p2p: add dynamic DNS resolution for nodes

p2p/dial.go

@@ -24,13 +24,15 @@ import (
 	"fmt"
 	mrand "math/rand"
 	"net"
+	"net/netip"
 	"sync"
 	"sync/atomic"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common/mclock"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/p2p/enr"
 	"github.com/ethereum/go-ethereum/p2p/netutil"
 )
 
@@ -77,6 +79,7 @@ var (
 	errRecentlyDialed   = errors.New("recently dialed")
 	errNetRestrict      = errors.New("not contained in netrestrict list")
 	errNoPort           = errors.New("node does not provide TCP port")
+	errNoResolvedIP     = errors.New("node does not provide a resolved IP")
 )
 
 // dialer creates outbound connections and submits them into Server.
@@ -90,16 +93,17 @@ var (
 //     to create peer connections to nodes arriving through the iterator.
 type dialScheduler struct {
 	dialConfig
-	setupFunc   dialSetupFunc
-	wg          sync.WaitGroup
-	cancel      context.CancelFunc
-	ctx         context.Context
-	nodesIn     chan *enode.Node
-	doneCh      chan *dialTask
-	addStaticCh chan *enode.Node
-	remStaticCh chan *enode.Node
-	addPeerCh   chan *conn
-	remPeerCh   chan *conn
+	setupFunc     dialSetupFunc
+	dnsLookupFunc func(ctx context.Context, network string, name string) ([]netip.Addr, error)
+	wg            sync.WaitGroup
+	cancel        context.CancelFunc
+	ctx           context.Context
+	nodesIn       chan *enode.Node
+	doneCh        chan *dialTask
+	addStaticCh   chan *enode.Node
+	remStaticCh   chan *enode.Node
+	addPeerCh     chan *conn
+	remPeerCh     chan *conn
 
 	// Everything below here belongs to loop and
 	// should only be accessed by code on the loop goroutine.
@@ -159,18 +163,19 @@ func (cfg dialConfig) withDefaults() dialConfig {
 func newDialScheduler(config dialConfig, it enode.Iterator, setupFunc dialSetupFunc) *dialScheduler {
 	cfg := config.withDefaults()
 	d := &dialScheduler{
-		dialConfig:   cfg,
-		historyTimer: mclock.NewAlarm(cfg.clock),
-		setupFunc:    setupFunc,
-		dialing:      make(map[enode.ID]*dialTask),
-		static:       make(map[enode.ID]*dialTask),
-		peers:        make(map[enode.ID]struct{}),
-		doneCh:       make(chan *dialTask),
-		nodesIn:      make(chan *enode.Node),
-		addStaticCh:  make(chan *enode.Node),
-		remStaticCh:  make(chan *enode.Node),
-		addPeerCh:    make(chan *conn),
-		remPeerCh:    make(chan *conn),
+		dialConfig:    cfg,
+		historyTimer:  mclock.NewAlarm(cfg.clock),
+		setupFunc:     setupFunc,
+		dnsLookupFunc: net.DefaultResolver.LookupNetIP,
+		dialing:       make(map[enode.ID]*dialTask),
+		static:        make(map[enode.ID]*dialTask),
+		peers:         make(map[enode.ID]struct{}),
+		doneCh:        make(chan *dialTask),
+		nodesIn:       make(chan *enode.Node),
+		addStaticCh:   make(chan *enode.Node),
+		remStaticCh:   make(chan *enode.Node),
+		addPeerCh:     make(chan *conn),
+		remPeerCh:     make(chan *conn),
 	}
 	d.lastStatsLog = d.clock.Now()
 	d.ctx, d.cancel = context.WithCancel(context.Background())
@@ -274,7 +279,7 @@ loop:
 		case node := <-d.addStaticCh:
 			id := node.ID()
 			_, exists := d.static[id]
-			d.log.Trace("Adding static node", "id", id, "ip", node.IPAddr(), "added", !exists)
+			d.log.Trace("Adding static node", "id", id, "endpoint", nodeEndpointForLog(node), "added", !exists)
 			if exists {
 				continue loop
 			}
@@ -433,10 +438,68 @@ func (d *dialScheduler) removeFromStaticPool(idx int) {
 	task.staticPoolIndex = -1
 }
 
+// dnsResolveHostname updates the given node from its DNS hostname.
+// This is used to resolve static dial targets.
+func (d *dialScheduler) dnsResolveHostname(n *enode.Node) (*enode.Node, error) {
+	if n.Hostname() == "" {
+		return n, nil
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	foundIPs, err := d.dnsLookupFunc(ctx, "ip", n.Hostname())
+	if err != nil {
+		return n, err
+	}
+
+	// Check for IP updates.
+	var (
+		nodeIP4, nodeIP6   netip.Addr
+		foundIP4, foundIP6 netip.Addr
+	)
+	n.Load((*enr.IPv4Addr)(&nodeIP4))
+	n.Load((*enr.IPv6Addr)(&nodeIP6))
+	for _, ip := range foundIPs {
+		if ip.Is4() && !foundIP4.IsValid() {
+			foundIP4 = ip
+		}
+		if ip.Is6() && !foundIP6.IsValid() {
+			foundIP6 = ip
+		}
+	}
+
+	if !foundIP4.IsValid() && !foundIP6.IsValid() {
+		// Lookup failed.
+		return n, errNoResolvedIP
+	}
+	if foundIP4 == nodeIP4 && foundIP6 == nodeIP6 {
+		// No updates necessary.
+		d.log.Trace("Node DNS lookup had no update", "id", n.ID(), "name", n.Hostname(), "ip", foundIP4, "ip6", foundIP6)
+		return n, nil
+	}
+
+	// Update the node. Note this invalidates the ENR signature, because we use SignNull
+	// to create a modified copy. But this should be OK, since we just use the node as a
+	// dial target. And nodes will usually only have a DNS hostname if they came from a
+	// enode:// URL, which has no signature anyway. If it ever becomes a problem, the
+	// resolved IP could also be stored into dialTask instead of the node.
+	rec := n.Record()
+	if foundIP4.IsValid() {
+		rec.Set(enr.IPv4Addr(foundIP4))
+	}
+	if foundIP6.IsValid() {
+		rec.Set(enr.IPv6Addr(foundIP6))
+	}
+	rec.SetSeq(n.Seq()) // ensure seq not bumped by update
+	newNode := enode.SignNull(rec, n.ID()).WithHostname(n.Hostname())
+	d.log.Debug("Node updated from DNS lookup", "id", n.ID(), "name", n.Hostname(), "ip", newNode.IP())
+	return newNode, nil
+}
+
 // startDial runs the given dial task in a separate goroutine.
 func (d *dialScheduler) startDial(task *dialTask) {
 	node := task.dest()
-	d.log.Trace("Starting p2p dial", "id", node.ID(), "ip", node.IPAddr(), "flag", task.flags)
+	d.log.Trace("Starting p2p dial", "id", node.ID(), "endpoint", nodeEndpointForLog(node), "flag", task.flags)
 	hkey := string(node.ID().Bytes())
 	d.history.add(hkey, d.clock.Now().Add(dialHistoryExpiration))
 	d.dialing[node.ID()] = task
@@ -473,23 +536,38 @@ func (t *dialTask) dest() *enode.Node {
 }
 
 func (t *dialTask) run(d *dialScheduler) {
-	if t.needResolve() && !t.resolve(d) {
-		return
+	if t.isStatic() {
+		// Resolve DNS.
+		if n := t.dest(); n.Hostname() != "" {
+			resolved, err := d.dnsResolveHostname(n)
+			if err != nil {
+				d.log.Warn("DNS lookup of static node failed", "id", n.ID(), "name", n.Hostname(), "err", err)
+			} else {
+				t.destPtr.Store(resolved)
+			}
+		}
+		// Try resolving node ID through the DHT if there is no IP address.
+		if !t.dest().IPAddr().IsValid() {
+			if !t.resolve(d) {
+				return // DHT resolve failed, skip dial.
+			}
+		}
 	}
 
 	err := t.dial(d, t.dest())
 	if err != nil {
 		// For static nodes, resolve one more time if dialing fails.
-		if _, ok := err.(*dialError); ok && t.flags&staticDialedConn != 0 {
+		var dialErr *dialError
+		if errors.As(err, &dialErr) && t.isStatic() {
 			if t.resolve(d) {
 				t.dial(d, t.dest())
 			}
 		}
 	}
 }
 
-func (t *dialTask) needResolve() bool {
-	return t.flags&staticDialedConn != 0 && !t.dest().IPAddr().IsValid()
+func (t *dialTask) isStatic() bool {
+	return t.flags&staticDialedConn != 0
 }
 
 // resolve attempts to find the current endpoint for the destination
@@ -553,3 +631,10 @@ func cleanupDialErr(err error) error {
 	}
 	return err
 }
+
+func nodeEndpointForLog(n *enode.Node) string {
+	if n.Hostname() != "" {
+		return n.Hostname()
+	}
+	return n.IPAddr().String()
+}

p2p/dial_test.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"math/rand"
 	"net"
+	"net/netip"
 	"reflect"
 	"sync"
 	"testing"
@@ -394,6 +395,34 @@ func TestDialSchedResolve(t *testing.T) {
 	})
 }
 
+func TestDialSchedDNSHostname(t *testing.T) {
+	t.Parallel()
+
+	config := dialConfig{
+		maxActiveDials: 1,
+		maxDialPeers:   1,
+	}
+	node := newNode(uintID(0x01), ":30303").WithHostname("node-hostname")
+	resolved := newNode(uintID(0x01), "1.2.3.4:30303").WithHostname("node-hostname")
+	runDialTest(t, config, []dialTestRound{
+		{
+			update: func(d *dialScheduler) {
+				d.dnsLookupFunc = func(ctx context.Context, network string, name string) ([]netip.Addr, error) {
+					if name != "node-hostname" {
+						t.Error("wrong hostname in DNS lookup:", name)
+					}
+					result := []netip.Addr{netip.MustParseAddr("1.2.3.4")}
+					return result, nil
+				}
+				d.addStatic(node)
+			},
+			wantNewDials: []*enode.Node{
+				resolved,
+			},
+		},
+	})
+}
+
 // -------
 // Code below here is the framework for the tests above.
 

p2p/enode/node.go

@@ -37,6 +37,10 @@ var errMissingPrefix = errors.New("missing 'enr:' prefix for base64-encoded reco
 type Node struct {
 	r  enr.Record
 	id ID
+
+	// hostname tracks the DNS name of the node.
+	hostname string
+
 	// endpoint information
 	ip  netip.Addr
 	udp uint16
@@ -77,6 +81,8 @@ func newNodeWithID(r *enr.Record, id ID) *Node {
 		n.setIP4(ip4)
 	case valid6:
 		n.setIP6(ip6)
+	default:
+		n.setIPv4Ports()
 	}
 	return n
 }
@@ -103,6 +109,10 @@ func localityScore(ip netip.Addr) int {
 
 func (n *Node) setIP4(ip netip.Addr) {
 	n.ip = ip
+	n.setIPv4Ports()
+}
+
+func (n *Node) setIPv4Ports() {
 	n.Load((*enr.UDP)(&n.udp))
 	n.Load((*enr.TCP)(&n.tcp))
 }
@@ -184,6 +194,18 @@ func (n *Node) TCP() int {
 	return int(n.tcp)
 }
 
+// WithHostname adds a DNS hostname to the node.
+func (n *Node) WithHostname(hostname string) *Node {
+	cpy := *n
+	cpy.hostname = hostname
+	return &cpy
+}
+
+// Hostname returns the DNS name assigned by WithHostname.
+func (n *Node) Hostname() string {
+	return n.hostname
+}
+
 // UDPEndpoint returns the announced UDP endpoint.
 func (n *Node) UDPEndpoint() (netip.AddrPort, bool) {
 	if !n.ip.IsValid() || n.ip.IsUnspecified() || n.udp == 0 {

p2p/enode/node_test.go

@@ -74,6 +74,7 @@ func TestNodeEndpoints(t *testing.T) {
 		wantUDP  int
 		wantTCP  int
 		wantQUIC int
+		wantDNS  string
 	}
 	tests := []endpointTest{
 		{
@@ -90,6 +91,7 @@ func TestNodeEndpoints(t *testing.T) {
 				r.Set(enr.UDP(9000))
 				return SignNull(&r, id)
 			}(),
+			wantUDP: 9000,
 		},
 		{
 			name: "tcp-only",
@@ -98,6 +100,7 @@ func TestNodeEndpoints(t *testing.T) {
 				r.Set(enr.TCP(9000))
 				return SignNull(&r, id)
 			}(),
+			wantTCP: 9000,
 		},
 		{
 			name: "quic-only",
@@ -268,6 +271,19 @@ func TestNodeEndpoints(t *testing.T) {
 			wantIP:   netip.MustParseAddr("2001::ff00:0042:8329"),
 			wantQUIC: 9001,
 		},
+		{
+			name: "dns-only",
+			node: func() *Node {
+				var r enr.Record
+				r.Set(enr.UDP(30303))
+				r.Set(enr.TCP(30303))
+				n := SignNull(&r, id).WithHostname("example.com")
+				return n
+			}(),
+			wantTCP: 30303,
+			wantUDP: 30303,
+			wantDNS: "example.com",
+		},
 	}
 
 	for _, test := range tests {
@@ -284,6 +300,9 @@ func TestNodeEndpoints(t *testing.T) {
 			if quic, _ := test.node.QUICEndpoint(); test.wantQUIC != int(quic.Port()) {
 				t.Errorf("node has wrong QUIC port %d, want %d", quic.Port(), test.wantQUIC)
 			}
+			if test.wantDNS != test.node.Hostname() {
+				t.Errorf("node has wrong DNS name %s, want %s", test.node.Hostname(), test.wantDNS)
+			}
 		})
 	}
 }