p2p/discover: implement node bonding

This a fix for an attack vector where the discovery protocol could be
used to amplify traffic in a DDOS attack. A malicious actor would send a
findnode request with the IP address and UDP port of the target as the
source address. The recipient of the findnode packet would then send a
neighbors packet (which is 16x the size of findnode) to the victim.

Our solution is to require a 'bond' with the sender of findnode. If no
bond exists, the findnode packet is not processed. A bond between nodes
α and β is created when α replies to a ping from β.

This (initial) version of the bonding implementation might still be
vulnerable against replay attacks during the expiration time window.
We will add stricter source address validation later.

p2p/discover/node.go

@@ -13,6 +13,8 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
+	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/ethereum/go-ethereum/crypto"
@@ -30,7 +32,8 @@ type Node struct {
 	DiscPort int // UDP listening port for discovery protocol
 	TCPPort  int // TCP listening port for RLPx
 
-	active time.Time
+	// this must be set/read using atomic load and store.
+	activeStamp int64
 }
 
 func newNode(id NodeID, addr *net.UDPAddr) *Node {
@@ -39,7 +42,6 @@ func newNode(id NodeID, addr *net.UDPAddr) *Node {
 		IP:       addr.IP,
 		DiscPort: addr.Port,
 		TCPPort:  addr.Port,
-		active:   time.Now(),
 	}
 }
 
@@ -48,6 +50,20 @@ func (n *Node) isValid() bool {
 	return !n.IP.IsMulticast() && !n.IP.IsUnspecified() && n.TCPPort != 0 && n.DiscPort != 0
 }
 
+func (n *Node) bumpActive() {
+	stamp := time.Now().Unix()
+	atomic.StoreInt64(&n.activeStamp, stamp)
+}
+
+func (n *Node) active() time.Time {
+	stamp := atomic.LoadInt64(&n.activeStamp)
+	return time.Unix(stamp, 0)
+}
+
+func (n *Node) addr() *net.UDPAddr {
+	return &net.UDPAddr{IP: n.IP, Port: n.DiscPort}
+}
+
 // The string representation of a Node is a URL.
 // Please see ParseNode for a description of the format.
 func (n *Node) String() string {
@@ -304,3 +320,26 @@ func randomID(a NodeID, n int) (b NodeID) {
 	}
 	return b
 }
+
+// nodeDB stores all nodes we know about.
+type nodeDB struct {
+	mu   sync.RWMutex
+	byID map[NodeID]*Node
+}
+
+func (db *nodeDB) get(id NodeID) *Node {
+	db.mu.RLock()
+	defer db.mu.RUnlock()
+	return db.byID[id]
+}
+
+func (db *nodeDB) add(id NodeID, addr *net.UDPAddr, tcpPort uint16) *Node {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	if db.byID == nil {
+		db.byID = make(map[NodeID]*Node)
+	}
+	n := &Node{ID: id, IP: addr.IP, DiscPort: addr.Port, TCPPort: int(tcpPort)}
+	db.byID[n.ID] = n
+	return n
+}

p2p/discover/table.go

@@ -17,6 +17,7 @@ const (
 	alpha               = 3              // Kademlia concurrency factor
 	bucketSize          = 16             // Kademlia bucket size
 	nBuckets            = nodeIDBits + 1 // Number of buckets
+	maxBondingPingPongs = 10
 )
 
 type Table struct {
@@ -24,27 +25,50 @@ type Table struct {
 	buckets [nBuckets]*bucket // index of known nodes by distance
 	nursery []*Node           // bootstrap nodes
 
+	bondmu    sync.Mutex
+	bonding   map[NodeID]*bondproc
+	bondslots chan struct{} // limits total number of active bonding processes
+
 	net  transport
 	self *Node // metadata of the local node
+	db   *nodeDB
+}
+
+type bondproc struct {
+	err  error
+	n    *Node
+	done chan struct{}
 }
 
 // transport is implemented by the UDP transport.
 // it is an interface so we can test without opening lots of UDP
 // sockets and without generating a private key.
 type transport interface {
-	ping(*Node) error
+	ping(NodeID, *net.UDPAddr) error
-	findnode(e *Node, target NodeID) ([]*Node, error)
+	waitping(NodeID) error
+	findnode(toid NodeID, addr *net.UDPAddr, target NodeID) ([]*Node, error)
 	close()
 }
 
 // bucket contains nodes, ordered by their last activity.
+// the entry that was most recently active is the last element
+// in entries.
 type bucket struct {
 	lastLookup time.Time
 	entries    []*Node
 }
 
 func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr) *Table {
-	tab := &Table{net: t, self: newNode(ourID, ourAddr)}
+	tab := &Table{
+		net:       t,
+		db:        new(nodeDB),
+		self:      newNode(ourID, ourAddr),
+		bonding:   make(map[NodeID]*bondproc),
+		bondslots: make(chan struct{}, maxBondingPingPongs),
+	}
+	for i := 0; i < cap(tab.bondslots); i++ {
+		tab.bondslots <- struct{}{}
+	}
 	for i := range tab.buckets {
 		tab.buckets[i] = new(bucket)
 	}
@@ -107,8 +131,8 @@ func (tab *Table) Lookup(target NodeID) []*Node {
 				asked[n.ID] = true
 				pendingQueries++
 				go func() {
-					result, _ := tab.net.findnode(n, target)
+					r, _ := tab.net.findnode(n.ID, n.addr(), target)
-					reply <- result
+					reply <- tab.bondall(r)
 				}()
 			}
 		}
@@ -116,13 +140,11 @@ func (tab *Table) Lookup(target NodeID) []*Node {
 			// we have asked all closest nodes, stop the search
 			break
 		}
-
 		// wait for the next reply
 		for _, n := range <-reply {
-			cn := n
+			if n != nil && !seen[n.ID] {
-			if !seen[n.ID] {
 				seen[n.ID] = true
-				result.push(cn, bucketSize)
+				result.push(n, bucketSize)
 			}
 		}
 		pendingQueries--
@@ -145,8 +167,9 @@ func (tab *Table) refresh() {
 	result := tab.Lookup(randomID(tab.self.ID, ld))
 	if len(result) == 0 {
 		// bootstrap the table with a self lookup
+		all := tab.bondall(tab.nursery)
 		tab.mutex.Lock()
-		tab.add(tab.nursery)
+		tab.add(all)
 		tab.mutex.Unlock()
 		tab.Lookup(tab.self.ID)
 		// TODO: the Kademlia paper says that we're supposed to perform
@@ -176,45 +199,105 @@ func (tab *Table) len() (n int) {
 	return n
 }
 
-// bumpOrAdd updates the activity timestamp for the given node and
+// bondall bonds with all given nodes concurrently and returns
-// attempts to insert the node into a bucket. The returned Node might
+// those nodes for which bonding has probably succeeded.
-// not be part of the table. The caller must hold tab.mutex.
+func (tab *Table) bondall(nodes []*Node) (result []*Node) {
-func (tab *Table) bumpOrAdd(node NodeID, from *net.UDPAddr) (n *Node) {
+	rc := make(chan *Node, len(nodes))
-	b := tab.buckets[logdist(tab.self.ID, node)]
+	for i := range nodes {
-	if n = b.bump(node); n == nil {
+		go func(n *Node) {
-		n = newNode(node, from)
+			nn, _ := tab.bond(false, n.ID, n.addr(), uint16(n.TCPPort))
-		if len(b.entries) == bucketSize {
+			rc <- nn
-			tab.pingReplace(n, b)
+		}(nodes[i])
+	}
+	for _ = range nodes {
+		if n := <-rc; n != nil {
+			result = append(result, n)
+		}
+	}
+	return result
+}
+
+// bond ensures the local node has a bond with the given remote node.
+// It also attempts to insert the node into the table if bonding succeeds.
+// The caller must not hold tab.mutex.
+//
+// A bond is must be established before sending findnode requests.
+// Both sides must have completed a ping/pong exchange for a bond to
+// exist. The total number of active bonding processes is limited in
+// order to restrain network use.
+//
+// bond is meant to operate idempotently in that bonding with a remote
+// node which still remembers a previously established bond will work.
+// The remote node will simply not send a ping back, causing waitping
+// to time out.
+//
+// If pinged is true, the remote node has just pinged us and one half
+// of the process can be skipped.
+func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) (*Node, error) {
+	var n *Node
+	if n = tab.db.get(id); n == nil {
+		tab.bondmu.Lock()
+		w := tab.bonding[id]
+		if w != nil {
+			// Wait for an existing bonding process to complete.
+			tab.bondmu.Unlock()
+			<-w.done
 		} else {
-			b.entries = append(b.entries, n)
+			// Register a new bonding process.
+			w = &bondproc{done: make(chan struct{})}
+			tab.bonding[id] = w
+			tab.bondmu.Unlock()
+			// Do the ping/pong. The result goes into w.
+			tab.pingpong(w, pinged, id, addr, tcpPort)
+			// Unregister the process after it's done.
+			tab.bondmu.Lock()
+			delete(tab.bonding, id)
+			tab.bondmu.Unlock()
+		}
+		n = w.n
+		if w.err != nil {
+			return nil, w.err
 		}
 	}
-	return n
+	tab.mutex.Lock()
+	defer tab.mutex.Unlock()
+	if b := tab.buckets[logdist(tab.self.ID, n.ID)]; !b.bump(n) {
+		tab.pingreplace(n, b)
+	}
+	return n, nil
 }
 
-func (tab *Table) pingReplace(n *Node, b *bucket) {
+func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) {
-	old := b.entries[bucketSize-1]
+	<-tab.bondslots
-	go func() {
+	defer func() { tab.bondslots <- struct{}{} }()
-		if err := tab.net.ping(old); err == nil {
+	if w.err = tab.net.ping(id, addr); w.err != nil {
-			// it responded, we don't need to replace it.
+		close(w.done)
 		return
 	}
-		// it didn't respond, replace the node if it is still the oldest node.
+	if !pinged {
-		tab.mutex.Lock()
+		// Give the remote node a chance to ping us before we start
-		if len(b.entries) > 0 && b.entries[len(b.entries)-1] == old {
+		// sending findnode requests. If they still remember us,
-			// slide down other entries and put the new one in front.
+		// waitping will simply time out.
-			// TODO: insert in correct position to keep the order
+		tab.net.waitping(id)
-			copy(b.entries[1:], b.entries)
-			b.entries[0] = n
 	}
-		tab.mutex.Unlock()
+	w.n = tab.db.add(id, addr, tcpPort)
-	}()
+	close(w.done)
 }
 
-// bump updates the activity timestamp for the given node.
+func (tab *Table) pingreplace(new *Node, b *bucket) {
-// The caller must hold tab.mutex.
+	if len(b.entries) == bucketSize {
-func (tab *Table) bump(node NodeID) {
+		oldest := b.entries[bucketSize-1]
-	tab.buckets[logdist(tab.self.ID, node)].bump(node)
+		if err := tab.net.ping(oldest.ID, oldest.addr()); err == nil {
+			// The node responded, we don't need to replace it.
+			return
+		}
+	} else {
+		// Add a slot at the end so the last entry doesn't
+		// fall off when adding the new node.
+		b.entries = append(b.entries, nil)
+	}
+	copy(b.entries[1:], b.entries)
+	b.entries[0] = new
 }
 
 // add puts the entries into the table if their corresponding
@@ -240,17 +323,17 @@ outer:
 	}
 }
 
-func (b *bucket) bump(id NodeID) *Node {
+func (b *bucket) bump(n *Node) bool {
-	for i, n := range b.entries {
+	for i := range b.entries {
-		if n.ID == id {
+		if b.entries[i].ID == n.ID {
-			n.active = time.Now()
+			n.bumpActive()
 			// move it to the front
 			copy(b.entries[1:], b.entries[:i+1])
 			b.entries[0] = n
-			return n
+			return true
 		}
 	}
-	return nil
+	return false
 }
 
 // nodesByDistance is a list of nodes, ordered by

p2p/discover/table_test.go

@@ -2,80 +2,69 @@ package discover
 
 import (
 	"crypto/ecdsa"
-	"errors"
 	"fmt"
 	"math/rand"
 	"net"
 	"reflect"
 	"testing"
 	"testing/quick"
-	"time"
 
 	"github.com/ethereum/go-ethereum/crypto"
 )
 
-func TestTable_bumpOrAddBucketAssign(t *testing.T) {
+func TestTable_pingReplace(t *testing.T) {
-	tab := newTable(nil, NodeID{}, &net.UDPAddr{})
+	doit := func(newNodeIsResponding, lastInBucketIsResponding bool) {
-	for i := 1; i < len(tab.buckets); i++ {
+		transport := newPingRecorder()
-		tab.bumpOrAdd(randomID(tab.self.ID, i), &net.UDPAddr{})
+		tab := newTable(transport, NodeID{}, &net.UDPAddr{})
-	}
-	for i, b := range tab.buckets {
-		if i > 0 && len(b.entries) != 1 {
-			t.Errorf("bucket %d has %d entries, want 1", i, len(b.entries))
-		}
-	}
-}
-
-func TestTable_bumpOrAddPingReplace(t *testing.T) {
-	pingC := make(pingC)
-	tab := newTable(pingC, NodeID{}, &net.UDPAddr{})
 		last := fillBucket(tab, 200)
+		pingSender := randomID(tab.self.ID, 200)
 
-	// this bumpOrAdd should not replace the last node
+		// this gotPing should replace the last node
-	// because the node replies to ping.
+		// if the last node is not responding.
-	new := tab.bumpOrAdd(randomID(tab.self.ID, 200), &net.UDPAddr{})
+		transport.responding[last.ID] = lastInBucketIsResponding
+		transport.responding[pingSender] = newNodeIsResponding
+		tab.bond(true, pingSender, &net.UDPAddr{}, 0)
 
-	pinged := <-pingC
+		// first ping goes to sender (bonding pingback)
-	if pinged != last.ID {
+		if !transport.pinged[pingSender] {
-		t.Fatalf("pinged wrong node: %v\nwant %v", pinged, last.ID)
+			t.Error("table did not ping back sender")
+		}
+		if newNodeIsResponding {
+			// second ping goes to oldest node in bucket
+			// to see whether it is still alive.
+			if !transport.pinged[last.ID] {
+				t.Error("table did not ping last node in bucket")
+			}
 		}
 
 		tab.mutex.Lock()
 		defer tab.mutex.Unlock()
 		if l := len(tab.buckets[200].entries); l != bucketSize {
-		t.Errorf("wrong bucket size after bumpOrAdd: got %d, want %d", bucketSize, l)
+			t.Errorf("wrong bucket size after gotPing: got %d, want %d", bucketSize, l)
 		}
+
+		if lastInBucketIsResponding || !newNodeIsResponding {
 			if !contains(tab.buckets[200].entries, last.ID) {
 				t.Error("last entry was removed")
 			}
-	if contains(tab.buckets[200].entries, new.ID) {
+			if contains(tab.buckets[200].entries, pingSender) {
 				t.Error("new entry was added")
 			}
-}
+		} else {
-
-func TestTable_bumpOrAddPingTimeout(t *testing.T) {
-	tab := newTable(pingC(nil), NodeID{}, &net.UDPAddr{})
-	last := fillBucket(tab, 200)
-
-	// this bumpOrAdd should replace the last node
-	// because the node does not reply to ping.
-	new := tab.bumpOrAdd(randomID(tab.self.ID, 200), &net.UDPAddr{})
-
-	// wait for async bucket update. damn. this needs to go away.
-	time.Sleep(2 * time.Millisecond)
-
-	tab.mutex.Lock()
-	defer tab.mutex.Unlock()
-	if l := len(tab.buckets[200].entries); l != bucketSize {
-		t.Errorf("wrong bucket size after bumpOrAdd: got %d, want %d", bucketSize, l)
-	}
 			if contains(tab.buckets[200].entries, last.ID) {
 				t.Error("last entry was not removed")
 			}
-	if !contains(tab.buckets[200].entries, new.ID) {
+			if !contains(tab.buckets[200].entries, pingSender) {
 				t.Error("new entry was not added")
 			}
 		}
+	}
+
+	doit(true, true)
+	doit(false, true)
+	doit(false, true)
+	doit(false, false)
+}
 
 func fillBucket(tab *Table, ld int) (last *Node) {
 	b := tab.buckets[ld]
@@ -85,44 +74,27 @@ func fillBucket(tab *Table, ld int) (last *Node) {
 	return b.entries[bucketSize-1]
 }
 
-type pingC chan NodeID
+type pingRecorder struct{ responding, pinged map[NodeID]bool }
 
-func (t pingC) findnode(n *Node, target NodeID) ([]*Node, error) {
+func newPingRecorder() *pingRecorder {
+	return &pingRecorder{make(map[NodeID]bool), make(map[NodeID]bool)}
+}
+
+func (t *pingRecorder) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
 	panic("findnode called on pingRecorder")
 }
-func (t pingC) close() {
+func (t *pingRecorder) close() {
 	panic("close called on pingRecorder")
 }
-func (t pingC) ping(n *Node) error {
+func (t *pingRecorder) waitping(from NodeID) error {
-	if t == nil {
+	return nil // remote always pings
-		return errTimeout
 }
-	t <- n.ID
+func (t *pingRecorder) ping(toid NodeID, toaddr *net.UDPAddr) error {
+	t.pinged[toid] = true
+	if t.responding[toid] {
 		return nil
-}
+	} else {
-
+		return errTimeout
-func TestTable_bump(t *testing.T) {
-	tab := newTable(nil, NodeID{}, &net.UDPAddr{})
-
-	// add an old entry and two recent ones
-	oldactive := time.Now().Add(-2 * time.Minute)
-	old := &Node{ID: randomID(tab.self.ID, 200), active: oldactive}
-	others := []*Node{
-		&Node{ID: randomID(tab.self.ID, 200), active: time.Now()},
-		&Node{ID: randomID(tab.self.ID, 200), active: time.Now()},
-	}
-	tab.add(append(others, old))
-	if tab.buckets[200].entries[0] == old {
-		t.Fatal("old entry is at front of bucket")
-	}
-
-	// bumping the old entry should move it to the front
-	tab.bump(old.ID)
-	if old.active == oldactive {
-		t.Error("activity timestamp not updated")
-	}
-	if tab.buckets[200].entries[0] != old {
-		t.Errorf("bumped entry did not move to the front of bucket")
 	}
 }
 
@@ -210,7 +182,7 @@ func TestTable_Lookup(t *testing.T) {
 		t.Fatalf("lookup on empty table returned %d results: %#v", len(results), results)
 	}
 	// seed table with initial node (otherwise lookup will terminate immediately)
-	tab.bumpOrAdd(randomID(target, 200), &net.UDPAddr{Port: 200})
+	tab.add([]*Node{newNode(randomID(target, 200), &net.UDPAddr{Port: 200})})
 
 	results := tab.Lookup(target)
 	t.Logf("results:")
@@ -238,16 +210,16 @@ type findnodeOracle struct {
 	target NodeID
 }
 
-func (t findnodeOracle) findnode(n *Node, target NodeID) ([]*Node, error) {
+func (t findnodeOracle) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
-	t.t.Logf("findnode query at dist %d", n.DiscPort)
+	t.t.Logf("findnode query at dist %d", toaddr.Port)
 	// current log distance is encoded in port number
 	var result []*Node
-	switch n.DiscPort {
+	switch toaddr.Port {
 	case 0:
 		panic("query to node at distance 0")
 	default:
 		// TODO: add more randomness to distances
-		next := n.DiscPort - 1
+		next := toaddr.Port - 1
 		for i := 0; i < bucketSize; i++ {
 			result = append(result, &Node{ID: randomID(t.target, next), DiscPort: next})
 		}
@@ -256,10 +228,8 @@ func (t findnodeOracle) findnode(n *Node, target NodeID) ([]*Node, error) {
 }
 
 func (t findnodeOracle) close()                                      {}
-
+func (t findnodeOracle) waitping(from NodeID) error                  { return nil }
-func (t findnodeOracle) ping(n *Node) error {
+func (t findnodeOracle) ping(toid NodeID, toaddr *net.UDPAddr) error { return nil }
-	return errors.New("ping is not supported by this transport")
-}
 
 func hasDuplicates(slice []*Node) bool {
 	seen := make(map[NodeID]bool)

p2p/discover/udp.go

@@ -24,6 +24,8 @@ var (
 	errBadHash          = errors.New("bad hash")
 	errExpired          = errors.New("expired")
 	errBadVersion       = errors.New("version mismatch")
+	errUnsolicitedReply = errors.New("unsolicited reply")
+	errUnknownNode      = errors.New("unknown node")
 	errTimeout          = errors.New("RPC timeout")
 	errClosed           = errors.New("socket closed")
 )
@@ -80,12 +82,25 @@ type rpcNode struct {
 	ID   NodeID
 }
 
+type packet interface {
+	handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error
+}
+
+type conn interface {
+	ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error)
+	WriteToUDP(b []byte, addr *net.UDPAddr) (n int, err error)
+	Close() error
+	LocalAddr() net.Addr
+}
+
 // udp implements the RPC protocol.
 type udp struct {
-	conn       *net.UDPConn
+	conn conn
 	priv *ecdsa.PrivateKey
+
 	addpending chan *pending
-	replies    chan reply
+	gotreply   chan reply
+
 	closing chan struct{}
 	nat     nat.Interface
 
@@ -124,6 +139,9 @@ type reply struct {
 	from  NodeID
 	ptype byte
 	data  interface{}
+	// loop indicates whether there was
+	// a matching request by sending on this channel.
+	matched chan<- bool
 }
 
 // ListenUDP returns a new table that listens for UDP packets on laddr.
@@ -136,15 +154,20 @@ func ListenUDP(priv *ecdsa.PrivateKey, laddr string, natm nat.Interface) (*Table
 	if err != nil {
 		return nil, err
 	}
+	tab, _ := newUDP(priv, conn, natm)
+	log.Infoln("Listening,", tab.self)
+	return tab, nil
+}
+
+func newUDP(priv *ecdsa.PrivateKey, c conn, natm nat.Interface) (*Table, *udp) {
 	udp := &udp{
-		conn:       conn,
+		conn:       c,
 		priv:       priv,
 		closing:    make(chan struct{}),
+		gotreply:   make(chan reply),
 		addpending: make(chan *pending),
-		replies:    make(chan reply),
 	}
-
+	realaddr := c.LocalAddr().(*net.UDPAddr)
-	realaddr := conn.LocalAddr().(*net.UDPAddr)
 	if natm != nil {
 		if !realaddr.IP.IsLoopback() {
 			go nat.Map(natm, udp.closing, "udp", realaddr.Port, realaddr.Port, "ethereum discovery")
@@ -155,11 +178,9 @@ func ListenUDP(priv *ecdsa.PrivateKey, laddr string, natm nat.Interface) (*Table
 		}
 	}
 	udp.Table = newTable(udp, PubkeyID(&priv.PublicKey), realaddr)
-
 	go udp.loop()
 	go udp.readLoop()
-	log.Infoln("Listening, ", udp.self)
+	return udp.Table, udp
-	return udp.Table, nil
 }
 
 func (t *udp) close() {
@@ -169,10 +190,10 @@ func (t *udp) close() {
 }
 
 // ping sends a ping message to the given node and waits for a reply.
-func (t *udp) ping(e *Node) error {
+func (t *udp) ping(toid NodeID, toaddr *net.UDPAddr) error {
 	// TODO: maybe check for ReplyTo field in callback to measure RTT
-	errc := t.pending(e.ID, pongPacket, func(interface{}) bool { return true })
+	errc := t.pending(toid, pongPacket, func(interface{}) bool { return true })
-	t.send(e, pingPacket, ping{
+	t.send(toaddr, pingPacket, ping{
 		Version:    Version,
 		IP:         t.self.IP.String(),
 		Port:       uint16(t.self.TCPPort),
@@ -181,12 +202,16 @@ func (t *udp) ping(e *Node) error {
 	return <-errc
 }
 
+func (t *udp) waitping(from NodeID) error {
+	return <-t.pending(from, pingPacket, func(interface{}) bool { return true })
+}
+
 // findnode sends a findnode request to the given node and waits until
 // the node has sent up to k neighbors.
-func (t *udp) findnode(to *Node, target NodeID) ([]*Node, error) {
+func (t *udp) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
 	nodes := make([]*Node, 0, bucketSize)
 	nreceived := 0
-	errc := t.pending(to.ID, neighborsPacket, func(r interface{}) bool {
+	errc := t.pending(toid, neighborsPacket, func(r interface{}) bool {
 		reply := r.(*neighbors)
 		for _, n := range reply.Nodes {
 			nreceived++
@@ -196,8 +221,7 @@ func (t *udp) findnode(to *Node, target NodeID) ([]*Node, error) {
 		}
 		return nreceived >= bucketSize
 	})
-
+	t.send(toaddr, findnodePacket, findnode{
-	t.send(to, findnodePacket, findnode{
 		Target:     target,
 		Expiration: uint64(time.Now().Add(expiration).Unix()),
 	})
@@ -219,6 +243,17 @@ func (t *udp) pending(id NodeID, ptype byte, callback func(interface{}) bool) <-
 	return ch
 }
 
+func (t *udp) handleReply(from NodeID, ptype byte, req packet) bool {
+	matched := make(chan bool)
+	select {
+	case t.gotreply <- reply{from, ptype, req, matched}:
+		// loop will handle it
+		return <-matched
+	case <-t.closing:
+		return false
+	}
+}
+
 // loop runs in its own goroutin. it keeps track of
 // the refresh timer and the pending reply queue.
 func (t *udp) loop() {
@@ -249,6 +284,7 @@ func (t *udp) loop() {
 			for _, p := range pending {
 				p.errc <- errClosed
 			}
+			pending = nil
 			return
 
 		case p := <-t.addpending:
@@ -256,18 +292,21 @@ func (t *udp) loop() {
 			pending = append(pending, p)
 			rearmTimeout()
 
-		case reply := <-t.replies:
+		case r := <-t.gotreply:
-			// run matching callbacks, remove if they return false.
+			var matched bool
 			for i := 0; i < len(pending); i++ {
-				p := pending[i]
+				if p := pending[i]; p.from == r.from && p.ptype == r.ptype {
-				if reply.from == p.from && reply.ptype == p.ptype && p.callback(reply.data) {
+					matched = true
+					if p.callback(r.data) {
+						// callback indicates the request is done, remove it.
 						p.errc <- nil
 						copy(pending[i:], pending[i+1:])
 						pending = pending[:len(pending)-1]
 						i--
 					}
 				}
-			rearmTimeout()
+			}
+			r.matched <- matched
 
 		case now := <-timeout.C:
 			// notify and remove callbacks whose deadline is in the past.
@@ -292,33 +331,38 @@ const (
 
 var headSpace = make([]byte, headSize)
 
-func (t *udp) send(to *Node, ptype byte, req interface{}) error {
+func (t *udp) send(toaddr *net.UDPAddr, ptype byte, req interface{}) error {
+	packet, err := encodePacket(t.priv, ptype, req)
+	if err != nil {
+		return err
+	}
+	log.DebugDetailf(">>> %v %T %v\n", toaddr, req, req)
+	if _, err = t.conn.WriteToUDP(packet, toaddr); err != nil {
+		log.DebugDetailln("UDP send failed:", err)
+	}
+	return err
+}
+
+func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte, error) {
 	b := new(bytes.Buffer)
 	b.Write(headSpace)
 	b.WriteByte(ptype)
 	if err := rlp.Encode(b, req); err != nil {
 		log.Errorln("error encoding packet:", err)
-		return err
+		return nil, err
 	}
-
 	packet := b.Bytes()
-	sig, err := crypto.Sign(crypto.Sha3(packet[headSize:]), t.priv)
+	sig, err := crypto.Sign(crypto.Sha3(packet[headSize:]), priv)
 	if err != nil {
 		log.Errorln("could not sign packet:", err)
-		return err
+		return nil, err
 	}
 	copy(packet[macSize:], sig)
 	// add the hash to the front. Note: this doesn't protect the
 	// packet in any way. Our public key will be part of this hash in
-	// the future.
+	// The future.
 	copy(packet, crypto.Sha3(packet[macSize:]))
-
+	return packet, nil
-	toaddr := &net.UDPAddr{IP: to.IP, Port: to.DiscPort}
-	log.DebugDetailf(">>> %v %T %v\n", toaddr, req, req)
-	if _, err = t.conn.WriteToUDP(packet, toaddr); err != nil {
-		log.DebugDetailln("UDP send failed:", err)
-	}
-	return err
 }
 
 // readLoop runs in its own goroutine. it handles incoming UDP packets.
@@ -330,29 +374,34 @@ func (t *udp) readLoop() {
 		if err != nil {
 			return
 		}
-		if err := t.packetIn(from, buf[:nbytes]); err != nil {
+		packet, fromID, hash, err := decodePacket(buf[:nbytes])
+		if err != nil {
 			log.Debugf("Bad packet from %v: %v\n", from, err)
+			continue
+		}
+		log.DebugDetailf("<<< %v %T %v\n", from, packet, packet)
+		go func() {
+			if err := packet.handle(t, from, fromID, hash); err != nil {
+				log.Debugf("error handling %T from %v: %v", packet, from, err)
 			}
+		}()
 	}
 }
 
-func (t *udp) packetIn(from *net.UDPAddr, buf []byte) error {
+func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
 	if len(buf) < headSize+1 {
-		return errPacketTooSmall
+		return nil, NodeID{}, nil, errPacketTooSmall
 	}
 	hash, sig, sigdata := buf[:macSize], buf[macSize:headSize], buf[headSize:]
 	shouldhash := crypto.Sha3(buf[macSize:])
 	if !bytes.Equal(hash, shouldhash) {
-		return errBadHash
+		return nil, NodeID{}, nil, errBadHash
 	}
 	fromID, err := recoverNodeID(crypto.Sha3(buf[headSize:]), sig)
 	if err != nil {
-		return err
+		return nil, NodeID{}, hash, err
-	}
-
-	var req interface {
-		handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error
 	}
+	var req packet
 	switch ptype := sigdata[0]; ptype {
 	case pingPacket:
 		req = new(ping)
@@ -363,13 +412,10 @@ func (t *udp) packetIn(from *net.UDPAddr, buf []byte) error {
 	case neighborsPacket:
 		req = new(neighbors)
 	default:
-		return fmt.Errorf("unknown type: %d", ptype)
+		return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
-	}
-	if err := rlp.Decode(bytes.NewReader(sigdata[1:]), req); err != nil {
-		return err
 	}
-	log.DebugDetailf("<<< %v %T %v\n", from, req, req)
+	err = rlp.Decode(bytes.NewReader(sigdata[1:]), req)
-	return req.handle(t, from, fromID, hash)
+	return req, fromID, hash, err
 }
 
 func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
@@ -379,18 +425,14 @@ func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) er
 	if req.Version != Version {
 		return errBadVersion
 	}
-	t.mutex.Lock()
+	t.send(from, pongPacket, pong{
-	// Note: we're ignoring the provided IP address right now
-	n := t.bumpOrAdd(fromID, from)
-	if req.Port != 0 {
-		n.TCPPort = int(req.Port)
-	}
-	t.mutex.Unlock()
-
-	t.send(n, pongPacket, pong{
 		ReplyTok:   mac,
 		Expiration: uint64(time.Now().Add(expiration).Unix()),
 	})
+	if !t.handleReply(fromID, pingPacket, req) {
+		// Note: we're ignoring the provided IP address right now
+		t.bond(true, fromID, from, req.Port)
+	}
 	return nil
 }
 
@@ -398,11 +440,9 @@ func (req *pong) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) er
 	if expired(req.Expiration) {
 		return errExpired
 	}
-	t.mutex.Lock()
+	if !t.handleReply(fromID, pongPacket, req) {
-	t.bump(fromID)
+		return errUnsolicitedReply
-	t.mutex.Unlock()
+	}
-
-	t.replies <- reply{fromID, pongPacket, req}
 	return nil
 }
 
@@ -410,12 +450,21 @@ func (req *findnode) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte
 	if expired(req.Expiration) {
 		return errExpired
 	}
+	if t.db.get(fromID) == nil {
+		// No bond exists, we don't process the packet. This prevents
+		// an attack vector where the discovery protocol could be used
+		// to amplify traffic in a DDOS attack. A malicious actor
+		// would send a findnode request with the IP address and UDP
+		// port of the target as the source address. The recipient of
+		// the findnode packet would then send a neighbors packet
+		// (which is a much bigger packet than findnode) to the victim.
+		return errUnknownNode
+	}
 	t.mutex.Lock()
-	e := t.bumpOrAdd(fromID, from)
 	closest := t.closest(req.Target, bucketSize).entries
 	t.mutex.Unlock()
 
-	t.send(e, neighborsPacket, neighbors{
+	t.send(from, neighborsPacket, neighbors{
 		Nodes:      closest,
 		Expiration: uint64(time.Now().Add(expiration).Unix()),
 	})
@@ -426,12 +475,9 @@ func (req *neighbors) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byt
 	if expired(req.Expiration) {
 		return errExpired
 	}
-	t.mutex.Lock()
+	if !t.handleReply(fromID, neighborsPacket, req) {
-	t.bump(fromID)
+		return errUnsolicitedReply
-	t.add(req.Nodes)
+	}
-	t.mutex.Unlock()
-
-	t.replies <- reply{fromID, neighborsPacket, req}
 	return nil
 }
 

p2p/discover/udp_test.go

@@ -1,10 +1,18 @@
 package discover
 
 import (
+	"bytes"
+	"crypto/ecdsa"
+	"errors"
 	"fmt"
+	"io"
 	logpkg "log"
 	"net"
 	"os"
+	"path"
+	"reflect"
+	"runtime"
+	"sync"
 	"testing"
 	"time"
 
@@ -15,197 +23,317 @@ func init() {
 	logger.AddLogSystem(logger.NewStdLogSystem(os.Stdout, logpkg.LstdFlags, logger.ErrorLevel))
 }
 
-func TestUDP_ping(t *testing.T) {
+type udpTest struct {
-	t.Parallel()
+	t                   *testing.T
-
+	pipe                *dgramPipe
-	n1, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+	table               *Table
-	n2, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+	udp                 *udp
-	defer n1.Close()
+	sent                [][]byte
-	defer n2.Close()
+	localkey, remotekey *ecdsa.PrivateKey
-
+	remoteaddr          *net.UDPAddr
-	if err := n1.net.ping(n2.self); err != nil {
-		t.Fatalf("ping error: %v", err)
 }
-	if find(n2, n1.self.ID) == nil {
+
-		t.Errorf("node 2 does not contain id of node 1")
+func newUDPTest(t *testing.T) *udpTest {
-	}
+	test := &udpTest{
-	if e := find(n1, n2.self.ID); e != nil {
+		t:          t,
-		t.Errorf("node 1 does contains id of node 2: %v", e)
+		pipe:       newpipe(),
+		localkey:   newkey(),
+		remotekey:  newkey(),
+		remoteaddr: &net.UDPAddr{IP: net.IP{1, 2, 3, 4}, Port: 30303},
 	}
+	test.table, test.udp = newUDP(test.localkey, test.pipe, nil)
+	return test
 }
 
-func find(tab *Table, id NodeID) *Node {
+// handles a packet as if it had been sent to the transport.
-	for _, b := range tab.buckets {
+func (test *udpTest) packetIn(wantError error, ptype byte, data packet) error {
-		for _, e := range b.entries {
+	enc, err := encodePacket(test.remotekey, ptype, data)
-			if e.ID == id {
+	if err != nil {
-				return e
+		return test.errorf("packet (%d) encode error: %v", err)
-			}
 	}
+	test.sent = append(test.sent, enc)
+	err = data.handle(test.udp, test.remoteaddr, PubkeyID(&test.remotekey.PublicKey), enc[:macSize])
+	if err != wantError {
+		return test.errorf("error mismatch: got %q, want %q", err, wantError)
 	}
 	return nil
 }
 
-func TestUDP_findnode(t *testing.T) {
+// waits for a packet to be sent by the transport.
-	t.Parallel()
+// validate should have type func(*udpTest, X) error, where X is a packet type.
-
+func (test *udpTest) waitPacketOut(validate interface{}) error {
-	n1, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+	dgram := test.pipe.waitPacketOut()
-	n2, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+	p, _, _, err := decodePacket(dgram)
-	defer n1.Close()
+	if err != nil {
-	defer n2.Close()
+		return test.errorf("sent packet decode error: %v", err)
-
-	// put a few nodes into n2. the exact distribution shouldn't
-	// matter much, altough we need to take care not to overflow
-	// any bucket.
-	target := randomID(n1.self.ID, 100)
-	nodes := &nodesByDistance{target: target}
-	for i := 0; i < bucketSize; i++ {
-		n2.add([]*Node{&Node{
-			IP:       net.IP{1, 2, 3, byte(i)},
-			DiscPort: i + 2,
-			TCPPort:  i + 2,
-			ID:       randomID(n2.self.ID, i+2),
-		}})
-	}
-	n2.add(nodes.entries)
-	n2.bumpOrAdd(n1.self.ID, &net.UDPAddr{IP: n1.self.IP, Port: n1.self.DiscPort})
-	expected := n2.closest(target, bucketSize)
-
-	err := runUDP(10, func() error {
-		result, _ := n1.net.findnode(n2.self, target)
-		if len(result) != bucketSize {
-			return fmt.Errorf("wrong number of results: got %d, want %d", len(result), bucketSize)
-		}
-		for i := range result {
-			if result[i].ID != expected.entries[i].ID {
-				return fmt.Errorf("result mismatch at %d:\n  got:  %v\n  want: %v", i, result[i], expected.entries[i])
 	}
+	fn := reflect.ValueOf(validate)
+	exptype := fn.Type().In(0)
+	if reflect.TypeOf(p) != exptype {
+		return test.errorf("sent packet type mismatch, got: %v, want: %v", reflect.TypeOf(p), exptype)
 	}
+	fn.Call([]reflect.Value{reflect.ValueOf(p)})
 	return nil
-	})
-	if err != nil {
-		t.Error(err)
 }
+
+func (test *udpTest) errorf(format string, args ...interface{}) error {
+	_, file, line, ok := runtime.Caller(2) // errorf + waitPacketOut
+	if ok {
+		file = path.Base(file)
+	} else {
+		file = "???"
+		line = 1
+	}
+	err := fmt.Errorf(format, args...)
+	fmt.Printf("\t%s:%d: %v\n", file, line, err)
+	test.t.Fail()
+	return err
 }
 
-func TestUDP_replytimeout(t *testing.T) {
+// shared test variables
-	t.Parallel()
+var (
+	futureExp  = uint64(time.Now().Add(10 * time.Hour).Unix())
+	testTarget = MustHexID("01010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101")
+)
 
-	// reserve a port so we don't talk to an existing service by accident
+func TestUDP_packetErrors(t *testing.T) {
-	addr, _ := net.ResolveUDPAddr("udp", "127.0.0.1:0")
+	test := newUDPTest(t)
-	fd, err := net.ListenUDP("udp", addr)
+	defer test.table.Close()
-	if err != nil {
+
-		t.Fatal(err)
+	test.packetIn(errExpired, pingPacket, &ping{IP: "foo", Port: 99, Version: Version})
+	test.packetIn(errBadVersion, pingPacket, &ping{IP: "foo", Port: 99, Version: 99, Expiration: futureExp})
+	test.packetIn(errUnsolicitedReply, pongPacket, &pong{ReplyTok: []byte{}, Expiration: futureExp})
+	test.packetIn(errUnknownNode, findnodePacket, &findnode{Expiration: futureExp})
+	test.packetIn(errUnsolicitedReply, neighborsPacket, &neighbors{Expiration: futureExp})
 }
-	defer fd.Close()
 
-	n1, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+func TestUDP_pingTimeout(t *testing.T) {
-	defer n1.Close()
+	t.Parallel()
-	n2 := n1.bumpOrAdd(randomID(n1.self.ID, 10), fd.LocalAddr().(*net.UDPAddr))
+	test := newUDPTest(t)
+	defer test.table.Close()
 
-	if err := n1.net.ping(n2); err != errTimeout {
+	toaddr := &net.UDPAddr{IP: net.ParseIP("1.2.3.4"), Port: 2222}
+	toid := NodeID{1, 2, 3, 4}
+	if err := test.udp.ping(toid, toaddr); err != errTimeout {
 		t.Error("expected timeout error, got", err)
 	}
+}
+
+func TestUDP_findnodeTimeout(t *testing.T) {
+	t.Parallel()
+	test := newUDPTest(t)
+	defer test.table.Close()
 
-	if result, err := n1.net.findnode(n2, n1.self.ID); err != errTimeout {
+	toaddr := &net.UDPAddr{IP: net.ParseIP("1.2.3.4"), Port: 2222}
+	toid := NodeID{1, 2, 3, 4}
+	target := NodeID{4, 5, 6, 7}
+	result, err := test.udp.findnode(toid, toaddr, target)
+	if err != errTimeout {
 		t.Error("expected timeout error, got", err)
-	} else if len(result) > 0 {
+	}
+	if len(result) > 0 {
 		t.Error("expected empty result, got", result)
 	}
 }
 
-func TestUDP_findnodeMultiReply(t *testing.T) {
+func TestUDP_findnode(t *testing.T) {
-	t.Parallel()
+	test := newUDPTest(t)
+	defer test.table.Close()
 
-	n1, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+	// put a few nodes into the table. their exact
-	n2, _ := ListenUDP(newkey(), "127.0.0.1:0", nil)
+	// distribution shouldn't matter much, altough we need to
-	udp2 := n2.net.(*udp)
+	// take care not to overflow any bucket.
-	defer n1.Close()
+	target := testTarget
-	defer n2.Close()
+	nodes := &nodesByDistance{target: target}
+	for i := 0; i < bucketSize; i++ {
+		nodes.push(&Node{
+			IP:       net.IP{1, 2, 3, byte(i)},
+			DiscPort: i + 2,
+			TCPPort:  i + 2,
+			ID:       randomID(test.table.self.ID, i+2),
+		}, bucketSize)
+	}
+	test.table.add(nodes.entries)
 
-	err := runUDP(10, func() error {
+	// ensure there's a bond with the test node,
-		nodes := make([]*Node, bucketSize)
+	// findnode won't be accepted otherwise.
-		for i := range nodes {
+	test.table.db.add(PubkeyID(&test.remotekey.PublicKey), test.remoteaddr, 99)
-			nodes[i] = &Node{
+
-				IP:       net.IP{1, 2, 3, 4},
+	// check that closest neighbors are returned.
-				DiscPort: i + 1,
+	test.packetIn(nil, findnodePacket, &findnode{Target: testTarget, Expiration: futureExp})
-				TCPPort:  i + 1,
+	test.waitPacketOut(func(p *neighbors) {
-				ID:       randomID(n2.self.ID, i+1),
+		expected := test.table.closest(testTarget, bucketSize)
+		if len(p.Nodes) != bucketSize {
+			t.Errorf("wrong number of results: got %d, want %d", len(p.Nodes), bucketSize)
+		}
+		for i := range p.Nodes {
+			if p.Nodes[i].ID != expected.entries[i].ID {
+				t.Errorf("result mismatch at %d:\n  got:  %v\n  want: %v", i, p.Nodes[i], expected.entries[i])
+			}
 		}
+	})
 }
 
-		// ask N2 for neighbors. it will send an empty reply back.
+func TestUDP_findnodeMultiReply(t *testing.T) {
-		// the request will wait for up to bucketSize replies.
+	test := newUDPTest(t)
-		resultc := make(chan []*Node)
+	defer test.table.Close()
-		errc := make(chan error)
+
+	// queue a pending findnode request
+	resultc, errc := make(chan []*Node), make(chan error)
 	go func() {
-			ns, err := n1.net.findnode(n2.self, n1.self.ID)
+		rid := PubkeyID(&test.remotekey.PublicKey)
-			if err != nil {
+		ns, err := test.udp.findnode(rid, test.remoteaddr, testTarget)
+		if err != nil && len(ns) == 0 {
 			errc <- err
 		} else {
 			resultc <- ns
 		}
 	}()
 
-		// send a few more neighbors packets to N1.
+	// wait for the findnode to be sent.
-		// it should collect those.
+	// after it is sent, the transport is waiting for a reply
-		for end := 0; end < len(nodes); {
+	test.waitPacketOut(func(p *findnode) {
-			off := end
+		if p.Target != testTarget {
-			if end = end + 5; end > len(nodes) {
+			t.Errorf("wrong target: got %v, want %v", p.Target, testTarget)
-				end = len(nodes)
 		}
-			udp2.send(n1.self, neighborsPacket, neighbors{
-				Nodes:      nodes[off:end],
-				Expiration: uint64(time.Now().Add(10 * time.Second).Unix()),
 	})
-		}
 
-		// check that they are all returned. we cannot just check for
+	// send the reply as two packets.
-		// equality because they might not be returned in the order they
+	list := []*Node{
-		// were sent.
+		MustParseNode("enode://ba85011c70bcc5c04d8607d3a0ed29aa6179c092cbdda10d5d32684fb33ed01bd94f588ca8f91ac48318087dcb02eaf36773a7a453f0eedd6742af668097b29c@10.0.1.16:30303"),
-		var result []*Node
+		MustParseNode("enode://81fa361d25f157cd421c60dcc28d8dac5ef6a89476633339c5df30287474520caca09627da18543d9079b5b288698b542d56167aa5c09111e55acdbbdf2ef799@10.0.1.16:30303"),
+		MustParseNode("enode://9bffefd833d53fac8e652415f4973bee289e8b1a5c6c4cbe70abf817ce8a64cee11b823b66a987f51aaa9fba0d6a91b3e6bf0d5a5d1042de8e9eeea057b217f8@10.0.1.36:30301"),
+		MustParseNode("enode://1b5b4aa662d7cb44a7221bfba67302590b643028197a7d5214790f3bac7aaa4a3241be9e83c09cf1f6c69d007c634faae3dc1b1221793e8446c0b3a09de65960@10.0.1.16:30303"),
+	}
+	test.packetIn(nil, neighborsPacket, &neighbors{Expiration: futureExp, Nodes: list[:2]})
+	test.packetIn(nil, neighborsPacket, &neighbors{Expiration: futureExp, Nodes: list[2:]})
+
+	// check that the sent neighbors are all returned by findnode
 	select {
-		case result = <-resultc:
+	case result := <-resultc:
+		if !reflect.DeepEqual(result, list) {
+			t.Errorf("neighbors mismatch:\n  got:  %v\n  want: %v", result, list)
+		}
 	case err := <-errc:
-			return err
+		t.Errorf("findnode error: %v", err)
+	case <-time.After(5 * time.Second):
+		t.Error("findnode did not return within 5 seconds")
 	}
-		if hasDuplicates(result) {
-			return fmt.Errorf("result slice contains duplicates")
 }
-		if len(result) != len(nodes) {
+
-			return fmt.Errorf("wrong number of nodes returned: got %d, want %d", len(result), len(nodes))
+func TestUDP_successfulPing(t *testing.T) {
+	test := newUDPTest(t)
+	defer test.table.Close()
+
+	done := make(chan struct{})
+	go func() {
+		test.packetIn(nil, pingPacket, &ping{IP: "foo", Port: 99, Version: Version, Expiration: futureExp})
+		close(done)
+	}()
+
+	// the ping is replied to.
+	test.waitPacketOut(func(p *pong) {
+		pinghash := test.sent[0][:macSize]
+		if !bytes.Equal(p.ReplyTok, pinghash) {
+			t.Errorf("got ReplyTok %x, want %x", p.ReplyTok, pinghash)
 		}
-		matched := make(map[NodeID]bool)
+	})
-		for _, n := range result {
+
-			for _, expn := range nodes {
+	// remote is unknown, the table pings back.
-				if n.ID == expn.ID { // && bytes.Equal(n.Addr.IP, expn.Addr.IP) && n.Addr.Port == expn.Addr.Port {
+	test.waitPacketOut(func(p *ping) error { return nil })
-					matched[n.ID] = true
+	test.packetIn(nil, pongPacket, &pong{Expiration: futureExp})
+
+	// ping should return shortly after getting the pong packet.
+	<-done
+
+	// check that the node was added.
+	rid := PubkeyID(&test.remotekey.PublicKey)
+	rnode := find(test.table, rid)
+	if rnode == nil {
+		t.Fatalf("node %v not found in table", rid)
 	}
+	if !bytes.Equal(rnode.IP, test.remoteaddr.IP) {
+		t.Errorf("node has wrong IP: got %v, want: %v", rnode.IP, test.remoteaddr.IP)
+	}
+	if rnode.DiscPort != test.remoteaddr.Port {
+		t.Errorf("node has wrong Port: got %v, want: %v", rnode.DiscPort, test.remoteaddr.Port)
+	}
+	if rnode.TCPPort != 99 {
+		t.Errorf("node has wrong Port: got %v, want: %v", rnode.TCPPort, 99)
+	}
+}
+
+func find(tab *Table, id NodeID) *Node {
+	for _, b := range tab.buckets {
+		for _, e := range b.entries {
+			if e.ID == id {
+				return e
 			}
 		}
-		if len(matched) != len(nodes) {
-			return fmt.Errorf("wrong number of matching nodes: got %d, want %d", len(matched), len(nodes))
 	}
 	return nil
-	})
-	if err != nil {
-		t.Error(err)
 }
+
+// dgramPipe is a fake UDP socket. It queues all sent datagrams.
+type dgramPipe struct {
+	mu      *sync.Mutex
+	cond    *sync.Cond
+	closing chan struct{}
+	closed  bool
+	queue   [][]byte
 }
 
-// runUDP runs a test n times and returns an error if the test failed
+func newpipe() *dgramPipe {
-// in all n runs. This is necessary because UDP is unreliable even for
+	mu := new(sync.Mutex)
-// connections on the local machine, causing test failures.
+	return &dgramPipe{
-func runUDP(n int, test func() error) error {
+		closing: make(chan struct{}),
-	errcount := 0
+		cond:    &sync.Cond{L: mu},
-	errors := ""
+		mu:      mu,
-	for i := 0; i < n; i++ {
+	}
-		if err := test(); err != nil {
-			errors += fmt.Sprintf("\n#%d: %v", i, err)
-			errcount++
 }
+
+// WriteToUDP queues a datagram.
+func (c *dgramPipe) WriteToUDP(b []byte, to *net.UDPAddr) (n int, err error) {
+	msg := make([]byte, len(b))
+	copy(msg, b)
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.closed {
+		return 0, errors.New("closed")
+	}
+	c.queue = append(c.queue, msg)
+	c.cond.Signal()
+	return len(b), nil
 }
-	if errcount == n {
+
-		return fmt.Errorf("failed on all %d iterations:%s", n, errors)
+// ReadFromUDP just hangs until the pipe is closed.
+func (c *dgramPipe) ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error) {
+	<-c.closing
+	return 0, nil, io.EOF
+}
+
+func (c *dgramPipe) Close() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if !c.closed {
+		close(c.closing)
+		c.closed = true
 	}
 	return nil
 }
+
+func (c *dgramPipe) LocalAddr() net.Addr {
+	return &net.UDPAddr{}
+}
+
+func (c *dgramPipe) waitPacketOut() []byte {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	for len(c.queue) == 0 {
+		c.cond.Wait()
+	}
+	p := c.queue[0]
+	copy(c.queue, c.queue[1:])
+	c.queue = c.queue[:len(c.queue)-1]
+	return p
+}