package ethash
/*
#include "src/libethash/internal.h"
int ethashGoCallback_cgo(unsigned);
*/
import "C"
import (
"errors"
"fmt"
"io/ioutil"
"math/big"
"math/rand"
"os"
"os/user"
"path/filepath"
"runtime"
"sync"
"time"
"unsafe"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"github.com/ethereum/go-ethereum/pow"
)
var (
minDifficulty = new(big.Int).Exp(big.NewInt(2), big.NewInt(256), big.NewInt(0))
sharedLight = new(Light)
)
const (
epochLength uint64 = 30000
cacheSizeForTesting C.uint64_t = 1024
dagSizeForTesting C.uint64_t = 1024 * 32
)
var DefaultDir = defaultDir()
func defaultDir() string {
home := os.Getenv("HOME")
if user, err := user.Current(); err == nil {
home = user.HomeDir
}
if runtime.GOOS == "windows" {
return filepath.Join(home, "AppData", "Ethash")
}
return filepath.Join(home, ".ethash")
}
// cache wraps an ethash_light_t with some metadata
// and automatic memory management.
type cache struct {
epoch uint64
test bool
gen sync.Once // ensures cache is only generated once.
ptr *C.struct_ethash_light
}
// generate creates the actual cache. it can be called from multiple
// goroutines. the first call will generate the cache, subsequent
// calls wait until it is generated.
func (cache *cache) generate() {
cache.gen.Do(func() {
started := time.Now()
seedHash := makeSeedHash(cache.epoch)
glog.V(logger.Debug).Infof("Generating cache for epoch %d (%x)", cache.epoch, seedHash)
size := C.ethash_get_cachesize(C.uint64_t(cache.epoch * epochLength))
if cache.test {
size = cacheSizeForTesting
}
cache.ptr = C.ethash_light_new_internal(size, (*C.ethash_h256_t)(unsafe.Pointer(&seedHash[0])))
runtime.SetFinalizer(cache, freeCache)
glog.V(logger.Debug).Infof("Done generating cache for epoch %d, it took %v", cache.epoch, time.Since(started))
})
}
func freeCache(cache *cache) {
C.ethash_light_delete(cache.ptr)
cache.ptr = nil
}
// Light implements the Verify half of the proof of work.
// It uses a small in-memory cache to verify the nonces
// found by Full.
type Light struct {
test bool // if set use a smaller cache size
mu sync.Mutex // protects current
current *cache // last cache which was generated.
// TODO: keep multiple caches.
}
// Verify checks whether the block's nonce is valid.
func (l *Light) Verify(block pow.Block) bool {
// TODO: do ethash_quick_verify before getCache in order
// to prevent DOS attacks.
var (
blockNum = block.NumberU64()
difficulty = block.Difficulty()
cache = l.getCache(blockNum)
dagSize = C.ethash_get_datasize(C.uint64_t(blockNum))
)
if l.test {
dagSize = dagSizeForTesting
}
if blockNum >= epochLength*2048 {
glog.V(logger.Debug).Infof("block number %d too high, limit is %d", epochLength*2048)
return false
}
// Recompute the hash using the cache.
hash := hashToH256(block.HashNoNonce())
ret := C.ethash_light_compute_internal(cache.ptr, dagSize, hash, C.uint64_t(block.Nonce()))
if !ret.success {
return false
}
// Make sure cache is live until after the C call.
// This is important because a GC might happen and execute
// the finalizer before the call completes.
_ = cache
// The actual check.
target := new(big.Int).Div(minDifficulty, difficulty)
return h256ToHash(ret.result).Big().Cmp(target) <= 0
}
func h256ToHash(in C.ethash_h256_t) common.Hash {
return *(*common.Hash)(unsafe.Pointer(&in.b))
}
func hashToH256(in common.Hash) C.ethash_h256_t {
return C.ethash_h256_t{b: *(*[32]C.uint8_t)(unsafe.Pointer(&in[0]))}
}
func (l *Light) getCache(blockNum uint64) *cache {
var c *cache
epoch := blockNum / epochLength
// Update or reuse the last cache.
l.mu.Lock()
if l.current != nil && l.current.epoch == epoch {
c = l.current
} else {
c = &cache{epoch: epoch, test: l.test}
l.current = c
}
l.mu.Unlock()
// Wait for the cache to finish generating.
c.generate()
return c
}
// dag wraps an ethash_full_t with some metadata
// and automatic memory management.
type dag struct {
epoch uint64
test bool
dir string
gen sync.Once // ensures DAG is only generated once.
ptr *C.struct_ethash_full
}
// generate creates the actual DAG. it can be called from multiple
// goroutines. the first call will generate the DAG, subsequent
// calls wait until it is generated.
func (d *dag) generate() {
d.gen.Do(func() {
var (
started = time.Now()
seedHash = makeSeedHash(d.epoch)
blockNum = C.uint64_t(d.epoch * epochLength)
cacheSize = C.ethash_get_cachesize(blockNum)
dagSize = C.ethash_get_datasize(blockNum)
)
if d.test {
cacheSize = cacheSizeForTesting
dagSize = dagSizeForTesting
}
if d.dir == "" {
d.dir = DefaultDir
}
glog.V(logger.Info).Infof("Generating DAG for epoch %d (%x)", d.epoch, seedHash)
// Generate a temporary cache.
// TODO: this could share the cache with Light
cache := C.ethash_light_new_internal(cacheSize, (*C.ethash_h256_t)(unsafe.Pointer(&seedHash[0])))
defer C.ethash_light_delete(cache)
// Generate the actual DAG.
d.ptr = C.ethash_full_new_internal(
C.CString(d.dir),
hashToH256(seedHash),
dagSize,
cache,
(C.ethash_callback_t)(unsafe.Pointer(C.ethashGoCallback_cgo)),
)
if d.ptr == nil {
panic("ethash_full_new IO or memory error")
}
runtime.SetFinalizer(d, freeDAG)
glog.V(logger.Info).Infof("Done generating DAG for epoch %d, it took %v", d.epoch, time.Since(started))
})
}
func freeDAG(h *dag) {
C.ethash_full_delete(h.ptr)
h.ptr = nil
}
//export ethashGoCallback
func ethashGoCallback(percent C.unsigned) C.int {
glog.V(logger.Info).Infof("Still generating DAG: %d%%", percent)
return 0
}
// MakeDAG pre-generates a DAG file for the given block number in the
// given directory. If dir is the empty string, the default directory
// is used.
func MakeDAG(blockNum uint64, dir string) error {
d := &dag{epoch: blockNum / epochLength, dir: dir}
if blockNum >= epochLength*2048 {
return fmt.Errorf("block number too high, limit is %d", epochLength*2048)
}
d.generate()
if d.ptr == nil {
return errors.New("failed")
}
return nil
}
// Full implements the Search half of the proof of work.
type Full struct {
Dir string // use this to specify a non-default DAG directory
test bool // if set use a smaller DAG size
turbo bool
hashRate int64
mu sync.Mutex // protects dag
current *dag // current full DAG
}
func (pow *Full) getDAG(blockNum uint64) (d *dag) {
epoch := blockNum / epochLength
pow.mu.Lock()
if pow.current != nil && pow.current.epoch == epoch {
d = pow.current
} else {
d = &dag{epoch: epoch, test: pow.test, dir: pow.Dir}
pow.current = d
}
pow.mu.Unlock()
// wait for it to finish generating.
d.generate()
return d
}
func (pow *Full) Search(block pow.Block, stop <-chan struct{}) (nonce uint64, mixDigest []byte) {
dag := pow.getDAG(block.NumberU64())
r := rand.New(rand.NewSource(time.Now().UnixNano()))
diff := block.Difficulty()
i := int64(0)
starti := i
start := time.Now().UnixNano()
nonce = uint64(r.Int63())
hash := hashToH256(block.HashNoNonce())
target := new(big.Int).Div(minDifficulty, diff)
for {
select {
case <-stop:
pow.hashRate = 0
return 0, nil
default:
i++
elapsed := time.Now().UnixNano() - start
hashes := ((float64(1e9) / float64(elapsed)) * float64(i-starti)) / 1000
pow.hashRate = int64(hashes)
ret := C.ethash_full_compute(dag.ptr, hash, C.uint64_t(nonce))
result := h256ToHash(ret.result).Big()
// TODO: disagrees with the spec https://github.com/ethereum/wiki/wiki/Ethash#mining
if ret.success && result.Cmp(target) <= 0 {
mixDigest = C.GoBytes(unsafe.Pointer(&ret.mix_hash), C.int(32))
return nonce, mixDigest
}
nonce += 1
}
if !pow.turbo {
time.Sleep(20 * time.Microsecond)
}
}
}
func (pow *Full) GetHashrate() int64 {
// TODO: this needs to use an atomic operation.
return pow.hashRate
}
func (pow *Full) Turbo(on bool) {
// TODO: this needs to use an atomic operation.
pow.turbo = on
}
// Ethash combines block verification with Light and
// nonce searching with Full into a single proof of work.
type Ethash struct {
*Light
*Full
}
// New creates an instance of the proof of work.
// A single instance of Light is shared across all instances
// created with New.
func New() *Ethash {
return &Ethash{sharedLight, &Full{turbo: true}}
}
// NewForTesting creates a proof of work for use in unit tests.
// It uses a smaller DAG and cache size to keep test times low.
// DAG files are stored in a temporary directory.
//
// Nonces found by a testing instance are not verifiable with a
// regular-size cache.
func NewForTesting() (*Ethash, error) {
dir, err := ioutil.TempDir("", "ethash-test")
if err != nil {
return nil, err
}
return &Ethash{&Light{test: true}, &Full{Dir: dir, test: true}}, nil
}
func GetSeedHash(blockNum uint64) ([]byte, error) {
if blockNum >= epochLength*2048 {
return nil, fmt.Errorf("block number too high, limit is %d", epochLength*2048)
}
sh := makeSeedHash(blockNum / epochLength)
return sh[:], nil
}
func makeSeedHash(epoch uint64) (sh common.Hash) {
for ; epoch > 0; epoch-- {
sh = crypto.Sha3Hash(sh[:])
}
return sh
}
