Indexer: its reader of its own seat list reads again as the states it answers from are bound, with no definition moving (ADR 0636 §1; issue 1966)

modules/mesh-delivery-indexer/cmd/mesh-delivery-indexer/main.go

@@ -408,7 +408,8 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	seatDefs := process.AwaitBucket(ctx, js, conn, index.SeatDefinitionsBucket, "no seat definition is kept", logger.Printf)
 	marks := process.AwaitBucket(ctx, js, conn, index.MarksBucket, "no change is said on the views family, so every reader waits on its first view", logger.Printf)
 	seatBus := &seatBus{defs: awaitedSource{ctx, seatDefs}, marks: awaitedSource{ctx, marks}}
-	_, saySeats := followSeatList(seatBus, saySeatDefinition(js, cred), logger.Printf)
+	seatReader, saySeats := followSeatList(seatBus, saySeatDefinition(js, cred), logger.Printf)
+	readWhenBound(seatReader, seatDefs, marks)
 	ix := &index.Indexer{Findings: awaitedStore{findings}, OldSections: awaitedStore{oldSections}, Requirements: awaitedStore{requirements}, Store: kvStore{candidates}, Modules: kvStore{modules}, Manifests: kvStore{manifests}, Taken: awaitedStore{taken}, Builds: known,
 		Verdicts: awaitedStore{verdicts}, SayRefused: sayRefused(js, cred, logger.Printf), SayAccepted: sayAccepted(js, cred),
 		Predefined: awaitedStore{predefined}, ConfigCandidates: awaitedStore{configCandidates}, Logf: logger.Printf,

modules/mesh-delivery-indexer/cmd/mesh-delivery-indexer/seatlist.go

@@ -129,3 +129,22 @@ func followSeatList(bus *seatBus, say func(context.Context, index.SeatDefinition
 		return nil
 	}
 }
+
+// bucket is a state bound when it appears (process.AwaitedBucket).
+type bucket interface{ Ready(func(jetstream.KeyValue)) }
+
+// readWhenBound has the reader read the list again as each of the states it is answered from is bound. The reader starts before
+// they are, its first read finds them missing and leaves it unread, and the indexer's own events (said) are the only other thing
+// that reads it again: a trunk that moves no definition after a start would leave the list unread for good (ADR 0636 §1).
+func readWhenBound(reader *seatlist.Reader, states ...bucket) {
+	if reader == nil {
+		return
+	}
+	for _, state := range states {
+		state.Ready(func(jetstream.KeyValue) {
+			if !reader.Status().Heard {
+				go func() { _ = reader.Reload() }()
+			}
+		})
+	}
+}

modules/mesh-delivery-indexer/cmd/mesh-delivery-indexer/seatlist_test.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"errors"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/seatlist"
+	"git.novox.be/novox/mesh-sdk/go/views"
+)
+
+type unboundSource struct {
+	mu    sync.Mutex
+	bound bool
+}
+
+func (s *unboundSource) Keys() ([]string, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if !s.bound {
+		return nil, errors.New("not yet")
+	}
+	return nil, nil
+}
+
+func (s *unboundSource) Get(string) (*views.Entry, bool, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if !s.bound {
+		return nil, false, errors.New("not yet")
+	}
+	return nil, false, nil
+}
+
+type awaitedFake struct{ ready []func(jetstream.KeyValue) }
+
+func (b *awaitedFake) Ready(f func(jetstream.KeyValue)) { b.ready = append(b.ready, f) }
+
+// The indexer's reader of its own seat list starts before its states are bound, so its first read finds them missing; it reads the
+// list again when they are bound, with no definition moving (ADR 0636 §1).
+func TestTheSeatListIsReadAgainWhenItsStatesAreBound(t *testing.T) {
+	src := &unboundSource{}
+	bus := &seatBus{defs: src, marks: src}
+	reader, _ := followSeatList(bus, nil, t.Logf)
+	<-reader.Ready()
+	if reader.Status().Heard {
+		t.Fatal("the list was read with its states missing")
+	}
+	b := &awaitedFake{}
+	readWhenBound(reader, b)
+	src.mu.Lock()
+	src.bound = true
+	src.mu.Unlock()
+	for _, f := range b.ready {
+		f(nil)
+	}
+	for deadline := time.Now().Add(5 * time.Second); !reader.Status().Heard; time.Sleep(10 * time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatal("the list was not read after its states were bound")
+		}
+	}
+	var _ seatlist.Bus = bus
+}