fix atrocious bug on pool.subMany(): we were missing events because of a badly designed select{}

pool.go

@@ -72,14 +72,15 @@ func (pool *SimplePool) SubManyNonUnique(ctx context.Context, urls []string, fil
 }
 
 func (pool *SimplePool) subMany(ctx context.Context, urls []string, filters Filters, unique bool) chan IncomingEvent {
+	ctx, cancel := context.WithCancel(ctx)
+	_ = cancel // do this so `go vet` will stop complaining
 	events := make(chan IncomingEvent)
 	seenAlready := xsync.NewMapOf[Timestamp]()
 	ticker := time.NewTicker(seenAlreadyDropTick)
 	eose := false
 
 	pending := xsync.NewCounter()
-	initial := len(urls)
-	pending.Add(int64(initial))
+	pending.Add(int64(len(urls)))
 	for _, url := range urls {
 		go func(nm string) {
 			relay, err := pool.EnsureRelay(nm)
@@ -92,23 +93,38 @@ func (pool *SimplePool) subMany(ctx context.Context, urls []string, filters Filt
 				return
 			}
 
-			for evt := range sub.Events {
-				if unique {
-					if _, seen := seenAlready.LoadOrStore(evt.ID, evt.CreatedAt); seen {
-						continue
-					}
+			defer func() {
+				pending.Dec()
+				if pending.Value() == 0 {
+					close(events)
 				}
+				cancel()
+			}()
 
+			for {
 				select {
+				case evt, more := <-sub.Events:
+					if !more {
+						return
+					}
+					if unique {
+						if _, seen := seenAlready.LoadOrStore(evt.ID, evt.CreatedAt); seen {
+							continue
+						}
+					}
+					select {
+					case events <- IncomingEvent{Event: evt, Relay: relay}:
+					case <-ctx.Done():
+					}
 				case <-sub.EndOfStoredEvents:
 					eose = true
 				case <-ticker.C:
 					if eose {
 						del := map[string]struct{}{}
 						old := Timestamp(time.Now().Add(-seenAlreadyDropTick).Unix())
-						seenAlready.Range(func(key string, value Timestamp) bool {
+						seenAlready.Range(func(id string, value Timestamp) bool {
 							if value < old {
-								del[evt.ID] = struct{}{}
+								del[id] = struct{}{}
 							}
 							return true
 						})
@@ -116,7 +132,6 @@ func (pool *SimplePool) subMany(ctx context.Context, urls []string, filters Filt
 							seenAlready.Delete(k)
 						}
 					}
-				case events <- IncomingEvent{Event: evt, Relay: relay}:
 				case reason := <-sub.ClosedReason:
 					log.Printf("CLOSED from %s: '%s'\n", nm, reason)
 					return
@@ -124,11 +139,6 @@ func (pool *SimplePool) subMany(ctx context.Context, urls []string, filters Filt
 					return
 				}
 			}
-
-			pending.Dec()
-			if pending.Value() == 0 {
-				close(events)
-			}
 		}(NormalizeURL(url))
 	}