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/handover_test.go

@@ -132,3 +132,38 @@ func TestAHandOverAsksOnlyAKnownNodeAndFailsOnARefusal(t *testing.T) {
 		t.Fatal("an ask that failed was a success")
 	}
 }
+
+// The setuid search's line asks only a known node, one name and nothing else, and fails on a refusal
+// (novox/hq issue 361).
+func TestASetuidSearchAsksOnlyAKnownNodeAndFailsOnARefusal(t *testing.T) {
+	t.Setenv(link.CallerVar, "jo through mesh-cli on anchor")
+	asked := 0
+	ask := func(answer link.HandOverAnswer) func(node, by string) (link.HandOverAnswer, error) {
+		return func(node, by string) (link.HandOverAnswer, error) {
+			asked++
+			if node != "novox" || by != "jo through mesh-cli on anchor" {
+				t.Fatalf("asked %q %q", node, by)
+			}
+			return answer, nil
+		}
+	}
+	known := func(string) error { return nil }
+	var out bytes.Buffer
+	for _, args := range [][]string{nil, {"novox", "extra"}, {"-x"}} {
+		if err := setuidSearchAsked(args, known, ask(link.HandOverAnswer{Said: "x"}), &out); err == nil || asked != 0 {
+			t.Fatalf("%v was asked: %v", args, err)
+		}
+	}
+	if err := setuidSearchAsked([]string{"novox"}, func(string) error { return errors.New("no node called novox") },
+		ask(link.HandOverAnswer{Said: "x"}), &out); err == nil || asked != 0 {
+		t.Fatalf("an unknown node: %v", err)
+	}
+	if err := setuidSearchAsked([]string{"novox"}, known, ask(link.HandOverAnswer{Refused: "no; no search was started"}),
+		&out); err == nil || !strings.Contains(err.Error(), "novox refused") || out.Len() != 0 {
+		t.Fatalf("a refusal: %v, printed %q", err, out.String())
+	}
+	if err := setuidSearchAsked([]string{"novox"}, known, ask(link.HandOverAnswer{Said: "a new search starts"}),
+		&out); err != nil || !strings.HasPrefix(out.String(), "a new search starts\n") {
+		t.Fatalf("a start: %v, printed %q", err, out.String())
+	}
+}