {
it.trie = nil
return nil
}
}
// Continue iteration to the next child
for {
parent := it.stack[len(it.stack)-1]
ancestor := parent.hash
if (ancestor == common.Hash{}) {
ancestor = parent.parent
}
if node, ok := parent.node.(*fullNode); ok {
// Full node, traverse all children, then the node itself
if parent.child >= len(node.Children) {
break
}
for parent.child++; parent.child < len(node.Children); parent.child++ {
if current := node.Children[parent.child]; current != nil {
it.stack = append(it.stack, &nodeIteratorState{
hash: common.BytesToHash(node.flags.hash),
node: current,
parent: ancestor,
child: -1,
})
break
}
}
} else if node, ok := parent.node.(*shortNode); ok {
// Short node, traverse the pointer singleton child, then the node itself
if parent.child >= 0 {
break
}
parent.child++
it.stack = append(it.stack, &nodeIteratorState{
hash: common.BytesToHash(node.flags.hash),
node: node.Val,
parent: ancestor,
child: -1,
})
} else if hash, ok := parent.node.(hashNode); ok {
// Hash node, resolve the hash child from the database, then the node itself
if parent.child >= 0 {
break
}
parent.child++
node, err := it.trie.resolveHash(hash, nil, nil)
if err != nil {
return err
}
it.stack = append(it.stack, &nodeIteratorState{
hash: common.BytesToHash(hash),
node: node,
parent: ancestor,
child: -1,
})
} else {
break
}
}
return nil
}
// retrieve pulls and caches the current trie node the iterator is traversing.
// In case of a value node, the additional leaf blob is also populated with the
// data contents for external interpretation.
//
// The method returns whether there are any more data left for inspection.
func (it *NodeIterator) retrieve() bool {
// Clear out any previously set values
it.Hash, it.Node, it.Parent, it.Leaf, it.LeafBlob = common.Hash{}, nil, common.Hash{}, false, nil
// If the iteration's done, return no available data
if it.trie == nil {
return false
}
// Otherwise retrieve the current node and resolve leaf accessors
state := it.stack[len(it.stack)-1]
it.Hash, it.Node, it.Parent = state.hash, state.node, state.parent
if value, ok := it.Node.(valueNode); ok {
it.Leaf, it.LeafBlob = true, []byte(value)
}
return true
}