context cancelation for relay connections and subscriptions.

relay.go

@@ -43,9 +43,10 @@ type Relay struct {
 	Connection    *Connection
 	subscriptions s.MapOf[string, *Subscription]
 
-	Challenges      chan string // NIP-42 Challenges
-	Notices         chan string
-	ConnectionError chan error
+	Challenges        chan string // NIP-42 Challenges
+	Notices           chan string
+	ConnectionError   chan error
+	ConnectionContext context.Context // will be canceled when the connection closes
 
 	okCallbacks s.MapOf[string, func(bool)]
 
@@ -72,7 +73,11 @@ func (r *Relay) String() string {
 // Once successfully connected, context expiration has no effect: call r.Close
 // to close the connection.
 func (r *Relay) Connect(ctx context.Context) error {
+	ctx, cancel := context.WithCancel(ctx)
+	r.ConnectionContext = ctx
+
 	if r.URL == "" {
+		cancel()
 		return fmt.Errorf("invalid relay URL '%s'", r.URL)
 	}
 
@@ -85,6 +90,7 @@ func (r *Relay) Connect(ctx context.Context) error {
 
 	socket, _, err := websocket.DefaultDialer.DialContext(ctx, r.URL, r.RequestHeader)
 	if err != nil {
+		cancel()
 		return fmt.Errorf("error opening websocket to '%s': %w", r.URL, err)
 	}
 
@@ -198,6 +204,8 @@ func (r *Relay) Connect(ctx context.Context) error {
 				}
 			}
 		}
+
+		cancel()
 	}()
 
 	return nil
@@ -360,7 +368,6 @@ func (r *Relay) PrepareSubscription() *Subscription {
 	random := make([]byte, 7)
 	rand.Read(random)
 	id := hex.EncodeToString(random)
-
 	return r.prepareSubscription(id)
 }
 

subscription.go

@@ -14,6 +14,7 @@ type Subscription struct {
 	Filters           Filters
 	Events            chan *Event
 	EndOfStoredEvents chan struct{}
+	Context           context.Context
 
 	stopped  bool
 	emitEose sync.Once
@@ -46,6 +47,9 @@ func (sub *Subscription) Sub(ctx context.Context, filters Filters) {
 // Fire sends the "REQ" command to the relay.
 // When ctx is cancelled, sub.Unsub() is called, closing the subscription.
 func (sub *Subscription) Fire(ctx context.Context) {
+	ctx, cancel := context.WithCancel(ctx)
+	sub.Context = ctx
+
 	message := []interface{}{"REQ", sub.id}
 	for _, filter := range sub.Filters {
 		message = append(message, filter)
@@ -58,4 +62,16 @@ func (sub *Subscription) Fire(ctx context.Context) {
 		<-ctx.Done()
 		sub.Unsub()
 	}()
+
+	// or when the relay connection is closed
+	go func() {
+		<-sub.Relay.ConnectionContext.Done()
+
+		// this will close the Events channel,
+		// which can be used by an external reader to learn the subscription has stopped
+		sub.Unsub()
+
+		// we also cancel the context
+		cancel()
+	}()
 }