Carry brother's certificate check on a watch process beside the device unit check, as fail2ban does (issue 1510)

modules/brother/cmd/brother/main.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"os/signal"
+	"syscall"
 	"time"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
@@ -13,12 +15,26 @@ func main() {
 	if len(os.Args) > 1 && os.Args[1] == "device" {
 		os.Exit(device())
 	}
+	if len(os.Args) > 1 && os.Args[1] == "watch" {
+		os.Exit(watch())
+	}
 	if err := stdio.Serve("", tools(os.Getenv("BROTHER_SETTINGS"), time.Now)); err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
 }
 
+// watch is `brother watch`: the process that carries the tool check brother_health beside the device process's unit
+// check, as fail2ban's watch does (ADR 0240: a tool check is only beside a check the module does not run itself).
+// It does nothing itself; the node-engine asks the tool, and this stays up until it is stopped.
+func watch() int {
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	fmt.Fprintln(os.Stderr, "[brother] watch is up; the node-engine asks brother_health")
+	<-ctx.Done()
+	return 0
+}
+
 // intArg reads a whole number out of a tool's arguments: a JSON number, which arrives as a float64.
 func intArg(args map[string]any, name string) (int, error) {
 	v, ok := args[name]

modules/brother/cmd/brother/manifest_test.go

@@ -256,9 +256,7 @@ func TestTheAdminProcessIsDeclaredAsMeshMailsSenderIs(t *testing.T) {
 	if !reflect.DeepEqual(bus["queues"], []any{"device-asks"}) || !reflect.DeepEqual(bus["state"], []any{"device-answers"}) {
 		t.Errorf("bus = %v", bus)
 	}
-	// 1510: liveness is judged for every process without a declaration (ADR 0240 §1); the declared check is the
-	// tool that compares the printer's certificates with the pins.
-	if h, _ := p["health"].(map[string]any); h["kind"] != "tool" || h["tool"] != "brother_health" {
+	if h, _ := p["health"].(map[string]any); h["kind"] != "unit" {
 		t.Errorf("health = %v", p["health"])
 	}
 	env, _ := p["env"].(map[string]any)
@@ -397,3 +395,17 @@ func TestEachConfigPatternAdmitsARealValueWhole(t *testing.T) {
 		}
 	}
 }
+
+// 1510: the certificate check is a tool check on a process of its own beside the device process's unit check, as
+// fail2ban's watch is (ADR 0227 rule 8, ADR 0240: a tool check only beside a check of another kind).
+func TestTheCertificateCheckIsAToolCheckBesideTheUnitCheck(t *testing.T) {
+	m := readManifest(t)
+	w := resource(t, m, "watch")
+	h, _ := w["health"].(map[string]any)
+	if w["type"] != "process" || w["artifact"] != "tools" || h["kind"] != "tool" || h["tool"] != "brother_health" || !reflect.DeepEqual(w["run"], []any{"./brother", "watch"}) {
+		t.Errorf("watch = %v", w)
+	}
+	if !slices.Contains(m.Tools, "brother_health") {
+		t.Errorf("tools = %v", m.Tools)
+	}
+}

modules/brother/module.json

@@ -230,6 +230,20 @@
           "scan.added"
         ]
       },
+      "health": {
+        "kind": "unit"
+      }
+    },
+    {
+      "id": "watch",
+      "type": "process",
+      "name": "brother-watch",
+      "artifact": "tools",
+      "run": [
+        "./brother",
+        "watch"
+      ],
+      "user": "brother-device",
       "health": {
         "kind": "tool",
         "tool": "brother_health",