// Copyright 2017 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 pow
import (
"bufio"
"bytes"
"errors"
"fmt"
"io/ioutil"
"math/big"
"os"
"path/filepath"
"sync"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/common/hexutil"
"github.com/ethereum/go-ethereum/log"
metrics "github.com/rcrowley/go-metrics"
)
var (
ErrNonceOutOfRange = errors.New("nonce out of range")
ErrInvalidDifficulty = errors.New("non-positive difficulty")
ErrInvalidMixDigest = errors.New("invalid mix digest")
ErrInvalidPoW = errors.New("pow difficulty invalid")
)
var (
// maxUint256 is a big integer representing 2^256-1
maxUint256 = new(big.Int).Exp(big.NewInt(2), big.NewInt(256), big.NewInt(0))
// sharedEthash is a full instance that can be shared between multiple users.
sharedEthash = NewFullEthash("", 3, 0, "", 0)
// algorithmRevision is the data structure version used for file naming.
algorithmRevision = 23
// dumpMagic is a dataset dump header to sanity check a data dump.
dumpMagic = hexutil.MustDecode("0xfee1deadbaddcafe")
)
// cache wraps an ethash cache with some metadata to allow easier concurrent use.
type cache struct {
epoch uint64 // Epoch for which this cache is relevant
cache []uint32 // The actual cache data content
used time.Time // Timestamp of the last use for smarter eviction
once sync.Once // Ensures the cache is generated only once
lock sync.Mutex // Ensures thread safety for updating the usage time
}
// generate ensures that the cache content is generates.
func (c *cache) generate(dir string, limit int, test bool) {
c.once.Do(func() {
// If we have a testing cache, generate and return
if test {
rawCache := generateCache(1024, seedHash(c.epoch*epochLength+1))
c.cache = prepare(uint64(len(rawCache)), bytes.NewReader(rawCache))
return
}
// Full cache generation is needed, check cache dir for existing data
size := cacheSize(c.epoch*epochLength + 1)
seed := seedHash(c.epoch*epochLength + 1)
path := filepath.Join(dir, fmt.Sprintf("cache-R%d-%x", algorithmRevision, seed))
logger := log.New("seed", hexutil.Bytes(seed))
if dir != "" {
dump, err := os.Open(path)
if err == nil {
logger.Info("Loading ethash cache from disk")
start := time.Now()
c.cache = prepare(size, bufio.NewReader(dump))
logger.Info("Loaded ethash cache from disk", "elapsed", common.PrettyDuration(time.Since(start)))
dump.Close()
return
}
}
// No previous disk cache was available, generate on the fly
rawCache := generateCache(size, seed)
c.cache = prepare(size, bytes.NewReader(rawCache))
// If a cache directory is given, attempt to serialize for next time
if dir != "" {
// Store the ethash cache to disk
start := time.Now()
if err := os.MkdirAll(filepath.Dir(path), os.ModePerm); err != nil {
logger.Error("Failed to create ethash cache dir", "err", err)
} else if err := ioutil.WriteFile(path, rawCache, os.ModePerm); err != nil {
logger.Error("Failed to write ethash cache to disk", "err", err)
} else {
logger.Info("Stored ethash cache to disk", "elapsed", common.PrettyDuration(time.Since(start)))
}
// Iterate over all previous instances and delete old ones
for ep := int(c.epoch) - limit; ep >= 0; ep-- {
seed := seedHash(uint64(ep)*epochLength + 1)
path := filepath.Join(dir, fmt.Sprintf("cache-R%d-%x", algorithmRevision, seed))
os.Remove(path)
}
}
})
}
// Ethash is a PoW data struture implementing the ethash algorithm.
type Ethash struct {
cachedir string // Data directory to store the verification caches
cachesinmem int // Number of caches to keep in memory
cachesondisk int // Number of caches to keep on disk
dagdir string // Data directory to store full mining datasets
dagsondisk int // Number of mining datasets to keep on disk
caches map[uint64]*cache // In memory caches to avoid regenerating too often
future *cache // Pre-generated cache for the estimated future epoch
lock sync.Mutex // Ensures thread safety for the in-memory caches
hashrate *metrics.StandardMeter // Meter tracking the average hashrate
tester bool // Flag whether to use a smaller test dataset
}
// NewFullEthash creates a full sized ethash PoW scheme.
func NewFullEthash(cachedir string, cachesinmem, cachesondisk int, dagdir string, dagsondisk int) PoW {
if cachesinmem <= 0 {
log.Warn("One ethash cache must alwast be in memory", "requested", cachesinmem)
cachesinmem = 1
}
if cachedir != "" && cachesondisk > 0 {
log.Info("Disk storage enabled for ethash caches", "dir", cachedir, "count", cachesondisk)
}
if dagdir != "" && dagsondisk > 0 {
log.Info("Disk storage enabled for ethash DAGs", "dir", dagdir, "count", dagsondisk)
}
return &Ethash{
cachedir: cachedir,
cachesinmem: cachesinmem,
cachesondisk: cachesondisk,
dagdir: dagdir,
dagsondisk: dagsondisk,
caches: make(map[uint64]*cache),
}
}
// NewTestEthash creates a small sized ethash PoW scheme useful only for testing
// purposes.
func NewTestEthash() PoW {
return &Ethash{
cachesinmem: 1,
caches: make(map[uint64]*cache),
tester: true,
}
}
// NewSharedEthash creates a full sized ethash PoW shared between all requesters
// running in the same process.
func NewSharedEthash() PoW {
return sharedEthash
}
// Verify implements PoW, checking whether the given block satisfies the PoW
// difficulty requirements.
func (ethash *Ethash) Verify(block Block) error {
// Sanity check that the block number is below the lookup table size (60M blocks)
number := block.NumberU64()
if number/epochLength >= uint64(len(cacheSizes)) {
// Go < 1.7 cannot calculate new cache/dataset sizes (no fast prime check)
return ErrNonceOutOfRange
}
// Ensure twe have a valid difficulty for the block
difficulty := block.Difficulty()
if difficulty.Sign() <= 0 {
return ErrInvalidDifficulty
}
// Recompute the digest and PoW value and verify against the block
cache := ethash.cache(number)
size := datasetSize(number)
if ethash.tester {
size = 32 * 1024
}
digest, result := hashimotoLight(size, cache, block.HashNoNonce().Bytes(), block.Nonce())
if !bytes.Equal(block.MixDigest().Bytes(), digest) {
return ErrInvalidMixDigest
}
target := new(big.Int).Div(maxUint256, difficulty)
if new(big.Int).SetBytes(result).Cmp(target) > 0 {
return ErrInvalidPoW
}
return nil
}
// cache tries to retrieve a verification cache for the specified block number
// by first checking against a list of in-memory caches, then against caches
// stored on disk, and finally generating one if none can be found.
func (ethash *Ethash) cache(block uint64) []uint32 {
epoch := block / epochLength
// If we have a PoW for that epoch, use that
ethash.lock.Lock()
current, future := ethash.caches[epoch], (*cache)(nil)
if current == nil {
// No in-memory cache, evict the oldest if the cache limit was reached
for len(ethash.caches) >= ethash.cachesinmem {
var evict *cache
for _, cache := range ethash.caches {
if evict == nil || evict.used.After(cache.used) {
evict = cache
}
}
delete(ethash.caches, evict.epoch)
log.Debug("Evicted ethash cache", "epoch", evict.epoch, "used", evict.used)
}
// If we have the new cache pre-generated, use that, otherwise create a new one
if ethash.future != nil && ethash.future.epoch == epoch {
log.Debug("Using pre-generated cache", "epoch", epoch)
current, ethash.future = ethash.future, nil
} else {
log.Debug("Requiring new ethash cache", "epoch", epoch)
current = &cache{epoch: epoch}
}
ethash.caches[epoch] = current
// If we just used up the future cache, or need a refresh, regenerate
if ethash.future == nil || ethash.future.epoch <= epoch {
log.Debug("Requiring new future ethash cache", "epoch", epoch+1)
future = &cache{epoch: epoch + 1}
ethash.future = future
}
}
current.used = time.Now()
ethash.lock.Unlock()
// Wait for generation finish, bump the timestamp and finalize the cache
current.generate(ethash.cachedir, ethash.cachesondisk, ethash.tester)
current.lock.Lock()
current.used = time.Now()
current.lock.Unlock()
// If we exhusted the future cache, now's a goot time to regenerate it
if future != nil {
go future.generate(ethash.cachedir, ethash.cachesondisk, ethash.tester)
}
return current.cache
}
// Search implements PoW, attempting to find a nonce that satisfies the block's
// difficulty requirements.
func (ethash *Ethash) Search(block Block, stop <-chan struct{}) (uint64, []byte) {
return 0, nil
}
// Hashrate implements PoW, returning the measured rate of the search invocations
// per second over the last minute.
func (ethash *Ethash) Hashrate() float64 {
return ethash.hashrate.Rate1()
}
// EthashSeedHash is the seed to use for generating a vrification cache and the
// mining dataset.
func EthashSeedHash(block uint64) []byte {
return seedHash(block)
}
