package server import ( "context" "encoding/json" "fmt" "log" "strings" firebase "firebase.google.com/go/v4" "firebase.google.com/go/v4/messaging" "google.golang.org/api/option" "heckel.io/ntfy/auth" ) const ( fcmMessageLimit = 4000 fcmApnsBodyMessageLimit = 100 ) func createFirebaseSubscriber(credentialsFile string, auther auth.Auther) (subscriber, error) { fb, err := firebase.NewApp(context.Background(), nil, option.WithCredentialsFile(credentialsFile)) if err != nil { return nil, err } msg, err := fb.Messaging(context.Background()) if err != nil { return nil, err } return func(v *visitor, m *message) error { if err := v.FirebaseAllowed(); err != nil { return errHTTPTooManyRequestsFirebaseQuotaReached } fbm, err := toFirebaseMessage(m, auther) if err != nil { return err } _, err = msg.Send(context.Background(), fbm) if err != nil && messaging.IsQuotaExceeded(err) { log.Printf("[%s] FB quota exceeded when trying to publish to topic %s, temporarily denying FB access", v.ip, m.Topic) v.FirebaseTemporarilyDeny() return errHTTPTooManyRequestsFirebaseQuotaReached } return err }, nil } // toFirebaseMessage converts a message to a Firebase message. // // Normal messages ("message"): // - For Android, we can receive data messages from Firebase and process them as code, so we just send all fields // in the "data" attribute. In the Android app, we then turn those into a notification and display it. // - On iOS, we are not allowed to receive data-only messages, so we build messages with an "alert" (with title and // message), and still send the rest of the data along in the "aps" attribute. We can then locally modify the // message in the Notification Service Extension. // // Keepalive messages ("keepalive"): // - On Android, we subscribe to the "~control" topic, which is used to restart the foreground service (if it died, // e.g. after an app update). We send these keepalive messages regularly (see Config.FirebaseKeepaliveInterval). // - On iOS, we subscribe to the "~poll" topic, which is used to poll all topics regularly. This is because iOS // does not allow any background or scheduled activity at all. // // Poll request messages ("poll_request"): // - Normal messages are turned into poll request messages if anonymous users are not allowed to read the message. // On Android, this will trigger the app to poll the topic and thereby displaying new messages. // - If UpstreamBaseURL is set, messages are forwarded as poll requests to an upstream server and then forwarded // to Firebase here. This is mainly for iOS to support self-hosted servers. func toFirebaseMessage(m *message, auther auth.Auther) (*messaging.Message, error) { var data map[string]string // Mostly matches https://ntfy.sh/docs/subscribe/api/#json-message-format var apnsConfig *messaging.APNSConfig switch m.Event { case keepaliveEvent, openEvent: data = map[string]string{ "id": m.ID, "time": fmt.Sprintf("%d", m.Time), "event": m.Event, "topic": m.Topic, } apnsConfig = createAPNSBackgroundConfig(data) case pollRequestEvent: data = map[string]string{ "id": m.ID, "time": fmt.Sprintf("%d", m.Time), "event": m.Event, "topic": m.Topic, "message": m.Message, "poll_id": m.PollID, } apnsConfig = createAPNSAlertConfig(m, data) case messageEvent: allowForward := true if auther != nil { allowForward = auther.Authorize(nil, m.Topic, auth.PermissionRead) == nil } if allowForward { data = map[string]string{ "id": m.ID, "time": fmt.Sprintf("%d", m.Time), "event": m.Event, "topic": m.Topic, "priority": fmt.Sprintf("%d", m.Priority), "tags": strings.Join(m.Tags, ","), "click": m.Click, "title": m.Title, "message": m.Message, "encoding": m.Encoding, } if len(m.Actions) > 0 { actions, err := json.Marshal(m.Actions) if err != nil { return nil, err } data["actions"] = string(actions) } if m.Attachment != nil { data["attachment_name"] = m.Attachment.Name data["attachment_type"] = m.Attachment.Type data["attachment_size"] = fmt.Sprintf("%d", m.Attachment.Size) data["attachment_expires"] = fmt.Sprintf("%d", m.Attachment.Expires) data["attachment_url"] = m.Attachment.URL } apnsConfig = createAPNSAlertConfig(m, data) } else { // If anonymous read for a topic is not allowed, we cannot send the message along // via Firebase. Instead, we send a "poll_request" message, asking the client to poll. data = map[string]string{ "id": m.ID, "time": fmt.Sprintf("%d", m.Time), "event": pollRequestEvent, "topic": m.Topic, } // TODO Handle APNS? } } var androidConfig *messaging.AndroidConfig if m.Priority >= 4 { androidConfig = &messaging.AndroidConfig{ Priority: "high", } } return maybeTruncateFCMMessage(&messaging.Message{ Topic: m.Topic, Data: data, Android: androidConfig, APNS: apnsConfig, }), nil } // maybeTruncateFCMMessage performs best-effort truncation of FCM messages. // The docs say the limit is 4000 characters, but during testing it wasn't quite clear // what fields matter; so we're just capping the serialized JSON to 4000 bytes. func maybeTruncateFCMMessage(m *messaging.Message) *messaging.Message { s, err := json.Marshal(m) if err != nil { return m } if len(s) > fcmMessageLimit { over := len(s) - fcmMessageLimit + 16 // = len("truncated":"1",), sigh ... message, ok := m.Data["message"] if ok && len(message) > over { m.Data["truncated"] = "1" m.Data["message"] = message[:len(message)-over] } } return m } // createAPNSAlertConfig creates an APNS config for iOS notifications that show up as an alert (only relevant for iOS). // We must set the Alert struct ("alert"), and we need to set MutableContent ("mutable-content"), so the Notification Service // Extension in iOS can modify the message. func createAPNSAlertConfig(m *message, data map[string]string) *messaging.APNSConfig { apnsData := make(map[string]interface{}) for k, v := range data { apnsData[k] = v } return &messaging.APNSConfig{ Payload: &messaging.APNSPayload{ CustomData: apnsData, Aps: &messaging.Aps{ MutableContent: true, Alert: &messaging.ApsAlert{ Title: m.Title, Body: maybeTruncateAPNSBodyMessage(m.Message), }, }, }, } } // createAPNSBackgroundConfig creates an APNS config for a silent background message (only relevant for iOS). Apple only // allows us to send 2-3 of these notifications per hour, and delivery not guaranteed. We use this only for the ~poll // topic, which triggers the iOS app to poll all topics for changes. // // See https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/pushing_background_updates_to_your_app func createAPNSBackgroundConfig(data map[string]string) *messaging.APNSConfig { apnsData := make(map[string]interface{}) for k, v := range data { apnsData[k] = v } return &messaging.APNSConfig{ Headers: map[string]string{ "apns-push-type": "background", "apns-priority": "5", }, Payload: &messaging.APNSPayload{ Aps: &messaging.Aps{ ContentAvailable: true, }, CustomData: apnsData, }, } } // maybeTruncateAPNSBodyMessage truncates the body for APNS. // // The "body" of the push notification can contain the entire message, which would count doubly for the overall length // of the APNS payload. I set a limit of 100 characters before truncating the notification "body" with ellipsis. // The message would not be changed (unless truncated for being too long). Note: if the payload is too large (>4KB), // APNS will simply reject / discard the notification, meaning it will never arrive on the iOS device. func maybeTruncateAPNSBodyMessage(s string) string { if len(s) >= fcmApnsBodyMessageLimit { over := len(s) - fcmApnsBodyMessageLimit + 3 // len("...") return s[:len(s)-over] + "..." } return s }