cmd/devp2p, p2p: dial using node iterator, discovery crawler (#20132)

* p2p/enode: add Iterator and associated utilities

* p2p/discover: add RandomNodes iterator

* p2p: dial using iterator

* cmd/devp2p: add discv4 crawler

* cmd/devp2p: WIP nodeset filter

* cmd/devp2p: fixup lesFilter

* core/forkid: add NewStaticFilter

* cmd/devp2p: make -eth-network filter actually work

* cmd/devp2p: improve crawl timestamp handling

* cmd/devp2p: fix typo

* p2p/enode: fix comment typos

* p2p/discover: fix comment typos

* p2p/discover: rename lookup.next to 'advance'

* p2p: lower discovery mixer timeout

* p2p/enode: implement dynamic FairMix timeouts

* cmd/devp2p: add ropsten support in -eth-network filter

* cmd/devp2p: tweak crawler log message

cmd/devp2p/crawl.go

@@ -0,0 +1,152 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"time"
+
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/p2p/discover"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+type crawler struct {
+	input     nodeSet
+	output    nodeSet
+	disc      *discover.UDPv4
+	iters     []enode.Iterator
+	inputIter enode.Iterator
+	ch        chan *enode.Node
+	closed    chan struct{}
+
+	// settings
+	revalidateInterval time.Duration
+}
+
+func newCrawler(input nodeSet, disc *discover.UDPv4, iters ...enode.Iterator) *crawler {
+	c := &crawler{
+		input:     input,
+		output:    make(nodeSet, len(input)),
+		disc:      disc,
+		iters:     iters,
+		inputIter: enode.IterNodes(input.nodes()),
+		ch:        make(chan *enode.Node),
+		closed:    make(chan struct{}),
+	}
+	c.iters = append(c.iters, c.inputIter)
+	// Copy input to output initially. Any nodes that fail validation
+	// will be dropped from output during the run.
+	for id, n := range input {
+		c.output[id] = n
+	}
+	return c
+}
+
+func (c *crawler) run(timeout time.Duration) nodeSet {
+	var (
+		timeoutTimer = time.NewTimer(timeout)
+		timeoutCh    <-chan time.Time
+		doneCh       = make(chan enode.Iterator, len(c.iters))
+		liveIters    = len(c.iters)
+	)
+	for _, it := range c.iters {
+		go c.runIterator(doneCh, it)
+	}
+
+loop:
+	for {
+		select {
+		case n := <-c.ch:
+			c.updateNode(n)
+		case it := <-doneCh:
+			if it == c.inputIter {
+				// Enable timeout when we're done revalidating the input nodes.
+				log.Info("Revalidation of input set is done", "len", len(c.input))
+				if timeout > 0 {
+					timeoutCh = timeoutTimer.C
+				}
+			}
+			if liveIters--; liveIters == 0 {
+				break loop
+			}
+		case <-timeoutCh:
+			break loop
+		}
+	}
+
+	close(c.closed)
+	for _, it := range c.iters {
+		it.Close()
+	}
+	for ; liveIters > 0; liveIters-- {
+		<-doneCh
+	}
+	return c.output
+}
+
+func (c *crawler) runIterator(done chan<- enode.Iterator, it enode.Iterator) {
+	defer func() { done <- it }()
+	for it.Next() {
+		select {
+		case c.ch <- it.Node():
+		case <-c.closed:
+			return
+		}
+	}
+}
+
+func (c *crawler) updateNode(n *enode.Node) {
+	node, ok := c.output[n.ID()]
+
+	// Skip validation of recently-seen nodes.
+	if ok && time.Since(node.LastCheck) < c.revalidateInterval {
+		return
+	}
+
+	// Request the node record.
+	nn, err := c.disc.RequestENR(n)
+	node.LastCheck = truncNow()
+	if err != nil {
+		if node.Score == 0 {
+			// Node doesn't implement EIP-868.
+			log.Debug("Skipping node", "id", n.ID())
+			return
+		}
+		node.Score /= 2
+	} else {
+		node.N = nn
+		node.Seq = nn.Seq()
+		node.Score++
+		if node.FirstResponse.IsZero() {
+			node.FirstResponse = node.LastCheck
+		}
+		node.LastResponse = node.LastCheck
+	}
+
+	// Store/update node in output set.
+	if node.Score <= 0 {
+		log.Info("Removing node", "id", n.ID())
+		delete(c.output, n.ID())
+	} else {
+		log.Info("Updating node", "id", n.ID(), "seq", n.Seq(), "score", node.Score)
+		c.output[n.ID()] = node
+	}
+}
+
+func truncNow() time.Time {
+	return time.Now().UTC().Truncate(1 * time.Second)
+}

cmd/devp2p/discv4cmd.go

@@ -39,6 +39,7 @@ var (
 			discv4RequestRecordCommand,
 			discv4ResolveCommand,
 			discv4ResolveJSONCommand,
+			discv4CrawlCommand,
 		},
 	}
 	discv4PingCommand = cli.Command{
@@ -67,12 +68,25 @@ var (
 		Flags:     []cli.Flag{bootnodesFlag},
 		ArgsUsage: "<nodes.json file>",
 	}
+	discv4CrawlCommand = cli.Command{
+		Name:   "crawl",
+		Usage:  "Updates a nodes.json file with random nodes found in the DHT",
+		Action: discv4Crawl,
+		Flags:  []cli.Flag{bootnodesFlag, crawlTimeoutFlag},
+	}
 )
 
-var bootnodesFlag = cli.StringFlag{
+var (
+	bootnodesFlag = cli.StringFlag{
 		Name:  "bootnodes",
 		Usage: "Comma separated nodes used for bootstrapping",
 	}
+	crawlTimeoutFlag = cli.DurationFlag{
+		Name:  "timeout",
+		Usage: "Time limit for the crawl.",
+		Value: 30 * time.Minute,
+	}
+)
 
 func discv4Ping(ctx *cli.Context) error {
 	n := getNodeArg(ctx)
@@ -113,30 +127,48 @@ func discv4ResolveJSON(ctx *cli.Context) error {
 	if ctx.NArg() < 1 {
 		return fmt.Errorf("need nodes file as argument")
 	}
-	disc := startV4(ctx)
+	nodesFile := ctx.Args().Get(0)
-	defer disc.Close()
+	inputSet := make(nodeSet)
-	file := ctx.Args().Get(0)
+	if common.FileExist(nodesFile) {
-
+		inputSet = loadNodesJSON(nodesFile)
-	// Load existing nodes in file.
-	var nodes []*enode.Node
-	if common.FileExist(file) {
-		nodes = loadNodesJSON(file).nodes()
 	}
-	// Add nodes from command line arguments.
+
+	// Add extra nodes from command line arguments.
+	var nodeargs []*enode.Node
 	for i := 1; i < ctx.NArg(); i++ {
 		n, err := parseNode(ctx.Args().Get(i))
 		if err != nil {
 			exit(err)
 		}
-		nodes = append(nodes, n)
+		nodeargs = append(nodeargs, n)
 	}
 
-	result := make(nodeSet, len(nodes))
+	// Run the crawler.
-	for _, n := range nodes {
+	disc := startV4(ctx)
-		n = disc.Resolve(n)
+	defer disc.Close()
-		result[n.ID()] = nodeJSON{Seq: n.Seq(), N: n}
+	c := newCrawler(inputSet, disc, enode.IterNodes(nodeargs))
+	c.revalidateInterval = 0
+	output := c.run(0)
+	writeNodesJSON(nodesFile, output)
+	return nil
 }
-	writeNodesJSON(file, result)
+
+func discv4Crawl(ctx *cli.Context) error {
+	if ctx.NArg() < 1 {
+		return fmt.Errorf("need nodes file as argument")
+	}
+	nodesFile := ctx.Args().First()
+	var inputSet nodeSet
+	if common.FileExist(nodesFile) {
+		inputSet = loadNodesJSON(nodesFile)
+	}
+
+	disc := startV4(ctx)
+	defer disc.Close()
+	c := newCrawler(inputSet, disc, disc.RandomNodes())
+	c.revalidateInterval = 10 * time.Minute
+	output := c.run(ctx.Duration(crawlTimeoutFlag.Name))
+	writeNodesJSON(nodesFile, output)
 	return nil
 }
 

cmd/devp2p/dnscmd.go

@@ -109,7 +109,8 @@ func dnsSync(ctx *cli.Context) error {
 	}
 	def := treeToDefinition(url, t)
 	def.Meta.LastModified = time.Now()
-	writeTreeDefinition(outdir, def)
+	writeTreeMetadata(outdir, def)
+	writeTreeNodes(outdir, def)
 	return nil
 }
 
@@ -151,7 +152,7 @@ func dnsSign(ctx *cli.Context) error {
 
 	def = treeToDefinition(url, t)
 	def.Meta.LastModified = time.Now()
-	writeTreeDefinition(defdir, def)
+	writeTreeMetadata(defdir, def)
 	return nil
 }
 
@@ -315,26 +316,28 @@ func ensureValidTreeSignature(t *dnsdisc.Tree, pubkey *ecdsa.PublicKey, sig stri
 	return nil
 }
 
-// writeTreeDefinition writes a DNS node tree definition to the given directory.
+// writeTreeMetadata writes a DNS node tree metadata file to the given directory.
-func writeTreeDefinition(directory string, def *dnsDefinition) {
+func writeTreeMetadata(directory string, def *dnsDefinition) {
 	metaJSON, err := json.MarshalIndent(&def.Meta, "", jsonIndent)
 	if err != nil {
 		exit(err)
 	}
-	// Convert nodes.
-	nodes := make(nodeSet, len(def.Nodes))
-	nodes.add(def.Nodes...)
-	// Write.
 	if err := os.Mkdir(directory, 0744); err != nil && !os.IsExist(err) {
 		exit(err)
 	}
-	metaFile, nodesFile := treeDefinitionFiles(directory)
+	metaFile, _ := treeDefinitionFiles(directory)
-	writeNodesJSON(nodesFile, nodes)
 	if err := ioutil.WriteFile(metaFile, metaJSON, 0644); err != nil {
 		exit(err)
 	}
 }
 
+func writeTreeNodes(directory string, def *dnsDefinition) {
+	ns := make(nodeSet, len(def.Nodes))
+	ns.add(def.Nodes...)
+	_, nodesFile := treeDefinitionFiles(directory)
+	writeNodesJSON(nodesFile, ns)
+}
+
 func treeDefinitionFiles(directory string) (string, string) {
 	meta := filepath.Join(directory, "enrtree-info.json")
 	nodes := filepath.Join(directory, "nodes.json")

cmd/devp2p/main.go

@@ -60,6 +60,7 @@ func init() {
 		enrdumpCommand,
 		discv4Command,
 		dnsCommand,
+		nodesetCommand,
 	}
 }
 

cmd/devp2p/nodeset.go

@@ -21,7 +21,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"os"
 	"sort"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/p2p/enode"
@@ -36,6 +38,15 @@ type nodeSet map[enode.ID]nodeJSON
 type nodeJSON struct {
 	Seq uint64      `json:"seq"`
 	N   *enode.Node `json:"record"`
+
+	// The score tracks how many liveness checks were performed. It is incremented by one
+	// every time the node passes a check, and halved every time it doesn't.
+	Score int `json:"score,omitempty"`
+	// These two track the time of last successful contact.
+	FirstResponse time.Time `json:"firstResponse,omitempty"`
+	LastResponse  time.Time `json:"lastResponse,omitempty"`
+	// This one tracks the time of our last attempt to contact the node.
+	LastCheck time.Time `json:"lastCheck,omitempty"`
 }
 
 func loadNodesJSON(file string) nodeSet {
@@ -51,6 +62,10 @@ func writeNodesJSON(file string, nodes nodeSet) {
 	if err != nil {
 		exit(err)
 	}
+	if file == "-" {
+		os.Stdout.Write(nodesJSON)
+		return
+	}
 	if err := ioutil.WriteFile(file, nodesJSON, 0644); err != nil {
 		exit(err)
 	}

cmd/devp2p/nodesetcmd.go

@@ -0,0 +1,193 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/ethereum/go-ethereum/core/forkid"
+	"github.com/ethereum/go-ethereum/p2p/enr"
+	"github.com/ethereum/go-ethereum/params"
+	"github.com/ethereum/go-ethereum/rlp"
+	"gopkg.in/urfave/cli.v1"
+)
+
+var (
+	nodesetCommand = cli.Command{
+		Name:  "nodeset",
+		Usage: "Node set tools",
+		Subcommands: []cli.Command{
+			nodesetInfoCommand,
+			nodesetFilterCommand,
+		},
+	}
+	nodesetInfoCommand = cli.Command{
+		Name:      "info",
+		Usage:     "Shows statistics about a node set",
+		Action:    nodesetInfo,
+		ArgsUsage: "<nodes.json>",
+	}
+	nodesetFilterCommand = cli.Command{
+		Name:      "filter",
+		Usage:     "Filters a node set",
+		Action:    nodesetFilter,
+		ArgsUsage: "<nodes.json> filters..",
+
+		SkipFlagParsing: true,
+	}
+)
+
+func nodesetInfo(ctx *cli.Context) error {
+	if ctx.NArg() < 1 {
+		return fmt.Errorf("need nodes file as argument")
+	}
+
+	ns := loadNodesJSON(ctx.Args().First())
+	fmt.Printf("Set contains %d nodes.\n", len(ns))
+	return nil
+}
+
+func nodesetFilter(ctx *cli.Context) error {
+	if ctx.NArg() < 1 {
+		return fmt.Errorf("need nodes file as argument")
+	}
+	ns := loadNodesJSON(ctx.Args().First())
+	filter, err := andFilter(ctx.Args().Tail())
+	if err != nil {
+		return err
+	}
+
+	result := make(nodeSet)
+	for id, n := range ns {
+		if filter(n) {
+			result[id] = n
+		}
+	}
+	writeNodesJSON("-", result)
+	return nil
+}
+
+type nodeFilter func(nodeJSON) bool
+
+type nodeFilterC struct {
+	narg int
+	fn   func([]string) (nodeFilter, error)
+}
+
+var filterFlags = map[string]nodeFilterC{
+	"-ip":          {1, ipFilter},
+	"-min-age":     {1, minAgeFilter},
+	"-eth-network": {1, ethFilter},
+	"-les-server":  {0, lesFilter},
+}
+
+func parseFilters(args []string) ([]nodeFilter, error) {
+	var filters []nodeFilter
+	for len(args) > 0 {
+		fc, ok := filterFlags[args[0]]
+		if !ok {
+			return nil, fmt.Errorf("invalid filter %q", args[0])
+		}
+		if len(args) < fc.narg {
+			return nil, fmt.Errorf("filter %q wants %d arguments, have %d", args[0], fc.narg, len(args))
+		}
+		filter, err := fc.fn(args[1:])
+		if err != nil {
+			return nil, fmt.Errorf("%s: %v", args[0], err)
+		}
+		filters = append(filters, filter)
+		args = args[fc.narg+1:]
+	}
+	return filters, nil
+}
+
+func andFilter(args []string) (nodeFilter, error) {
+	checks, err := parseFilters(args)
+	if err != nil {
+		return nil, err
+	}
+	f := func(n nodeJSON) bool {
+		for _, filter := range checks {
+			if !filter(n) {
+				return false
+			}
+		}
+		return true
+	}
+	return f, nil
+}
+
+func ipFilter(args []string) (nodeFilter, error) {
+	_, cidr, err := net.ParseCIDR(args[0])
+	if err != nil {
+		return nil, err
+	}
+	f := func(n nodeJSON) bool { return cidr.Contains(n.N.IP()) }
+	return f, nil
+}
+
+func minAgeFilter(args []string) (nodeFilter, error) {
+	minage, err := time.ParseDuration(args[0])
+	if err != nil {
+		return nil, err
+	}
+	f := func(n nodeJSON) bool {
+		age := n.LastResponse.Sub(n.FirstResponse)
+		return age >= minage
+	}
+	return f, nil
+}
+
+func ethFilter(args []string) (nodeFilter, error) {
+	var filter func(forkid.ID) error
+	switch args[0] {
+	case "mainnet":
+		filter = forkid.NewStaticFilter(params.MainnetChainConfig, params.MainnetGenesisHash)
+	case "rinkeby":
+		filter = forkid.NewStaticFilter(params.RinkebyChainConfig, params.RinkebyGenesisHash)
+	case "goerli":
+		filter = forkid.NewStaticFilter(params.GoerliChainConfig, params.GoerliGenesisHash)
+	case "ropsten":
+		filter = forkid.NewStaticFilter(params.TestnetChainConfig, params.TestnetGenesisHash)
+	default:
+		return nil, fmt.Errorf("unknown network %q", args[0])
+	}
+
+	f := func(n nodeJSON) bool {
+		var eth struct {
+			ForkID forkid.ID
+			_      []rlp.RawValue `rlp:"tail"`
+		}
+		if n.N.Load(enr.WithEntry("eth", &eth)) != nil {
+			return false
+		}
+		return filter(eth.ForkID) == nil
+	}
+	return f, nil
+}
+
+func lesFilter(args []string) (nodeFilter, error) {
+	f := func(n nodeJSON) bool {
+		var les struct {
+			_ []rlp.RawValue `rlp:"tail"`
+		}
+		return n.N.Load(enr.WithEntry("les", &les)) == nil
+	}
+	return f, nil
+}

core/forkid/forkid.go

@@ -80,7 +80,7 @@ func newID(config *params.ChainConfig, genesis common.Hash, head uint64) ID {
 	return ID{Hash: checksumToBytes(hash), Next: next}
 }
 
-// NewFilter creates an filter that returns if a fork ID should be rejected or not
+// NewFilter creates a filter that returns if a fork ID should be rejected or not
 // based on the local chain's status.
 func NewFilter(chain *core.BlockChain) func(id ID) error {
 	return newFilter(
@@ -92,6 +92,12 @@ func NewFilter(chain *core.BlockChain) func(id ID) error {
 	)
 }
 
+// NewStaticFilter creates a filter at block zero.
+func NewStaticFilter(config *params.ChainConfig, genesis common.Hash) func(id ID) error {
+	head := func() uint64 { return 0 }
+	return newFilter(config, genesis, head)
+}
+
 // newFilter is the internal version of NewFilter, taking closures as its arguments
 // instead of a chain. The reason is to allow testing it without having to simulate
 // an entire blockchain.

p2p/dial.go

@@ -33,12 +33,7 @@ const (
 	// private networks.
 	dialHistoryExpiration = inboundThrottleTime + 5*time.Second
 
-	// Discovery lookups are throttled and can only run
+	// If no peers are found for this amount of time, the initial bootnodes are dialed.
-	// once every few seconds.
-	lookupInterval = 4 * time.Second
-
-	// If no peers are found for this amount of time, the initial bootnodes are
-	// attempted to be connected.
 	fallbackInterval = 20 * time.Second
 
 	// Endpoint resolution is throttled with bounded backoff.
@@ -52,6 +47,10 @@ type NodeDialer interface {
 	Dial(*enode.Node) (net.Conn, error)
 }
 
+type nodeResolver interface {
+	Resolve(*enode.Node) *enode.Node
+}
+
 // TCPDialer implements the NodeDialer interface by using a net.Dialer to
 // create TCP connections to nodes in the network
 type TCPDialer struct {
@@ -69,7 +68,6 @@ func (t TCPDialer) Dial(dest *enode.Node) (net.Conn, error) {
 // of the main loop in Server.run.
 type dialstate struct {
 	maxDynDials int
-	ntab        discoverTable
 	netrestrict *netutil.Netlist
 	self        enode.ID
 	bootnodes   []*enode.Node // default dials when there are no peers
@@ -79,55 +77,23 @@ type dialstate struct {
 	lookupRunning bool
 	dialing       map[enode.ID]connFlag
 	lookupBuf     []*enode.Node // current discovery lookup results
-	randomNodes   []*enode.Node // filled from Table
 	static        map[enode.ID]*dialTask
 	hist          expHeap
 }
 
-type discoverTable interface {
-	Close()
-	Resolve(*enode.Node) *enode.Node
-	LookupRandom() []*enode.Node
-	ReadRandomNodes([]*enode.Node) int
-}
-
 type task interface {
 	Do(*Server)
 }
 
-// A dialTask is generated for each node that is dialed. Its
+func newDialState(self enode.ID, maxdyn int, cfg *Config) *dialstate {
-// fields cannot be accessed while the task is running.
-type dialTask struct {
-	flags        connFlag
-	dest         *enode.Node
-	lastResolved time.Time
-	resolveDelay time.Duration
-}
-
-// discoverTask runs discovery table operations.
-// Only one discoverTask is active at any time.
-// discoverTask.Do performs a random lookup.
-type discoverTask struct {
-	results []*enode.Node
-}
-
-// A waitExpireTask is generated if there are no other tasks
-// to keep the loop in Server.run ticking.
-type waitExpireTask struct {
-	time.Duration
-}
-
-func newDialState(self enode.ID, ntab discoverTable, maxdyn int, cfg *Config) *dialstate {
 	s := &dialstate{
 		maxDynDials: maxdyn,
-		ntab:        ntab,
 		self:        self,
 		netrestrict: cfg.NetRestrict,
 		log:         cfg.Logger,
 		static:      make(map[enode.ID]*dialTask),
 		dialing:     make(map[enode.ID]connFlag),
 		bootnodes:   make([]*enode.Node, len(cfg.BootstrapNodes)),
-		randomNodes: make([]*enode.Node, maxdyn/2),
 	}
 	copy(s.bootnodes, cfg.BootstrapNodes)
 	if s.log == nil {
@@ -151,10 +117,6 @@ func (s *dialstate) removeStatic(n *enode.Node) {
 }
 
 func (s *dialstate) newTasks(nRunning int, peers map[enode.ID]*Peer, now time.Time) []task {
-	if s.start.IsZero() {
-		s.start = now
-	}
-
 	var newtasks []task
 	addDial := func(flag connFlag, n *enode.Node) bool {
 		if err := s.checkDial(n, peers); err != nil {
@@ -166,20 +128,9 @@ func (s *dialstate) newTasks(nRunning int, peers map[enode.ID]*Peer, now time.Ti
 		return true
 	}
 
-	// Compute number of dynamic dials necessary at this point.
+	if s.start.IsZero() {
-	needDynDials := s.maxDynDials
+		s.start = now
-	for _, p := range peers {
-		if p.rw.is(dynDialedConn) {
-			needDynDials--
 	}
-	}
-	for _, flag := range s.dialing {
-		if flag&dynDialedConn != 0 {
-			needDynDials--
-		}
-	}
-
-	// Expire the dial history on every invocation.
 	s.hist.expire(now)
 
 	// Create dials for static nodes if they are not connected.
@@ -194,6 +145,20 @@ func (s *dialstate) newTasks(nRunning int, peers map[enode.ID]*Peer, now time.Ti
 			newtasks = append(newtasks, t)
 		}
 	}
+
+	// Compute number of dynamic dials needed.
+	needDynDials := s.maxDynDials
+	for _, p := range peers {
+		if p.rw.is(dynDialedConn) {
+			needDynDials--
+		}
+	}
+	for _, flag := range s.dialing {
+		if flag&dynDialedConn != 0 {
+			needDynDials--
+		}
+	}
+
 	// If we don't have any peers whatsoever, try to dial a random bootnode. This
 	// scenario is useful for the testnet (and private networks) where the discovery
 	// table might be full of mostly bad peers, making it hard to find good ones.
@@ -201,24 +166,12 @@ func (s *dialstate) newTasks(nRunning int, peers map[enode.ID]*Peer, now time.Ti
 		bootnode := s.bootnodes[0]
 		s.bootnodes = append(s.bootnodes[:0], s.bootnodes[1:]...)
 		s.bootnodes = append(s.bootnodes, bootnode)
-
 		if addDial(dynDialedConn, bootnode) {
 			needDynDials--
 		}
 	}
-	// Use random nodes from the table for half of the necessary
+
-	// dynamic dials.
+	// Create dynamic dials from discovery results.
-	randomCandidates := needDynDials / 2
-	if randomCandidates > 0 {
-		n := s.ntab.ReadRandomNodes(s.randomNodes)
-		for i := 0; i < randomCandidates && i < n; i++ {
-			if addDial(dynDialedConn, s.randomNodes[i]) {
-				needDynDials--
-			}
-		}
-	}
-	// Create dynamic dials from random lookup results, removing tried
-	// items from the result buffer.
 	i := 0
 	for ; i < len(s.lookupBuf) && needDynDials > 0; i++ {
 		if addDial(dynDialedConn, s.lookupBuf[i]) {
@@ -226,10 +179,11 @@ func (s *dialstate) newTasks(nRunning int, peers map[enode.ID]*Peer, now time.Ti
 		}
 	}
 	s.lookupBuf = s.lookupBuf[:copy(s.lookupBuf, s.lookupBuf[i:])]
+
 	// Launch a discovery lookup if more candidates are needed.
 	if len(s.lookupBuf) < needDynDials && !s.lookupRunning {
 		s.lookupRunning = true
-		newtasks = append(newtasks, &discoverTask{})
+		newtasks = append(newtasks, &discoverTask{want: needDynDials - len(s.lookupBuf)})
 	}
 
 	// Launch a timer to wait for the next node to expire if all
@@ -279,6 +233,15 @@ func (s *dialstate) taskDone(t task, now time.Time) {
 	}
 }
 
+// A dialTask is generated for each node that is dialed. Its
+// fields cannot be accessed while the task is running.
+type dialTask struct {
+	flags        connFlag
+	dest         *enode.Node
+	lastResolved time.Time
+	resolveDelay time.Duration
+}
+
 func (t *dialTask) Do(srv *Server) {
 	if t.dest.Incomplete() {
 		if !t.resolve(srv) {
@@ -304,8 +267,8 @@ func (t *dialTask) Do(srv *Server) {
 // discovery network with useless queries for nodes that don't exist.
 // The backoff delay resets when the node is found.
 func (t *dialTask) resolve(srv *Server) bool {
-	if srv.ntab == nil {
+	if srv.staticNodeResolver == nil {
-		srv.log.Debug("Can't resolve node", "id", t.dest.ID, "err", "discovery is disabled")
+		srv.log.Debug("Can't resolve node", "id", t.dest.ID(), "err", "discovery is disabled")
 		return false
 	}
 	if t.resolveDelay == 0 {
@@ -314,20 +277,20 @@ func (t *dialTask) resolve(srv *Server) bool {
 	if time.Since(t.lastResolved) < t.resolveDelay {
 		return false
 	}
-	resolved := srv.ntab.Resolve(t.dest)
+	resolved := srv.staticNodeResolver.Resolve(t.dest)
 	t.lastResolved = time.Now()
 	if resolved == nil {
 		t.resolveDelay *= 2
 		if t.resolveDelay > maxResolveDelay {
 			t.resolveDelay = maxResolveDelay
 		}
-		srv.log.Debug("Resolving node failed", "id", t.dest.ID, "newdelay", t.resolveDelay)
+		srv.log.Debug("Resolving node failed", "id", t.dest.ID(), "newdelay", t.resolveDelay)
 		return false
 	}
 	// The node was found.
 	t.resolveDelay = initialResolveDelay
 	t.dest = resolved
-	srv.log.Debug("Resolved node", "id", t.dest.ID, "addr", &net.TCPAddr{IP: t.dest.IP(), Port: t.dest.TCP()})
+	srv.log.Debug("Resolved node", "id", t.dest.ID(), "addr", &net.TCPAddr{IP: t.dest.IP(), Port: t.dest.TCP()})
 	return true
 }
 
@@ -350,26 +313,34 @@ func (t *dialTask) String() string {
 	return fmt.Sprintf("%v %x %v:%d", t.flags, id[:8], t.dest.IP(), t.dest.TCP())
 }
 
-func (t *discoverTask) Do(srv *Server) {
+// discoverTask runs discovery table operations.
-	// newTasks generates a lookup task whenever dynamic dials are
+// Only one discoverTask is active at any time.
-	// necessary. Lookups need to take some time, otherwise the
+// discoverTask.Do performs a random lookup.
-	// event loop spins too fast.
+type discoverTask struct {
-	next := srv.lastLookup.Add(lookupInterval)
+	want    int
-	if now := time.Now(); now.Before(next) {
+	results []*enode.Node
-		time.Sleep(next.Sub(now))
 }
-	srv.lastLookup = time.Now()
+
-	t.results = srv.ntab.LookupRandom()
+func (t *discoverTask) Do(srv *Server) {
+	t.results = enode.ReadNodes(srv.discmix, t.want)
 }
 
 func (t *discoverTask) String() string {
-	s := "discovery lookup"
+	s := "discovery query"
 	if len(t.results) > 0 {
 		s += fmt.Sprintf(" (%d results)", len(t.results))
+	} else {
+		s += fmt.Sprintf(" (want %d)", t.want)
 	}
 	return s
 }
 
+// A waitExpireTask is generated if there are no other tasks
+// to keep the loop in Server.run ticking.
+type waitExpireTask struct {
+	time.Duration
+}
+
 func (t waitExpireTask) Do(*Server) {
 	time.Sleep(t.Duration)
 }

p2p/dial_test.go

@@ -73,7 +73,7 @@ func runDialTest(t *testing.T, test dialtest) {
 			t.Errorf("ERROR round %d: got %v\nwant %v\nstate: %v\nrunning: %v",
 				i, spew.Sdump(new), spew.Sdump(round.new), spew.Sdump(test.init), spew.Sdump(running))
 		}
-		t.Logf("round %d new tasks: %s", i, strings.TrimSpace(spew.Sdump(new)))
+		t.Logf("round %d (running %d) new tasks: %s", i, running, strings.TrimSpace(spew.Sdump(new)))
 
 		// Time advances by 16 seconds on every round.
 		vtime = vtime.Add(16 * time.Second)
@@ -81,19 +81,11 @@ func runDialTest(t *testing.T, test dialtest) {
 	}
 }
 
-type fakeTable []*enode.Node
-
-func (t fakeTable) Self() *enode.Node                     { return new(enode.Node) }
-func (t fakeTable) Close()                                {}
-func (t fakeTable) LookupRandom() []*enode.Node           { return nil }
-func (t fakeTable) Resolve(*enode.Node) *enode.Node       { return nil }
-func (t fakeTable) ReadRandomNodes(buf []*enode.Node) int { return copy(buf, t) }
-
 // This test checks that dynamic dials are launched from discovery results.
 func TestDialStateDynDial(t *testing.T) {
 	config := &Config{Logger: testlog.Logger(t, log.LvlTrace)}
 	runDialTest(t, dialtest{
-		init: newDialState(enode.ID{}, fakeTable{}, 5, config),
+		init: newDialState(enode.ID{}, 5, config),
 		rounds: []round{
 			// A discovery query is launched.
 			{
@@ -102,7 +94,9 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(1), nil)}},
 					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(2), nil)}},
 				},
-				new: []task{&discoverTask{}},
+				new: []task{
+					&discoverTask{want: 3},
+				},
 			},
 			// Dynamic dials are launched when it completes.
 			{
@@ -188,7 +182,7 @@ func TestDialStateDynDial(t *testing.T) {
 				},
 				new: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(7), nil)},
-					&discoverTask{},
+					&discoverTask{want: 2},
 				},
 			},
 			// Peer 7 is connected, but there still aren't enough dynamic peers
@@ -218,7 +212,7 @@ func TestDialStateDynDial(t *testing.T) {
 					&discoverTask{},
 				},
 				new: []task{
-					&discoverTask{},
+					&discoverTask{want: 2},
 				},
 			},
 		},
@@ -235,35 +229,37 @@ func TestDialStateDynDialBootnode(t *testing.T) {
 		},
 		Logger: testlog.Logger(t, log.LvlTrace),
 	}
-	table := fakeTable{
+	runDialTest(t, dialtest{
+		init: newDialState(enode.ID{}, 5, config),
+		rounds: []round{
+			{
+				new: []task{
+					&discoverTask{want: 5},
+				},
+			},
+			{
+				done: []task{
+					&discoverTask{
+						results: []*enode.Node{
 							newNode(uintID(4), nil),
 							newNode(uintID(5), nil),
-		newNode(uintID(6), nil),
+						},
-		newNode(uintID(7), nil),
+					},
-		newNode(uintID(8), nil),
+				},
-	}
-	runDialTest(t, dialtest{
-		init: newDialState(enode.ID{}, table, 5, config),
-		rounds: []round{
-			// 2 dynamic dials attempted, bootnodes pending fallback interval
-			{
 				new: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(4), nil)},
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(5), nil)},
-					&discoverTask{},
+					&discoverTask{want: 3},
 				},
 			},
 			// No dials succeed, bootnodes still pending fallback interval
+			{},
+			// 1 bootnode attempted as fallback interval was reached
 			{
 				done: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(4), nil)},
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(5), nil)},
 				},
-			},
-			// No dials succeed, bootnodes still pending fallback interval
-			{},
-			// No dials succeed, 2 dynamic dials attempted and 1 bootnode too as fallback interval was reached
-			{
 				new: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(1), nil)},
 				},
@@ -275,15 +271,12 @@ func TestDialStateDynDialBootnode(t *testing.T) {
 				},
 				new: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(2), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(4), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(5), nil)},
 				},
 			},
 			// No dials succeed, 3rd bootnode is attempted
 			{
 				done: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(2), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(5), nil)},
 				},
 				new: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(3), nil)},
@@ -293,115 +286,19 @@ func TestDialStateDynDialBootnode(t *testing.T) {
 			{
 				done: []task{
 					&dialTask{flags: dynDialedConn, dest: newNode(uintID(3), nil)},
-				},
-				new: []task{},
-			},
-			// Random dial succeeds, no more bootnodes are attempted
-			{
-				new: []task{
-					&waitExpireTask{3 * time.Second},
-				},
-				peers: []*Peer{
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(4), nil)}},
-				},
-				done: []task{
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(1), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(4), nil)},
-				},
-			},
-		},
-	})
-}
-
-func TestDialStateDynDialFromTable(t *testing.T) {
-	// This table always returns the same random nodes
-	// in the order given below.
-	table := fakeTable{
-		newNode(uintID(1), nil),
-		newNode(uintID(2), nil),
-		newNode(uintID(3), nil),
-		newNode(uintID(4), nil),
-		newNode(uintID(5), nil),
-		newNode(uintID(6), nil),
-		newNode(uintID(7), nil),
-		newNode(uintID(8), nil),
-	}
-
-	runDialTest(t, dialtest{
-		init: newDialState(enode.ID{}, table, 10, &Config{Logger: testlog.Logger(t, log.LvlTrace)}),
-		rounds: []round{
-			// 5 out of 8 of the nodes returned by ReadRandomNodes are dialed.
-			{
-				new: []task{
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(1), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(2), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(3), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(4), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(5), nil)},
-					&discoverTask{},
-				},
-			},
-			// Dialing nodes 1,2 succeeds. Dials from the lookup are launched.
-			{
-				peers: []*Peer{
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(1), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(2), nil)}},
-				},
-				done: []task{
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(1), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(2), nil)},
 					&discoverTask{results: []*enode.Node{
-						newNode(uintID(10), nil),
+						newNode(uintID(6), nil),
-						newNode(uintID(11), nil),
-						newNode(uintID(12), nil),
 					}},
 				},
 				new: []task{
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(10), nil)},
+					&dialTask{flags: dynDialedConn, dest: newNode(uintID(6), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(11), nil)},
+					&discoverTask{want: 4},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(12), nil)},
-					&discoverTask{},
 				},
 			},
-			// Dialing nodes 3,4,5 fails. The dials from the lookup succeed.
+			// Random dial succeeds, no more bootnodes are attempted
 			{
 				peers: []*Peer{
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(1), nil)}},
+					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(6), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(2), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(10), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(11), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(12), nil)}},
-				},
-				done: []task{
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(3), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(4), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(5), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(10), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(11), nil)},
-					&dialTask{flags: dynDialedConn, dest: newNode(uintID(12), nil)},
-				},
-			},
-			// Waiting for expiry. No waitExpireTask is launched because the
-			// discovery query is still running.
-			{
-				peers: []*Peer{
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(1), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(2), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(10), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(11), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(12), nil)}},
-				},
-			},
-			// Nodes 3,4 are not tried again because only the first two
-			// returned random nodes (nodes 1,2) are tried and they're
-			// already connected.
-			{
-				peers: []*Peer{
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(1), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(2), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(10), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(11), nil)}},
-					{rw: &conn{flags: dynDialedConn, node: newNode(uintID(12), nil)}},
 				},
 			},
 		},
@@ -416,11 +313,11 @@ func newNode(id enode.ID, ip net.IP) *enode.Node {
 	return enode.SignNull(&r, id)
 }
 
-// This test checks that candidates that do not match the netrestrict list are not dialed.
+// // This test checks that candidates that do not match the netrestrict list are not dialed.
 func TestDialStateNetRestrict(t *testing.T) {
 	// This table always returns the same random nodes
 	// in the order given below.
-	table := fakeTable{
+	nodes := []*enode.Node{
 		newNode(uintID(1), net.ParseIP("127.0.0.1")),
 		newNode(uintID(2), net.ParseIP("127.0.0.2")),
 		newNode(uintID(3), net.ParseIP("127.0.0.3")),
@@ -434,12 +331,23 @@ func TestDialStateNetRestrict(t *testing.T) {
 	restrict.Add("127.0.2.0/24")
 
 	runDialTest(t, dialtest{
-		init: newDialState(enode.ID{}, table, 10, &Config{NetRestrict: restrict}),
+		init: newDialState(enode.ID{}, 10, &Config{NetRestrict: restrict}),
 		rounds: []round{
 			{
 				new: []task{
-					&dialTask{flags: dynDialedConn, dest: table[4]},
+					&discoverTask{want: 10},
-					&discoverTask{},
+				},
+			},
+			{
+				done: []task{
+					&discoverTask{results: nodes},
+				},
+				new: []task{
+					&dialTask{flags: dynDialedConn, dest: nodes[4]},
+					&dialTask{flags: dynDialedConn, dest: nodes[5]},
+					&dialTask{flags: dynDialedConn, dest: nodes[6]},
+					&dialTask{flags: dynDialedConn, dest: nodes[7]},
+					&discoverTask{want: 6},
 				},
 			},
 		},
@@ -459,7 +367,7 @@ func TestDialStateStaticDial(t *testing.T) {
 		Logger: testlog.Logger(t, log.LvlTrace),
 	}
 	runDialTest(t, dialtest{
-		init: newDialState(enode.ID{}, fakeTable{}, 0, config),
+		init: newDialState(enode.ID{}, 0, config),
 		rounds: []round{
 			// Static dials are launched for the nodes that
 			// aren't yet connected.
@@ -544,7 +452,7 @@ func TestDialStateCache(t *testing.T) {
 		Logger: testlog.Logger(t, log.LvlTrace),
 	}
 	runDialTest(t, dialtest{
-		init: newDialState(enode.ID{}, fakeTable{}, 0, config),
+		init: newDialState(enode.ID{}, 0, config),
 		rounds: []round{
 			// Static dials are launched for the nodes that
 			// aren't yet connected.
@@ -618,8 +526,8 @@ func TestDialResolve(t *testing.T) {
 		Dialer: TCPDialer{&net.Dialer{Deadline: time.Now().Add(-5 * time.Minute)}},
 	}
 	resolved := newNode(uintID(1), net.IP{127, 0, 55, 234})
-	table := &resolveMock{answer: resolved}
+	resolver := &resolveMock{answer: resolved}
-	state := newDialState(enode.ID{}, table, 0, config)
+	state := newDialState(enode.ID{}, 0, config)
 
 	// Check that the task is generated with an incomplete ID.
 	dest := newNode(uintID(1), nil)
@@ -630,10 +538,14 @@ func TestDialResolve(t *testing.T) {
 	}
 
 	// Now run the task, it should resolve the ID once.
-	srv := &Server{ntab: table, log: config.Logger, Config: *config}
+	srv := &Server{
+		Config:             *config,
+		log:                config.Logger,
+		staticNodeResolver: resolver,
+	}
 	tasks[0].Do(srv)
-	if !reflect.DeepEqual(table.resolveCalls, []*enode.Node{dest}) {
+	if !reflect.DeepEqual(resolver.calls, []*enode.Node{dest}) {
-		t.Fatalf("wrong resolve calls, got %v", table.resolveCalls)
+		t.Fatalf("wrong resolve calls, got %v", resolver.calls)
 	}
 
 	// Report it as done to the dialer, which should update the static node record.
@@ -666,18 +578,13 @@ func uintID(i uint32) enode.ID {
 	return id
 }
 
-// implements discoverTable for TestDialResolve
+// for TestDialResolve
 type resolveMock struct {
-	resolveCalls []*enode.Node
+	calls  []*enode.Node
 	answer *enode.Node
 }
 
 func (t *resolveMock) Resolve(n *enode.Node) *enode.Node {
-	t.resolveCalls = append(t.resolveCalls, n)
+	t.calls = append(t.calls, n)
 	return t.answer
 }
-
-func (t *resolveMock) Self() *enode.Node                     { return new(enode.Node) }
-func (t *resolveMock) Close()                                {}
-func (t *resolveMock) LookupRandom() []*enode.Node           { return nil }
-func (t *resolveMock) ReadRandomNodes(buf []*enode.Node) int { return 0 }

p2p/discover/common.go

@@ -25,6 +25,7 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/netutil"
 )
 
+// UDPConn is a network connection on which discovery can operate.
 type UDPConn interface {
 	ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error)
 	WriteToUDP(b []byte, addr *net.UDPAddr) (n int, err error)
@@ -32,7 +33,7 @@ type UDPConn interface {
 	LocalAddr() net.Addr
 }
 
-// Config holds Table-related settings.
+// Config holds settings for the discovery listener.
 type Config struct {
 	// These settings are required and configure the UDP listener:
 	PrivateKey *ecdsa.PrivateKey
@@ -50,7 +51,7 @@ func ListenUDP(c UDPConn, ln *enode.LocalNode, cfg Config) (*UDPv4, error) {
 }
 
 // ReadPacket is a packet that couldn't be handled. Those packets are sent to the unhandled
-// channel if configured.
+// channel if configured. This is exported for internal use, do not use this type.
 type ReadPacket struct {
 	Data []byte
 	Addr *net.UDPAddr

p2p/discover/lookup.go

@@ -0,0 +1,209 @@
+// Copyright 2019 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 discover
+
+import (
+	"context"
+
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+// lookup performs a network search for nodes close to the given target. It approaches the
+// target by querying nodes that are closer to it on each iteration. The given target does
+// not need to be an actual node identifier.
+type lookup struct {
+	tab         *Table
+	queryfunc   func(*node) ([]*node, error)
+	replyCh     chan []*node
+	cancelCh    <-chan struct{}
+	asked, seen map[enode.ID]bool
+	result      nodesByDistance
+	replyBuffer []*node
+	queries     int
+}
+
+type queryFunc func(*node) ([]*node, error)
+
+func newLookup(ctx context.Context, tab *Table, target enode.ID, q queryFunc) *lookup {
+	it := &lookup{
+		tab:       tab,
+		queryfunc: q,
+		asked:     make(map[enode.ID]bool),
+		seen:      make(map[enode.ID]bool),
+		result:    nodesByDistance{target: target},
+		replyCh:   make(chan []*node, alpha),
+		cancelCh:  ctx.Done(),
+		queries:   -1,
+	}
+	// Don't query further if we hit ourself.
+	// Unlikely to happen often in practice.
+	it.asked[tab.self().ID()] = true
+	return it
+}
+
+// run runs the lookup to completion and returns the closest nodes found.
+func (it *lookup) run() []*enode.Node {
+	for it.advance() {
+	}
+	return unwrapNodes(it.result.entries)
+}
+
+// advance advances the lookup until any new nodes have been found.
+// It returns false when the lookup has ended.
+func (it *lookup) advance() bool {
+	for it.startQueries() {
+		select {
+		case nodes := <-it.replyCh:
+			it.replyBuffer = it.replyBuffer[:0]
+			for _, n := range nodes {
+				if n != nil && !it.seen[n.ID()] {
+					it.seen[n.ID()] = true
+					it.result.push(n, bucketSize)
+					it.replyBuffer = append(it.replyBuffer, n)
+				}
+			}
+			it.queries--
+			if len(it.replyBuffer) > 0 {
+				return true
+			}
+		case <-it.cancelCh:
+			it.shutdown()
+		}
+	}
+	return false
+}
+
+func (it *lookup) shutdown() {
+	for it.queries > 0 {
+		<-it.replyCh
+		it.queries--
+	}
+	it.queryfunc = nil
+	it.replyBuffer = nil
+}
+
+func (it *lookup) startQueries() bool {
+	if it.queryfunc == nil {
+		return false
+	}
+
+	// The first query returns nodes from the local table.
+	if it.queries == -1 {
+		it.tab.mutex.Lock()
+		closest := it.tab.closest(it.result.target, bucketSize, false)
+		it.tab.mutex.Unlock()
+		it.queries = 1
+		it.replyCh <- closest.entries
+		return true
+	}
+
+	// Ask the closest nodes that we haven't asked yet.
+	for i := 0; i < len(it.result.entries) && it.queries < alpha; i++ {
+		n := it.result.entries[i]
+		if !it.asked[n.ID()] {
+			it.asked[n.ID()] = true
+			it.queries++
+			go it.query(n, it.replyCh)
+		}
+	}
+	// The lookup ends when no more nodes can be asked.
+	return it.queries > 0
+}
+
+func (it *lookup) query(n *node, reply chan<- []*node) {
+	fails := it.tab.db.FindFails(n.ID(), n.IP())
+	r, err := it.queryfunc(n)
+	if err == errClosed {
+		// Avoid recording failures on shutdown.
+		reply <- nil
+		return
+	} else if len(r) == 0 {
+		fails++
+		it.tab.db.UpdateFindFails(n.ID(), n.IP(), fails)
+		it.tab.log.Trace("Findnode failed", "id", n.ID(), "failcount", fails, "err", err)
+		if fails >= maxFindnodeFailures {
+			it.tab.log.Trace("Too many findnode failures, dropping", "id", n.ID(), "failcount", fails)
+			it.tab.delete(n)
+		}
+	} else if fails > 0 {
+		// Reset failure counter because it counts _consecutive_ failures.
+		it.tab.db.UpdateFindFails(n.ID(), n.IP(), 0)
+	}
+
+	// Grab as many nodes as possible. Some of them might not be alive anymore, but we'll
+	// just remove those again during revalidation.
+	for _, n := range r {
+		it.tab.addSeenNode(n)
+	}
+	reply <- r
+}
+
+// lookupIterator performs lookup operations and iterates over all seen nodes.
+// When a lookup finishes, a new one is created through nextLookup.
+type lookupIterator struct {
+	buffer     []*node
+	nextLookup lookupFunc
+	ctx        context.Context
+	cancel     func()
+	lookup     *lookup
+}
+
+type lookupFunc func(ctx context.Context) *lookup
+
+func newLookupIterator(ctx context.Context, next lookupFunc) *lookupIterator {
+	ctx, cancel := context.WithCancel(ctx)
+	return &lookupIterator{ctx: ctx, cancel: cancel, nextLookup: next}
+}
+
+// Node returns the current node.
+func (it *lookupIterator) Node() *enode.Node {
+	if len(it.buffer) == 0 {
+		return nil
+	}
+	return unwrapNode(it.buffer[0])
+}
+
+// Next moves to the next node.
+func (it *lookupIterator) Next() bool {
+	// Consume next node in buffer.
+	if len(it.buffer) > 0 {
+		it.buffer = it.buffer[1:]
+	}
+	// Advance the lookup to refill the buffer.
+	for len(it.buffer) == 0 {
+		if it.ctx.Err() != nil {
+			it.lookup = nil
+			it.buffer = nil
+			return false
+		}
+		if it.lookup == nil {
+			it.lookup = it.nextLookup(it.ctx)
+			continue
+		}
+		if !it.lookup.advance() {
+			it.lookup = nil
+			continue
+		}
+		it.buffer = it.lookup.replyBuffer
+	}
+	return true
+}
+
+// Close ends the iterator.
+func (it *lookupIterator) Close() {
+	it.cancel()
+}

p2p/discover/table_util_test.go

@@ -17,11 +17,14 @@
 package discover
 
 import (
+	"bytes"
 	"crypto/ecdsa"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"math/rand"
 	"net"
+	"reflect"
 	"sort"
 	"sync"
 
@@ -169,6 +172,28 @@ func hasDuplicates(slice []*node) bool {
 	return false
 }
 
+func checkNodesEqual(got, want []*enode.Node) error {
+	if reflect.DeepEqual(got, want) {
+		return nil
+	}
+	output := new(bytes.Buffer)
+	fmt.Fprintf(output, "got %d nodes:\n", len(got))
+	for _, n := range got {
+		fmt.Fprintf(output, "  %v %v\n", n.ID(), n)
+	}
+	fmt.Fprintf(output, "want %d:\n", len(want))
+	for _, n := range want {
+		fmt.Fprintf(output, "  %v %v\n", n.ID(), n)
+	}
+	return errors.New(output.String())
+}
+
+func sortByID(nodes []*enode.Node) {
+	sort.Slice(nodes, func(i, j int) bool {
+		return string(nodes[i].ID().Bytes()) < string(nodes[j].ID().Bytes())
+	})
+}
+
 func sortedByDistanceTo(distbase enode.ID, slice []*node) bool {
 	return sort.SliceIsSorted(slice, func(i, j int) bool {
 		return enode.DistCmp(distbase, slice[i].ID(), slice[j].ID()) < 0

p2p/discover/v4_lookup_test.go

@@ -20,7 +20,6 @@ import (
 	"crypto/ecdsa"
 	"fmt"
 	"net"
-	"reflect"
 	"sort"
 	"testing"
 
@@ -49,19 +48,7 @@ func TestUDPv4_Lookup(t *testing.T) {
 	}()
 
 	// Answer lookup packets.
-	for done := false; !done; {
+	serveTestnet(test, lookupTestnet)
-		done = test.waitPacketOut(func(p packetV4, to *net.UDPAddr, hash []byte) {
-			n, key := lookupTestnet.nodeByAddr(to)
-			switch p.(type) {
-			case *pingV4:
-				test.packetInFrom(nil, key, to, &pongV4{Expiration: futureExp, ReplyTok: hash})
-			case *findnodeV4:
-				dist := enode.LogDist(n.ID(), lookupTestnet.target.id())
-				nodes := lookupTestnet.nodesAtDistance(dist - 1)
-				test.packetInFrom(nil, key, to, &neighborsV4{Expiration: futureExp, Nodes: nodes})
-			}
-		})
-	}
 
 	// Verify result nodes.
 	results := <-resultC
@@ -78,8 +65,94 @@ func TestUDPv4_Lookup(t *testing.T) {
 	if !sortedByDistanceTo(lookupTestnet.target.id(), wrapNodes(results)) {
 		t.Errorf("result set not sorted by distance to target")
 	}
-	if !reflect.DeepEqual(results, lookupTestnet.closest(bucketSize)) {
+	if err := checkNodesEqual(results, lookupTestnet.closest(bucketSize)); err != nil {
-		t.Errorf("results aren't the closest %d nodes", bucketSize)
+		t.Errorf("results aren't the closest %d nodes\n%v", bucketSize, err)
+	}
+}
+
+func TestUDPv4_LookupIterator(t *testing.T) {
+	t.Parallel()
+	test := newUDPTest(t)
+	defer test.close()
+
+	// Seed table with initial nodes.
+	bootnodes := make([]*node, len(lookupTestnet.dists[256]))
+	for i := range lookupTestnet.dists[256] {
+		bootnodes[i] = wrapNode(lookupTestnet.node(256, i))
+	}
+	fillTable(test.table, bootnodes)
+	go serveTestnet(test, lookupTestnet)
+
+	// Create the iterator and collect the nodes it yields.
+	iter := test.udp.RandomNodes()
+	seen := make(map[enode.ID]*enode.Node)
+	for limit := lookupTestnet.len(); iter.Next() && len(seen) < limit; {
+		seen[iter.Node().ID()] = iter.Node()
+	}
+	iter.Close()
+
+	// Check that all nodes in lookupTestnet were seen by the iterator.
+	results := make([]*enode.Node, 0, len(seen))
+	for _, n := range seen {
+		results = append(results, n)
+	}
+	sortByID(results)
+	want := lookupTestnet.nodes()
+	if err := checkNodesEqual(results, want); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// TestUDPv4_LookupIteratorClose checks that lookupIterator ends when its Close
+// method is called.
+func TestUDPv4_LookupIteratorClose(t *testing.T) {
+	t.Parallel()
+	test := newUDPTest(t)
+	defer test.close()
+
+	// Seed table with initial nodes.
+	bootnodes := make([]*node, len(lookupTestnet.dists[256]))
+	for i := range lookupTestnet.dists[256] {
+		bootnodes[i] = wrapNode(lookupTestnet.node(256, i))
+	}
+	fillTable(test.table, bootnodes)
+	go serveTestnet(test, lookupTestnet)
+
+	it := test.udp.RandomNodes()
+	if ok := it.Next(); !ok || it.Node() == nil {
+		t.Fatalf("iterator didn't return any node")
+	}
+
+	it.Close()
+
+	ncalls := 0
+	for ; ncalls < 100 && it.Next(); ncalls++ {
+		if it.Node() == nil {
+			t.Error("iterator returned Node() == nil node after Next() == true")
+		}
+	}
+	t.Logf("iterator returned %d nodes after close", ncalls)
+	if it.Next() {
+		t.Errorf("Next() == true after close and %d more calls", ncalls)
+	}
+	if n := it.Node(); n != nil {
+		t.Errorf("iterator returned non-nil node after close and %d more calls", ncalls)
+	}
+}
+
+func serveTestnet(test *udpTest, testnet *preminedTestnet) {
+	for done := false; !done; {
+		done = test.waitPacketOut(func(p packetV4, to *net.UDPAddr, hash []byte) {
+			n, key := testnet.nodeByAddr(to)
+			switch p.(type) {
+			case *pingV4:
+				test.packetInFrom(nil, key, to, &pongV4{Expiration: futureExp, ReplyTok: hash})
+			case *findnodeV4:
+				dist := enode.LogDist(n.ID(), testnet.target.id())
+				nodes := testnet.nodesAtDistance(dist - 1)
+				test.packetInFrom(nil, key, to, &neighborsV4{Expiration: futureExp, Nodes: nodes})
+			}
+		})
 	}
 }
 
@@ -148,6 +221,25 @@ type preminedTestnet struct {
 	dists  [hashBits + 1][]*ecdsa.PrivateKey
 }
 
+func (tn *preminedTestnet) len() int {
+	n := 0
+	for _, keys := range tn.dists {
+		n += len(keys)
+	}
+	return n
+}
+
+func (tn *preminedTestnet) nodes() []*enode.Node {
+	result := make([]*enode.Node, 0, tn.len())
+	for dist, keys := range tn.dists {
+		for index := range keys {
+			result = append(result, tn.node(dist, index))
+		}
+	}
+	sortByID(result)
+	return result
+}
+
 func (tn *preminedTestnet) node(dist, index int) *enode.Node {
 	key := tn.dists[dist][index]
 	ip := net.IP{127, byte(dist >> 8), byte(dist), byte(index)}

p2p/discover/v4_udp.go

@@ -19,6 +19,7 @@ package discover
 import (
 	"bytes"
 	"container/list"
+	"context"
 	"crypto/ecdsa"
 	crand "crypto/rand"
 	"errors"
@@ -207,7 +208,8 @@ type UDPv4 struct {
 
 	addReplyMatcher chan *replyMatcher
 	gotreply        chan reply
-	closing         chan struct{}
+	closeCtx        context.Context
+	cancelCloseCtx  func()
 }
 
 // replyMatcher represents a pending reply.
@@ -256,20 +258,23 @@ type reply struct {
 }
 
 func ListenV4(c UDPConn, ln *enode.LocalNode, cfg Config) (*UDPv4, error) {
+	closeCtx, cancel := context.WithCancel(context.Background())
 	t := &UDPv4{
 		conn:            c,
 		priv:            cfg.PrivateKey,
 		netrestrict:     cfg.NetRestrict,
 		localNode:       ln,
 		db:              ln.Database(),
-		closing:         make(chan struct{}),
 		gotreply:        make(chan reply),
 		addReplyMatcher: make(chan *replyMatcher),
+		closeCtx:        closeCtx,
+		cancelCloseCtx:  cancel,
 		log:             cfg.Log,
 	}
 	if t.log == nil {
 		t.log = log.Root()
 	}
+
 	tab, err := newTable(t, ln.Database(), cfg.Bootnodes, t.log)
 	if err != nil {
 		return nil, err
@@ -291,126 +296,13 @@ func (t *UDPv4) Self() *enode.Node {
 // Close shuts down the socket and aborts any running queries.
 func (t *UDPv4) Close() {
 	t.closeOnce.Do(func() {
-		close(t.closing)
+		t.cancelCloseCtx()
 		t.conn.Close()
 		t.wg.Wait()
 		t.tab.close()
 	})
 }
 
-// ReadRandomNodes reads random nodes from the local table.
-func (t *UDPv4) ReadRandomNodes(buf []*enode.Node) int {
-	return t.tab.ReadRandomNodes(buf)
-}
-
-// LookupRandom finds random nodes in the network.
-func (t *UDPv4) LookupRandom() []*enode.Node {
-	if t.tab.len() == 0 {
-		// All nodes were dropped, refresh. The very first query will hit this
-		// case and run the bootstrapping logic.
-		<-t.tab.refresh()
-	}
-	return t.lookupRandom()
-}
-
-func (t *UDPv4) LookupPubkey(key *ecdsa.PublicKey) []*enode.Node {
-	if t.tab.len() == 0 {
-		// All nodes were dropped, refresh. The very first query will hit this
-		// case and run the bootstrapping logic.
-		<-t.tab.refresh()
-	}
-	return unwrapNodes(t.lookup(encodePubkey(key)))
-}
-
-func (t *UDPv4) lookupRandom() []*enode.Node {
-	var target encPubkey
-	crand.Read(target[:])
-	return unwrapNodes(t.lookup(target))
-}
-
-func (t *UDPv4) lookupSelf() []*enode.Node {
-	return unwrapNodes(t.lookup(encodePubkey(&t.priv.PublicKey)))
-}
-
-// lookup performs a network search for nodes close to the given target. It approaches the
-// target by querying nodes that are closer to it on each iteration. The given target does
-// not need to be an actual node identifier.
-func (t *UDPv4) lookup(targetKey encPubkey) []*node {
-	var (
-		target         = enode.ID(crypto.Keccak256Hash(targetKey[:]))
-		asked          = make(map[enode.ID]bool)
-		seen           = make(map[enode.ID]bool)
-		reply          = make(chan []*node, alpha)
-		pendingQueries = 0
-		result         *nodesByDistance
-	)
-	// Don't query further if we hit ourself.
-	// Unlikely to happen often in practice.
-	asked[t.Self().ID()] = true
-
-	// Generate the initial result set.
-	t.tab.mutex.Lock()
-	result = t.tab.closest(target, bucketSize, false)
-	t.tab.mutex.Unlock()
-
-	for {
-		// ask the alpha closest nodes that we haven't asked yet
-		for i := 0; i < len(result.entries) && pendingQueries < alpha; i++ {
-			n := result.entries[i]
-			if !asked[n.ID()] {
-				asked[n.ID()] = true
-				pendingQueries++
-				go t.lookupWorker(n, targetKey, reply)
-			}
-		}
-		if pendingQueries == 0 {
-			// we have asked all closest nodes, stop the search
-			break
-		}
-		select {
-		case nodes := <-reply:
-			for _, n := range nodes {
-				if n != nil && !seen[n.ID()] {
-					seen[n.ID()] = true
-					result.push(n, bucketSize)
-				}
-			}
-		case <-t.tab.closeReq:
-			return nil // shutdown, no need to continue.
-		}
-		pendingQueries--
-	}
-	return result.entries
-}
-
-func (t *UDPv4) lookupWorker(n *node, targetKey encPubkey, reply chan<- []*node) {
-	fails := t.db.FindFails(n.ID(), n.IP())
-	r, err := t.findnode(n.ID(), n.addr(), targetKey)
-	if err == errClosed {
-		// Avoid recording failures on shutdown.
-		reply <- nil
-		return
-	} else if len(r) == 0 {
-		fails++
-		t.db.UpdateFindFails(n.ID(), n.IP(), fails)
-		t.log.Trace("Findnode failed", "id", n.ID(), "failcount", fails, "err", err)
-		if fails >= maxFindnodeFailures {
-			t.log.Trace("Too many findnode failures, dropping", "id", n.ID(), "failcount", fails)
-			t.tab.delete(n)
-		}
-	} else if fails > 0 {
-		// Reset failure counter because it counts _consecutive_ failures.
-		t.db.UpdateFindFails(n.ID(), n.IP(), 0)
-	}
-
-	// Grab as many nodes as possible. Some of them might not be alive anymore, but we'll
-	// just remove those again during revalidation.
-	for _, n := range r {
-		t.tab.addSeenNode(n)
-	}
-	reply <- r
-}
-
 // Resolve searches for a specific node with the given ID and tries to get the most recent
 // version of the node record for it. It returns n if the node could not be resolved.
 func (t *UDPv4) Resolve(n *enode.Node) *enode.Node {
@@ -498,6 +390,45 @@ func (t *UDPv4) makePing(toaddr *net.UDPAddr) *pingV4 {
 	}
 }
 
+// LookupPubkey finds the closest nodes to the given public key.
+func (t *UDPv4) LookupPubkey(key *ecdsa.PublicKey) []*enode.Node {
+	if t.tab.len() == 0 {
+		// All nodes were dropped, refresh. The very first query will hit this
+		// case and run the bootstrapping logic.
+		<-t.tab.refresh()
+	}
+	return t.newLookup(t.closeCtx, encodePubkey(key)).run()
+}
+
+// RandomNodes is an iterator yielding nodes from a random walk of the DHT.
+func (t *UDPv4) RandomNodes() enode.Iterator {
+	return newLookupIterator(t.closeCtx, t.newRandomLookup)
+}
+
+// lookupRandom implements transport.
+func (t *UDPv4) lookupRandom() []*enode.Node {
+	return t.newRandomLookup(t.closeCtx).run()
+}
+
+// lookupSelf implements transport.
+func (t *UDPv4) lookupSelf() []*enode.Node {
+	return t.newLookup(t.closeCtx, encodePubkey(&t.priv.PublicKey)).run()
+}
+
+func (t *UDPv4) newRandomLookup(ctx context.Context) *lookup {
+	var target encPubkey
+	crand.Read(target[:])
+	return t.newLookup(ctx, target)
+}
+
+func (t *UDPv4) newLookup(ctx context.Context, targetKey encPubkey) *lookup {
+	target := enode.ID(crypto.Keccak256Hash(targetKey[:]))
+	it := newLookup(ctx, t.tab, target, func(n *node) ([]*node, error) {
+		return t.findnode(n.ID(), n.addr(), targetKey)
+	})
+	return it
+}
+
 // findnode sends a findnode request to the given node and waits until
 // the node has sent up to k neighbors.
 func (t *UDPv4) findnode(toid enode.ID, toaddr *net.UDPAddr, target encPubkey) ([]*node, error) {
@@ -575,7 +506,7 @@ func (t *UDPv4) pending(id enode.ID, ip net.IP, ptype byte, callback replyMatchF
 	select {
 	case t.addReplyMatcher <- p:
 		// loop will handle it
-	case <-t.closing:
+	case <-t.closeCtx.Done():
 		ch <- errClosed
 	}
 	return p
@@ -589,7 +520,7 @@ func (t *UDPv4) handleReply(from enode.ID, fromIP net.IP, req packetV4) bool {
 	case t.gotreply <- reply{from, fromIP, req, matched}:
 		// loop will handle it
 		return <-matched
-	case <-t.closing:
+	case <-t.closeCtx.Done():
 		return false
 	}
 }
@@ -635,7 +566,7 @@ func (t *UDPv4) loop() {
 		resetTimeout()
 
 		select {
-		case <-t.closing:
+		case <-t.closeCtx.Done():
 			for el := plist.Front(); el != nil; el = el.Next() {
 				el.Value.(*replyMatcher).errc <- errClosed
 			}

p2p/enode/iter.go

@@ -0,0 +1,286 @@
+// Copyright 2019 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 enode
+
+import (
+	"sync"
+	"time"
+)
+
+// Iterator represents a sequence of nodes. The Next method moves to the next node in the
+// sequence. It returns false when the sequence has ended or the iterator is closed. Close
+// may be called concurrently with Next and Node, and interrupts Next if it is blocked.
+type Iterator interface {
+	Next() bool  // moves to next node
+	Node() *Node // returns current node
+	Close()      // ends the iterator
+}
+
+// ReadNodes reads at most n nodes from the given iterator. The return value contains no
+// duplicates and no nil values. To prevent looping indefinitely for small repeating node
+// sequences, this function calls Next at most n times.
+func ReadNodes(it Iterator, n int) []*Node {
+	seen := make(map[ID]*Node, n)
+	for i := 0; i < n && it.Next(); i++ {
+		// Remove duplicates, keeping the node with higher seq.
+		node := it.Node()
+		prevNode, ok := seen[node.ID()]
+		if ok && prevNode.Seq() > node.Seq() {
+			continue
+		}
+		seen[node.ID()] = node
+	}
+	result := make([]*Node, 0, len(seen))
+	for _, node := range seen {
+		result = append(result, node)
+	}
+	return result
+}
+
+// IterNodes makes an iterator which runs through the given nodes once.
+func IterNodes(nodes []*Node) Iterator {
+	return &sliceIter{nodes: nodes, index: -1}
+}
+
+// CycleNodes makes an iterator which cycles through the given nodes indefinitely.
+func CycleNodes(nodes []*Node) Iterator {
+	return &sliceIter{nodes: nodes, index: -1, cycle: true}
+}
+
+type sliceIter struct {
+	mu    sync.Mutex
+	nodes []*Node
+	index int
+	cycle bool
+}
+
+func (it *sliceIter) Next() bool {
+	it.mu.Lock()
+	defer it.mu.Unlock()
+
+	if len(it.nodes) == 0 {
+		return false
+	}
+	it.index++
+	if it.index == len(it.nodes) {
+		if it.cycle {
+			it.index = 0
+		} else {
+			it.nodes = nil
+			return false
+		}
+	}
+	return true
+}
+
+func (it *sliceIter) Node() *Node {
+	if len(it.nodes) == 0 {
+		return nil
+	}
+	return it.nodes[it.index]
+}
+
+func (it *sliceIter) Close() {
+	it.mu.Lock()
+	defer it.mu.Unlock()
+
+	it.nodes = nil
+}
+
+// Filter wraps an iterator such that Next only returns nodes for which
+// the 'check' function returns true.
+func Filter(it Iterator, check func(*Node) bool) Iterator {
+	return &filterIter{it, check}
+}
+
+type filterIter struct {
+	Iterator
+	check func(*Node) bool
+}
+
+func (f *filterIter) Next() bool {
+	for f.Iterator.Next() {
+		if f.check(f.Node()) {
+			return true
+		}
+	}
+	return false
+}
+
+// FairMix aggregates multiple node iterators. The mixer itself is an iterator which ends
+// only when Close is called. Source iterators added via AddSource are removed from the
+// mix when they end.
+//
+// The distribution of nodes returned by Next is approximately fair, i.e. FairMix
+// attempts to draw from all sources equally often. However, if a certain source is slow
+// and doesn't return a node within the configured timeout, a node from any other source
+// will be returned.
+//
+// It's safe to call AddSource and Close concurrently with Next.
+type FairMix struct {
+	wg      sync.WaitGroup
+	fromAny chan *Node
+	timeout time.Duration
+	cur     *Node
+
+	mu      sync.Mutex
+	closed  chan struct{}
+	sources []*mixSource
+	last    int
+}
+
+type mixSource struct {
+	it      Iterator
+	next    chan *Node
+	timeout time.Duration
+}
+
+// NewFairMix creates a mixer.
+//
+// The timeout specifies how long the mixer will wait for the next fairly-chosen source
+// before giving up and taking a node from any other source. A good way to set the timeout
+// is deciding how long you'd want to wait for a node on average. Passing a negative
+// timeout makes the mixer completely fair.
+func NewFairMix(timeout time.Duration) *FairMix {
+	m := &FairMix{
+		fromAny: make(chan *Node),
+		closed:  make(chan struct{}),
+		timeout: timeout,
+	}
+	return m
+}
+
+// AddSource adds a source of nodes.
+func (m *FairMix) AddSource(it Iterator) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.closed == nil {
+		return
+	}
+	m.wg.Add(1)
+	source := &mixSource{it, make(chan *Node), m.timeout}
+	m.sources = append(m.sources, source)
+	go m.runSource(m.closed, source)
+}
+
+// Close shuts down the mixer and all current sources.
+// Calling this is required to release resources associated with the mixer.
+func (m *FairMix) Close() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.closed == nil {
+		return
+	}
+	for _, s := range m.sources {
+		s.it.Close()
+	}
+	close(m.closed)
+	m.wg.Wait()
+	close(m.fromAny)
+	m.sources = nil
+	m.closed = nil
+}
+
+// Next returns a node from a random source.
+func (m *FairMix) Next() bool {
+	m.cur = nil
+
+	var timeout <-chan time.Time
+	if m.timeout >= 0 {
+		timer := time.NewTimer(m.timeout)
+		timeout = timer.C
+		defer timer.Stop()
+	}
+	for {
+		source := m.pickSource()
+		if source == nil {
+			return m.nextFromAny()
+		}
+		select {
+		case n, ok := <-source.next:
+			if ok {
+				m.cur = n
+				source.timeout = m.timeout
+				return true
+			}
+			// This source has ended.
+			m.deleteSource(source)
+		case <-timeout:
+			source.timeout /= 2
+			return m.nextFromAny()
+		}
+	}
+}
+
+// Node returns the current node.
+func (m *FairMix) Node() *Node {
+	return m.cur
+}
+
+// nextFromAny is used when there are no sources or when the 'fair' choice
+// doesn't turn up a node quickly enough.
+func (m *FairMix) nextFromAny() bool {
+	n, ok := <-m.fromAny
+	if ok {
+		m.cur = n
+	}
+	return ok
+}
+
+// pickSource chooses the next source to read from, cycling through them in order.
+func (m *FairMix) pickSource() *mixSource {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if len(m.sources) == 0 {
+		return nil
+	}
+	m.last = (m.last + 1) % len(m.sources)
+	return m.sources[m.last]
+}
+
+// deleteSource deletes a source.
+func (m *FairMix) deleteSource(s *mixSource) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	for i := range m.sources {
+		if m.sources[i] == s {
+			copy(m.sources[i:], m.sources[i+1:])
+			m.sources[len(m.sources)-1] = nil
+			m.sources = m.sources[:len(m.sources)-1]
+			break
+		}
+	}
+}
+
+// runSource reads a single source in a loop.
+func (m *FairMix) runSource(closed chan struct{}, s *mixSource) {
+	defer m.wg.Done()
+	defer close(s.next)
+	for s.it.Next() {
+		n := s.it.Node()
+		select {
+		case s.next <- n:
+		case m.fromAny <- n:
+		case <-closed:
+			return
+		}
+	}
+}

p2p/enode/iter_test.go

@@ -0,0 +1,291 @@
+// Copyright 2019 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 enode
+
+import (
+	"encoding/binary"
+	"runtime"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/p2p/enr"
+)
+
+func TestReadNodes(t *testing.T) {
+	nodes := ReadNodes(new(genIter), 10)
+	checkNodes(t, nodes, 10)
+}
+
+// This test checks that ReadNodes terminates when reading N nodes from an iterator
+// which returns less than N nodes in an endless cycle.
+func TestReadNodesCycle(t *testing.T) {
+	iter := &callCountIter{
+		Iterator: CycleNodes([]*Node{
+			testNode(0, 0),
+			testNode(1, 0),
+			testNode(2, 0),
+		}),
+	}
+	nodes := ReadNodes(iter, 10)
+	checkNodes(t, nodes, 3)
+	if iter.count != 10 {
+		t.Fatalf("%d calls to Next, want %d", iter.count, 100)
+	}
+}
+
+func TestFilterNodes(t *testing.T) {
+	nodes := make([]*Node, 100)
+	for i := range nodes {
+		nodes[i] = testNode(uint64(i), uint64(i))
+	}
+
+	it := Filter(IterNodes(nodes), func(n *Node) bool {
+		return n.Seq() >= 50
+	})
+	for i := 50; i < len(nodes); i++ {
+		if !it.Next() {
+			t.Fatal("Next returned false")
+		}
+		if it.Node() != nodes[i] {
+			t.Fatalf("iterator returned wrong node %v\nwant %v", it.Node(), nodes[i])
+		}
+	}
+	if it.Next() {
+		t.Fatal("Next returned true after underlying iterator has ended")
+	}
+}
+
+func checkNodes(t *testing.T, nodes []*Node, wantLen int) {
+	if len(nodes) != wantLen {
+		t.Errorf("slice has %d nodes, want %d", len(nodes), wantLen)
+		return
+	}
+	seen := make(map[ID]bool)
+	for i, e := range nodes {
+		if e == nil {
+			t.Errorf("nil node at index %d", i)
+			return
+		}
+		if seen[e.ID()] {
+			t.Errorf("slice has duplicate node %v", e.ID())
+			return
+		}
+		seen[e.ID()] = true
+	}
+}
+
+// This test checks fairness of FairMix in the happy case where all sources return nodes
+// within the context's deadline.
+func TestFairMix(t *testing.T) {
+	for i := 0; i < 500; i++ {
+		testMixerFairness(t)
+	}
+}
+
+func testMixerFairness(t *testing.T) {
+	mix := NewFairMix(1 * time.Second)
+	mix.AddSource(&genIter{index: 1})
+	mix.AddSource(&genIter{index: 2})
+	mix.AddSource(&genIter{index: 3})
+	defer mix.Close()
+
+	nodes := ReadNodes(mix, 500)
+	checkNodes(t, nodes, 500)
+
+	// Verify that the nodes slice contains an approximately equal number of nodes
+	// from each source.
+	d := idPrefixDistribution(nodes)
+	for _, count := range d {
+		if approxEqual(count, len(nodes)/3, 30) {
+			t.Fatalf("ID distribution is unfair: %v", d)
+		}
+	}
+}
+
+// This test checks that FairMix falls back to an alternative source when
+// the 'fair' choice doesn't return a node within the timeout.
+func TestFairMixNextFromAll(t *testing.T) {
+	mix := NewFairMix(1 * time.Millisecond)
+	mix.AddSource(&genIter{index: 1})
+	mix.AddSource(CycleNodes(nil))
+	defer mix.Close()
+
+	nodes := ReadNodes(mix, 500)
+	checkNodes(t, nodes, 500)
+
+	d := idPrefixDistribution(nodes)
+	if len(d) > 1 || d[1] != len(nodes) {
+		t.Fatalf("wrong ID distribution: %v", d)
+	}
+}
+
+// This test ensures FairMix works for Next with no sources.
+func TestFairMixEmpty(t *testing.T) {
+	var (
+		mix   = NewFairMix(1 * time.Second)
+		testN = testNode(1, 1)
+		ch    = make(chan *Node)
+	)
+	defer mix.Close()
+
+	go func() {
+		mix.Next()
+		ch <- mix.Node()
+	}()
+
+	mix.AddSource(CycleNodes([]*Node{testN}))
+	if n := <-ch; n != testN {
+		t.Errorf("got wrong node: %v", n)
+	}
+}
+
+// This test checks closing a source while Next runs.
+func TestFairMixRemoveSource(t *testing.T) {
+	mix := NewFairMix(1 * time.Second)
+	source := make(blockingIter)
+	mix.AddSource(source)
+
+	sig := make(chan *Node)
+	go func() {
+		<-sig
+		mix.Next()
+		sig <- mix.Node()
+	}()
+
+	sig <- nil
+	runtime.Gosched()
+	source.Close()
+
+	wantNode := testNode(0, 0)
+	mix.AddSource(CycleNodes([]*Node{wantNode}))
+	n := <-sig
+
+	if len(mix.sources) != 1 {
+		t.Fatalf("have %d sources, want one", len(mix.sources))
+	}
+	if n != wantNode {
+		t.Fatalf("mixer returned wrong node")
+	}
+}
+
+type blockingIter chan struct{}
+
+func (it blockingIter) Next() bool {
+	<-it
+	return false
+}
+
+func (it blockingIter) Node() *Node {
+	return nil
+}
+
+func (it blockingIter) Close() {
+	close(it)
+}
+
+func TestFairMixClose(t *testing.T) {
+	for i := 0; i < 20 && !t.Failed(); i++ {
+		testMixerClose(t)
+	}
+}
+
+func testMixerClose(t *testing.T) {
+	mix := NewFairMix(-1)
+	mix.AddSource(CycleNodes(nil))
+	mix.AddSource(CycleNodes(nil))
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		if mix.Next() {
+			t.Error("Next returned true")
+		}
+	}()
+	// This call is supposed to make it more likely that NextNode is
+	// actually executing by the time we call Close.
+	runtime.Gosched()
+
+	mix.Close()
+	select {
+	case <-done:
+	case <-time.After(3 * time.Second):
+		t.Fatal("Next didn't unblock on Close")
+	}
+
+	mix.Close() // shouldn't crash
+}
+
+func idPrefixDistribution(nodes []*Node) map[uint32]int {
+	d := make(map[uint32]int)
+	for _, node := range nodes {
+		id := node.ID()
+		d[binary.BigEndian.Uint32(id[:4])]++
+	}
+	return d
+}
+
+func approxEqual(x, y, ε int) bool {
+	if y > x {
+		x, y = y, x
+	}
+	return x-y > ε
+}
+
+// genIter creates fake nodes with numbered IDs based on 'index' and 'gen'
+type genIter struct {
+	node       *Node
+	index, gen uint32
+}
+
+func (s *genIter) Next() bool {
+	index := atomic.LoadUint32(&s.index)
+	if index == ^uint32(0) {
+		s.node = nil
+		return false
+	}
+	s.node = testNode(uint64(index)<<32|uint64(s.gen), 0)
+	s.gen++
+	return true
+}
+
+func (s *genIter) Node() *Node {
+	return s.node
+}
+
+func (s *genIter) Close() {
+	s.index = ^uint32(0)
+}
+
+func testNode(id, seq uint64) *Node {
+	var nodeID ID
+	binary.BigEndian.PutUint64(nodeID[:], id)
+	r := new(enr.Record)
+	r.SetSeq(seq)
+	return SignNull(r, nodeID)
+}
+
+// callCountIter counts calls to NextNode.
+type callCountIter struct {
+	Iterator
+	count int
+}
+
+func (it *callCountIter) Next() bool {
+	it.count++
+	return it.Iterator.Next()
+}

p2p/protocol.go

@@ -54,6 +54,11 @@ type Protocol struct {
 	// but returns nil, it is assumed that the protocol handshake is still running.
 	PeerInfo func(id enode.ID) interface{}
 
+	// DialCandidates, if non-nil, is a way to tell Server about protocol-specific nodes
+	// that should be dialed. The server continuously reads nodes from the iterator and
+	// attempts to create connections to them.
+	DialCandidates enode.Iterator
+
 	// Attributes contains protocol specific information for the node record.
 	Attributes []enr.Entry
 }

p2p/server.go

@@ -45,6 +45,11 @@ import (
 const (
 	defaultDialTimeout = 15 * time.Second
 
+	// This is the fairness knob for the discovery mixer. When looking for peers, we'll
+	// wait this long for a single source of candidates before moving on and trying other
+	// sources.
+	discmixTimeout = 5 * time.Second
+
 	// Connectivity defaults.
 	maxActiveDialTasks     = 16
 	defaultMaxPendingPeers = 50
@@ -167,16 +172,20 @@ type Server struct {
 	lock    sync.Mutex // protects running
 	running bool
 
-	nodedb       *enode.DB
-	localnode    *enode.LocalNode
-	ntab         discoverTable
 	listener     net.Listener
 	ourHandshake *protoHandshake
-	DiscV5       *discv5.Network
 	loopWG       sync.WaitGroup // loop, listenLoop
 	peerFeed     event.Feed
 	log          log.Logger
 
+	nodedb    *enode.DB
+	localnode *enode.LocalNode
+	ntab      *discover.UDPv4
+	DiscV5    *discv5.Network
+	discmix   *enode.FairMix
+
+	staticNodeResolver nodeResolver
+
 	// Channels into the run loop.
 	quit                    chan struct{}
 	addstatic               chan *enode.Node
@@ -470,7 +479,7 @@ func (srv *Server) Start() (err error) {
 	}
 
 	dynPeers := srv.maxDialedConns()
-	dialer := newDialState(srv.localnode.ID(), srv.ntab, dynPeers, &srv.Config)
+	dialer := newDialState(srv.localnode.ID(), dynPeers, &srv.Config)
 	srv.loopWG.Add(1)
 	go srv.run(dialer)
 	return nil
@@ -521,6 +530,18 @@ func (srv *Server) setupLocalNode() error {
 }
 
 func (srv *Server) setupDiscovery() error {
+	srv.discmix = enode.NewFairMix(discmixTimeout)
+
+	// Add protocol-specific discovery sources.
+	added := make(map[string]bool)
+	for _, proto := range srv.Protocols {
+		if proto.DialCandidates != nil && !added[proto.Name] {
+			srv.discmix.AddSource(proto.DialCandidates)
+			added[proto.Name] = true
+		}
+	}
+
+	// Don't listen on UDP endpoint if DHT is disabled.
 	if srv.NoDiscovery && !srv.DiscoveryV5 {
 		return nil
 	}
@@ -562,7 +583,10 @@ func (srv *Server) setupDiscovery() error {
 			return err
 		}
 		srv.ntab = ntab
+		srv.discmix.AddSource(ntab.RandomNodes())
+		srv.staticNodeResolver = ntab
 	}
+
 	// Discovery V5
 	if srv.DiscoveryV5 {
 		var ntab *discv5.Network
@@ -620,6 +644,7 @@ func (srv *Server) run(dialstate dialer) {
 	srv.log.Info("Started P2P networking", "self", srv.localnode.Node().URLv4())
 	defer srv.loopWG.Done()
 	defer srv.nodedb.Close()
+	defer srv.discmix.Close()
 
 	var (
 		peers        = make(map[enode.ID]*Peer)

p2p/server_test.go

@@ -233,8 +233,8 @@ func TestServerTaskScheduling(t *testing.T) {
 		Config:    Config{MaxPeers: 10},
 		localnode: enode.NewLocalNode(db, newkey()),
 		nodedb:    db,
+		discmix:   enode.NewFairMix(0),
 		quit:      make(chan struct{}),
-		ntab:      fakeTable{},
 		running:   true,
 		log:       log.New(),
 	}
@@ -282,9 +282,9 @@ func TestServerManyTasks(t *testing.T) {
 			quit:      make(chan struct{}),
 			localnode: enode.NewLocalNode(db, newkey()),
 			nodedb:    db,
-			ntab:      fakeTable{},
 			running:   true,
 			log:       log.New(),
+			discmix:   enode.NewFairMix(0),
 		}
 		done       = make(chan *testTask)
 		start, end = 0, 0