les: implement retrieve manager

les/handler.go

@@ -102,7 +102,9 @@ type ProtocolManager struct {
 	odr         *LesOdr
 	server      *LesServer
 	serverPool  *serverPool
+	lesTopic    discv5.Topic
 	reqDist     *requestDistributor
+	retriever   *retrieveManager
 
 	downloader *downloader.Downloader
 	fetcher    *lightFetcher
@@ -202,29 +204,25 @@ func NewProtocolManager(chainConfig *params.ChainConfig, lightSync bool, network
 		manager.downloader = downloader.New(downloader.LightSync, chainDb, manager.eventMux, blockchain.HasHeader, nil, blockchain.GetHeaderByHash,
 			nil, blockchain.CurrentHeader, nil, nil, nil, blockchain.GetTdByHash,
 			blockchain.InsertHeaderChain, nil, nil, blockchain.Rollback, removePeer)
-	}
 
-	manager.reqDist = newRequestDistributor(func() map[distPeer]struct{} {
-		m := make(map[distPeer]struct{})
-		peers := manager.peers.AllPeers()
-		for _, peer := range peers {
-			m[peer] = struct{}{}
+		manager.reqDist = newRequestDistributor(func() map[distPeer]struct{} {
+			m := make(map[distPeer]struct{})
+			peers := manager.peers.AllPeers()
+			for _, peer := range peers {
+				m[peer] = struct{}{}
+			}
+			return m
+		}, manager.quitSync)
+
+		manager.lesTopic = discv5.Topic("LES@" + common.Bytes2Hex(manager.blockchain.Genesis().Hash().Bytes()[0:8]))
+		manager.serverPool = newServerPool(manager.chainDb, []byte("serverPool/"), manager.lesTopic, manager.quitSync, &manager.wg)
+		manager.retriever = newRetrieveManager(manager.reqDist, manager.serverPool, removePeer)
+		if odr != nil {
+			odr.retriever = manager.retriever
 		}
-		return m
-	}, manager.quitSync)
-	if odr != nil {
-		odr.removePeer = removePeer
-		odr.reqDist = manager.reqDist
+		manager.fetcher = newLightFetcher(manager)
 	}
 
-	/*validator := func(block *types.Block, parent *types.Block) error {
-		return core.ValidateHeader(pow, block.Header(), parent.Header(), true, false)
-	}
-	heighter := func() uint64 {
-		return chainman.LastBlockNumberU64()
-	}
-	manager.fetcher = fetcher.New(chainman.GetBlockNoOdr, validator, nil, heighter, chainman.InsertChain, manager.removePeer)
-	*/
 	return manager, nil
 }
 
@@ -261,23 +259,20 @@ func (pm *ProtocolManager) Start(srvr *p2p.Server) {
 	if srvr != nil {
 		topicDisc = srvr.DiscV5
 	}
-	lesTopic := discv5.Topic("LES@" + common.Bytes2Hex(pm.blockchain.Genesis().Hash().Bytes()[0:8]))
 	if pm.lightSync {
 		// start sync handler
 		if srvr != nil { // srvr is nil during testing
-			pm.serverPool = newServerPool(pm.chainDb, []byte("serverPool/"), srvr, lesTopic, pm.quitSync, &pm.wg)
-			pm.odr.serverPool = pm.serverPool
-			pm.fetcher = newLightFetcher(pm)
+			pm.serverPool.setServer(srvr)
 		}
 		go pm.syncer()
 	} else {
 		if topicDisc != nil {
 			go func() {
-				logger := log.New("topic", lesTopic)
+				logger := log.New("topic", pm.lesTopic)
 				logger.Info("Starting topic registration")
 				defer logger.Info("Terminated topic registration")
 
-				topicDisc.RegisterTopic(lesTopic, pm.quitSync)
+				topicDisc.RegisterTopic(pm.lesTopic, pm.quitSync)
 			}()
 		}
 		go func() {
@@ -926,7 +921,7 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 	}
 
 	if deliverMsg != nil {
-		err := pm.odr.Deliver(p, deliverMsg)
+		err := pm.retriever.deliver(p, deliverMsg)
 		if err != nil {
 			p.responseErrors++
 			if p.responseErrors > maxResponseErrors {

les/odr.go

@@ -18,45 +18,23 @@ package les
 
 import (
 	"context"
-	"crypto/rand"
-	"encoding/binary"
-	"sync"
-	"time"
 
-	"github.com/ethereum/go-ethereum/common/mclock"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/light"
 	"github.com/ethereum/go-ethereum/log"
 )
 
-var (
-	softRequestTimeout = time.Millisecond * 500
-	hardRequestTimeout = time.Second * 10
-)
-
-// peerDropFn is a callback type for dropping a peer detected as malicious.
-type peerDropFn func(id string)
-
-type odrPeerSelector interface {
-	adjustResponseTime(*poolEntry, time.Duration, bool)
-}
-
+// LesOdr implements light.OdrBackend
 type LesOdr struct {
-	light.OdrBackend
-	db           ethdb.Database
-	stop         chan struct{}
-	removePeer   peerDropFn
-	mlock, clock sync.Mutex
-	sentReqs     map[uint64]*sentReq
-	serverPool   odrPeerSelector
-	reqDist      *requestDistributor
+	db        ethdb.Database
+	stop      chan struct{}
+	retriever *retrieveManager
 }
 
 func NewLesOdr(db ethdb.Database) *LesOdr {
 	return &LesOdr{
-		db:       db,
-		stop:     make(chan struct{}),
-		sentReqs: make(map[uint64]*sentReq),
+		db:   db,
+		stop: make(chan struct{}),
 	}
 }
 
@@ -68,17 +46,6 @@ func (odr *LesOdr) Database() ethdb.Database {
 	return odr.db
 }
 
-// validatorFunc is a function that processes a message.
-type validatorFunc func(ethdb.Database, *Msg) error
-
-// sentReq is a request waiting for an answer that satisfies its valFunc
-type sentReq struct {
-	valFunc  validatorFunc
-	sentTo   map[*peer]chan struct{}
-	lock     sync.RWMutex  // protects acces to sentTo
-	answered chan struct{} // closed and set to nil when any peer answers it
-}
-
 const (
 	MsgBlockBodies = iota
 	MsgCode
@@ -94,88 +61,11 @@ type Msg struct {
 	Obj     interface{}
 }
 
-// Deliver is called by the LES protocol manager to deliver ODR reply messages to waiting requests
-func (self *LesOdr) Deliver(peer *peer, msg *Msg) error {
-	var delivered chan struct{}
-	self.mlock.Lock()
-	req, ok := self.sentReqs[msg.ReqID]
-	self.mlock.Unlock()
-	if ok {
-		req.lock.Lock()
-		delivered, ok = req.sentTo[peer]
-		req.lock.Unlock()
-	}
+// Retrieve tries to fetch an object from the LES network.
+// If the network retrieval was successful, it stores the object in local db.
+func (self *LesOdr) Retrieve(ctx context.Context, req light.OdrRequest) (err error) {
+	lreq := LesRequest(req)
 
-	if !ok {
-		return errResp(ErrUnexpectedResponse, "reqID = %v", msg.ReqID)
-	}
-
-	if err := req.valFunc(self.db, msg); err != nil {
-		peer.Log().Warn("Invalid odr response", "err", err)
-		return errResp(ErrInvalidResponse, "reqID = %v", msg.ReqID)
-	}
-	close(delivered)
-	req.lock.Lock()
-	delete(req.sentTo, peer)
-	if req.answered != nil {
-		close(req.answered)
-		req.answered = nil
-	}
-	req.lock.Unlock()
-	return nil
-}
-
-func (self *LesOdr) requestPeer(req *sentReq, peer *peer, delivered, timeout chan struct{}, reqWg *sync.WaitGroup) {
-	stime := mclock.Now()
-	defer func() {
-		req.lock.Lock()
-		delete(req.sentTo, peer)
-		req.lock.Unlock()
-		reqWg.Done()
-	}()
-
-	select {
-	case <-delivered:
-		if self.serverPool != nil {
-			self.serverPool.adjustResponseTime(peer.poolEntry, time.Duration(mclock.Now()-stime), false)
-		}
-		return
-	case <-time.After(softRequestTimeout):
-		close(timeout)
-	case <-self.stop:
-		return
-	}
-
-	select {
-	case <-delivered:
-	case <-time.After(hardRequestTimeout):
-		peer.Log().Debug("Request timed out hard")
-		go self.removePeer(peer.id)
-	case <-self.stop:
-		return
-	}
-	if self.serverPool != nil {
-		self.serverPool.adjustResponseTime(peer.poolEntry, time.Duration(mclock.Now()-stime), true)
-	}
-}
-
-// networkRequest sends a request to known peers until an answer is received
-// or the context is cancelled
-func (self *LesOdr) networkRequest(ctx context.Context, lreq LesOdrRequest) error {
-	answered := make(chan struct{})
-	req := &sentReq{
-		valFunc:  lreq.Validate,
-		sentTo:   make(map[*peer]chan struct{}),
-		answered: answered, // reply delivered by any peer
-	}
-
-	exclude := make(map[*peer]struct{})
-
-	reqWg := new(sync.WaitGroup)
-	reqWg.Add(1)
-	defer reqWg.Done()
-
-	var timeout chan struct{}
 	reqID := getNextReqID()
 	rq := &distReq{
 		getCost: func(dp distPeer) uint64 {
@@ -183,67 +73,17 @@ func (self *LesOdr) networkRequest(ctx context.Context, lreq LesOdrRequest) erro
 		},
 		canSend: func(dp distPeer) bool {
 			p := dp.(*peer)
-			_, ok := exclude[p]
-			return !ok && lreq.CanSend(p)
+			return lreq.CanSend(p)
 		},
 		request: func(dp distPeer) func() {
 			p := dp.(*peer)
-			exclude[p] = struct{}{}
-			delivered := make(chan struct{})
-			timeout = make(chan struct{})
-			req.lock.Lock()
-			req.sentTo[p] = delivered
-			req.lock.Unlock()
-			reqWg.Add(1)
 			cost := lreq.GetCost(p)
 			p.fcServer.QueueRequest(reqID, cost)
-			go self.requestPeer(req, p, delivered, timeout, reqWg)
 			return func() { lreq.Request(reqID, p) }
 		},
 	}
 
-	self.mlock.Lock()
-	self.sentReqs[reqID] = req
-	self.mlock.Unlock()
-
-	go func() {
-		reqWg.Wait()
-		self.mlock.Lock()
-		delete(self.sentReqs, reqID)
-		self.mlock.Unlock()
-	}()
-
-	for {
-		peerChn := self.reqDist.queue(rq)
-		select {
-		case <-ctx.Done():
-			self.reqDist.cancel(rq)
-			return ctx.Err()
-		case <-answered:
-			self.reqDist.cancel(rq)
-			return nil
-		case _, ok := <-peerChn:
-			if !ok {
-				return ErrNoPeers
-			}
-		}
-
-		select {
-		case <-ctx.Done():
-			return ctx.Err()
-		case <-answered:
-			return nil
-		case <-timeout:
-		}
-	}
-}
-
-// Retrieve tries to fetch an object from the LES network.
-// If the network retrieval was successful, it stores the object in local db.
-func (self *LesOdr) Retrieve(ctx context.Context, req light.OdrRequest) (err error) {
-	lreq := LesRequest(req)
-	err = self.networkRequest(ctx, lreq)
-	if err == nil {
+	if err = self.retriever.retrieve(ctx, reqID, rq, func(p distPeer, msg *Msg) error { return lreq.Validate(self.db, msg) }); err == nil {
 		// retrieved from network, store in db
 		req.StoreResult(self.db)
 	} else {
@@ -251,9 +91,3 @@ func (self *LesOdr) Retrieve(ctx context.Context, req light.OdrRequest) (err err
 	}
 	return
 }
-
-func getNextReqID() uint64 {
-	var rnd [8]byte
-	rand.Read(rnd[:])
-	return binary.BigEndian.Uint64(rnd[:])
-}

les/retrieve.go

@@ -0,0 +1,323 @@
+// Copyright 2016 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 light implements on-demand retrieval capable state and chain objects
+// for the Ethereum Light Client.
+package les
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/binary"
+	"sync"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/mclock"
+)
+
+var (
+	retryQueue         = time.Millisecond * 100
+	softRequestTimeout = time.Millisecond * 500
+	hardRequestTimeout = time.Second * 10
+)
+
+// retrieveManager is a layer on top of requestDistributor which takes care of
+// matching replies by request ID and handles timeouts and resends if necessary.
+type retrieveManager struct {
+	dist       *requestDistributor
+	serverPool peerSelector
+	removePeer peerDropFn
+
+	lock     sync.RWMutex
+	sentReqs map[uint64]*sentReq
+}
+
+// validatorFunc is a function that processes a reply message
+type validatorFunc func(distPeer, *Msg) error
+
+// peerDropFn is a callback type for dropping a peer detected as malicious.
+type peerDropFn func(id string)
+
+// peerSelector receives feedback info about response times and timeouts
+type peerSelector interface {
+	adjustResponseTime(*poolEntry, time.Duration, bool)
+}
+
+type sentReq struct {
+	rm                      *retrieveManager
+	req                     *distReq
+	validate                validatorFunc
+	stopChn                 chan struct{}
+	stopped                 bool
+	err                     error
+	lock                    sync.RWMutex               // protect access to sentTo map
+	sentTo                  map[distPeer]chan struct{} // channel signaling a reply from the given peer
+	reqWg                   sync.WaitGroup             // wait until every peer replied or reached hard timeout and we can forget about the request
+	sentCnt, softTimeoutCnt int
+}
+
+// reqPeerCallback is called after a request sent to a certain peer has either been
+// answered or timed out hard
+type reqPeerCallback func(p distPeer, respTime time.Duration, srto, hrto bool)
+
+// newRetrieveManager creates the retrieve manager
+func newRetrieveManager(dist *requestDistributor, serverPool peerSelector, removePeer peerDropFn) *retrieveManager {
+	return &retrieveManager{
+		dist:       dist,
+		serverPool: serverPool,
+		removePeer: removePeer,
+		sentReqs:   make(map[uint64]*sentReq),
+	}
+}
+
+// retrieve sends a request (to multiple peers if necessary) and waits for an answer
+// that is delivered through the deliver function and successfully validated by the
+// validator callback. It returns when a valid answer is delivered or the context is
+// cancelled.
+func (rm *retrieveManager) retrieve(ctx context.Context, reqID uint64, req *distReq, val validatorFunc) error {
+	sentReq := rm.sendReq(reqID, req, val)
+	select {
+	case <-sentReq.stopChn:
+	case <-ctx.Done():
+		sentReq.stop(ctx.Err())
+	}
+	return sentReq.getError()
+}
+
+// sendReq starts a process that keeps trying to retrieve a valid answer for a
+// request from any suitable peers until stopped or succeeded.
+func (rm *retrieveManager) sendReq(reqID uint64, req *distReq, val validatorFunc) *sentReq {
+	r := &sentReq{
+		rm:       rm,
+		req:      req,
+		sentTo:   make(map[distPeer]chan struct{}),
+		stopChn:  make(chan struct{}),
+		validate: val,
+	}
+
+	canSend := req.canSend
+	req.canSend = func(p distPeer) bool {
+		r.lock.RLock()
+		_, sent := r.sentTo[p]
+		r.lock.RUnlock()
+		return !sent && canSend(p)
+	}
+
+	rm.lock.Lock()
+	rm.sentReqs[reqID] = r
+	rm.lock.Unlock()
+
+	r.reqWg.Add(1)
+	r.tryRetrieve()
+	go func() {
+		r.reqWg.Wait()
+		rm.lock.Lock()
+		delete(rm.sentReqs, reqID)
+		rm.lock.Unlock()
+	}()
+	r.reqWg.Done()
+
+	return r
+}
+
+// deliver is called by the LES protocol manager to deliver reply messages to waiting requests
+func (rm *retrieveManager) deliver(peer distPeer, msg *Msg) error {
+	rm.lock.RLock()
+	req, ok := rm.sentReqs[msg.ReqID]
+	rm.lock.RUnlock()
+	if ok {
+		ok = req.expectResponseFrom(peer)
+	}
+
+	if !ok {
+		return errResp(ErrUnexpectedResponse, "reqID = %v", msg.ReqID)
+	}
+
+	if err := req.validate(peer, msg); err != nil {
+		req.delivered(peer, false)
+		return errResp(ErrInvalidResponse, "reqID = %v", msg.ReqID)
+	}
+	req.delivered(peer, true)
+	return nil
+}
+
+// tryRetrieve starts a retrieval process for a single peer. If no request has been
+// sent yet and no suitable peer found, it sets an ErrNoPeers error code and returns.
+// Otherwise it keeps trying until it sends the request to a peer, then waits for an
+// answer or a timeout.
+func (r *sentReq) tryRetrieve() {
+	r.reqWg.Add(1)
+	go func() {
+		defer r.reqWg.Done()
+
+		for {
+			sent := r.rm.dist.queue(r.req)
+			var p distPeer
+			select {
+			case p = <-sent:
+			case <-r.stopChn:
+				if r.rm.dist.cancel(r.req) {
+					p = nil
+				} else {
+					p = <-sent
+				}
+			}
+			if p == nil {
+				if r.waiting() {
+					time.Sleep(retryQueue)
+					if r.waiting() {
+						continue
+					}
+				} else {
+					r.stop(ErrNoPeers) // no effect if already stopped for another reason
+				}
+			} else {
+				r.lock.Lock()
+				if r.sentTo[p] == nil {
+					r.sentTo[p] = make(chan struct{})
+					r.sentCnt++
+				}
+				r.lock.Unlock()
+				respTime, srto, hrto := r.runTimer(p)
+				// send feedback to server pool and remove peer if hard timeout happened
+				pp, ok := p.(*peer)
+				if ok && r.rm.serverPool != nil {
+					r.rm.serverPool.adjustResponseTime(pp.poolEntry, respTime, srto)
+				}
+				if hrto {
+					pp.Log().Debug("Request timed out hard")
+					if r.rm.removePeer != nil {
+						r.rm.removePeer(pp.id)
+					}
+				}
+			}
+			break
+		}
+	}()
+}
+
+// getError returns any retrieval error (either internally generated or set by the
+// stop function) after stopChn has been closed
+func (r *sentReq) getError() error {
+	return r.err
+}
+
+// expectResponseFrom tells if we are expecting a response from a given peer.
+// A response to a sent request is expected even after another peer have delivered
+// a valid response. If a hard timeout occurs, no response is expected any more.
+func (r *sentReq) expectResponseFrom(peer distPeer) bool {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
+	return r.sentTo[peer] != nil
+}
+
+// delivered notifies the retrieval mechanism that a reply (either valid
+// or invalid) has been received from a certain peer
+func (r *sentReq) delivered(peer distPeer, valid bool) bool {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
+	delivered, ok := r.sentTo[peer]
+	if ok {
+		close(delivered)
+		delete(r.sentTo, peer)
+		if valid && !r.stopped {
+			r.stopped = true
+			close(r.stopChn)
+		}
+		if !r.stopped && r.sentCnt == 0 {
+			r.tryRetrieve()
+		}
+
+	}
+	return ok
+}
+
+// stop stops the retrieval process and sets an error code that will be returned
+// by getError
+func (r *sentReq) stop(err error) {
+	r.lock.Lock()
+	if !r.stopped {
+		r.stopped = true
+		r.err = err
+		close(r.stopChn)
+	}
+	r.lock.Unlock()
+}
+
+// waiting returns true if the retrieval mechanism is waiting for an answer from
+// any peer
+func (r *sentReq) waiting() bool {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	return !r.stopped && r.sentCnt+r.softTimeoutCnt != 0
+}
+
+// runTimer starts a request timeout for a single peer. If a certain (short) period
+// of time passes with no reply received, it switches from "sent" to "soft timeout"
+// state and the retrieval mechanism will start trying to send another request to a
+// new peer. If another (longer) timeout period passes, it switches to "hard timeout"
+// state, after which a reply is no longer expected and the peer should be dropped.
+func (r *sentReq) runTimer(peer distPeer) (respTime time.Duration, srto, hrto bool) {
+	start := mclock.Now()
+
+	r.lock.RLock()
+	delivered := r.sentTo[peer]
+	r.lock.RUnlock()
+	if delivered == nil {
+		panic(nil)
+	}
+
+	select {
+	case <-delivered:
+		r.lock.Lock()
+		r.sentCnt--
+		r.lock.Unlock()
+		return time.Duration(mclock.Now() - start), false, false
+	case <-time.After(softRequestTimeout):
+		r.lock.Lock()
+		r.sentCnt--
+		resend := !r.stopped && r.sentCnt == 0
+		r.softTimeoutCnt++
+		r.lock.Unlock()
+		if resend {
+			r.tryRetrieve()
+		}
+	}
+
+	hrto = false
+	select {
+	case <-delivered:
+	case <-time.After(hardRequestTimeout):
+		hrto = true
+	}
+
+	r.lock.Lock()
+	r.softTimeoutCnt--
+	// do not delete sentTo entry, nil means that we are not expecting an answer
+	// but we also do not want to send to that peer again
+	r.sentTo[peer] = nil
+	r.lock.Unlock()
+	return time.Duration(mclock.Now() - start), true, hrto
+}
+
+func getNextReqID() uint64 {
+	var rnd [8]byte
+	rand.Read(rnd[:])
+	return binary.BigEndian.Uint64(rnd[:])
+}

les/serverpool.go

@@ -102,6 +102,8 @@ type serverPool struct {
 	wg     *sync.WaitGroup
 	connWg sync.WaitGroup
 
+	topic discv5.Topic
+
 	discSetPeriod chan time.Duration
 	discNodes     chan *discv5.Node
 	discLookups   chan bool
@@ -118,13 +120,13 @@ type serverPool struct {
 }
 
 // newServerPool creates a new serverPool instance
-func newServerPool(db ethdb.Database, dbPrefix []byte, server *p2p.Server, topic discv5.Topic, quit chan struct{}, wg *sync.WaitGroup) *serverPool {
+func newServerPool(db ethdb.Database, dbPrefix []byte, topic discv5.Topic, quit chan struct{}, wg *sync.WaitGroup) *serverPool {
 	pool := &serverPool{
 		db:           db,
 		dbKey:        append(dbPrefix, []byte(topic)...),
-		server:       server,
 		quit:         quit,
 		wg:           wg,
+		topic:        topic,
 		entries:      make(map[discover.NodeID]*poolEntry),
 		timeout:      make(chan *poolEntry, 1),
 		adjustStats:  make(chan poolStatAdjust, 100),
@@ -137,17 +139,20 @@ func newServerPool(db ethdb.Database, dbPrefix []byte, server *p2p.Server, topic
 	pool.newQueue = newPoolEntryQueue(maxNewEntries, pool.removeEntry)
 	wg.Add(1)
 	pool.loadNodes()
-	pool.checkDial()
 
+	go pool.eventLoop()
+	return pool
+}
+
+func (pool *serverPool) setServer(server *p2p.Server) {
+	pool.server = server
+	pool.checkDial()
 	if pool.server.DiscV5 != nil {
 		pool.discSetPeriod = make(chan time.Duration, 1)
 		pool.discNodes = make(chan *discv5.Node, 100)
 		pool.discLookups = make(chan bool, 100)
-		go pool.server.DiscV5.SearchTopic(topic, pool.discSetPeriod, pool.discNodes, pool.discLookups)
+		go pool.server.DiscV5.SearchTopic(pool.topic, pool.discSetPeriod, pool.discNodes, pool.discLookups)
 	}
-
-	go pool.eventLoop()
-	return pool
 }
 
 // connect should be called upon any incoming connection. If the connection has been
@@ -485,7 +490,7 @@ func (pool *serverPool) checkDial() {
 
 // dial initiates a new connection
 func (pool *serverPool) dial(entry *poolEntry, knownSelected bool) {
-	if entry.state != psNotConnected {
+	if pool.server == nil || entry.state != psNotConnected {
 		return
 	}
 	entry.state = psDialed