Ask a node's engine for a fresh setuid search at the terminal (hq issue 361)

After the operator removes by hand what the last search found, no apply says so and nothing searched again
until the next day. node setuid-search <node> signs the ask as a hand-over is, under its own context, on a
subject only the node's engine hears and only the controller may publish.

cmd/mesh-controller/nodes.go

@@ -120,8 +120,16 @@ func nodeCommand(ctx context.Context, args []string) error {
 		// the module declares, and whoever may call a verb includes agents.
 		return nodeHandOver(ctx, open, args[1:])
 
+	case "setuid-search":
+		// A fresh search for setuid programs on a node (novox/hq issue 361), after the operator changed by hand
+		// what the last one found. Here, at the controller's terminal, and nowhere else: a search never makes a
+		// machine free wrongly, but asked again and again it would keep the machine unjudged and its disks busy,
+		// and whoever may call a verb includes agents.
+		return nodeSetuidSearch(ctx, open, args[1:])
+
 	default:
-		return fmt.Errorf("node has no %q; it has add, list, show, public-domain, account, agent-account and hand-over", args[0])
+		return fmt.Errorf("node has no %q; it has add, list, show, public-domain, account, agent-account, hand-over "+
+			"and setuid-search", args[0])
 	}
 }
 
@@ -210,6 +218,59 @@ func handOverAsked(args []string, known func(node string) error,
 	return nil
 }
 
+const setuidSearchUsage = "node setuid-search <node> — throw away the node-engine's last search for setuid " +
+	"programs on <node> and start a full one: after a setuid-root program it found was removed by hand. Until it " +
+	"completes, root-free says the node is not judged yet"
+
+// nodeSetuidSearch asks the node's engine for a fresh search, signed with the mesh's key as a hand-over is.
+func nodeSetuidSearch(ctx context.Context, open *stores, args []string) error {
+	known := func(node string) error {
+		_, err := open.inventory.NodeByName(ctx, node)
+		return err
+	}
+	ask := func(node, by string) (link.HandOverAnswer, error) {
+		ident, err := open.Identity(ctx)
+		if err != nil {
+			return link.HandOverAnswer{}, fmt.Errorf("the mesh's signing key cannot be read, so nothing was asked of %s: %w",
+				node, err)
+		}
+		address, err := broker.BusAddress()
+		if err != nil {
+			return link.HandOverAnswer{}, err
+		}
+		js, err := broker.Dial(address)
+		if err != nil {
+			return link.HandOverAnswer{}, fmt.Errorf("cannot reach the bus, so nothing was asked of %s: %w", node, err)
+		}
+		defer js.Close()
+		return link.AskSetuidSearch(ctx, js.Conn(), ident, node, by, link.HandOverWithin)
+	}
+	return setuidSearchAsked(args, known, ask, os.Stdout)
+}
+
+// setuidSearchAsked is the line with its two acts given: whether the mesh knows the node, and the ask. The
+// engine's refusal is this command's failure.
+func setuidSearchAsked(args []string, known func(node string) error,
+	ask func(node, by string) (link.HandOverAnswer, error), out io.Writer) error {
+	if len(args) != 1 || args[0] == "" || strings.HasPrefix(args[0], "-") {
+		return errors.New(setuidSearchUsage)
+	}
+	node := args[0]
+	if err := known(node); err != nil {
+		return fmt.Errorf("nothing was asked: %w", err)
+	}
+	answer, err := ask(node, handOverBy())
+	if err != nil {
+		return err
+	}
+	if answer.Refused != "" {
+		return fmt.Errorf("%s refused: %s", node, answer.Refused)
+	}
+	fmt.Fprintln(out, answer.Said)
+	fmt.Fprintf(out, "  the controller's root-free verb shows the search's progress until it completes\n")
+	return nil
+}
+
 // addNode creates a node record, adopted when the operator says so (novox/hq ADR 0100).
 func addNode(ctx context.Context, inv *inventory.Inventory, args []string) error {
 	set := flag.NewFlagSet("node add", flag.ContinueOnError)