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 (
    "bytes"
    "fmt"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
)

// Iterator is a key-value trie iterator to traverse the data contents.
type Iterator struct {
    trie *Trie

    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, Key: nil}
}

// Next moves the iterator forward with one key-value entry.
func (self *Iterator) Next() bool {
    isIterStart := false
    if self.Key == nil {
        isIterStart = true
        self.Key = make([]byte, 32)
    }

    key := remTerm(compactHexDecode(self.Key))
    k := self.next(self.trie.root, key, isIterStart)

    self.Key = []byte(decodeCompact(k))

    return len(k) > 0
}

func (self *Iterator) next(node interface{}, key []byte, isIterStart bool) []byte {
    if node == nil {
        return nil
    }

    switch node := node.(type) {
    case fullNode:
        if len(key) > 0 {
            k := self.next(node[key[0]], key[1:], isIterStart)
            if k != nil {
                return append([]byte{key[0]}, k...)
            }
        }

        var r byte
        if len(key) > 0 {
            r = key[0] + 1
        }

        for i := r; i < 16; i++ {
            k := self.key(node[i])
            if k != nil {
                return append([]byte{i}, k...)
            }
        }

    case shortNode:
        k := remTerm(node.Key)
        if vnode, ok := node.Val.(valueNode); ok {
            switch bytes.Compare([]byte(k), key) {
            case 0:
                if isIterStart {
                    self.Value = vnode
                    return k
                }
            case 1:
                self.Value = vnode
                return k
            }
        } else {
            cnode := node.Val

            var ret []byte
            skey := key[len(k):]
            if bytes.HasPrefix(key, k) {
                ret = self.next(cnode, skey, isIterStart)
            } else if bytes.Compare(k, key[:len(k)]) > 0 {
                return self.key(node)
            }

            if ret != nil {
                return append(k, ret...)
            }
        }

    case hashNode:
        rn, err := self.trie.resolveHash(node, nil, nil)
        if err != nil && glog.V(logger.Error) {
            glog.Errorf("Unhandled trie error: %v", err)
        }
        return self.next(rn, key, isIterStart)
    }
    return nil
}

func (self *Iterator) key(node interface{}) []byte {
    switch node := node.(type) {
    case shortNode:
        // Leaf node
        k := remTerm(node.Key)
        if vnode, ok := node.Val.(valueNode); ok {
            self.Value = vnode
            return k
        }
        return append(k, self.key(node.Val)...)
    case fullNode:
        if node[16] != nil {
            self.Value = node[16].(valueNode)
            return []byte{16}
        }
        for i := 0; i < 16; i++ {
            k := self.key(node[i])
            if k != nil {
                return append([]byte{byte(i)}, k...)
            }
        }
    case hashNode:
        rn, err := self.trie.resolveHash(node, nil, nil)
        if err != nil && glog.V(logger.Error) {
            glog.Errorf("Unhandled trie error: %v", err)
        }
        return self.key(rn)
    }
    return nil
}

// 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 bytes.Compare(trie.Root(), emptyRoot.Bytes()) == 0 {
        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 {
    // Abort if we reached the end of the iteration
    if it.trie == nil {
        return nil
    }
    // Initialize the iterator if we've just started, or pop off the old node otherwise
    if len(it.stack) == 0 {
        it.stack = append(it.stack, &nodeIteratorState{node: it.trie.root, child: -1})
        if it.stack[0].node == nil {
            return fmt.Errorf("root node missing: %x", it.trie.Root())
        }
    } else {
        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) {
                break
            }
            for parent.child++; parent.child < len(node); parent.child++ {
                if current := node[parent.child]; current != nil {
                    it.stack = append(it.stack, &nodeIteratorState{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{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
}