path: root/trie/hasher.go

// Copyright 2016 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"
    "hash"
    "sync"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto/sha3"
    "github.com/ethereum/go-ethereum/rlp"
)

type hasher struct {
    tmp                  *bytes.Buffer
    sha                  hash.Hash
    cachegen, cachelimit uint16
}

// hashers live in a global pool.
var hasherPool = sync.Pool{
    New: func() interface{} {
        return &hasher{tmp: new(bytes.Buffer), sha: sha3.NewKeccak256()}
    },
}

func newHasher(cachegen, cachelimit uint16) *hasher {
    h := hasherPool.Get().(*hasher)
    h.cachegen, h.cachelimit = cachegen, cachelimit
    return h
}

func returnHasherToPool(h *hasher) {
    hasherPool.Put(h)
}

// hash collapses a node down into a hash node, also returning a copy of the
// original node initialzied with the computed hash to replace the original one.
func (h *hasher) hash(n node, db DatabaseWriter, force bool) (node, node, error) {
    // If we're not storing the node, just hashing, use avaialble cached data
    if hash, dirty := n.cache(); hash != nil {
        if db == nil {
            return hash, n, nil
        }
        if n.canUnload(h.cachegen, h.cachelimit) {
            // Evict the node from cache. All of its subnodes will have a lower or equal
            // cache generation number.
            return hash, hash, nil
        }
        if !dirty {
            return hash, n, nil
        }
    }
    // Trie not processed yet or needs storage, walk the children
    collapsed, cached, err := h.hashChildren(n, db)
    if err != nil {
        return hashNode{}, n, err
    }
    hashed, err := h.store(collapsed, db, force)
    if err != nil {
        return hashNode{}, n, err
    }
    // Cache the hash of the ndoe for later reuse.
    if hash, ok := hashed.(hashNode); ok && !force {
        switch cached := cached.(type) {
        case *shortNode:
            cached = cached.copy()
            cached.flags.hash = hash
            if db != nil {
                cached.flags.dirty = false
            }
            return hashed, cached, nil
        case *fullNode:
            cached = cached.copy()
            cached.flags.hash = hash
            if db != nil {
                cached.flags.dirty = false
            }
            return hashed, cached, nil
        }
    }
    return hashed, cached, nil
}

// hashChildren replaces the children of a node with their hashes if the encoded
// size of the child is larger than a hash, returning the collapsed node as well
// as a replacement for the original node with the child hashes cached in.
func (h *hasher) hashChildren(original node, db DatabaseWriter) (node, node, error) {
    var err error

    switch n := original.(type) {
    case *shortNode:
        // Hash the short node's child, caching the newly hashed subtree
        collapsed, cached := n.copy(), n.copy()
        collapsed.Key = compactEncode(n.Key)
        cached.Key = common.CopyBytes(n.Key)

        if _, ok := n.Val.(valueNode); !ok {
            collapsed.Val, cached.Val, err = h.hash(n.Val, db, false)
            if err != nil {
                return original, original, err
            }
        }
        if collapsed.Val == nil {
            collapsed.Val = valueNode(nil) // Ensure that nil children are encoded as empty strings.
        }
        return collapsed, cached, nil

    case *fullNode:
        // Hash the full node's children, caching the newly hashed subtrees
        collapsed, cached := n.copy(), n.copy()

        for i := 0; i < 16; i++ {
            if n.Children[i] != nil {
                collapsed.Children[i], cached.Children[i], err = h.hash(n.Children[i], db, false)
                if err != nil {
                    return original, original, err
                }
            } else {
                collapsed.Children[i] = valueNode(nil) // Ensure that nil children are encoded as empty strings.
            }
        }
        cached.Children[16] = n.Children[16]
        if collapsed.Children[16] == nil {
            collapsed.Children[16] = valueNode(nil)
        }
        return collapsed, cached, nil

    default:
        // Value and hash nodes don't have children so they're left as were
        return n, original, nil
    }
}

func (h *hasher) store(n node, db DatabaseWriter, force bool) (node, error) {
    // Don't store hashes or empty nodes.
    if _, isHash := n.(hashNode); n == nil || isHash {
        return n, nil
    }
    // Generate the RLP encoding of the node
    h.tmp.Reset()
    if err := rlp.Encode(h.tmp, n); err != nil {
        panic("encode error: " + err.Error())
    }

    if h.tmp.Len() < 32 && !force {
        return n, nil // Nodes smaller than 32 bytes are stored inside their parent
    }
    // Larger nodes are replaced by their hash and stored in the database.
    hash, _ := n.cache()
    if hash == nil {
        h.sha.Reset()
        h.sha.Write(h.tmp.Bytes())
        hash = hashNode(h.sha.Sum(nil))
    }
    if db != nil {
        return hash, db.Put(hash, h.tmp.Bytes())
    }
    return hash, nil
}