cmd/devp2p: print enode:// URL in enrdump (#21270)

Co-authored-by: NFelix Lange <fjl@twurst.com>

cmd/devp2p/enrcmd.go

@@ -21,6 +21,7 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net"
 	"os"
@@ -69,22 +70,30 @@ func enrdump(ctx *cli.Context) error {
 	if err != nil {
 		return fmt.Errorf("INVALID: %v", err)
 	}
-	fmt.Print(dumpRecord(r))
+	dumpRecord(os.Stdout, r)
 	return nil
 }
 
 // dumpRecord creates a human-readable description of the given node record.
-func dumpRecord(r *enr.Record) string {
-	out := new(bytes.Buffer)
-	if n, err := enode.New(enode.ValidSchemes, r); err != nil {
+func dumpRecord(out io.Writer, r *enr.Record) {
+	n, err := enode.New(enode.ValidSchemes, r)
+	if err != nil {
 		fmt.Fprintf(out, "INVALID: %v\n", err)
 	} else {
 		fmt.Fprintf(out, "Node ID: %v\n", n.ID())
+		dumpNodeURL(out, n)
 	}
 	kv := r.AppendElements(nil)[1:]
 	fmt.Fprintf(out, "Record has sequence number %d and %d key/value pairs.\n", r.Seq(), len(kv)/2)
 	fmt.Fprint(out, dumpRecordKV(kv, 2))
-	return out.String()
+}
+
+func dumpNodeURL(out io.Writer, n *enode.Node) {
+	var key enode.Secp256k1
+	if n.Load(&key) != nil {
+		return // no secp256k1 public key
+	}
+	fmt.Fprintf(out, "URLv4:   %s\n", n.URLv4())
 }
 
 func dumpRecordKV(kv []interface{}, indent int) string {