p2p/enode: add back DNS hostname resolution at parsing time

- removed in ethereum/go-ethereum#30822 in favor of on-demand runtime dialling
- reported to have removed bootnodes DNS resolution at ethereum/go-ethereum#31208
- possibly broke DNS resolution for other methods of adding peers

Author: sebastianst

p2p/enode/urlv4.go

@@ -33,6 +33,7 @@ import (
 
 var (
 	incompleteNodeURL = regexp.MustCompile("(?i)^(?:enode://)?([0-9a-f]+)$")
+	lookupIPFunc      = net.LookupIP
 )
 
 // MustParseV4 parses a node URL. It panics if the URL is not valid.
@@ -128,6 +129,25 @@ func parseComplete(rawurl string) (*Node, error) {
 
 	// Parse the IP and ports.
 	ip := net.ParseIP(u.Hostname())
+
+	// OP-Stack diff: add back DNS hostname resolution at parsing time
+	// - removed in https://github.com/ethereum/go-ethereum/pull/30822 in favor of on-demand runtime dialling
+	// - reported to have removed bootnodes DNS resolution at https://github.com/ethereum/go-ethereum/issues/31208
+	// - possibly broke DNS resolution for other methods of adding peers
+	var resolved bool
+	if ip == nil {
+		ips, err := lookupIPFunc(u.Hostname())
+		if err != nil {
+			return nil, err
+		}
+		resolved = true
+		ip = ips[0]
+	}
+	// Ensure the IP is 4 bytes long for IPv4 addresses.
+	if ipv4 := ip.To4(); ipv4 != nil {
+		ip = ipv4
+	}
+
 	if tcpPort, err = strconv.ParseUint(u.Port(), 10, 16); err != nil {
 		return nil, errors.New("invalid port")
 	}
@@ -142,7 +162,7 @@ func parseComplete(rawurl string) (*Node, error) {
 
 	// Create the node.
 	node := NewV4(id, ip, int(tcpPort), int(udpPort))
-	if ip == nil && u.Hostname() != "" {
+	if resolved {
 		node = node.WithHostname(u.Hostname())
 	}
 	return node, nil

p2p/enode/urlv4_test.go

@@ -18,6 +18,7 @@ package enode
 
 import (
 	"crypto/ecdsa"
+	"errors"
 	"net"
 	"reflect"
 	"strings"
@@ -27,6 +28,15 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/enr"
 )
 
+func init() {
+	lookupIPFunc = func(name string) ([]net.IP, error) {
+		if name == "valid." {
+			return []net.IP{{33, 44, 55, 66}}, nil
+		}
+		return nil, errors.New("no such host")
+	}
+}
+
 var parseNodeTests = []struct {
 	input      string
 	wantError  string
@@ -81,7 +91,7 @@ var parseNodeTests = []struct {
 		input: "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@valid.:3",
 		wantResult: NewV4(
 			hexPubkey("1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
-			nil,
+			net.IP{33, 44, 55, 66}, // OP-Stack adds back DNS resolution at parsing time
 			3,
 			3,
 		).WithHostname("valid."),