p2p: add dynamic name resolution for the dialer

p2p/dial.go

@@ -135,6 +135,7 @@ type dialConfig struct {
 	log            log.Logger
 	clock          mclock.Clock
 	rand           *mrand.Rand
+	ttl            time.Duration
 }
 
 func (cfg dialConfig) withDefaults() dialConfig {
@@ -274,13 +275,15 @@ 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, "addr", node.DisplayAddr(), "ip", node.IPAddr(), "added", !exists)
 			if exists {
 				continue loop
 			}
 			task := newDialTask(node, staticDialedConn)
 			d.static[id] = task
-			if d.checkDial(node) == nil {
+			if err := d.checkDial(node); err != nil {
+				d.log.Trace("Discarding dial candidate", "id", node.ID(), "addr", node.DisplayAddr(), "ip", node.IPAddr(), "reason", err)
+			} else {
 				d.addToStaticPool(task)
 			}
 
@@ -436,7 +439,7 @@ func (d *dialScheduler) removeFromStaticPool(idx int) {
 // 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(), "addr", node.DisplayAddr(), "ip", node.IPAddr(), "flag", task.flags)
 	hkey := string(node.ID().Bytes())
 	d.history.add(hkey, d.clock.Now().Add(dialHistoryExpiration))
 	d.dialing[node.ID()] = task
@@ -473,7 +476,7 @@ func (t *dialTask) dest() *enode.Node {
 }
 
 func (t *dialTask) run(d *dialScheduler) {
-	if t.needResolve() && !t.resolve(d) {
+	if !t.resolveIfNeeded(d) {
 		return
 	}
 
@@ -488,8 +491,36 @@ func (t *dialTask) run(d *dialScheduler) {
 	}
 }
 
-func (t *dialTask) needResolve() bool {
-	return t.flags&staticDialedConn != 0 && !t.dest().IPAddr().IsValid()
+// resolveIfNeeded attempts to resolve the node's IP address if it is invalid.
+// It returns true if the node's IP address is valid after resolution attempts.
+func (t *dialTask) resolveIfNeeded(d *dialScheduler) bool {
+	node := t.dest()
+
+	if t.flags&staticDialedConn != 0 {
+		if t.resolve(d) && node.IPAddr().IsValid() {
+			return true
+		}
+	}
+
+	if node.NeedsDNSResolve() {
+		if t.resolveDNS(d) && node.IPAddr().IsValid() {
+			return true
+		}
+	}
+
+	return false
+}
+
+// resolveDNS attempts to resolve the DNS name of the destination node.
+// It returns true if resolution succeeds.
+func (t *dialTask) resolveDNS(d *dialScheduler) bool {
+	node := t.dest()
+	d.log.Trace("Starting DNS resolution", "id", node.ID(), "addr", node.DisplayAddr())
+	if err := node.RefreshDNS(d.dialConfig.ttl); err != nil {
+		d.log.Trace("DNS resolution failed", "id", node.ID(), "addr", node.DisplayAddr())
+		return false
+	}
+	return true
 }
 
 // resolve attempts to find the current endpoint for the destination
@@ -533,8 +564,7 @@ func (t *dialTask) dial(d *dialScheduler, dest *enode.Node) error {
 	dialMeter.Mark(1)
 	fd, err := d.dialer.Dial(d.ctx, dest)
 	if err != nil {
-		addr, _ := dest.TCPEndpoint()
-		d.log.Trace("Dial error", "id", dest.ID(), "addr", addr, "conn", t.flags, "err", cleanupDialErr(err))
+		d.log.Trace("Dial error", "id", dest.ID(), "addr", dest.DisplayAddr(), "ip", dest.IPAddr(), "conn", t.flags, "err", cleanupDialErr(err))
 		dialConnectionError.Mark(1)
 		return &dialError{err}
 	}

p2p/enode/node.go

@@ -26,6 +26,7 @@ import (
 	"net"
 	"net/netip"
 	"strings"
+	"time"
 
 	"github.com/ethereum/go-ethereum/p2p/enr"
 	"github.com/ethereum/go-ethereum/rlp"
@@ -41,6 +42,10 @@ type Node struct {
 	ip  netip.Addr
 	udp uint16
 	tcp uint16
+	// dns information
+	dnsName     string
+	dnsResolved time.Time
+	dnsTTL      time.Duration
 }
 
 // New wraps a node record. The record must be valid according to the given
@@ -257,6 +262,84 @@ func (n *Node) String() string {
 	return "enr:" + b64
 }
 
+// resolveDNS attempts to resolve a DNS name to an IP address
+func (n *Node) resolveDNS(dnsName string) (netip.Addr, error) {
+	ips, err := net.LookupIP(dnsName)
+	if err != nil {
+		return netip.Addr{}, err
+	}
+	for _, ip := range ips {
+		if ip4 := ip.To4(); ip4 != nil {
+			addr, ok := netip.AddrFromSlice(ip4)
+			if ok {
+				return addr, nil
+			}
+		}
+	}
+	// Fall back to IPv6 if no IPv4 is available
+	for _, ip := range ips {
+		addr, ok := netip.AddrFromSlice(ip)
+		if ok {
+			return addr, nil
+		}
+	}
+
+	return netip.Addr{}, errors.New("no valid IP address found")
+}
+
+// SetDNS sets the DNS name and resolves it to an IP address
+func (n *Node) SetDNS(dnsName string, ttl time.Duration) error {
+	ip, err := n.resolveDNS(dnsName)
+	if err != nil {
+		return err
+	}
+
+	n.dnsName = dnsName
+	n.dnsResolved = time.Now()
+	n.dnsTTL = ttl
+
+	if ip.Is4() {
+		n.setIP4(ip)
+	} else {
+		n.setIP6(ip)
+	}
+	return nil
+}
+
+// DNSName returns the stored DNS name
+func (n *Node) DNSName() string {
+	return n.dnsName
+}
+
+// RefreshDNS updates the IP address from the stored DNS name
+func (n *Node) RefreshDNS(ttl time.Duration) error {
+	if n.dnsName == "" {
+		return errors.New("no DNS name set")
+	}
+	return n.SetDNS(n.dnsName, ttl)
+}
+
+// DisplayAddr returns either "hostname:port" or "ip:port"
+func (n *Node) DisplayAddr() string {
+	addr := n.dnsName
+	if addr == "" {
+		addr = n.ip.String()
+	}
+	return fmt.Sprintf("%s:%d", addr, n.tcp)
+}
+
+// NeedsDNSResolve returns true if the node has a DNS name that needs resolution
+func (n *Node) NeedsDNSResolve() bool {
+	if n.dnsName == "" {
+		return false
+	}
+	return !n.ip.IsValid() || time.Since(n.dnsResolved) > n.dnsTTL
+}
+
+func (n *Node) GetTTL() time.Duration {
+	return n.dnsTTL
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (n *Node) MarshalText() ([]byte, error) {
 	return []byte(n.String()), nil

p2p/enode/urlv4.go

@@ -126,20 +126,6 @@ func parseComplete(rawurl string) (*Node, error) {
 	if id, err = parsePubkey(u.User.String()); err != nil {
 		return nil, fmt.Errorf("invalid public key (%v)", err)
 	}
-	// Parse the IP address.
-	ip := net.ParseIP(u.Hostname())
-	if ip == nil {
-		ips, err := lookupIPFunc(u.Hostname())
-		if err != nil {
-			return nil, err
-		}
-		ip = ips[0]
-	}
-	// Ensure the IP is 4 bytes long for IPv4 addresses.
-	if ipv4 := ip.To4(); ipv4 != nil {
-		ip = ipv4
-	}
-	// Parse the port numbers.
 	if tcpPort, err = strconv.ParseUint(u.Port(), 10, 16); err != nil {
 		return nil, errors.New("invalid port")
 	}
@@ -151,7 +137,18 @@ func parseComplete(rawurl string) (*Node, error) {
 			return nil, errors.New("invalid discport in query")
 		}
 	}
-	return NewV4(id, ip, int(tcpPort), int(udpPort)), nil
+	// Check if hostname is an IP address and create node accordingly
+	hostname := u.Hostname()
+	if ip := net.ParseIP(hostname); ip != nil {
+		// Create node with IP
+		node := NewV4(id, ip, int(tcpPort), int(udpPort))
+		return node, nil
+	}
+
+	// Create node for DNS name
+	node := NewV4(id, nil, int(tcpPort), int(udpPort))
+	node.dnsName = hostname
+	return node, nil
 }
 
 // parsePubkey parses a hex-encoded secp256k1 public key.
@@ -184,9 +181,14 @@ func (n *Node) URLv4() string {
 	if !n.ip.IsValid() {
 		u.Host = nodeid
 	} else {
-		addr := net.TCPAddr{IP: n.IP(), Port: n.TCP()}
 		u.User = url.User(nodeid)
-		u.Host = addr.String()
+		// Use DNS name if available, otherwise use IP
+		if n.DNSName() != "" {
+			u.Host = fmt.Sprintf("%s:%d", n.DNSName(), n.TCP())
+		} else {
+			addr := net.TCPAddr{IP: n.IP(), Port: n.TCP()}
+			u.Host = addr.String()
+		}
 		if n.UDP() != n.TCP() {
 			u.RawQuery = "discport=" + strconv.Itoa(n.UDP())
 		}

p2p/server.go

@@ -64,6 +64,10 @@ const (
 
 	// Maximum amount of time allowed for writing a complete message.
 	frameWriteTimeout = 20 * time.Second
+
+	defaultTTL = 5 * time.Minute
+	minTTL     = 1 * time.Second
+	maxTTL     = 24 * time.Hour
 )
 
 var (
@@ -122,6 +126,11 @@ type Config struct {
 	// allowed to connect, even above the peer limit.
 	TrustedNodes []*enode.Node
 
+	// TTL is the time-to-live for DNS discovery queries
+	// This value is passed to the DNS resolvers when performing name
+	// resolutions.
+	TTL time.Duration `toml:",omitempty"`
+
 	// Connectivity can be restricted to certain IP networks.
 	// If this option is set to a non-nil value, only hosts which match one of the
 	// IP networks contained in the list are considered.
@@ -620,6 +629,11 @@ func (srv *Server) setupDialScheduler() {
 	if config.dialer == nil {
 		config.dialer = tcpDialer{&net.Dialer{Timeout: defaultDialTimeout}}
 	}
+	if srv.TTL >= minTTL && srv.TTL <= maxTTL {
+		config.ttl = srv.TTL
+	} else {
+		config.ttl = defaultTTL
+	}
 	srv.dialsched = newDialScheduler(config, srv.discmix, srv.SetupConn)
 	for _, n := range srv.StaticNodes {
 		srv.dialsched.addStatic(n)