path: root/consensus/ethash/sealer.go

// 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 ethash

import (
    "bytes"
    crand "crypto/rand"
    "encoding/json"
    "errors"
    "math"
    "math/big"
    "math/rand"
    "net/http"
    "runtime"
    "sync"
    "time"

    "github.com/dexon-foundation/dexon/common"
    "github.com/dexon-foundation/dexon/common/hexutil"
    "github.com/dexon-foundation/dexon/consensus"
    "github.com/dexon-foundation/dexon/core/types"
    "github.com/dexon-foundation/dexon/log"
)

const (
    // staleThreshold is the maximum depth of the acceptable stale but valid ethash solution.
    staleThreshold = 7
)

var (
    errNoMiningWork      = errors.New("no mining work available yet")
    errInvalidSealResult = errors.New("invalid or stale proof-of-work solution")
)

// Seal implements consensus.Engine, attempting to find a nonce that satisfies
// the block's difficulty requirements.
func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, results chan<- *types.Block, stop <-chan struct{}) error {
    // If we're running a fake PoW, simply return a 0 nonce immediately
    if ethash.config.PowMode == ModeFake || ethash.config.PowMode == ModeFullFake {
        header := block.Header()
        header.Nonce, header.MixDigest = types.BlockNonce{}, common.Hash{}
        select {
        case results <- block.WithSeal(header):
        default:
            log.Warn("Sealing result is not read by miner", "mode", "fake", "sealhash", ethash.SealHash(block.Header()))
        }
        return nil
    }
    // If we're running a shared PoW, delegate sealing to it
    if ethash.shared != nil {
        return ethash.shared.Seal(chain, block, results, stop)
    }
    // Create a runner and the multiple search threads it directs
    abort := make(chan struct{})

    ethash.lock.Lock()
    threads := ethash.threads
    if ethash.rand == nil {
        seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
        if err != nil {
            ethash.lock.Unlock()
            return err
        }
        ethash.rand = rand.New(rand.NewSource(seed.Int64()))
    }
    ethash.lock.Unlock()
    if threads == 0 {
        threads = runtime.NumCPU()
    }
    if threads < 0 {
        threads = 0 // Allows disabling local mining without extra logic around local/remote
    }
    // Push new work to remote sealer
    if ethash.workCh != nil {
        ethash.workCh <- &sealTask{block: block, results: results}
    }
    var (
        pend   sync.WaitGroup
        locals = make(chan *types.Block)
    )
    for i := 0; i < threads; i++ {
        pend.Add(1)
        go func(id int, nonce uint64) {
            defer pend.Done()
            ethash.mine(block, id, nonce, abort, locals)
        }(i, uint64(ethash.rand.Int63()))
    }
    // Wait until sealing is terminated or a nonce is found
    go func() {
        var result *types.Block
        select {
        case <-stop:
            // Outside abort, stop all miner threads
            close(abort)
        case result = <-locals:
            // One of the threads found a block, abort all others
            select {
            case results <- result:
            default:
                log.Warn("Sealing result is not read by miner", "mode", "local", "sealhash", ethash.SealHash(block.Header()))
            }
            close(abort)
        case <-ethash.update:
            // Thread count was changed on user request, restart
            close(abort)
            if err := ethash.Seal(chain, block, results, stop); err != nil {
                log.Error("Failed to restart sealing after update", "err", err)
            }
        }
        // Wait for all miners to terminate and return the block
        pend.Wait()
    }()
    return nil
}

// mine is the actual proof-of-work miner that searches for a nonce starting from
// seed that results in correct final block difficulty.
func (ethash *Ethash) mine(block *types.Block, id int, seed uint64, abort chan struct{}, found chan *types.Block) {
    // Extract some data from the header
    var (
        header  = block.Header()
        hash    = ethash.SealHash(header).Bytes()
        target  = new(big.Int).Div(two256, header.Difficulty)
        number  = header.Number.Uint64()
        dataset = ethash.dataset(number, false)
    )
    // Start generating random nonces until we abort or find a good one
    var (
        attempts = int64(0)
        nonce    = seed
    )
    logger := log.New("miner", id)
    logger.Trace("Started ethash search for new nonces", "seed", seed)
search:
    for {
        select {
        case <-abort:
            // Mining terminated, update stats and abort
            logger.Trace("Ethash nonce search aborted", "attempts", nonce-seed)
            ethash.hashrate.Mark(attempts)
            break search

        default:
            // We don't have to update hash rate on every nonce, so update after after 2^X nonces
            attempts++
            if (attempts % (1 << 15)) == 0 {
                ethash.hashrate.Mark(attempts)
                attempts = 0
            }
            // Compute the PoW value of this nonce
            digest, result := hashimotoFull(dataset.dataset, hash, nonce)
            if new(big.Int).SetBytes(result).Cmp(target) <= 0 {
                // Correct nonce found, create a new header with it
                header = types.CopyHeader(header)
                header.Nonce = types.EncodeNonce(nonce)
                header.MixDigest = common.BytesToHash(digest)

                // Seal and return a block (if still needed)
                select {
                case found <- block.WithSeal(header):
                    logger.Trace("Ethash nonce found and reported", "attempts", nonce-seed, "nonce", nonce)
                case <-abort:
                    logger.Trace("Ethash nonce found but discarded", "attempts", nonce-seed, "nonce", nonce)
                }
                break search
            }
            nonce++
        }
    }
    // Datasets are unmapped in a finalizer. Ensure that the dataset stays live
    // during sealing so it's not unmapped while being read.
    runtime.KeepAlive(dataset)
}

// remote is a standalone goroutine to handle remote mining related stuff.
func (ethash *Ethash) remote(notify []string, noverify bool) {
    var (
        works = make(map[common.Hash]*types.Block)
        rates = make(map[common.Hash]hashrate)

        results      chan<- *types.Block
        currentBlock *types.Block
        currentWork  [4]string

        notifyTransport = &http.Transport{}
        notifyClient    = &http.Client{
            Transport: notifyTransport,
            Timeout:   time.Second,
        }
        notifyReqs = make([]*http.Request, len(notify))
    )
    // notifyWork notifies all the specified mining endpoints of the availability of
    // new work to be processed.
    notifyWork := func() {
        work := currentWork
        blob, _ := json.Marshal(work)

        for i, url := range notify {
            // Terminate any previously pending request and create the new work
            if notifyReqs[i] != nil {
                notifyTransport.CancelRequest(notifyReqs[i])
            }
            notifyReqs[i], _ = http.NewRequest("POST", url, bytes.NewReader(blob))
            notifyReqs[i].Header.Set("Content-Type", "application/json")

            // Push the new work concurrently to all the remote nodes
            go func(req *http.Request, url string) {
                res, err := notifyClient.Do(req)
                if err != nil {
                    log.Warn("Failed to notify remote miner", "err", err)
                } else {
                    log.Trace("Notified remote miner", "miner", url, "hash", log.Lazy{Fn: func() common.Hash { return common.HexToHash(work[0]) }}, "target", work[2])
                    res.Body.Close()
                }
            }(notifyReqs[i], url)
        }
    }
    // makeWork creates a work package for external miner.
    //
    // The work package consists of 3 strings:
    //   result[0], 32 bytes hex encoded current block header pow-hash
    //   result[1], 32 bytes hex encoded seed hash used for DAG
    //   result[2], 32 bytes hex encoded boundary condition ("target"), 2^256/difficulty
    //   result[3], hex encoded block number
    makeWork := func(block *types.Block) {
        hash := ethash.SealHash(block.Header())

        currentWork[0] = hash.Hex()
        currentWork[1] = common.BytesToHash(SeedHash(block.NumberU64())).Hex()
        currentWork[2] = common.BytesToHash(new(big.Int).Div(two256, block.Difficulty()).Bytes()).Hex()
        currentWork[3] = hexutil.EncodeBig(block.Number())

        // Trace the seal work fetched by remote sealer.
        currentBlock = block
        works[hash] = block
    }
    // submitWork verifies the submitted pow solution, returning
    // whether the solution was accepted or not (not can be both a bad pow as well as
    // any other error, like no pending work or stale mining result).
    submitWork := func(nonce types.BlockNonce, mixDigest common.Hash, sealhash common.Hash) bool {
        if currentBlock == nil {
            log.Error("Pending work without block", "sealhash", sealhash)
            return false
        }
        // Make sure the work submitted is present
        block := works[sealhash]
        if block == nil {
            log.Warn("Work submitted but none pending", "sealhash", sealhash, "curnumber", currentBlock.NumberU64())
            return false
        }
        // Verify the correctness of submitted result.
        header := block.Header()
        header.Nonce = nonce
        header.MixDigest = mixDigest

        start := time.Now()
        if !noverify {
            if err := ethash.verifySeal(nil, header, true); err != nil {
                log.Warn("Invalid proof-of-work submitted", "sealhash", sealhash, "elapsed", time.Since(start), "err", err)
                return false
            }
        }
        // Make sure the result channel is assigned.
        if results == nil {
            log.Warn("Ethash result channel is empty, submitted mining result is rejected")
            return false
        }
        log.Trace("Verified correct proof-of-work", "sealhash", sealhash, "elapsed", time.Since(start))

        // Solutions seems to be valid, return to the miner and notify acceptance.
        solution := block.WithSeal(header)

        // The submitted solution is within the scope of acceptance.
        if solution.NumberU64()+staleThreshold > currentBlock.NumberU64() {
            select {
            case results <- solution:
                log.Debug("Work submitted is acceptable", "number", solution.NumberU64(), "sealhash", sealhash, "hash", solution.Hash())
                return true
            default:
                log.Warn("Sealing result is not read by miner", "mode", "remote", "sealhash", sealhash)
                return false
            }
        }
        // The submitted block is too old to accept, drop it.
        log.Warn("Work submitted is too old", "number", solution.NumberU64(), "sealhash", sealhash, "hash", solution.Hash())
        return false
    }

    ticker := time.NewTicker(5 * time.Second)
    defer ticker.Stop()

    for {
        select {
        case work := <-ethash.workCh:
            // Update current work with new received block.
            // Note same work can be past twice, happens when changing CPU threads.
            results = work.results

            makeWork(work.block)

            // Notify and requested URLs of the new work availability
            notifyWork()

        case work := <-ethash.fetchWorkCh:
            // Return current mining work to remote miner.
            if currentBlock == nil {
                work.errc <- errNoMiningWork
            } else {
                work.res <- currentWork
            }

        case result := <-ethash.submitWorkCh:
            // Verify submitted PoW solution based on maintained mining blocks.
            if submitWork(result.nonce, result.mixDigest, result.hash) {
                result.errc <- nil
            } else {
                result.errc <- errInvalidSealResult
            }

        case result := <-ethash.submitRateCh:
            // Trace remote sealer's hash rate by submitted value.
            rates[result.id] = hashrate{rate: result.rate, ping: time.Now()}
            close(result.done)

        case req := <-ethash.fetchRateCh:
            // Gather all hash rate submitted by remote sealer.
            var total uint64
            for _, rate := range rates {
                // this could overflow
                total += rate.rate
            }
            req <- total

        case <-ticker.C:
            // Clear stale submitted hash rate.
            for id, rate := range rates {
                if time.Since(rate.ping) > 10*time.Second {
                    delete(rates, id)
                }
            }
            // Clear stale pending blocks
            if currentBlock != nil {
                for hash, block := range works {
                    if block.NumberU64()+staleThreshold <= currentBlock.NumberU64() {
                        delete(works, hash)
                    }
                }
            }

        case errc := <-ethash.exitCh:
            // Exit remote loop if ethash is closed and return relevant error.
            errc <- nil
            log.Trace("Ethash remote sealer is exiting")
            return
        }
    }
}