Sign the hand-over ask, and fail the line on the engine's refusal (hq issue 356, review)

The subject proved nothing: the bus lets any principal allowed to answer reply to a message it received on the reply subject that message named, so a tool server — the operator's account, every agent — could deliver a hand-over to an engine. The controller now signs the ask with the mesh's key over a fixed context (node, path, who asked, a minute's expiry, a fresh nonce), as declarations are signed, and the engine verifies it. The writers table gains the row for mesh.node.*.ask.hand-over; the subject's comment no longer claims who the engine hears. The line's known-node check and the refusal branch are tested; every check was removed in turn and a test failed.

cmd/mesh-controller/handover_test.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"bytes"
+	"errors"
 	"strings"
 	"testing"
 	"time"
@@ -88,3 +90,45 @@ func TestTheUsedAsFoundConditionNamesTheOperatorsLine(t *testing.T) {
 		t.Fatalf("the module's health reads %v %q; want the operator's line", h, why)
 	}
 }
+
+// **Nothing is asked of a node the mesh does not know, and the engine's refusal is the command's failure**
+// (review of issue 356): a refused hand-over never exits as a success.
+func TestAHandOverAsksOnlyAKnownNodeAndFailsOnARefusal(t *testing.T) {
+	t.Setenv(link.CallerVar, "jo through mesh-cli on anchor")
+	asked := 0
+	ask := func(answer link.HandOverAnswer) func(node, path, by string) (link.HandOverAnswer, error) {
+		return func(node, path, by string) (link.HandOverAnswer, error) {
+			asked++
+			if node != "laptop" || path != "/srv/notes" || by != "jo through mesh-cli on anchor" {
+				t.Fatalf("asked %q %q %q", node, path, by)
+			}
+			return answer, nil
+		}
+	}
+	unknown := func(string) error { return errors.New("no node called laptop") }
+	known := func(string) error { return nil }
+	var out bytes.Buffer
+	err := handOverAsked([]string{"laptop", "/srv/notes"}, unknown, ask(link.HandOverAnswer{Said: "x"}), &out)
+	if err == nil || asked != 0 || !strings.Contains(err.Error(), "nothing was asked") {
+		t.Fatalf("an unknown node: %v, asked %d", err, asked)
+	}
+	err = handOverAsked([]string{"laptop", "/srv/../etc"}, known, ask(link.HandOverAnswer{Said: "x"}), &out)
+	if err == nil || asked != 0 {
+		t.Fatalf("a refused line was asked: %v, asked %d", err, asked)
+	}
+	err = handOverAsked([]string{"laptop", "/srv/notes"}, known,
+		ask(link.HandOverAnswer{Refused: "/srv/notes is not used as found; nothing was handed over"}), &out)
+	if err == nil || !strings.Contains(err.Error(), "laptop refused: /srv/notes is not used as found") || out.Len() != 0 {
+		t.Fatalf("a refusal: %v, printed %q", err, out.String())
+	}
+	err = handOverAsked([]string{"laptop", "/srv/notes"}, known, ask(link.HandOverAnswer{Said: "handed over"}), &out)
+	if err != nil || !strings.HasPrefix(out.String(), "handed over\n") || !strings.Contains(out.String(), "`nox push laptop`") {
+		t.Fatalf("a record: %v, printed %q", err, out.String())
+	}
+	failing := func(string, string, string) (link.HandOverAnswer, error) {
+		return link.HandOverAnswer{}, errors.New("no engine")
+	}
+	if err := handOverAsked([]string{"laptop", "/srv/notes"}, known, failing, &out); err == nil {
+		t.Fatal("an ask that failed was a success")
+	}
+}