361 lines
9.5 KiB
Go
361 lines
9.5 KiB
Go
package ethash
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/*
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#include "src/libethash/internal.h"
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int ethashGoCallback_cgo(unsigned);
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*/
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import "C"
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import (
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"errors"
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"fmt"
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"io/ioutil"
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"math/big"
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"math/rand"
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"os"
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"os/user"
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"path/filepath"
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"runtime"
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"sync"
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"sync/atomic"
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"time"
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"unsafe"
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/crypto"
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"github.com/ethereum/go-ethereum/logger"
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"github.com/ethereum/go-ethereum/logger/glog"
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"github.com/ethereum/go-ethereum/pow"
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)
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var (
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minDifficulty = new(big.Int).Exp(big.NewInt(2), big.NewInt(256), big.NewInt(0))
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sharedLight = new(Light)
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)
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const (
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epochLength uint64 = 30000
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cacheSizeForTesting C.uint64_t = 1024
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dagSizeForTesting C.uint64_t = 1024 * 32
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)
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var DefaultDir = defaultDir()
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func defaultDir() string {
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home := os.Getenv("HOME")
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if user, err := user.Current(); err == nil {
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home = user.HomeDir
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}
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if runtime.GOOS == "windows" {
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return filepath.Join(home, "AppData", "Ethash")
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}
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return filepath.Join(home, ".ethash")
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}
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// cache wraps an ethash_light_t with some metadata
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// and automatic memory management.
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type cache struct {
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epoch uint64
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test bool
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gen sync.Once // ensures cache is only generated once.
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ptr *C.struct_ethash_light
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}
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// generate creates the actual cache. it can be called from multiple
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// goroutines. the first call will generate the cache, subsequent
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// calls wait until it is generated.
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func (cache *cache) generate() {
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cache.gen.Do(func() {
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started := time.Now()
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seedHash := makeSeedHash(cache.epoch)
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glog.V(logger.Debug).Infof("Generating cache for epoch %d (%x)", cache.epoch, seedHash)
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size := C.ethash_get_cachesize(C.uint64_t(cache.epoch * epochLength))
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if cache.test {
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size = cacheSizeForTesting
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}
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cache.ptr = C.ethash_light_new_internal(size, (*C.ethash_h256_t)(unsafe.Pointer(&seedHash[0])))
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runtime.SetFinalizer(cache, freeCache)
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glog.V(logger.Debug).Infof("Done generating cache for epoch %d, it took %v", cache.epoch, time.Since(started))
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})
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}
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func freeCache(cache *cache) {
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C.ethash_light_delete(cache.ptr)
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cache.ptr = nil
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}
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// Light implements the Verify half of the proof of work.
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// It uses a small in-memory cache to verify the nonces
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// found by Full.
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type Light struct {
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test bool // if set use a smaller cache size
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mu sync.Mutex // protects current
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current *cache // last cache which was generated.
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// TODO: keep multiple caches.
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}
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// Verify checks whether the block's nonce is valid.
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func (l *Light) Verify(block pow.Block) bool {
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// TODO: do ethash_quick_verify before getCache in order
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// to prevent DOS attacks.
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var (
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blockNum = block.NumberU64()
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difficulty = block.Difficulty()
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cache = l.getCache(blockNum)
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dagSize = C.ethash_get_datasize(C.uint64_t(blockNum))
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)
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if l.test {
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dagSize = dagSizeForTesting
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}
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if blockNum >= epochLength*2048 {
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glog.V(logger.Debug).Infof("block number %d too high, limit is %d", epochLength*2048)
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return false
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}
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// Recompute the hash using the cache.
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hash := hashToH256(block.HashNoNonce())
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ret := C.ethash_light_compute_internal(cache.ptr, dagSize, hash, C.uint64_t(block.Nonce()))
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if !ret.success {
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return false
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}
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// Make sure cache is live until after the C call.
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// This is important because a GC might happen and execute
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// the finalizer before the call completes.
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_ = cache
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// The actual check.
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target := new(big.Int).Div(minDifficulty, difficulty)
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return h256ToHash(ret.result).Big().Cmp(target) <= 0
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}
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func h256ToHash(in C.ethash_h256_t) common.Hash {
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return *(*common.Hash)(unsafe.Pointer(&in.b))
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}
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func hashToH256(in common.Hash) C.ethash_h256_t {
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return C.ethash_h256_t{b: *(*[32]C.uint8_t)(unsafe.Pointer(&in[0]))}
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}
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func (l *Light) getCache(blockNum uint64) *cache {
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var c *cache
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epoch := blockNum / epochLength
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// Update or reuse the last cache.
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l.mu.Lock()
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if l.current != nil && l.current.epoch == epoch {
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c = l.current
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} else {
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c = &cache{epoch: epoch, test: l.test}
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l.current = c
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}
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l.mu.Unlock()
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// Wait for the cache to finish generating.
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c.generate()
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return c
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}
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// dag wraps an ethash_full_t with some metadata
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// and automatic memory management.
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type dag struct {
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epoch uint64
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test bool
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dir string
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gen sync.Once // ensures DAG is only generated once.
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ptr *C.struct_ethash_full
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}
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// generate creates the actual DAG. it can be called from multiple
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// goroutines. the first call will generate the DAG, subsequent
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// calls wait until it is generated.
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func (d *dag) generate() {
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d.gen.Do(func() {
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var (
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started = time.Now()
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seedHash = makeSeedHash(d.epoch)
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blockNum = C.uint64_t(d.epoch * epochLength)
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cacheSize = C.ethash_get_cachesize(blockNum)
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dagSize = C.ethash_get_datasize(blockNum)
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)
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if d.test {
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cacheSize = cacheSizeForTesting
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dagSize = dagSizeForTesting
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}
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if d.dir == "" {
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d.dir = DefaultDir
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}
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glog.V(logger.Info).Infof("Generating DAG for epoch %d (%x)", d.epoch, seedHash)
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// Generate a temporary cache.
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// TODO: this could share the cache with Light
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cache := C.ethash_light_new_internal(cacheSize, (*C.ethash_h256_t)(unsafe.Pointer(&seedHash[0])))
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defer C.ethash_light_delete(cache)
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// Generate the actual DAG.
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d.ptr = C.ethash_full_new_internal(
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C.CString(d.dir),
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hashToH256(seedHash),
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dagSize,
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cache,
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(C.ethash_callback_t)(unsafe.Pointer(C.ethashGoCallback_cgo)),
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)
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if d.ptr == nil {
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panic("ethash_full_new IO or memory error")
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}
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runtime.SetFinalizer(d, freeDAG)
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glog.V(logger.Info).Infof("Done generating DAG for epoch %d, it took %v", d.epoch, time.Since(started))
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})
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}
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func freeDAG(h *dag) {
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C.ethash_full_delete(h.ptr)
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h.ptr = nil
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}
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//export ethashGoCallback
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func ethashGoCallback(percent C.unsigned) C.int {
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glog.V(logger.Info).Infof("Still generating DAG: %d%%", percent)
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return 0
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}
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// MakeDAG pre-generates a DAG file for the given block number in the
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// given directory. If dir is the empty string, the default directory
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// is used.
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func MakeDAG(blockNum uint64, dir string) error {
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d := &dag{epoch: blockNum / epochLength, dir: dir}
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if blockNum >= epochLength*2048 {
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return fmt.Errorf("block number too high, limit is %d", epochLength*2048)
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}
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d.generate()
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if d.ptr == nil {
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return errors.New("failed")
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}
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return nil
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}
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// Full implements the Search half of the proof of work.
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type Full struct {
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Dir string // use this to specify a non-default DAG directory
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test bool // if set use a smaller DAG size
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turbo bool
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hashRate int32
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mu sync.Mutex // protects dag
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current *dag // current full DAG
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}
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func (pow *Full) getDAG(blockNum uint64) (d *dag) {
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epoch := blockNum / epochLength
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pow.mu.Lock()
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if pow.current != nil && pow.current.epoch == epoch {
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d = pow.current
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} else {
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d = &dag{epoch: epoch, test: pow.test, dir: pow.Dir}
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pow.current = d
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}
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pow.mu.Unlock()
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// wait for it to finish generating.
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d.generate()
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return d
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}
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func (pow *Full) Search(block pow.Block, stop <-chan struct{}) (nonce uint64, mixDigest []byte) {
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dag := pow.getDAG(block.NumberU64())
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r := rand.New(rand.NewSource(time.Now().UnixNano()))
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diff := block.Difficulty()
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i := int64(0)
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starti := i
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start := time.Now().UnixNano()
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previousHashrate := int32(0)
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nonce = uint64(r.Int63())
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hash := hashToH256(block.HashNoNonce())
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target := new(big.Int).Div(minDifficulty, diff)
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for {
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select {
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case <-stop:
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atomic.AddInt32(&pow.hashRate, -previousHashrate)
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return 0, nil
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default:
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i++
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// we don't have to update hash rate on every nonce, so update after
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// first nonce check and then after 2^X nonces
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if i == 2 || ((i % (1 << 16)) == 0) {
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elapsed := time.Now().UnixNano() - start
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hashes := (float64(1e9) / float64(elapsed)) * float64(i-starti)
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hashrateDiff := int32(hashes) - previousHashrate
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previousHashrate = int32(hashes)
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atomic.AddInt32(&pow.hashRate, hashrateDiff)
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}
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ret := C.ethash_full_compute(dag.ptr, hash, C.uint64_t(nonce))
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result := h256ToHash(ret.result).Big()
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// TODO: disagrees with the spec https://github.com/ethereum/wiki/wiki/Ethash#mining
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if ret.success && result.Cmp(target) <= 0 {
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mixDigest = C.GoBytes(unsafe.Pointer(&ret.mix_hash), C.int(32))
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atomic.AddInt32(&pow.hashRate, -previousHashrate)
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return nonce, mixDigest
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}
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nonce += 1
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}
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if !pow.turbo {
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time.Sleep(20 * time.Microsecond)
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}
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}
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}
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func (pow *Full) GetHashrate() int64 {
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return int64(atomic.LoadInt32(&pow.hashRate))
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}
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func (pow *Full) Turbo(on bool) {
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// TODO: this needs to use an atomic operation.
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pow.turbo = on
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}
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// Ethash combines block verification with Light and
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// nonce searching with Full into a single proof of work.
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type Ethash struct {
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*Light
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*Full
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}
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// New creates an instance of the proof of work.
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// A single instance of Light is shared across all instances
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// created with New.
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func New() *Ethash {
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return &Ethash{sharedLight, &Full{turbo: true}}
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}
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// NewForTesting creates a proof of work for use in unit tests.
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// It uses a smaller DAG and cache size to keep test times low.
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// DAG files are stored in a temporary directory.
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//
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// Nonces found by a testing instance are not verifiable with a
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// regular-size cache.
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func NewForTesting() (*Ethash, error) {
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dir, err := ioutil.TempDir("", "ethash-test")
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if err != nil {
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return nil, err
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}
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return &Ethash{&Light{test: true}, &Full{Dir: dir, test: true}}, nil
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}
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func GetSeedHash(blockNum uint64) ([]byte, error) {
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if blockNum >= epochLength*2048 {
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return nil, fmt.Errorf("block number too high, limit is %d", epochLength*2048)
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}
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sh := makeSeedHash(blockNum / epochLength)
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return sh[:], nil
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}
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func makeSeedHash(epoch uint64) (sh common.Hash) {
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for ; epoch > 0; epoch-- {
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sh = crypto.Sha3Hash(sh[:])
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}
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return sh
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}
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