path: root/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 "github.com/ethereum/go-ethereum/common"

// Iterator is a key-value trie iterator that traverses a Trie.
type Iterator struct {
    trie   *Trie
    nodeIt *NodeIterator
    keyBuf []byte

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

// NewIterator creates a new key-value iterator.
func NewIterator(trie *Trie) *Iterator {
    return &Iterator{
        trie:   trie,
        nodeIt: NewNodeIterator(trie),
        keyBuf: make([]byte, 0, 64),
        Key:    nil,
    }
}

// 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
        }
    }
    it.Key = nil
    it.Value = nil
    return false
}

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...)
            }
        }
    }
    return decodeCompact(key)
}

// 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
}