Merge pull request 'A machine says which links face outside without being asked' (#47) from fix/a-machine-says-unasked-which-links-face-outside into main

cmd/mesh-host/main.go

@@ -1077,7 +1077,12 @@ type adoptionWatch struct {
 // is what the controller previews a flip from, so a port that opens or closes between deliveries
 // must reach it too (novox/hq ADR 0100).
 func adoptionFingerprint(r link.Report) string {
-	parts := []string{"firewall=" + r.Firewall}
+	// **Which links face outside is part of it, though it is not about adoption** (novox/hq ADR
+	// 0140). The mesh composes no filter for a machine that has not said, so a machine whose links
+	// changed — or which has only just learnt to say — has to say so without being asked. Left out,
+	// it could only speak when a declaration arrived, and a declaration cannot be composed until it
+	// has spoken: a machine waiting for a push that is waiting for the machine.
+	parts := []string{"firewall=" + r.Firewall, "outward=" + strings.Join(r.Outward, ",")}
 	for _, h := range r.Held {
 		parts = append(parts, "held "+h.ID+"="+h.Changed)
 	}
@@ -1085,7 +1090,7 @@ func adoptionFingerprint(r link.Report) string {
 		parts = append(parts, fmt.Sprintf("reach %s %s:%d %s %v %d", reach.Protocol, reach.Address,
 			reach.Port, reach.By, reach.Published, reach.ContainerPort))
 	}
-	sort.Strings(parts[1:])
+	sort.Strings(parts[2:])
 	return strings.Join(parts, "\n")
 }
 

cmd/mesh-host/main_test.go

@@ -501,3 +501,35 @@ func TestReconcileAfterAControllerDeclarationDoesNotReapplyTheBundle(t *testing.
 		t.Errorf("with nothing said, reconcile did not reach for the carried bundle: %v", err)
 	}
 }
+
+// **A machine says which links face outside without being asked.**
+//
+// The mesh composes no filter for a machine that has not said (novox/hq ADR 0140), and a machine only
+// speaks unasked when this fingerprint changes. Left out of it, a machine that has just learnt to say
+// could speak only when a declaration arrived — and a declaration cannot be composed until it has
+// spoken. A machine waiting for a push that is waiting for the machine.
+func TestANewOutwardLinkIsSaidUnasked(t *testing.T) {
+	w := &adoptionWatch{}
+	first := link.Report{Firewall: "none"}
+	if !w.differs(first) {
+		t.Fatal("the first report should differ from nothing")
+	}
+	w.said(first)
+
+	// Only the links changed, and nothing about adoption.
+	learnt := link.Report{Firewall: "none", Outward: []string{"eth0"}}
+	if !w.differs(learnt) {
+		t.Fatal("a machine that has just learnt which links face outside would never say so, " +
+			"and could then never be sent a filter")
+	}
+	w.said(learnt)
+	if w.differs(link.Report{Firewall: "none", Outward: []string{"eth0"}}) {
+		t.Fatal("the same links are reported as a change, so the machine would speak on every reconcile")
+	}
+
+	// And a link that changes — a laptop moving from a cable to a radio — is said too, because the
+	// filter is written around the old one until it is.
+	if !w.differs(link.Report{Firewall: "none", Outward: []string{"wlan0"}}) {
+		t.Fatal("a changed outward link is not said, so the filter stays written around the old one")
+	}
+}