feat: allow deleting rDNS entries

internal/cmd/base/set_rdns.go

@@ -39,7 +39,7 @@ func (rc *SetRdnsCmd) CobraCommand(s state.State) *cobra.Command {
 		},
 	}
 	cmd.Flags().StringP("hostname", "r", "", "Hostname to set as a reverse DNS PTR entry (required)")
-	cmd.MarkFlagRequired("hostname")
+	cmd.Flags().Bool("reset", false, "Reset the reverse DNS entry to the default value")
 
 	cmd.Flags().IPP("ip", "i", net.IP{}, "IP address for which the reverse DNS entry should be set")
 	if rc.AdditionalFlags != nil {
@@ -67,8 +67,19 @@ func (rc *SetRdnsCmd) Run(s state.State, cmd *cobra.Command, args []string) erro
 	if ip.IsUnspecified() || ip == nil {
 		ip = rc.GetDefaultIP(resource)
 	}
-	hostname, _ := cmd.Flags().GetString("hostname")
-	action, _, err := s.Client().RDNS().ChangeDNSPtr(s, resource.(hcloud.RDNSSupporter), ip, hcloud.String(hostname))
+
+	var hostnamePtr *string
+	if reset, _ := cmd.Flags().GetBool("reset"); reset {
+		hostnamePtr = nil
+	} else {
+		hostname, _ := cmd.Flags().GetString("hostname")
+		if hostname == "" {
+			return fmt.Errorf("either --hostname or --reset must be specified")
+		}
+		hostnamePtr = &hostname
+	}
+
+	action, _, err := s.Client().RDNS().ChangeDNSPtr(s, resource.(hcloud.RDNSSupporter), ip, hostnamePtr)
 	if err != nil {
 		return err
 	}