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" "sync/atomic" "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 int32 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() previousHashrate := int32(0) nonce = uint64(r.Int63()) hash := hashToH256(block.HashNoNonce()) target := new(big.Int).Div(minDifficulty, diff) for { select { case <-stop: atomic.AddInt32(&pow.hashRate, -previousHashrate) return 0, nil default: i++ // we don't have to update hash rate on every nonce, so update after // first nonce check and then after 2^X nonces if i == 2 || ((i % (1 << 16)) == 0) { elapsed := time.Now().UnixNano() - start hashes := (float64(1e9) / float64(elapsed)) * float64(i-starti) hashrateDiff := int32(hashes) - previousHashrate previousHashrate = int32(hashes) atomic.AddInt32(&pow.hashRate, hashrateDiff) } 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)) atomic.AddInt32(&pow.hashRate, -previousHashrate) return nonce, mixDigest } nonce += 1 } if !pow.turbo { time.Sleep(20 * time.Microsecond) } } } func (pow *Full) GetHashrate() int64 { return int64(atomic.LoadInt32(&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 }