consensus/ethash: move remote agent logic to ethash internal (#15853)

* consensus/ethash: start remote ggoroutine to handle remote mining

* consensus/ethash: expose remote miner api

* consensus/ethash: expose submitHashrate api

* miner, ethash: push empty block to sealer without waiting execution

* consensus, internal: add getHashrate API for ethash

* consensus: add three method for consensus interface

* miner: expose consensus engine running status to miner

* eth, miner: specify etherbase when miner created

* miner: commit new work when consensus engine is started

* consensus, miner: fix some logics

* all: delete useless interfaces

* consensus: polish a bit

7 files changed, 483 insertions, 16 deletions

diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go
index 8968f500f..59bb3d40b 100644
--- a/consensus/clique/clique.go
+++ b/consensus/clique/clique.go
@@ -672,6 +672,11 @@ func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
 	return new(big.Int).Set(diffNoTurn)
 }
 
+// Close implements consensus.Engine. It's a noop for clique as there is are no background threads.
+func (c *Clique) Close() error {
+	return nil
+}
+
 // APIs implements consensus.Engine, returning the user facing RPC API to allow
 // controlling the signer voting.
 func (c *Clique) APIs(chain consensus.ChainReader) []rpc.API {
diff --git a/consensus/consensus.go b/consensus/consensus.go
index 5774af1a7..827175444 100644
--- a/consensus/consensus.go
+++ b/consensus/consensus.go
@@ -96,6 +96,9 @@ type Engine interface {
 
 	// APIs returns the RPC APIs this consensus engine provides.
 	APIs(chain ChainReader) []rpc.API
+
+	// Close terminates any background threads maintained by the consensus engine.
+	Close() error
 }
 
 // PoW is a consensus engine based on proof-of-work.
diff --git a/consensus/ethash/algorithm_test.go b/consensus/ethash/algorithm_test.go
index f0c6465fd..e7625f7c0 100644
--- a/consensus/ethash/algorithm_test.go
+++ b/consensus/ethash/algorithm_test.go
@@ -730,6 +730,7 @@ func TestConcurrentDiskCacheGeneration(t *testing.T) {
 		go func(idx int) {
 			defer pend.Done()
 			ethash := New(Config{cachedir, 0, 1, "", 0, 0, ModeNormal})
+			defer ethash.Close()
 			if err := ethash.VerifySeal(nil, block.Header()); err != nil {
 				t.Errorf("proc %d: block verification failed: %v", idx, err)
 			}
diff --git a/consensus/ethash/api.go b/consensus/ethash/api.go
new file mode 100644
index 000000000..a04ea235d
--- /dev/null
+++ b/consensus/ethash/api.go
@@ -0,0 +1,117 @@
+// Copyright 2018 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 (
+	"errors"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+var errEthashStopped = errors.New("ethash stopped")
+
+// API exposes ethash related methods for the RPC interface.
+type API struct {
+	ethash *Ethash // Make sure the mode of ethash is normal.
+}
+
+// GetWork returns 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
+func (api *API) GetWork() ([3]string, error) {
+	if api.ethash.config.PowMode != ModeNormal && api.ethash.config.PowMode != ModeTest {
+		return [3]string{}, errors.New("not supported")
+	}
+
+	var (
+		workCh = make(chan [3]string, 1)
+		errc   = make(chan error, 1)
+	)
+
+	select {
+	case api.ethash.fetchWorkCh <- &sealWork{errc: errc, res: workCh}:
+	case <-api.ethash.exitCh:
+		return [3]string{}, errEthashStopped
+	}
+
+	select {
+	case work := <-workCh:
+		return work, nil
+	case err := <-errc:
+		return [3]string{}, err
+	}
+}
+
+// SubmitWork can be used by external miner to submit their POW solution.
+// It returns an indication if the work was accepted.
+// Note either an invalid solution, a stale work a non-existent work will return false.
+func (api *API) SubmitWork(nonce types.BlockNonce, hash, digest common.Hash) bool {
+	if api.ethash.config.PowMode != ModeNormal && api.ethash.config.PowMode != ModeTest {
+		return false
+	}
+
+	var errc = make(chan error, 1)
+
+	select {
+	case api.ethash.submitWorkCh <- &mineResult{
+		nonce:     nonce,
+		mixDigest: digest,
+		hash:      hash,
+		errc:      errc,
+	}:
+	case <-api.ethash.exitCh:
+		return false
+	}
+
+	err := <-errc
+	return err == nil
+}
+
+// SubmitHashrate can be used for remote miners to submit their hash rate.
+// This enables the node to report the combined hash rate of all miners
+// which submit work through this node.
+//
+// It accepts the miner hash rate and an identifier which must be unique
+// between nodes.
+func (api *API) SubmitHashRate(rate hexutil.Uint64, id common.Hash) bool {
+	if api.ethash.config.PowMode != ModeNormal && api.ethash.config.PowMode != ModeTest {
+		return false
+	}
+
+	var done = make(chan struct{}, 1)
+
+	select {
+	case api.ethash.submitRateCh <- &hashrate{done: done, rate: uint64(rate), id: id}:
+	case <-api.ethash.exitCh:
+		return false
+	}
+
+	// Block until hash rate submitted successfully.
+	<-done
+
+	return true
+}
+
+// GetHashrate returns the current hashrate for local CPU miner and remote miner.
+func (api *API) GetHashrate() uint64 {
+	return uint64(api.ethash.Hashrate())
+}
diff --git a/consensus/ethash/ethash.go b/consensus/ethash/ethash.go
index f79dd6c36..0cb3059b9 100644
--- a/consensus/ethash/ethash.go
+++ b/consensus/ethash/ethash.go
@@ -33,7 +33,9 @@ import (
 	"unsafe"
 
 	mmap "github.com/edsrzf/mmap-go"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -389,6 +391,30 @@ type Config struct {
 	PowMode        Mode
 }
 
+// mineResult wraps the pow solution parameters for the specified block.
+type mineResult struct {
+	nonce     types.BlockNonce
+	mixDigest common.Hash
+	hash      common.Hash
+
+	errc chan error
+}
+
+// hashrate wraps the hash rate submitted by the remote sealer.
+type hashrate struct {
+	id   common.Hash
+	ping time.Time
+	rate uint64
+
+	done chan struct{}
+}
+
+// sealWork wraps a seal work package for remote sealer.
+type sealWork struct {
+	errc chan error
+	res  chan [3]string
+}
+
 // Ethash is a consensus engine based on proof-of-work implementing the ethash
 // algorithm.
 type Ethash struct {
@@ -403,15 +429,25 @@ type Ethash struct {
 	update   chan struct{} // Notification channel to update mining parameters
 	hashrate metrics.Meter // Meter tracking the average hashrate
 
+	// Remote sealer related fields
+	workCh       chan *types.Block // Notification channel to push new work to remote sealer
+	resultCh     chan *types.Block // Channel used by mining threads to return result
+	fetchWorkCh  chan *sealWork    // Channel used for remote sealer to fetch mining work
+	submitWorkCh chan *mineResult  // Channel used for remote sealer to submit their mining result
+	fetchRateCh  chan chan uint64  // Channel used to gather submitted hash rate for local or remote sealer.
+	submitRateCh chan *hashrate    // Channel used for remote sealer to submit their mining hashrate
+
 	// The fields below are hooks for testing
 	shared    *Ethash       // Shared PoW verifier to avoid cache regeneration
 	fakeFail  uint64        // Block number which fails PoW check even in fake mode
 	fakeDelay time.Duration // Time delay to sleep for before returning from verify
 
-	lock sync.Mutex // Ensures thread safety for the in-memory caches and mining fields
+	lock      sync.Mutex      // Ensures thread safety for the in-memory caches and mining fields
+	closeOnce sync.Once       // Ensures exit channel will not be closed twice.
+	exitCh    chan chan error // Notification channel to exiting backend threads
 }
 
-// New creates a full sized ethash PoW scheme.
+// New creates a full sized ethash PoW scheme and starts a background thread for remote mining.
 func New(config Config) *Ethash {
 	if config.CachesInMem <= 0 {
 		log.Warn("One ethash cache must always be in memory", "requested", config.CachesInMem)
@@ -423,19 +459,43 @@ func New(config Config) *Ethash {
 	if config.DatasetDir != "" && config.DatasetsOnDisk > 0 {
 		log.Info("Disk storage enabled for ethash DAGs", "dir", config.DatasetDir, "count", config.DatasetsOnDisk)
 	}
-	return &Ethash{
-		config:   config,
-		caches:   newlru("cache", config.CachesInMem, newCache),
-		datasets: newlru("dataset", config.DatasetsInMem, newDataset),
-		update:   make(chan struct{}),
-		hashrate: metrics.NewMeter(),
+	ethash := &Ethash{
+		config:       config,
+		caches:       newlru("cache", config.CachesInMem, newCache),
+		datasets:     newlru("dataset", config.DatasetsInMem, newDataset),
+		update:       make(chan struct{}),
+		hashrate:     metrics.NewMeter(),
+		workCh:       make(chan *types.Block),
+		resultCh:     make(chan *types.Block),
+		fetchWorkCh:  make(chan *sealWork),
+		submitWorkCh: make(chan *mineResult),
+		fetchRateCh:  make(chan chan uint64),
+		submitRateCh: make(chan *hashrate),
+		exitCh:       make(chan chan error),
 	}
+	go ethash.remote()
+	return ethash
 }
 
 // NewTester creates a small sized ethash PoW scheme useful only for testing
 // purposes.
 func NewTester() *Ethash {
-	return New(Config{CachesInMem: 1, PowMode: ModeTest})
+	ethash := &Ethash{
+		config:       Config{PowMode: ModeTest},
+		caches:       newlru("cache", 1, newCache),
+		datasets:     newlru("dataset", 1, newDataset),
+		update:       make(chan struct{}),
+		hashrate:     metrics.NewMeter(),
+		workCh:       make(chan *types.Block),
+		resultCh:     make(chan *types.Block),
+		fetchWorkCh:  make(chan *sealWork),
+		submitWorkCh: make(chan *mineResult),
+		fetchRateCh:  make(chan chan uint64),
+		submitRateCh: make(chan *hashrate),
+		exitCh:       make(chan chan error),
+	}
+	go ethash.remote()
+	return ethash
 }
 
 // NewFaker creates a ethash consensus engine with a fake PoW scheme that accepts
@@ -489,6 +549,22 @@ func NewShared() *Ethash {
 	return &Ethash{shared: sharedEthash}
 }
 
+// Close closes the exit channel to notify all backend threads exiting.
+func (ethash *Ethash) Close() error {
+	var err error
+	ethash.closeOnce.Do(func() {
+		// Short circuit if the exit channel is not allocated.
+		if ethash.exitCh == nil {
+			return
+		}
+		errc := make(chan error)
+		ethash.exitCh <- errc
+		err = <-errc
+		close(ethash.exitCh)
+	})
+	return err
+}
+
 // 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.
@@ -561,14 +637,44 @@ func (ethash *Ethash) SetThreads(threads int) {
 
 // Hashrate implements PoW, returning the measured rate of the search invocations
 // per second over the last minute.
+// Note the returned hashrate includes local hashrate, but also includes the total
+// hashrate of all remote miner.
 func (ethash *Ethash) Hashrate() float64 {
-	return ethash.hashrate.Rate1()
+	// Short circuit if we are run the ethash in normal/test mode.
+	if ethash.config.PowMode != ModeNormal && ethash.config.PowMode != ModeTest {
+		return ethash.hashrate.Rate1()
+	}
+	var res = make(chan uint64, 1)
+
+	select {
+	case ethash.fetchRateCh <- res:
+	case <-ethash.exitCh:
+		// Return local hashrate only if ethash is stopped.
+		return ethash.hashrate.Rate1()
+	}
+
+	// Gather total submitted hash rate of remote sealers.
+	return ethash.hashrate.Rate1() + float64(<-res)
 }
 
-// APIs implements consensus.Engine, returning the user facing RPC APIs. Currently
-// that is empty.
+// APIs implements consensus.Engine, returning the user facing RPC APIs.
 func (ethash *Ethash) APIs(chain consensus.ChainReader) []rpc.API {
-	return nil
+	// In order to ensure backward compatibility, we exposes ethash RPC APIs
+	// to both eth and ethash namespaces.
+	return []rpc.API{
+		{
+			Namespace: "eth",
+			Version:   "1.0",
+			Service:   &API{ethash},
+			Public:    true,
+		},
+		{
+			Namespace: "ethash",
+			Version:   "1.0",
+			Service:   &API{ethash},
+			Public:    true,
+		},
+	}
 }
 
 // SeedHash is the seed to use for generating a verification cache and the mining
diff --git a/consensus/ethash/ethash_test.go b/consensus/ethash/ethash_test.go
index 31116da43..ccdd30fb0 100644
--- a/consensus/ethash/ethash_test.go
+++ b/consensus/ethash/ethash_test.go
@@ -23,7 +23,10 @@ import (
 	"os"
 	"sync"
 	"testing"
+	"time"
 
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/types"
 )
 
@@ -32,6 +35,7 @@ func TestTestMode(t *testing.T) {
 	head := &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(100)}
 
 	ethash := NewTester()
+	defer ethash.Close()
 	block, err := ethash.Seal(nil, types.NewBlockWithHeader(head), nil)
 	if err != nil {
 		t.Fatalf("failed to seal block: %v", err)
@@ -52,6 +56,7 @@ func TestCacheFileEvict(t *testing.T) {
 	}
 	defer os.RemoveAll(tmpdir)
 	e := New(Config{CachesInMem: 3, CachesOnDisk: 10, CacheDir: tmpdir, PowMode: ModeTest})
+	defer e.Close()
 
 	workers := 8
 	epochs := 100
@@ -77,3 +82,90 @@ func verifyTest(wg *sync.WaitGroup, e *Ethash, workerIndex, epochs int) {
 		e.VerifySeal(nil, head)
 	}
 }
+
+func TestRemoteSealer(t *testing.T) {
+	ethash := NewTester()
+	defer ethash.Close()
+	api := &API{ethash}
+	if _, err := api.GetWork(); err != errNoMiningWork {
+		t.Error("expect to return an error indicate there is no mining work")
+	}
+
+	head := &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(100)}
+	block := types.NewBlockWithHeader(head)
+
+	// Push new work.
+	ethash.Seal(nil, block, nil)
+
+	var (
+		work [3]string
+		err  error
+	)
+	if work, err = api.GetWork(); err != nil || work[0] != block.HashNoNonce().Hex() {
+		t.Error("expect to return a mining work has same hash")
+	}
+
+	if res := api.SubmitWork(types.BlockNonce{}, block.HashNoNonce(), common.Hash{}); res {
+		t.Error("expect to return false when submit a fake solution")
+	}
+
+	// Push new block with same block number to replace the original one.
+	head = &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(1000)}
+	block = types.NewBlockWithHeader(head)
+	ethash.Seal(nil, block, nil)
+
+	if work, err = api.GetWork(); err != nil || work[0] != block.HashNoNonce().Hex() {
+		t.Error("expect to return the latest pushed work")
+	}
+
+	// Push block with higher block number.
+	newHead := &types.Header{Number: big.NewInt(2), Difficulty: big.NewInt(100)}
+	newBlock := types.NewBlockWithHeader(newHead)
+	ethash.Seal(nil, newBlock, nil)
+
+	if res := api.SubmitWork(types.BlockNonce{}, block.HashNoNonce(), common.Hash{}); res {
+		t.Error("expect to return false when submit a stale solution")
+	}
+}
+
+func TestHashRate(t *testing.T) {
+	var (
+		ethash   = NewTester()
+		api      = &API{ethash}
+		hashrate = []hexutil.Uint64{100, 200, 300}
+		expect   uint64
+		ids      = []common.Hash{common.HexToHash("a"), common.HexToHash("b"), common.HexToHash("c")}
+	)
+
+	defer ethash.Close()
+
+	if tot := ethash.Hashrate(); tot != 0 {
+		t.Error("expect the result should be zero")
+	}
+
+	for i := 0; i < len(hashrate); i += 1 {
+		if res := api.SubmitHashRate(hashrate[i], ids[i]); !res {
+			t.Error("remote miner submit hashrate failed")
+		}
+		expect += uint64(hashrate[i])
+	}
+	if tot := ethash.Hashrate(); tot != float64(expect) {
+		t.Error("expect total hashrate should be same")
+	}
+}
+
+func TestClosedRemoteSealer(t *testing.T) {
+	ethash := NewTester()
+	// Make sure exit channel has been listened
+	time.Sleep(1 * time.Second)
+	ethash.Close()
+
+	api := &API{ethash}
+	if _, err := api.GetWork(); err != errEthashStopped {
+		t.Error("expect to return an error to indicate ethash is stopped")
+	}
+
+	if res := api.SubmitHashRate(hexutil.Uint64(100), common.HexToHash("a")); res {
+		t.Error("expect to return false when submit hashrate to a stopped ethash")
+	}
+}
diff --git a/consensus/ethash/sealer.go b/consensus/ethash/sealer.go
index b5e742d8b..a9449d406 100644
--- a/consensus/ethash/sealer.go
+++ b/consensus/ethash/sealer.go
@@ -18,11 +18,13 @@ package ethash
 
 import (
 	crand "crypto/rand"
+	"errors"
 	"math"
 	"math/big"
 	"math/rand"
 	"runtime"
 	"sync"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/consensus"
@@ -30,6 +32,11 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 )
 
+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, stop <-chan struct{}) (*types.Block, error) {
@@ -45,7 +52,6 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	}
 	// Create a runner and the multiple search threads it directs
 	abort := make(chan struct{})
-	found := make(chan *types.Block)
 
 	ethash.lock.Lock()
 	threads := ethash.threads
@@ -64,12 +70,16 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	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 <- block
+	}
 	var pend sync.WaitGroup
 	for i := 0; i < threads; i++ {
 		pend.Add(1)
 		go func(id int, nonce uint64) {
 			defer pend.Done()
-			ethash.mine(block, id, nonce, abort, found)
+			ethash.mine(block, id, nonce, abort, ethash.resultCh)
 		}(i, uint64(ethash.rand.Int63()))
 	}
 	// Wait until sealing is terminated or a nonce is found
@@ -78,7 +88,7 @@ func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop
 	case <-stop:
 		// Outside abort, stop all miner threads
 		close(abort)
-	case result = <-found:
+	case result = <-ethash.resultCh:
 		// One of the threads found a block, abort all others
 		close(abort)
 	case <-ethash.update:
@@ -150,3 +160,136 @@ search:
 	// during sealing so it's not unmapped while being read.
 	runtime.KeepAlive(dataset)
 }
+
+// remote starts a standalone goroutine to handle remote mining related stuff.
+func (ethash *Ethash) remote() {
+	var (
+		works       = make(map[common.Hash]*types.Block)
+		rates       = make(map[common.Hash]hashrate)
+		currentWork *types.Block
+	)
+
+	// getWork returns 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
+	getWork := func() ([3]string, error) {
+		var res [3]string
+		if currentWork == nil {
+			return res, errNoMiningWork
+		}
+		res[0] = currentWork.HashNoNonce().Hex()
+		res[1] = common.BytesToHash(SeedHash(currentWork.NumberU64())).Hex()
+
+		// Calculate the "target" to be returned to the external sealer.
+		n := big.NewInt(1)
+		n.Lsh(n, 255)
+		n.Div(n, currentWork.Difficulty())
+		n.Lsh(n, 1)
+		res[2] = common.BytesToHash(n.Bytes()).Hex()
+
+		// Trace the seal work fetched by remote sealer.
+		works[currentWork.HashNoNonce()] = currentWork
+		return res, nil
+	}
+
+	// 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, hash common.Hash) bool {
+		// Make sure the work submitted is present
+		block := works[hash]
+		if block == nil {
+			log.Info("Work submitted but none pending", "hash", hash)
+			return false
+		}
+
+		// Verify the correctness of submitted result.
+		header := block.Header()
+		header.Nonce = nonce
+		header.MixDigest = mixDigest
+		if err := ethash.VerifySeal(nil, header); err != nil {
+			log.Warn("Invalid proof-of-work submitted", "hash", hash, "err", err)
+			return false
+		}
+
+		// Make sure the result channel is created.
+		if ethash.resultCh == nil {
+			log.Warn("Ethash result channel is empty, submitted mining result is rejected")
+			return false
+		}
+
+		// Solutions seems to be valid, return to the miner and notify acceptance.
+		select {
+		case ethash.resultCh <- block.WithSeal(header):
+			delete(works, hash)
+			return true
+		default:
+			log.Info("Work submitted is stale", "hash", hash)
+			return false
+		}
+	}
+
+	ticker := time.NewTicker(5 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case block := <-ethash.workCh:
+			if currentWork != nil && block.ParentHash() != currentWork.ParentHash() {
+				// Start new round mining, throw out all previous work.
+				works = make(map[common.Hash]*types.Block)
+			}
+			// Update current work with new received block.
+			// Note same work can be past twice, happens when changing CPU threads.
+			currentWork = block
+
+		case work := <-ethash.fetchWorkCh:
+			// Return current mining work to remote miner.
+			miningWork, err := getWork()
+			if err != nil {
+				work.errc <- err
+			} else {
+				work.res <- miningWork
+			}
+
+		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)
+				}
+			}
+
+		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
+		}
+	}
+}