Say which machines are inside the private network from placement, for route-proxy, whose membership read goes with the assignments stream (issue 774, research 072 rows 33 and 34)

go/delivery/placement_keys.go

@@ -578,3 +578,19 @@ func PlacementValues(p Placement) (map[string][]byte, error) {
 	}
 	return out, nil
 }
+
+// InsideAddresses is every node's address on the private network as its placement decides it (NodeDecided.Address),
+// sorted and each once: the machines inside the private network, which a membership's Mesh carried until the assignments
+// stream went (ADR 0167; research 072 rows 33 and 34). A node with no address decided is left out.
+func InsideAddresses(placements map[string]Placement) []string {
+	seen := map[string]bool{}
+	out := []string{}
+	for _, p := range placements {
+		if a := strings.TrimSpace(p.Decided.Address); a != "" && !seen[a] {
+			seen[a] = true
+			out = append(out, a)
+		}
+	}
+	sort.Strings(out)
+	return out
+}

go/delivery/placement_test.go

@@ -180,6 +180,9 @@ func TestPlacement(t *testing.T) {
 		if err != nil || !SamePlacement(got["g14"], g14) || len(got) != 1 {
 			t.Fatalf("PlacementsOf = %+v, %v", got, err)
 		}
+		if got := InsideAddresses(map[string]Placement{"g14": g14, "novox": novox, "x": {Node: "x"}, "y": {Node: "y", Decided: NodeDecided{Address: " 10.77.0.1"}}}); strings.Join(got, ",") != "10.77.0.1,10.77.0.2" {
+			t.Errorf("InsideAddresses = %v", got)
+		}
 		legacy, _ := EncodePlacement(novox)
 		stale, _ := EncodePlacement(Placement{Node: "g14"})
 		both := map[string][]byte{"placement.novox": legacy, "placement.g14": stale}