Checker: reads the seat list when its hub is heard while it is unread, since the seat's event before its consumer is lost to it (ADR 0636 §1; issue 1966)

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

@@ -465,6 +465,8 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	// check fails at its publish bound until the checker starts again.
 	if err := hub.Start(ctx, js, cred); err != nil {
 		logger.Printf("%v, so no package registry's published is heard and a group's check fails at its publish bound until the checker starts again", err)
+	} else {
+		readIfUnread(seats.reader)
 	}
 	defer hub.Stop()
 	// The checks, the tries and the hand asks, once every first view is answered (the lead's ruling for DLV-M2): a check

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

@@ -49,3 +49,13 @@ func (s seatList) Definitions() ([]json.RawMessage, error) {
 	}
 	return out, nil
 }
+
+// readIfUnread is called when the checker's hub is heard. The seat may have answered, and said that it does, before the
+// checker's consumer existed, whose events start at the stream's end: the first read found it silent and nothing else reads
+// again until its next event, so while the list is unread it is read now, on a goroutine of its own (ADR 0636 §1).
+func readIfUnread(reader *seatlist.Reader) {
+	if reader == nil || reader.Status().Heard {
+		return
+	}
+	go func() { _ = reader.Reload() }()
+}

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

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/seatlist"
+)
+
+// silentThenAnswering is a seat that is silent at the reader's first read and answers after.
+type silentThenAnswering struct{ answering atomic.Bool }
+
+func (b *silentThenAnswering) Ask(string, any) (json.RawMessage, error) {
+	if !b.answering.Load() {
+		return nil, errors.New("not connected yet")
+	}
+	return json.RawMessage(`{"revision":1,"seats":[]}`), nil
+}
+
+func (b *silentThenAnswering) Subscribe(string, func(string, json.RawMessage) error) error { return nil }
+
+// A seat that spoke before the checker's consumer existed is read when the hub is heard (ADR 0636 §1).
+func TestTheSeatListIsReadWhenTheHubIsHeard(t *testing.T) {
+	bus := &silentThenAnswering{}
+	reader := followSeatList(bus, t.Logf)
+	<-reader.Ready()
+	if reader.Status().Heard {
+		t.Fatal("a silent seat was heard")
+	}
+	bus.answering.Store(true)
+	readIfUnread(reader)
+	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 when the hub was heard")
+		}
+	}
+	var _ seatlist.Bus = bus
+}