Test the capability gate, the sweep's mark re-read and the lock use of a send and of the sweep, each failing under its mutation (issues 1696, 1697; review round 2)

cmd/mesh-controller/declaration_files_test.go

@@ -467,3 +467,68 @@ func TestAPutThatFailsSendAfterSendRaisesAConditionAndClearsWhenItWorks(t *testi
 		t.Fatal("the count did not start again after a put that worked")
 	}
 }
+
+// aBusThatSays is a bus that keeps the declarations published to it and, at each, asks whether the node's bucket is held.
+type aBusThatSays struct {
+	link.Bus
+	published     chan string
+	heldAtPublish func() bool
+}
+
+func (b *aBusThatSays) PublishDeclaration(_ context.Context, node string, _ []byte) error {
+	if b.heldAtPublish != nil && !b.heldAtPublish() {
+		return errors.New("published while the node's bucket was not held")
+	}
+	b.published <- node
+	return errors.New("stop here: nothing is recorded")
+}
+
+type aSignerOfZeros struct{}
+
+func (aSignerOfZeros) Sign(context.Context, []byte) ([]byte, error) { return make([]byte, 64), nil }
+
+// whileHeld says whether the node's lock is held by someone right now, without keeping it.
+func whileHeld(node string) bool {
+	got := make(chan struct{})
+	go func() {
+		defer lockFilesOf(node)()
+		close(got)
+	}()
+	select {
+	case <-got:
+		return false
+	case <-time.After(100 * time.Millisecond):
+		// held: the goroutine stays waiting and takes and releases the lock once it is let go.
+		return true
+	}
+}
+
+// 1696/AC9: a send holds the node's lock from the put to the publication, so the sweep never removes an object between them. The
+// test goes through overTheBus.declare: while another holds the lock the declaration is not published, and at the publication the
+// lock is held.
+func TestASendHoldsTheNodesLockFromThePutToThePublication(t *testing.T) { // 1696/AC9
+	const node = "lock-send-node"
+	bus := &aBusThatSays{published: make(chan string, 1)}
+	bus.heldAtPublish = func() bool { return whileHeld(node) }
+	send := overTheBus{server: link.SendingOn(bus), signer: aSignerOfZeros{}}
+	release := lockFilesOf(node) // a sweep is judging this node's bucket
+	done := make(chan error, 1)
+	go func() {
+		_, err := send.declare(t.Context(), readyNode{node: node}, []byte(`{}`))
+		done <- err
+	}()
+	select {
+	case n := <-bus.published:
+		t.Fatalf("%s was sent its declaration while the sweep held the node's bucket", n)
+	case <-time.After(150 * time.Millisecond):
+	}
+	release()
+	select {
+	case <-bus.published:
+	case <-time.After(5 * time.Second):
+		t.Fatal("the send did not go on once the sweep let go")
+	}
+	if err := <-done; err == nil || !strings.Contains(err.Error(), "nothing is recorded") {
+		t.Fatalf("the send did not reach the publication (a lock held at it): %v", err)
+	}
+}