path: root/trie/node.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 (
    "fmt"
    "io"
    "strings"

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

var indices = []string{"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f", "[17]"}

type node interface {
    fstring(string) string
    cache() (hashNode, bool)
    canUnload(cachegen, cachelimit uint16) bool
}

type (
    fullNode struct {
        Children [17]node // Actual trie node data to encode/decode (needs custom encoder)
        flags    nodeFlag
    }
    shortNode struct {
        Key   []byte
        Val   node
        flags nodeFlag
    }
    hashNode  []byte
    valueNode []byte
)

// nilValueNode is used when collapsing internal trie nodes for hashing, since
// unset children need to serialize correctly.
var nilValueNode = valueNode(nil)

// EncodeRLP encodes a full node into the consensus RLP format.
func (n *fullNode) EncodeRLP(w io.Writer) error {
    var nodes [17]node

    for i, child := range n.Children {
        if child != nil {
            nodes[i] = child
        } else {
            nodes[i] = nilValueNode
        }
    }
    return rlp.Encode(w, nodes)
}

func (n *fullNode) copy() *fullNode   { copy := *n; return &copy }
func (n *shortNode) copy() *shortNode { copy := *n; return &copy }

// nodeFlag contains caching-related metadata about a node.
type nodeFlag struct {
    hash  hashNode // cached hash of the node (may be nil)
    gen   uint16   // cache generation counter
    dirty bool     // whether the node has changes that must be written to the database
}

// canUnload tells whether a node can be unloaded.
func (n *nodeFlag) canUnload(cachegen, cachelimit uint16) bool {
    return !n.dirty && cachegen-n.gen >= cachelimit
}

func (n *fullNode) canUnload(gen, limit uint16) bool  { return n.flags.canUnload(gen, limit) }
func (n *shortNode) canUnload(gen, limit uint16) bool { return n.flags.canUnload(gen, limit) }
func (n hashNode) canUnload(uint16, uint16) bool      { return false }
func (n valueNode) canUnload(uint16, uint16) bool     { return false }

func (n *fullNode) cache() (hashNode, bool)  { return n.flags.hash, n.flags.dirty }
func (n *shortNode) cache() (hashNode, bool) { return n.flags.hash, n.flags.dirty }
func (n hashNode) cache() (hashNode, bool)   { return nil, true }
func (n valueNode) cache() (hashNode, bool)  { return nil, true }

// Pretty printing.
func (n *fullNode) String() string  { return n.fstring("") }
func (n *shortNode) String() string { return n.fstring("") }
func (n hashNode) String() string   { return n.fstring("") }
func (n valueNode) String() string  { return n.fstring("") }

func (n *fullNode) fstring(ind string) string {
    resp := fmt.Sprintf("[\n%s  ", ind)
    for i, node := range n.Children {
        if node == nil {
            resp += fmt.Sprintf("%s: <nil> ", indices[i])
        } else {
            resp += fmt.Sprintf("%s: %v", indices[i], node.fstring(ind+"  "))
        }
    }
    return resp + fmt.Sprintf("\n%s] ", ind)
}
func (n *shortNode) fstring(ind string) string {
    return fmt.Sprintf("{%x: %v} ", n.Key, n.Val.fstring(ind+"  "))
}
func (n hashNode) fstring(ind string) string {
    return fmt.Sprintf("<%x> ", []byte(n))
}
func (n valueNode) fstring(ind string) string {
    return fmt.Sprintf("%x ", []byte(n))
}

func mustDecodeNode(hash, buf []byte, cachegen uint16) node {
    n, err := decodeNode(hash, buf, cachegen)
    if err != nil {
        panic(fmt.Sprintf("node %x: %v", hash, err))
    }
    return n
}

// decodeNode parses the RLP encoding of a trie node.
func decodeNode(hash, buf []byte, cachegen uint16) (node, error) {
    if len(buf) == 0 {
        return nil, io.ErrUnexpectedEOF
    }
    elems, _, err := rlp.SplitList(buf)
    if err != nil {
        return nil, fmt.Errorf("decode error: %v", err)
    }
    switch c, _ := rlp.CountValues(elems); c {
    case 2:
        n, err := decodeShort(hash, elems, cachegen)
        return n, wrapError(err, "short")
    case 17:
        n, err := decodeFull(hash, elems, cachegen)
        return n, wrapError(err, "full")
    default:
        return nil, fmt.Errorf("invalid number of list elements: %v", c)
    }
}

func decodeShort(hash, elems []byte, cachegen uint16) (node, error) {
    kbuf, rest, err := rlp.SplitString(elems)
    if err != nil {
        return nil, err
    }
    flag := nodeFlag{hash: hash, gen: cachegen}
    key := compactToHex(kbuf)
    if hasTerm(key) {
        // value node
        val, _, err := rlp.SplitString(rest)
        if err != nil {
            return nil, fmt.Errorf("invalid value node: %v", err)
        }
        return &shortNode{key, append(valueNode{}, val...), flag}, nil
    }
    r, _, err := decodeRef(rest, cachegen)
    if err != nil {
        return nil, wrapError(err, "val")
    }
    return &shortNode{key, r, flag}, nil
}

func decodeFull(hash, elems []byte, cachegen uint16) (*fullNode, error) {
    n := &fullNode{flags: nodeFlag{hash: hash, gen: cachegen}}
    for i := 0; i < 16; i++ {
        cld, rest, err := decodeRef(elems, cachegen)
        if err != nil {
            return n, wrapError(err, fmt.Sprintf("[%d]", i))
        }
        n.Children[i], elems = cld, rest
    }
    val, _, err := rlp.SplitString(elems)
    if err != nil {
        return n, err
    }
    if len(val) > 0 {
        n.Children[16] = append(valueNode{}, val...)
    }
    return n, nil
}

const hashLen = len(common.Hash{})

func decodeRef(buf []byte, cachegen uint16) (node, []byte, error) {
    kind, val, rest, err := rlp.Split(buf)
    if err != nil {
        return nil, buf, err
    }
    switch {
    case kind == rlp.List:
        // 'embedded' node reference. The encoding must be smaller
        // than a hash in order to be valid.
        if size := len(buf) - len(rest); size > hashLen {
            err := fmt.Errorf("oversized embedded node (size is %d bytes, want size < %d)", size, hashLen)
            return nil, buf, err
        }
        n, err := decodeNode(nil, buf, cachegen)
        return n, rest, err
    case kind == rlp.String && len(val) == 0:
        // empty node
        return nil, rest, nil
    case kind == rlp.String && len(val) == 32:
        return append(hashNode{}, val...), rest, nil
    default:
        return nil, nil, fmt.Errorf("invalid RLP string size %d (want 0 or 32)", len(val))
    }
}

// wraps a decoding error with information about the path to the
// invalid child node (for debugging encoding issues).
type decodeError struct {
    what  error
    stack []string
}

func wrapError(err error, ctx string) error {
    if err == nil {
        return nil
    }
    if decErr, ok := err.(*decodeError); ok {
        decErr.stack = append(decErr.stack, ctx)
        return decErr
    }
    return &decodeError{err, []string{ctx}}
}

func (err *decodeError) Error() string {
    return fmt.Sprintf("%v (decode path: %s)", err.what, strings.Join(err.stack, "<-"))
}