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"
)

// calculator is a utility used by the hasher to calculate the hash value of the tree node.
type calculator struct {
    sha    hash.Hash
    buffer *bytes.Buffer
}

// calculatorPool is a set of temporary calculators that may be individually saved and retrieved.
var calculatorPool = sync.Pool{
    New: func() interface{} {
        return &calculator{buffer: new(bytes.Buffer), sha: sha3.NewKeccak256()}
    },
}

// hasher hasher is used to calculate the hash value of the whole tree.
type hasher struct {
    cachegen   uint16
    cachelimit uint16
    threaded   bool
    mu         sync.Mutex
}

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

// newCalculator retrieves a cleaned calculator from calculator pool.
func (h *hasher) newCalculator() *calculator {
    calculator := calculatorPool.Get().(*calculator)
    calculator.buffer.Reset()
    calculator.sha.Reset()
    return calculator
}

// returnCalculator returns a no longer used calculator to the pool.
func (h *hasher) returnCalculator(calculator *calculator) {
    calculatorPool.Put(calculator)
}

// hash collapses a node down into a hash node, also returning a copy of the
// original node initialized 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 available cached data
    if hash, dirty := n.cache(); hash != nil {
        if db == nil {
            return hash, n, nil
        }
        if n.canUnload(h.cachegen, h.cachelimit) {
            // Unload the node from cache. All of its subnodes will have a lower or equal
            // cache generation number.
            cacheUnloadCounter.Inc(1)
            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 node for later reuse and remove
    // the dirty flag in commit mode. It's fine to assign these values directly
    // without copying the node first because hashChildren copies it.
    cachedHash, _ := hashed.(hashNode)
    switch cn := cached.(type) {
    case *shortNode:
        cn.flags.hash = cachedHash
        if db != nil {
            cn.flags.dirty = false
        }
    case *fullNode:
        cn.flags.hash = cachedHash
        if db != nil {
            cn.flags.dirty = false
        }
    }
    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 = hexToCompact(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()

        // hashChild is a helper to hash a single child, which is called either on the
        // same thread as the caller or in a goroutine for the toplevel branching.
        hashChild := func(index int, wg *sync.WaitGroup) {
            if wg != nil {
                defer wg.Done()
            }
            // Ensure that nil children are encoded as empty strings.
            if collapsed.Children[index] == nil {
                collapsed.Children[index] = valueNode(nil)
                return
            }
            // Hash all other children properly
            var herr error
            collapsed.Children[index], cached.Children[index], herr = h.hash(n.Children[index], db, false)
            if herr != nil {
                h.mu.Lock() // rarely if ever locked, no congenstion
                err = herr
                h.mu.Unlock()
            }
        }
        // If we're not running in threaded mode yet, span a goroutine for each child
        if !h.threaded {
            // Disable further threading
            h.threaded = true

            // Hash all the children concurrently
            var wg sync.WaitGroup
            for i := 0; i < 16; i++ {
                wg.Add(1)
                go hashChild(i, &wg)
            }
            wg.Wait()

            // Reenable threading for subsequent hash calls
            h.threaded = false
        } else {
            for i := 0; i < 16; i++ {
                hashChild(i, nil)
            }
        }
        if err != nil {
            return original, original, err
        }
        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
    }
    calculator := h.newCalculator()
    defer h.returnCalculator(calculator)

    // Generate the RLP encoding of the node
    if err := rlp.Encode(calculator.buffer, n); err != nil {
        panic("encode error: " + err.Error())
    }
    if calculator.buffer.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 {
        calculator.sha.Write(calculator.buffer.Bytes())
        hash = hashNode(calculator.sha.Sum(nil))
    }
    if db != nil {
        // db might be a leveldb batch, which is not safe for concurrent writes
        h.mu.Lock()
        err := db.Put(hash, calculator.buffer.Bytes())
        h.mu.Unlock()

        return hash, err
    }
    return hash, nil
}