CAT-RD7: mesh-watcher asks the assigner's seat-holders once and follows its events, no reads

modules/mesh-watcher/cmd/mesh-watcher/main.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -17,6 +18,8 @@ import (
 	stdio "git.novox.be/novox/mesh-sdk/go"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 	"git.novox.be/novox/mesh-sdk/go/health"
+
+	"git.novox.be/novox/mesh-delivery/sdk/views"
 )
 
 func logf(format string, a ...any) { fmt.Fprintf(os.Stderr, format+"\n", a...) }
@@ -70,8 +73,10 @@ func main() {
 	node := os.Getenv("MESH_NODE")
 	w := NewWatcher(tg, time.Now, logf, node)
 	l := &listening{now: "not yet: starting"}
-	go run(w, l, node)
-	if err := stdio.Serve("", tools(w, l)); err != nil {
+	placement := &views.Reader{Module: "mesh-watcher", Logf: logf}
+	placement.Follow(delivery.AssignerModule, delivery.SeatHoldersState, SeatHoldersTool)
+	go run(w, l, node, placement)
+	if err := stdio.Serve("", append(tools(w, l), placement.Tools("watcher")...)); err != nil {
 		logf("%v", err)
 		os.Exit(1)
 	}
@@ -79,7 +84,7 @@ func main() {
 
 // run keeps time, makes the round trips, reads where the controller is, and listens for heartbeats.
 // The clock runs whatever the bus does: it is what notices the bus is gone.
-func run(w *Watcher, l *listening, node string) {
+func run(w *Watcher, l *listening, node string, placement *views.Reader) {
 	if err := w.Telegram.Ready(); err != nil {
 		logf("[mesh-watcher] BLIND until given: %v", err)
 	}
@@ -89,17 +94,17 @@ func run(w *Watcher, l *listening, node string) {
 			w.Tick()
 		}
 	}()
-	go func() {
-		time.Sleep(2 * time.Second)
-		for {
-			if nodes, err := controlNodes(); err == nil {
-				w.Placed(nodes)
-			} else {
-				logf("[mesh-watcher] cannot read where the bus runs (%v); asking again in ten minutes", err)
-			}
-			time.Sleep(10 * time.Minute)
+	// Where the bus runs: the assigner's seat-holders, asked once and then followed by its events (ADR 0615), never read
+	// from its state and never on a timer.
+	placed := func() {
+		if nodes, err := controlNodes(placement); err == nil {
+			w.Placed(nodes)
+		} else {
+			logf("[mesh-watcher] cannot read where the bus runs (%v)", err)
 		}
-	}()
+	}
+	placement.Changed = func(string, string, json.RawMessage, bool) { placed() }
+	placement.Start(context.Background())
 	handle := func(e stdio.Envelope) error {
 		if !isHeartbeat(e.Key) {
 			return nil
@@ -146,24 +151,17 @@ func roundTrip(node string) error {
 	}
 }
 
+// SeatHoldersTool is the assigner's read tool of the state of who holds which seat, which the manifest invokes; the
+// state is followed as a view (ADR 0615), named as the manifest named it before: SeatHoldersRead.
+const SeatHoldersTool = delivery.AssignerModule + ".assigner_read_seat_holders"
+
 // controlNodes reads which machines hold the bus, from the placement seat's state of who holds which seat (novox/hq
 // ADR 0571 clause 4). The controller is not placed (ADR 0590), so the bus's machines are the control node.
-func controlNodes() ([]string, error) {
-	st := stdio.State(delivery.SeatHoldersRead)
-	names, err := st.Keys()
+func controlNodes(seats *views.Reader) ([]string, error) {
+	keys, err := seats.Values(delivery.SeatHoldersRead)
 	if err != nil {
 		return nil, err
 	}
-	keys := map[string][]byte{}
-	for _, k := range names {
-		e, err := st.Get(k)
-		if err != nil {
-			return nil, err
-		}
-		if e != nil {
-			keys[k] = e.Value
-		}
-	}
 	return holderNodes(keys, "mesh-broker")
 }
 

modules/mesh-watcher/cmd/mesh-watcher/manifest_test.go

@@ -9,6 +9,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"git.novox.be/novox/mesh-delivery/sdk/views"
 )
 
 // The manifest says what the code does: it consumes the heartbeat and nothing else, calls its own
@@ -24,6 +26,7 @@ func TestTheManifestSaysWhatTheCodeDoes(t *testing.T) {
 		Module   string            `json:"module"`
 		Consumes []string          `json:"consumes"`
 		Invokes  []string          `json:"invokes"`
+		Reads    []string          `json:"reads"`
 		Claims   []any             `json:"claims"`
 		Own      map[string]string `json:"own-secrets"`
 		Tools    []string          `json:"tools"`
@@ -34,11 +37,12 @@ func TestTheManifestSaysWhatTheCodeDoes(t *testing.T) {
 	if err := json.Unmarshal(raw, &m); err != nil {
 		t.Fatal(err)
 	}
-	if !reflect.DeepEqual(m.Consumes, []string{"mesh-self-check.checked"}) {
+	// Where the bus runs is the assigner's seat-holders, asked once and followed by its events (ADR 0615), never read.
+	if !reflect.DeepEqual(m.Consumes, []string{"mesh-self-check.checked", "mesh-delivery-assigner.views.seat-holders"}) {
 		t.Fatalf("consumes %v", m.Consumes)
 	}
-	if !reflect.DeepEqual(m.Invokes, []string{m.Module + ".watcher_ping"}) {
-		t.Fatalf("invokes %v", m.Invokes)
+	if !reflect.DeepEqual(m.Invokes, []string{SeatHoldersTool, m.Module + ".watcher_ping"}) || len(m.Reads) != 0 {
+		t.Fatalf("invokes %v, reads %v", m.Invokes, m.Reads)
 	}
 	if len(m.Claims) != 0 {
 		t.Fatalf("a watcher holds no seat: %v", m.Claims)
@@ -48,7 +52,7 @@ func TestTheManifestSaysWhatTheCodeDoes(t *testing.T) {
 		t.Fatalf("token: own %v, env %v", m.Own, env)
 	}
 	var served []string
-	for _, tool := range tools(NewWatcher(&fakeTelegram{}, time.Now, t.Logf, ""), &listening{}) {
+	for _, tool := range append(tools(NewWatcher(&fakeTelegram{}, time.Now, t.Logf, ""), &listening{}), (&views.Reader{}).Tools("watcher")...) {
 		served = append(served, tool.Name)
 		if strings.TrimSpace(tool.Description) == "" {
 			t.Errorf("%s has no description", tool.Name)

modules/mesh-watcher/module.json

@@ -3,12 +3,11 @@
   "version": "1",
   "slug": "watch",
   "consumes": [
-    "mesh-self-check.checked"
-  ],
-  "reads": [
-    "mesh-delivery-assigner.seat-holders"
+    "mesh-self-check.checked",
+    "mesh-delivery-assigner.views.seat-holders"
   ],
   "invokes": [
+    "mesh-delivery-assigner.assigner_read_seat_holders",
     "mesh-watcher.watcher_ping"
   ],
   "own-secrets": {
@@ -18,7 +17,9 @@
     "watcher_status",
     "watcher_last_heard",
     "watcher_test",
-    "watcher_ping"
+    "watcher_ping",
+    "watcher_first_views",
+    "watcher_first_view_again"
   ],
   "config": {
     "telegram-chat-id": {